Actual Flying Rotax Installs

ArchiveBot · August 1, 2020, 5:00am

Actual Flying Rotax Installs

Posted: Sat Aug 01, 2020 8:54 pm

by CaseyCooper

So, I’ve been looking to try and find any Sonex with a Rotax that’s actually been flying. I’ve had luck on google seeing some, but with few or no information on performance or the install.
My Sonex is very close to being finished, and I have a Rotax installed with the factory mount.
With that being said, every plane I’ve seen exists in countries outside the U.S.
I wanted to know any, and all information anyone might have. And as I’m based in the U.S., I wanted to know if there are even any in the country.
Thanks guys!

Re: Actual Flying Rotax Installs

Posted: Sun Aug 02, 2020 1:34 am

by wlarson861

I would guess there are few to none in the US. Rotax was not an approved engine in this country due mainly to cost. Sonex didn’t offer the Rotax mount until a couple of years ago. The reasons I have read given those who have used the 912 were because their countries would not authorize auto conversions of any kind but those countries recognized Rotax an an aircraft engine and would certify them. Most of the previous Rotax users had to engineer their own engine mounts and fabricate them. One other comment I read in the past was they are so light that weight and balance was an issue that had to be dealt with.
I checked the builder database and only found one entry for the US

Re: Actual Flying Rotax Installs

Posted: Sun Aug 02, 2020 7:54 am

by Brett

I have one flying in Oz, performance is good and weight and balance is fine, but I made my own engine mount simply because of import costs yet moved it 1" forward of the standard aerovee prop position. CofG is slightly aft of my origional turbovee but still well within manufacturer specifications.

Re: Actual Flying Rotax Installs

Posted: Sun Aug 02, 2020 8:17 pm

by gcm52

I have an almost flying Rotax912ULS in a Onex. I am doing taxi tests which uncovered a couple of problems that I am working on. I have a nose wheel shimmy and the brakes are weak. I have hydraulic toe brakes and I am hoping a couple of hard braking episodes will improve the braking, braking in the brakes as it were. I am going to try balancing beads for the nose wheel.

Re: Actual Flying Rotax Installs

Posted: Sun Aug 02, 2020 11:01 pm

by WaiexN143NM

hi all,
jake is converting his tri gear sonex from aerovee to rotax 912. maybe he can give us an update.
he should be getting close to flying.
and good luck to george. waiting to hear his first flight report!
WaiexN143NM
Michael

Re: Actual Flying Rotax Installs

Posted: Mon Aug 03, 2020 9:41 pm

by CaseyCooper

Thank you for the replies guys.

Bill, very valid points and makes complete sense. I would just think Rotax installs would be catching on since Sonex offers the mount now. As Jabiru and Rotax are typically the go to manufacturer when you want power and reliability in a light sport aircraft, I would be interested to see the performance contrast between the 2.

Brett, what kind of numbers are you getting? What kind of propeller are you using? Very exciting stuff. Kudos to making your own mount, I can imagine importing would be a pain and far more expensive than making your own. Do you have any pictures available of your install?

George, I imagine that little Onex is going to be a rocket ship. What propeller are you using? 2 or 3 blade? Good luck on further testing! I’m sure you’ll get the bugs worked out and have a fun flying machine.

Michael, I just recently saw his posts. He looks to be doing a great job and I’d love to know his progress.

My Sonex is the Legacy with standard gear. I’m going to be using a tapered tip 62” Warp Drive. I’ll be posting pictures as I go, as of right now my plane is in the paint booth. Fuselage is partially painted and I’m looking to have it wrapped up on Thursday and roll it back in the shop to put all the glass back on and begin painting the wings

Re: Actual Flying Rotax Installs

Posted: Mon Aug 03, 2020 9:57 pm

by CaseyCooper

Currently in the booth

Re: Actual Flying Rotax Installs

Posted: Mon Aug 03, 2020 10:25 pm

by garyb

Hi All
My Rotax powered Sonex has been flying for 2 years now with about 80 hours. Cruise 117Kts IAS at 5200 rpm at 2500 feet, at max weight a little over 1150 lbs climb out from sea level we were seeing 1000 fpm at 70 kts all the way to 7000 feet. I am using a 68 inch wooden GT propeller that comes from a Tecnam 2008 which could be a little coarser. RPM runs to red line at WOT in level flight at 2500 feet. Ref podcast
http://www.sonexflight.com/52/index.html
Cheers.

Re: Actual Flying Rotax Installs

Posted: Tue Aug 04, 2020 5:16 am

by Kai

An EP 915 ECI engine. Normally aspirated, cubic capacity is 1484 ccm, EFI, oil cooled pistons and CR 10,5:1- 120HP@5800 rpm on the dyno.

Well- an explanation for the Rotax absence in Sonex might be that the greatest population of Jabiru is in the US. You also have the option of selecting alternative brands such as Aerovee and other VW-1 aeroderivatives, Corvair, etc. The rest of the world, save Oz of course, seem to favour Rotax: very much so in Europe. This has gone so far that thieves will not steal Jab engines!

What is more; with production of the Jab gen 4 range now in full swing it has become much harder to source main components as cylinders and pistons for the earlier models- and I finally gave up: onwards to Rotax!

For my Sonex A #0525 DS SG, after 550 hrs with Jab which included two top end overhauls, I decided to use the Sonex supplied mount for the 33A engine as a basis for the conversion, and in combination with the ring mount supplied by Rotax. The only components that had to be manufactured were the split radiator setup and two pcs t=12mm flat steel bars, suitably machined and shaped to accept supports and clear engine components, particularily the Rotax starter motor. This will put the Rotax prop flange on the same CL as the Jab, but 35mm further forward compared to the Jab 33A with the shortest prop drive flange on the driveshaft, provided you elect to use the Sonex supplied rubber isolators for the 33A. Lube oil cooling is by a heat exchanger.

Calculations show that the CG will migrate slightly forward compared to the Jab. This is great as I have a 10 gal seat back fuel tank- previously it could only be filled to 75% capacity due to CG issues.

The conversion is well under way now- see the photos. The issues with the cowling are next.

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Wed Aug 05, 2020 6:38 am

by peterp

Hi all,
I’m in Oz with Brett but on the east side, I know of two others here flying and another on the way.
My 912 uls powered legacy has been going for nearly 50 hrs. The started kit with not much done I bought was a tri with aerovee. I made the mount to incorporate the rotax ring mount,(supposedly better than a bed mount) and have longer main legs for a larger prop. It’s now a tailwheel. The prop flange is about an inch forward and an inch higher than the standard. W & B is good and cruise about 115 kts at 5000 rpm. The Bolly three blade prop I’m using is not optimal as to get 5200 rpm on take off (rotax recommendation) I can over speed in S & L any altitude. But overall happy with the result.
Cheers Peter

Re: Actual Flying Rotax Installs

Posted: Wed Aug 05, 2020 3:54 pm

by WaiexN143NM

hi all,
if you are interested in longer gear legs for a sonex check out www.titaniumjoe.com

best,

michael

Re: Actual Flying Rotax Installs

Posted: Thu Aug 20, 2020 1:05 pm

by CaseyCooper

So I have a 912 sitting in my Sonex until I get mine in the mail. For now I’m just using it for fitment of parts so when I receive my engine, it should be plug and play! But in the meantime I have run into some hurdles but nothing that can’t be fixed. One issue is my prop flange is a little low in my cowl, but with some persuasion and effort, it’ll work fine. My major problem is that at the back of the engine, the water pump has several outlets. One of which basically rests on the motor mount which means I can’t get a hose on, if I could it wouldn’t last long, and the outlet would likely break off or develop a leak. With that being said they are pressed and glued in. However all of them are in the same position from the factory. I may be able to remove, reorient, and reinstall to help save it. I talked to Mark at Sonex and helped me with what information that he had, very nice and helpful guy. But I found out Sonex has never installed a 912, and has only drawn up the mounting system in cad to satisfy customers who want to use the engine. So, with that being said, there are some hurdles to be overcome but nothing crazy, just like any aircraft build. Here is how it sits currently. I’ve been busy installing the firewall items, wiring,mock up exhaust, and ideas for radiator locations. I will keep posting progress as it comes.

Re: Actual Flying Rotax Installs

Posted: Fri Aug 21, 2020 9:48 am

by SonexN76ET

My Rotax powered Sonex should be up and flying in a couple of weeks. I will post some new photos soon.

The Homebuilt Help Rotax Installation video has been a great help. It shows how to adjust the water inlet tubes for different engine mounts. I had to purchase some water inlet tubes with different angles to get it to fit the Sonex engine mount. You have to carefully heat the water inlet tubes and very carefully unscrew them and then clean the threads and apply Locktite 243. You must note and mark the correct angle required for fitment before you screw them back into place. You likely will not be able to screw them on when the engine is seated in the mount due to clearance issues. Be careful as the threads are very fragile in the heads and on the inlet tubes. Please watch the Homebuilt Help videos as they show precisely how this is done.

I mounted my radiator to the aft and under the engine.

I am in the process of modifying my cowling. It will be about six inches narrower at the front than the Aerovee cowling and will be contoured to mate up with the larger spinner for my three bladed Sensenich propeller.

You should also check out Rotax-Owner.com for other videos and service instructions.

I modeled my installation after the Bristell LSA which is an improved version of the SportCruiser/PiperSport.

Jake

Re: Actual Flying Rotax Installs

Posted: Mon Oct 26, 2020 1:46 pm

by agwous

I do not have a Rotax on my Sonex, but I just recently installed a Rotax on another airplane I built. The water pump outlet also interfered with the engine mount and the standard fix was to remove the pump outer housing with the tubes. Add a bit of heat using a propane torch, and rotate it slightly. The tube is soldered in and the slight rotation doesn’t seem to cause it any problems.

Re: Actual Flying Rotax Installs

Posted: Sun Nov 22, 2020 10:01 pm

by CaseyCooper

So with some work I have completed the install of my Rotax with the Sonex mount. With some tweaks to the water pump, elbow replacement and orientation, the Sonex mount works. I had run my engine for the first time today. It’s not yet synced and tuned but it started right up. Currently going to run it for an hour on non synthetic 10w-40 Castrol oil and a Fram filter to break in, tune, and collect all the crap, then I’ll be doing an oil change to the standard Aeroshell and Rotax filter. It’s a 912 with 84mm pistons and cylinders. I had tigged up an exhaust into duals, made a scoop that houses my radiator and oil cooler, and a few other things. I’m running a 64” 3 blade taper and nickel tipped Warp Drive. Right now this is what I have and it’s about ready to be flown. I have a DAR appointment this next weekend to get my airworthiness.

Re: Actual Flying Rotax Installs

Posted: Sun Nov 22, 2020 10:04 pm

by CaseyCooper

The install

Re: Actual Flying Rotax Installs

Posted: Mon Nov 23, 2020 8:40 am

by Matt541

Congrats, it’s lookin’ good! Can’t wait to see it fly.

My buddy has over 1200 hrs on his Rotax 912 (80hp) in a Rans S7. He tried different types of oil and is currently settled on the Aeroshell Sport Plus 4. It’s pricier, but it’s what he believes his engine prefers. I personally can’t tell the difference.

YMMV

Re: Actual Flying Rotax Installs

Posted: Mon Nov 23, 2020 9:47 am

by SonexN76ET

Getting close to first flight with Rotax 912 ULS

Jake

Re: Actual Flying Rotax Installs

Posted: Mon Nov 23, 2020 9:53 am

by SonexN76ET

Re: Actual Flying Rotax Installs

Posted: Mon Nov 23, 2020 9:53 am

by Matt541

Excellent Jake! I’ve been wondering about your progress as well.

Re: Actual Flying Rotax Installs

Posted: Mon Nov 23, 2020 5:10 pm

by gcm52

I am in the process of flight testing my Rotax 912 ULS (100hp) powered Onex. I am quite pleased with this airframe and engine combination. Today I did some speed checks at 6000 ft MSL. At 5300 RPM I was showing 140 kts true airspeed. This could be considered a high cruise power setting (max continuous for the Rotax is 5500 RPM. At 5000 RPM (75% power) I was showing 126 kts TAS.

Re: Actual Flying Rotax Installs

Posted: Tue Nov 24, 2020 10:22 am

by 13brv3

Contrats George. Great to see you back on the forum. I’d love to get a measurement from the firewall to the ring mount tube for the Rotax when you get a chance. I’m just about to get started cutting tubes for my mount (912UL Onex) and that measurement would be a very helpful reference.

Thanks,
Rusty

Re: Actual Flying Rotax Installs

Posted: Tue Nov 24, 2020 10:54 am

by WesRagle

Hey George,

Congratulations! Very impressive!!

Wes

Re: Actual Flying Rotax Installs

Posted: Sun Dec 06, 2020 10:35 pm

by CaseyCooper

Yesterday I got my airworthiness certificate, today I flew my Sonex for the first time. Aside from a slight right roll, and a slight left yaw, it flies wonderfully. With the Rotax with my 3 blade tapered tip Warp Drive, my take off rpm is 5,300 rpm. Wot of 5,500. Cruise of 135 mph at 5,100 rpm. Climb of 2,000+ feet per minute with full fuel, I weigh 180 lbs, at a climb of 80 mph. Outside air temp was 72 degrees, airport elevation 2,120 feet. Density altitude unknown today. My Sonex empty weight is 666 lbs. Tomorrow I’ll be adding trim straws to dial the trim in, then begin flying off phase one.

Re: Actual Flying Rotax Installs

Posted: Sun Dec 06, 2020 10:36 pm

by CaseyCooper

Don’t mind the ugly mug

Re: Actual Flying Rotax Installs

Posted: Sun Dec 06, 2020 10:38 pm

by CaseyCooper

N7777X

Re: Actual Flying Rotax Installs

Posted: Mon Dec 07, 2020 8:50 am

by Matt541

Wow, that’s sweet lookin’! Well done.

Re: Actual Flying Rotax Installs

Posted: Mon Dec 07, 2020 8:53 am

by 13brv3

Congrats! What length prop are you running? 80 or 100 HP? Any pics of the engine installation would be excellent.

Cheers,
Rusty

Re: Actual Flying Rotax Installs

Posted: Mon Dec 07, 2020 9:36 am

by SonexN76ET

Congratulations on your first flight! I look forward to hearing more as you continue your test flights. Good job on the Rotax installation!

Jake

Re: Actual Flying Rotax Installs

Posted: Tue Jan 19, 2021 12:36 am

by CaseyCooper

This is a big one! But very insightful.

So I have some updates on my install and points of concern.
I have a 64” 3 blade warp drive, I develop 5200 rpm on climb out and 5550 in straight and level flight at full throttle. Right where is recommended by Rotax. Carbs are synced and everything is happy. BUT, my problem is not my engine. It’s related to it.
The Rotax mount from Sonex requires the use of their attach bars and the bushings used in mounting the Aerovee. When installed per Sonex instruction, I noticed my first problem. When installing the bolts that go through the mount, bushing, attach bar, and second bushing, I tightened the bolt until the bushings were slightly compressed/rounded, without the nut bottomed out on the shoulder of the bolt. The problem is, without an ability to tighten the bolt against something solid, you can keep tightening the bolts and compress the bushings until the cows come home. But I tried it anyway. Flew for 3 hours, began to smell burning fiberglass in the cockpit. Not a good thing. I thought my engine could be on fire, but I found it hard to believe, or some other problem arose. I quickly got on the ground and noticed my prop spacer had rubbed severely on my cowl. Which my spacer was centered before and after the flight. So I grabbed the engine and was able to rock it quite a bit up and down at the prop flange. Checked the bolts, they were not loosened and the mount bushings were still as I left them. The bolts were wiggling from the mount to the attach bars, because they had nothing solid to tighten against. So I turned on the lathe and machined some 5/16” id 0.030 wall pins/sleeves that would allow me to tighten the bolt good and tight, which removed the play a bit. So I put some more time on it.
I got to 10 hours and did another inspection because I began to feel a vibration through the fuselage that got progressively worse and then really bad all of a sudden. So, I began to check and double check a few things. My prop and spinner are balanced. Nothing changed, nothing out of place. My carbs were perfectly synced, no debris in the carbs, great fuel pressure. Pulled the magnetic plug to look for debris that might’ve come from a gear box problem, clean and clear. In flight I had perfect temperatures, no issues. Mag checks perfect, a 10 rpm difference. Flew it again having mentally felt better, then the terrible vibration in the pattern and back down I came.
So I had an epiphany, my mounts. So i took the bolts/pins out and inspected my mounting surfaces. My front attach points on the attach bars, were resting on my mount bolts. The bushings had shifted and deformed allowing this to happen. The rear however, was perfect. The Rotax produces far more torque than a jabiru 3300 and an aerovee because it’s gear driven. We are able to spin bigger props, more blades. Which in turn means more torque, and more load from p factor, which means a lot of pull back and forth at the prop flange upon acceleration, climb, and deceleration. So what I noticed was the attach bars, being mounted vertically, eventually spread the bushings apart from back and forth, and up and down movement, worked down to the bolts. It also doesn’t help that the bushings used, are 3 tiered. The large section rests on the outside, the second just in the attach bars, and the inner most around the bolt and between it and the attach bar. The finally tier is just about 3/32 of an inch of rubber separating the two from each other, in a vertical configuration, which is almost nothing. The second shelf is designed to help assist in shifting, but allowed them to shift anyway. The Jabiru bushings are wonderful, but too big for the application. The aerovee bushings for the aerovee ring mount, work great! The aerovee mount has pins, and the load is distributed differently on the ring mount, and they don’t put of the forces a Rotax does. A bushing that might work great is a lord mount, or Barry mount, but they are a different dimension than what the attach bars allow.
So upon recommendation by Mark at Sonex, I shimmed the outside bushings with more washers, and in this case, I used washers that were dished to encapsulate the bushings, and push them in tighter against the attach bars. I also noticed the front attach points (the engine mount) flex outward and inward slightly, about 1/8 of an inch, which can equate to a lot of movement at the engine. I flew it for 3 more hours and no luck in solving the problem. It was also suggested to try polyurethane bushings, that are much harder, which I wouldn’t believe would help the problem. It would cause less isolation from engine to airframe, which could translate the energy elsewhere and cause stress somewhere else.
With all this being said, I wiped out my mounts in 13 hours. I’m not going to fly it until I find a solution. I had told Mark at Sonex I’ll be happy to work with him any way I can to find a solution and make it work. But as of right now were at a stalemate. I’m waiting to hear back from Sonex about any improvements that can be made or changed. I feel like this is a great opportunity for us builders and Sonex to work together to fine tune these installs. The Sonex really is a wonderful aircraft, and the Rotax makes it that much better.
In no way am I attempting to poo poo Sonex. The company is extraordinary and produces some of the best bang for your buck aircraft money can buy. They are extremely thorough and wonderful people with a bulletproof reputation.

So if you made it this far, Jake I know you’re close, and anyone else that has a Sonex Rotax mount, this might be good information for you and things to look for. Let me know if anyone has any questions.

ArchiveBot · August 1, 2020, 5:00am

Re: Actual Flying Rotax Installs

Posted: Tue Jan 19, 2021 11:05 am

by SonexN76ET

I really appreciate your insight into the engine mount issue you are having. I hope you are able to get it figured out quickly and safely! I think I will go ahead and install polyurethane bushings and outside washers on the attach bar to engine mount initially before my first flight as a possible preventative measure. I hope this does not become a show stopper in using the Sonex Rotax mount without major modifications to the engine mount. I am wondering if the long term solution would be to modify the mount to allow use of Lord mounting bushings, although that would likely require a major change to the engine mount.

Thanks!

Jake

Re: Actual Flying Rotax Installs

Posted: Tue Jan 19, 2021 11:51 am

by 13brv3

One thing I thought was odd about the Sonex Rotax mount is that they used the same bushings, but changed the orientation. To me (not a mechanical engineer), it appears they were primarily loaded in the axial direction for the Aerovee, but for the Rotax they’re loaded nearly 100% in the radial direction. I have a Barry’s data sheet for similar type mounts, and the radial load limit on those is always far less than the axial limit, so I wonder if that isn’t the main problem here. I don’t really see an easy way to convert this back to axial loading though.

Rusty

Re: Actual Flying Rotax Installs

Posted: Tue Jan 19, 2021 9:58 pm

by Zack

Herraripower wrote:I have a 64” 3 blade warp drive

Do you have 9" of clearance at level attitude? I’m just about to place an order for a propeller and I was going to go with 62" to be safe. I have a calculated total height to centerline of 40.7", which gives a maximum 63.4" propeller diameter. I calculated total height to centerline by measuring actual to the fuselage (the main legs were installed flush, which was an additional 0.45" long) and measured from the plans to the centerline (22.8438" + 17.856" = 40.6998). My Rotax should be here soon and I’ll have an actual total height.

Herraripower wrote:So I had an epiphany, my mounts. So i took the bolts/pins out and inspected my mounting surfaces. My front attach points on the attach bars, were resting on my mount bolts. The bushings had shifted and deformed allowing this to happen.

…

So upon recommendation by Mark at Sonex, I shimmed the outside bushings with more washers, and in this case, I used washers that were dished to encapsulate the bushings, and push them in tighter against the attach bars. I also noticed the front attach points (the engine mount) flex outward and inward slightly, about 1/8 of an inch, which can equate to a lot of movement at the engine. I flew it for 3 more hours and no luck in solving the problem.

This was great information, thank you. I have my Rotax on order and it should be here soon. I’d hate to have to engineer a different mount, but now would be the time for me. I’m working with Mike from STOL Creek to do the engine install. He’s a Rotax dealer and Edge Performance dealer for the US. He’s recommending using the stock ring mount, but I don’t know where to turn to have someone engineer a Sonex Rotax mount from scratch or who can adapt the existing Sonex provided mount I have. Is Sonex actively working with you on a solution, or are you on your own? Here is my post about the mount solution I came up with. Just to be clear, is the attach bar (red) displacing the rubber bushings and resting on the steel bushing the bolt travels through?
viewtopic.php?f=60&t=5612

Re: Actual Flying Rotax Installs

Posted: Wed Jan 20, 2021 10:36 am

by SonexN76ET

I am questioning why Sonex did not have the pins from the outboard side of the engine mount the bolts go through not carry over to the inboard side for the bushings to slide onto as they do with the AeroVee mount? I am also wondering if Zach’s solution to put a 4130 spacer over the bolt between the inside of the bushing would be a good solution or if that should be welded to the mount like on the AeroVee mount?

Zach - I am referring to your earlier post and pictures.

http://www.sonexbuilders.net/viewtopic.php?f=60&t=5612

Jake

Re: Actual Flying Rotax Installs

Posted: Wed Jan 20, 2021 11:34 am

by Zack

SonexN76ET wrote:I am questioning why Sonex did not have the pins from the outboard side of the engine mount the bolts go through not carry over to the inboard side for the bushings to slide onto as they do with the AeroVee mount? I am also wondering if Zach’s solution to put a 4130 spacer over the bolt between the inside of the bushing would be a good solution or if that should be welded to the mount like on the AeroVee mount?

Zach - I am referring to your earlier post and pictures.

http://www.sonexbuilders.net/viewtopic.php?f=60&t=5612

Jake

Jake, I would have felt more comfortable with the pin carrying through the mount like the AeroVee mount pin specifications http://www.aeroconversions.com/images/p … nt_Pin.pdf. I was concerned about the shear loads on the AN4 bolt with a two part solution. https://www.youtube.com/watch?v=i9SJbCCoACg I reached out the Sonex and here’s what they said:

Hi Zack,

Our original assembly did use an AN4 bolt to support the engine and that is fine. We have a newer design that changed the wall thickness of the tubes that accept the bolts and now use AN5 bolts.

What you have done conforms to a proper adaption of the AN4 bolt installation.

Blue Skies….

Kerry

I’d like to know why they moved to an AN5 bolt, and what kind of safety margin the AN4 vs AN5 bolt has. I don’t see how you can mount the engine without a pin. The holes in the bushings are greater than either an AN4 or AN5 bolt, so you would have a lot of movement vertically. I used some some 4130 steel for the spacer and these washers, all from McMaster Carr: https://www.mcmaster.com/98032A492/

It looks like our AeroVee friends have similar issues with the bushings sagging (http://www.rynoth.com/wordpress/waiex/2 … ng-issues/ - thanks Ryan!). Would the extra torque from the Rotax gearbox and larger propeller really exacerbate this issue?

Re: Actual Flying Rotax Installs

Posted: Wed Jan 20, 2021 12:27 pm

by CaseyCooper

Zach,
I do have clearance! When building my plane I went to some Air Trac 5.00x5 tires which also helped with some ground clearance. They also still fit within my standard wheel pants from Sonex. A 64” swings great and I operate off of dirt. (Smooth dirt). But yes, the red bars have worked apart and torn up the rubber allowing them to rest on the steel sleeves on the an5 carry through bolts.

Jake,
One of the first things I did was machine a sleeve to go over the bolt. Like in my long run on story, it helped with my engine movement, but in the end did not solve my problem.

I agree with you guys in all aspects. Like I had mentioned in previous posts, upon receiving my mount I had some issues with my water pump fittings but those were easily solved. But In working though that, I was told by Sonex that they produce the mount for the urge in customers to produce one, BUT, they have not actually tested it. I don’t know if I’m the first person to test it, but this is just my experience.

Sonex went radio silent about a week ago on the issue, so I wouldn’t say they’re not working on it, I just haven’t heard back.

But I have designed and machined a new attach bar system this last weekend which turns the mount into a bed mount. The engine rests on a series of 6 sets of Barry mounts, each using a 3/8’s bolt. If there isn’t a solution in the near future I might just try my mounts out. I want to fly my plane! And I had mentioned previously I really wanted to work with Sonex to try and get this handled by helping them, myself, and anyone else using them so they can fly safely and have a seamless install. Plus it’s always better, in my opinion, to use factory parts if possible.

Re: Actual Flying Rotax Installs

Posted: Thu Jan 21, 2021 2:31 pm

by Zack

Herraripower wrote:Zach,
But yes, the red bars have worked apart and torn up the rubber allowing them to rest on the steel sleeves on the an5 carry through bolts.

That’s bad, I don’t see how we can use the current design and rubber bushings.

Re: Actual Flying Rotax Installs

Posted: Thu Jan 21, 2021 2:32 pm

by Zack

SonexN76ET wrote:install polyurethane bushings

Jake, where would you find polyurethane replacement bushings?

Re: Actual Flying Rotax Installs

Posted: Thu Jan 21, 2021 4:30 pm

by SonexN76ET

Here is a picture of my engine sagging on the mounting bars with the AeroVee bushings.

Zack, I am concerned that the polyurethane bushings may be way too hard. I just got a set and they feel like hard plastic, so I am hesitant to use or recommend them on the engine mount.
I am wondering if a Lord engine mount bushing could somehow be fitted to the Sonex Rotax mount?

I previously had not given much thought to the design of this engine mount but I am very concerned now that I look at mine and see the engine sagging on the mount after only being run twice on the ground. More significantly I can also see the dangerous situation Herraripower has encountered with the engine mount bushings splitting and having metal to metal contact with the mounting bars. Finally, I am alarmed with AN4 bolts being unsupported as they hold up the mounting bars after they penetrate the mount. There has got to be a better way!

As a side note, I never had the sagging issue with my AeroVee engine. This appears way more serious in my opinion. This is evidenced by Harriripower’s experience and the excessive sagging I see so early in the installation.

Jake

Re: Actual Flying Rotax Installs

Posted: Thu Jan 21, 2021 6:15 pm

by SonexN76ET

An idea I may speak to Sonex about is to use three bushings at each mounting point instead of two. My observation is that there is a void between the two AeroVee bushings in the mounting bar because the AeroVee bushings are primarily on the outside of the bar and only penetrate it slightly. Perhaps a small polyurethane bushing would work pressed into the mounting bar and then the AeroVee bushings sandwich it from both sides thus eliminating the void? So the only change to the design would be to indicate to use the spacer over the AN4 or AN5 bolts to fit the bushings as Sonex mentioned in their email you shared and to press a bushing into the mounting bar to eliminate the void. Possibly a fitted polyurethane bushing of some type due to the relatively small size.

What do you guys think?

Jake

Re: Actual Flying Rotax Installs

Posted: Thu Jan 21, 2021 7:13 pm

by GraemeSmith

SonexN76ET wrote:

What do you guys think?

Jake

Though on an AeroVee - my builder “stiffened” the exposed sagging rubber by applying a hose clamp around it.

My mental note to think of something better has now “been considering” the idea for 180 hours and I can’t some up with something better. Come the time - I’ll probably wade through the Lord Mount catalog and see if they have something with stiffer material.

Re: Actual Flying Rotax Installs

Posted: Thu Jan 21, 2021 7:45 pm

by SonexN76ET

Hi Graeme,

You have some good insight into this and the hose clamps are an interesting idea. The difference in the execution in design between the AeroVee mount and the Rotax mount is the AeroVee has 4130 steel rods that go all the way through the AeroVee accessory plate and when compressed the two rubber bushings on the AeroVee mount and accessory plate likely touch in the middle. On the Rotax mount and mounting bracket there is no 4130 rod on the side of the mount with the two bushings and mounting bracket. It is just a flat surface on the mount where the bushings hit up against the mount. Also on the mounting bar there is a rather large void between the two bushings so it is not just sagging in terms of rubber but to the point where there is now metal to metal contact without the benefit of shock absorption from the bushings when the bushings sag out of the way or tear as in the case described by Herriapower.

Jake

Re: Actual Flying Rotax Installs

Posted: Thu Jan 21, 2021 10:37 pm

by Zack

Jake, I agree with all of your points.

SonexN76ET wrote:My observation is that there is a void between the two AeroVee bushings in the mounting bar because the AeroVee bushings are primarily on the outside of the bar and only penetrate it slightly.

I noticed the same thing. I think custom polyurethane bushings would be a good place to start. I did a search and found a few places that will make custom bushings, if there is consensus we can go in together on a small run. I don’t have my plane near me, so I’d need someone to provide the dimensions on the attach bar. It has a weird two step inner diameter (ID).

BTW if you have an AN4 (0.250") bolt like I do, and the stock bushing ID is 0.364 (about 3/8") you’ll definitely need a sleeve.

Re: Actual Flying Rotax Installs

Posted: Thu Jan 21, 2021 11:48 pm

by CaseyCooper

Hey guys,
Just to inform you, I have an5 bolts, not an4’s, in my mount. They are slightly loose in the mount, but sleeves definitely helped. They are 0.030” sleeves which fill out the 0.375” holes in the bushings. But sleeves are definitely necessary to truly tighten and secure the bolts to not shift or wiggle. Mark at Sonex recommended some polyurethane bushings from jegs, but like you found out Jake, polyurethane is super hard. That’s why they use them in suspension (sway bars) applications on cars. Which would not offer much, or any, absorption from the engine to the mount, which could eventually fatigue and crack a mount (in my opinion), as well as just shake the crap out of the plane.
Hose clamps definitely work in some applications, guys with the Jabiru 3300 use that idea, but in this case, you still only have about 3/32” of rubber around the bolts separating the attach bars from the bolts, in a radial load.
Today Mark had contacted me and requested some photos to see exactly what can be done so I took a bunch and sent them his way. I should hear back soon if Mark has any further suggestions.

Re: Actual Flying Rotax Installs

Posted: Fri Jan 22, 2021 12:05 am

by SonexN76ET

http://www.aeroconversions.com/images/products/SNB-P53-01_Rotax_Attach_Bar.pdf

Re: Actual Flying Rotax Installs

Posted: Fri Jan 22, 2021 12:43 am

by SonexN76ET

If we machined the through holes on the mounting bars to .8 inches straight through we could potentially use Lord Engine Mount CB-2201. Perhaps we should run this by Sonex as a possible solution?

Specifications can be found here for the Lord engine mounts:

https://www.aircraftspruce.com/catalog/pdf/cb2201tds.pdf

Jake

Re: Actual Flying Rotax Installs

Posted: Fri Jan 22, 2021 2:36 pm

by Zack

SonexN76ET wrote:If we machined the through holes on the mounting bars

We would need to re-anodize the attach bars, as the anodized surface is much harder than non-anodized aluminum.

Re: Actual Flying Rotax Installs

Posted: Fri Jan 22, 2021 3:08 pm

by achesos

Make no mistake - vibration and damping is a complex animal. These are experimental aircraft, but some caution should be applied here when making design changes.

A quick reset perhaps -
What is the problem to be solved here? The appearance of the engine in the mounts in a static configuration?
Maybe more importantly, where does the engine locate itself in flight, while operating, and pulling the plane through the air? This is obviously harder to determine.

Isn’t it more important to correctly isolate the engine (while operating) so it can perform primary function (thrust) without destroying itself due to high cycle fatigue (think frequency of vibration amplitude). I seem to remember something about conservation of energy… pretty sure the physics involved here are real.
These isolators are also then protecting (hopefully) the rest of the aircraft and everything attached to it from vibration fatigue as well.
Randomly changing the stiffness of an engine isolator does not negate the energy (excitation forces) created from the engine rotating. That energy is either transmitted or remains self-contained (and absorbed) by the engine assembly.
This is serious R&D stuff. Appropriate caution and data collection is my unsolicited advice.

Re: Actual Flying Rotax Installs

Posted: Fri Jan 22, 2021 6:00 pm

by Zack

achesos wrote:What is the problem to be solved here? The appearance of the engine in the mounts in a static configuration?

Achesos, if I understand Herraripower correctly the problem is bushing failure which allows movement of the engine within the mount while it is running. Herraripower, do you have any pictures you can share? I agree that caution is important. Changing the hardness (durometer) of the bushings seems to be a reasonable (and affordable) place to start as it is just one variable and keeps the mount unchanged. Noise, vibration and harshness will increase with the durometer of the bushings. I don’t know how to quantify this and what are acceptable limits.

Re: Actual Flying Rotax Installs

Posted: Fri Jan 22, 2021 11:39 pm

by CaseyCooper

Sorry guys, I had to render some photos so I could actually post them.

Re: Actual Flying Rotax Installs

Posted: Fri Jan 22, 2021 11:44 pm

by CaseyCooper

Mark recommended that I add more washers to try and provide more pressure on the outer bushings to reduce movement. I used these washers to encapsulate the bushings and really hold them in there. Unfortunately no luck. Like I’ve mentioned before, rear bushings showed no obvious wear. The front right, slightly. The front left showed most fatigue.

Mark emailed and assured me that they’re actively working on a solution/improvement.

Re: Actual Flying Rotax Installs

Posted: Sat Jan 23, 2021 9:46 am

by Zack

Herraripower wrote:Sorry guys, I had to render some photos so I could actually post them.

Thanks! Those AN5 bolts look real beefy compared to my AN4s.

Re: Actual Flying Rotax Installs

Posted: Sat Jan 23, 2021 12:25 pm

by SonexN76ET

After looking at the engine mount bushings extensively, I do not think there is a quick or easy fix for this. The reason is that there are two separate causes that I see:

1- Most serious is the unsupported AN4 or AN5 bolt holding up the engine through the two bushings and attach bar. This unsupported bolt experiences a tremendous amount of lashing and flexing and wear at the intersection of where it passes through the engine mount. The AeroVee mount has a better design where the bolt is inside of the pin it’s entire length.

Bushings sagging as discussed earlier.

Jake

Re: Actual Flying Rotax Installs

Posted: Sat Jan 23, 2021 5:48 pm

by Kai

All,

An intrigueing situation and I would be very interested to see what the manufacurer turns out.

Getting the rubber isolators loaded axially/compression is most likely the main issue here. This could probably be accomplished by discarding the existing flat bar brackets and substituting them with a double set of structural 1/2’’ aluminium angular brackets of suitable dimensions to maintain propshaft cl and accomodate isolator dimensions, one set of brackets bolted to the bedmount and the other set to the engine sump, sandwiching one set of isolators between them.

However, as a national DAR, I would be reluctant to approve such an ‘eyeball’ setup, unless the airframe designer has issued some form of acceptance. Loads and displacements would have to be calculatd, especially the rocking motion prop traction would impose on the setup. The displacement caused by the moment arm between propshaft and isolators would likely be considerable unless the isolators were very hard.

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Sun Jan 24, 2021 12:55 am

by CaseyCooper

Kai,
I thought the exact same thing and I actually created some for an “if all else fails” situation if there isn’t a solution sometime soon so I can fly my airplane. I used suitable mounts used on other 912 applications, such as Rans, which offer plenty of support and isolation.
I recognize you as a DAR but in this case a letter or sign off from a DAR is not needed. This is not a major modification and being in the experimental category, just requires the signature of an A&P willing to put their name on it. Technically you wouldn’t need any input from the company that builds the aircraft components because they are not technically the manufacturer. On your airworthiness certificate in the experimental amateur built category, the manufacturer is the builder. You’re just building a plane from a kit or parts from a provider. But I 100% agree there is testing and at the least, research to be done of strengths of materials involved and loads placed upon them

Re: Actual Flying Rotax Installs

Posted: Sun Jan 24, 2021 1:01 am

by CaseyCooper

So, as something I may try if there isn’t a solution in the near future, are some motor mounts I machined based off of the blueprints for the existing attach bars. These began as 4 pieces of 9.75” long 3x3, 0.375” 6061. The measurements are exact and stepped according to Sonex’s plans. I used 6 pairs of Barry 22001-13 Green isolator bushings. I machined them to be a bed mount. As for the 6061 material there is a surplus of strength, each bushing set uses 3/8” bolts which offer plenty of tensile strength and shear. Much more material, but the bushings are loaded properly and have plenty of suspension. Cowling clears and everything fits great. Considering the original bars are 0.625” material and 4 sets of bushings less internal pins, these may be a bit overkill, but potentially more stable and durable.

Re: Actual Flying Rotax Installs

Posted: Sun Jan 24, 2021 1:10 am

by CaseyCooper

I haven’t tested them yet. Just test fitted in case I need to switch to them later.

Re: Actual Flying Rotax Installs

Posted: Sun Jan 24, 2021 4:13 am

by Kai

Wow!

That’s more like it: impressive! You are a much better machinist than me. However, you realize that the idea is neither ours nor new: airframe designers have in the past employed the principle extensively.

If four isolators are good, six should be better. This should add stability to the logitudinal rocking. I have no idea if it is at all possible, but since the antics of the R912 are scary during engine startup/stop, I would also have checked out the possibility to get them further (wider) apart- just a thought!

You have not asked for comments to your very good and illustrating photo’s, and I realize this is none of my business, but 30 years as an A&P tech with an inspector rating- DAR? I have come to hate the hose clamp in its simplest form. They tend to live their own life and in suction line applications you never know if they really seal off air tight. If not so, this could rapidly starve your engine of oil. If no other alternative is available, make sure that they are just big enough (for even clamping, too big and they tend to go out of round), get the ones with bent up edges to avoid the clamp cutting into the hose. And secure them with a safety wire. This also goes for the big oil outlet banjo bolt under the engine (!)

Great work!

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Sun Jan 24, 2021 4:39 am

by aripilot

Rotax 912 installation is designed with Rotax ring mount. You also need engine mount attached to ring mount and firewall. This combo will quarantee smooth and trouble free operation of the engine.

Ari

Re: Actual Flying Rotax Installs

Posted: Mon Jan 25, 2021 12:16 pm

by CaseyCooper

Kai,
Thank you very much. I appreciate that. Any suggestions are good suggestions! So I’ll take any criticism I can get!
The Rotax definitely has its own personality. The gear reduction and compression make for an interesting start up and shut down compared to something like a lycoming or continental. That’s definitely something to take into consideration.
Maybe I will try and make some new mounts and move them further apart, but unfortunately, I don’t have a ton of room to work with but every bit helps. It’s only in the “just in case” realm right now so fortunately I have time to prototype.
There is definitely concerns when installing your oil system. However the banjo bolt/sump is not under suction, it’s under pressure, from the oil pulled into the pump at the front of the engine and circulated through. If there was a leak, it wouldn’t starve it, unless the it was so substantial the oil can ran out! Which is a scary thought in itself. Always watch those oil pressures! But I agree on the clamp. This one is, like you say, barely big enough to where I have a small tail coming out. There is definitely an art when using a standard hose clamp knowing when enough is enough. Too little, leaks, too much, curled rubber coming out of the clamp.
Thank you very much for your insight, it’s always good to have someone to bounce around ideas with!

ArchiveBot · August 1, 2020, 5:01am

Re: Actual Flying Rotax Installs

Posted: Mon Jan 25, 2021 3:45 pm

by Kai

Casey,

Let me respectfully point out that there is suction at your lube oil pump hose barb oil inlet. In fact, the complete line from the oil tank to the pump inlet hose barb, is under suction. You need to make sure that the complete line is totally airtight. And pay special attention to the hoses in this cirquit. There have been cases where the hose wall has not been stiff enough to withstand suction, and consequently was sucked flat: exit some fine R912’s.

The external lube oil system works with crankcase pressure forcing the spent oil through our banjo and to the oil tank. The tank itself is vented and there is only ambient pressure in there. When replacing the oil in the tank we are supposed to do this with the aid of compressed air: do not exceed 1bar/15psi!, the manual says.

Then suction from the lube oil pump draws oil from the tank, through the cooler, and forces it into the oil galleries. Then back to the sump. Why the system designers in their infinitive wisdom decided that this was the salvation of mankind, is beyond me!

Remember : Murphy lives!

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Mon Jan 25, 2021 9:13 pm

by CaseyCooper

Kai,
I agree completely. Perhaps we’re saying the same thing differently. The line coming from the can to the oil pump, below the gear box, is under suction. The line from the sump, to the can, is under pressure. Like you said, crank case pressure.
But I agree with the compressed air. It’s important to prime the pump after an oil change, especially for first oil add when new, with a dry/partially dry pump.
However, your oil cooler should not be between the sump and can. It should be between can and oil pump. Reason being, if you cool the oil substantially before it reaches the can, the heated water in the oil system does not vapor off and go out the vent. It should go in the can hot, through the cooler, and back through engine cool, so we can get rid of that junk.
But I agree! I actually know a guy this happened to, he panicked and crashed his plane because he lost oil pressure, and instead of just flying the plane to a safer area and maybe toasting the engine, he put the plane down in a terrible spot and destroyed the plane. Sometimes panic just gets the better of you in those situations

Re: Actual Flying Rotax Installs

Posted: Tue Jan 26, 2021 2:47 am

by Kai

Casey,

Yes- and regarding the isolators I’m still very interested to see what Sonex comes up with. You will publish on these pages?

Panic should not be taken lightly. My former Jab engine had an electrical fire (shorted charging lines from alternator to rectifier) at 2700’ agl. The first thing I knew was that the oil pressure went to zero (shorted after insulation on lead from sender to gage melted). Then that acrid smell in the cockpit and gradually so full of smoke I could hardly see out. I was convinced I had a fuel leak and would go kaboom shortly. Switches off, fuel off: one smoking glider with poor specs.

I won’t say I panicked, but I became VERY focused on getting the thing back on terra firma.

This was in ‘12. Kerry Fores got the news just after he was back from his summer vacation- he flatly stated he refused to go on any more vacations if I/we insisted to carry on with these sort of things. Took me thirteen months and huge plywood box with airframe parts from Sonex to get #0525 back in the air again.

Try to avoid this yourself- I most certainly hated it. Install the R912 according to the book and operate it accordingly.

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Tue Jan 26, 2021 10:39 am

by SonexN76ET

Here is how Rotax specifies how the oil circuit is to be configured. From what I understand Herraripower is compliant with this configuration. I agree with Kai, however, that the oil hoses and fittings must be of top concern. I originally made my own oil lines with AN fittings but before first engine run learned more about the nuances of the suction technology Rotax was using and decided to order custom Teflon aircraft hoses with AN fittings from Aircraft Specialty that are designed for the suction used by Rotax engines. The oil lines were expensive however. $600

Jake

Re: Actual Flying Rotax Installs

Posted: Tue Jan 26, 2021 10:57 am

by SonexN76ET

While looking at images of other Rotax 912 engine mounts I came across these on the internet on a Titan Tornado with a 912. It looks similar to Herraripower’s design but with the angles turned outside instead of inside.

Jake

Re: Actual Flying Rotax Installs

Posted: Tue Jan 26, 2021 12:11 pm

by CaseyCooper

Kai,
I will absolutely! I want to make sure everyone is safe here. And if anyone can learn from something someone has encountered, that’s a good day! Keeps everyone from learning the hard way.
Yikes! I’m glad you made it down though. It’s most important that you were able to walk away and add it to your life’s adventures hopefully to never happen again! Sometimes planes can be your friend, sometimes they’re moody.

Jake,
Fittings and clamps are very important items to set properly! An is definitely the best way to go. The Teflon hoses are basically “forever” hoses, but everything has a lifespan. When installing any hoses you have to be sure of their max suction and pressure ratings. My 912 is not the newest, but the banjo/barb at the sump is factory, and barb fitting at the pump as well. Very common on the older models and have always worked. However, your setup is gorgeous, I was looking at it in your pictures, and definitely the ideal way to go. When my condition of my hoses are up, going that route is very enticing.
Those are on a titan? Those are mounts for a Rans s12! Maybe they use the same mounts? I haven’t seen a Titan out my way with a 912. Or many Tornados at all for that matter. That’s where I took my idea from. We have an s12 in the shop right now next to my Sonex so I just looked at it and reimagined the wheel. I mean it isn’t that hard of an idea to come up with, and like Kai said before, it’s not our idea or a new one. Just seemed like something that would work. But that’s exactly where I got it from. That’s where I got the thicknesses, bushing type, etc.

I did talk to Mark yesterday and he’s working with John on ideas. They’re working very hard and staying focused. Sonex does a great job and I think we’ll be reaching a solution soon.

Re: Actual Flying Rotax Installs

Posted: Wed Jan 27, 2021 10:04 am

by Zack

Herraripower wrote:I did talk to Mark yesterday and he’s working with John on ideas. They’re working very hard and staying focused. Sonex does a great job and I think we’ll be reaching a solution soon.

Thank you for keeping us posted! Please let Sonex know there are other builders waiting for this to be resolved. I just received my engine yesterday. I haven’t called Sonex yet because I figure a minute they spend on the phone with me is a minute they are not working on a solution

Re: Actual Flying Rotax Installs

Posted: Wed Jan 27, 2021 1:39 pm

by SonexN76ET

Here is some more food for thought on engine mounts. Here is the engine mount on a SeaRey Amphibian

I am wondering if a similar setup could be used with the Sonex engine mount?

Jake

Re: Actual Flying Rotax Installs

Posted: Wed Jan 27, 2021 3:28 pm

by Zack

This is what Thomas from Edge Performance in Norway is using. It’s his personal mount and not a product that he offers. I like how it uses the Rotax ring mount design versus a bed mount.

Edit: This isn’t completely accurate, please see Kai’s message below.

Re: Actual Flying Rotax Installs

Posted: Wed Jan 27, 2021 3:39 pm

by Kai

Jake,

Almost anything is possible!

My guess is Sonex will try to aim for a solution where the welded truss can still be used in its existing form, without having to undergo some form of change. In this way only the brackets will have to be replaced with something more suitable, for instance something along the lines Casey has already shown. However, this is pure speculation from me.

Previously it was pointed out that the isolators needed to be loaded axially. The design that Rotax employs with the ring mount was also mentioned as a proper example. However, is this an absolute fact? True, when the isolators in this design are torqued to specs, they compress axially, but what then? At least as long as the engine is not running with the prop pulling, there is no further axial load. On the contrary, engine weight will then at least partially impose a radial load on the isolators. This will over time cause them to deform, just as they do on Jab engines, where I have repleced dozens of them, notwithstanding the fact that there is a 3/4’’ steel tube in their center to support them.

Would it not be better to have the isolator totally encased in a steel housing like on the dynafocal mounts? As mentioned earlier, something like this could be attained by tightening up hefty hose clamps around them. Then again, when would such measures finally be sufficient? Talk about over engineering something!

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Tue Feb 02, 2021 12:14 pm

by CaseyCooper

So I figured I’d take a hiatus from the keyboard and spend more time flying, less time typing.
I went ahead and tested out my mount. First thing I noticed when I ran it up on the ground was the difference in start up and isolation of vibration of the engine from the airframe. It was very smooth.
When flying it, it felt great. I did a series of high speed turns, full power climbs at high angles of attack, stall work, slips, and just regular old flying to feel the characteristics of the plane now, compared to before. I tried to impose a good amount of torque load, gyroscopic forces from axis change, and load on the engine in a hard climb. As a test if felt appropriate to impose as many loads as possible to make sure it was safe. There was no issues of wear, fatigue, or stressed components.
However, there is one issue. But let’s start here;
Aerovee’s, Jabiru’s, and Rotax’s are all flat engines. (Horizontally opposed, boxers, pankcakes, whatever you want to call them). Both the Aerovee and Jabiru have a prop flange on the crankshaft end which puts all loads at the center of rotational mass of these engines. But these engines are limited by their pitch, diameter and number of blades.
Rotax however is smaller dimensionally, and in weight, than both the Aerovee and Jabiru but it’s gear driven which places the prop shaft about 6” above the crankshaft end. Which in turn gives it an arm with an incredible amount of leverage because of its power output and ability to spin much larger and much heavier propellers. So as you can imagine, the propeller flange moves quite a bit where on the Aerovee and Jabiru it stays relatively centered. With these two you may see some rubbing on the back of your propeller or slightly on your propeller spacer but that’s fairly common and it’s never a big issue.
With all that being said, my engine still torqued over and touched the edge of my prop flange hole.
One thing about Sonex as opposed to other manufactures that primarily use a Rotax, is that the exit hole is much smaller. On any Rotax powered aircraft with a cowl, you’ll notice the exit hole for the propeller shaft gives at least about 1.5” around the entire flange/spacer to allow for this torquing over. Other manufacturers such as Aerotrek, Rans, Kitfox, Vans, use about an 8” exit hole and sometimes a center-stepped spacer to allow for this to happen. That’s why you see spinners usually ranging from 8” and up on anything using a Rotax.
On Sonex’s, my opinion, is the hole is too small for a Rotax. I am running a larger spacer, not a center stepped spacer so I am running the tightest tolerance available. With both mounts (mine and Sonex’s), the spacer rubbed on the same spot on my cowl. If you’re sitting in the airplane, it’s the 7 o’clock area of the exit hole where it rubbed. So instead of fighting it, I began sculpting out a relief in my cowl. It’s not noticeable unless you’re really looking for it when looking at my propeller directly from the side. My 8” spinner pretty much hides it. I would fly and check this wear, and sand away as needed. Eventually I got to the point I just drew a dark area with a sharpie on the wear point on my spacer, and when it was no longer being rubbed away, I knew I had shaved off enough of my cowl and the two were no longer touching. Then just went back and wiped off the mark with some carb cleaner.
So to no fault of Sonex, this is just a characteristic of a Rotax.
I went ahead and flew another Sonex today with a Jabiru 3300 just to compare the engine to airframe isolation, and my plane felt just as good if not better.
But everything is working great.

Re: Actual Flying Rotax Installs

Posted: Wed Feb 03, 2021 7:51 am

by 13brv3

Thanks for the update, and for the heads-up on the prop hole in the cowl. I’ll be starting my mount soon, but using a ring rather than bed mount. I’ll make a mental note about the cowl hole size if I ever get to that point.
Rusty

Re: Actual Flying Rotax Installs

Posted: Thu Feb 04, 2021 2:46 am

by Kai

Zack wrote:

image1.png

This is what Thomas from Edge Performance in Norway is using. It’s his personal mount and not a product that he offers. I like how it uses the Rotax ring mount design versus a bed mount.

Zack,

Well- yes, but not quite.

Thomas of EP made up a mount for the combo Sonex/R912 intended for his personal Sonex Legacy #0036 (importet as an EXP-class from the US years ago, and then long since resold to a different owner). I was involved in the design of this mount, and let me tell you for a fact that as a one-off the work was massive. We were contemplating setting up a small series, but try as we might there was no way we could make any profit out of it. Way later someone decided to copy his mount for Sonex Legacy #0772 (also an EXP import from the US!), and this is what the photo you selected shows. This conversion is still ongoing.

You’re right about one thing, though: for a stable installation the R912 ring mount is essential. It positions the isoators so that engine movement, particularily during start up, is limited to acceptable values.

What is important here, is not the R912 ring mount as such, but the position of the isolators. How the isolators get to this location, is another matter. I especially like the idea from the chap in australia, who kept his Aerovee mount and made up a truss ring from square steel tubing with attachments for the isolators to go with. A while back he posted pictures on this group, and his flight reports are good. My own design with a Jab 33 mount, attachment bars, and the Rotax ring, go down the same road, but moves the CG a little further forward. I previously posted some photos of this configuration further up in this thread.

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Thu Feb 04, 2021 10:39 am

by 13brv3

Kai wrote:I especially like the idea from the chap in australia, who kept his Aerovee mount and made up a truss ring from square steel tubing with attachments for the isolators to go with. A while back he posted pictures on this group, and his flight reports are good.

This is probably the mount adapter you’re referring too. I thought really hard about doing something like this, but from past experience I know that all those extra bits of tubing are going to get in the way in a tight cowling.

http://www.sonexbuilders.net/viewtopic. … x&start=10

Rusty

Re: Actual Flying Rotax Installs

Posted: Fri Feb 05, 2021 2:39 am

by Kai

13brv3 wrote:

Kai wrote:I especially like the idea from the chap in australia, who kept his Aerovee mount and made up a truss ring from square steel tubing with attachments for the isolators to go with. A while back he posted pictures on this group, and his flight reports are good.

This is probably the mount adapter you’re referring too. I thought really hard about doing something like this, but from past experience I know that all those extra bits of tubing are going to get in the way in a tight cowling.

viewtopic.php?f=60&t=579&hilit=rotax&start=10

Rusty

Rusty,

Not a bad decision, albeit perhaps not quite for the correct reasons.

Deciding for either the Rotax ring- or something similar, leaves more than enough space for anything under the cowing. However, I will admit that placing radiator, oil tank, and muffler, is a bit of a challenge: it gets crowded in there. However, it can be done as many others have already shown.

The main issue as I see it, is the Sonex cowling which is too shallow up front for the Rotax oil pump housing, the exhaust pipes, and the reduction gear housing- at least if you want to keep the prop flange exactly where Sonex intended it to be. The cowling has to be modified, and I hate composite work, so I made my new one out of sheet: no english wheel so no compound curves. It is a lot of work.

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Fri Feb 05, 2021 12:23 pm

by CaseyCooper

Overall the Rotax mount Sonex produces is a good design. The only problem, which is obvious, it the attach bar system. With their mount I never had any issues of being able to fit my components. The oil pump clears just fine with plenty of room, exhaust also. On my aircraft I put my coolers where it seemed necessary. I fly in southern Arizona, so it’s not uncommon to see 100 degrees OAT by 9 o’clock in the summer time. So I made a scoop in place of the exhaust exit holes that are standard for the Jabirus and Aerovees. It just made sense to utilize that space, plus it created less work for myself. It allowed me to get my coolers partially in the open and let my engine run nice and cool. I haven’t flown it in the summer time yet but I may do some design changes later. My exhaust, I just wanted a sweet sounding, aggressive exhaust so I tigged up my own. However, I will say that the exhaust routing was a bit difficult but made much easier by going to duals instead of trying to join them in one muffler. The engine positioned slightly back like Sonex designed, with the use of a spacer, is exactly where it should be. Under vibration or change the components never touch. I’ll give Sonex credit, for designing it in CAD with dimensions provided by Rotax and their own files, they did a pretty great job straight off. I know that wouldn’t be something most home builders could do. However if you try to produce your own mount, that could present a lot of issues later. Unless you did an absolute stellar job it would be hard to get an A&P willing so sign off on it, resale of the aircraft, as well as support from Sonex.
Also, producing a mount, with proper jigging, proper materials, getting a great welder or if you are a great welder (I say great welder, because I don’t want a good welder making a mount for my lifeline), ensuring all proper measurements and everything is square, painting it afterward, then installing and testing it, you’re far in the hole. Far deeper than just paying Sonex for their hard work. It’s a lot cheaper, less stressful, and looks better to all parties involved when you use factory parts. They will be available for replacement parts, and technical support.
Some aircraft you have to create your own, and for those people, my hat is off to them. That is a great technical endeavor and takes a lot of patience.
I have some photos I’ll try and upload of my install as well as some fellows from France that Mark from Sonex sent me to help me get a few ideas for the project.

Kai,
If you put the prop flange where Sonex suggests for a Rotax, you do not have to modify the cowl. They want it positioned back with a propeller spacer. I used a 2” to save any issues. As I understand it, you had some input in the design of a ring mount Rotax in a Sonex? That would be helpful if you had any pictures of your input or process of helping move that along. That might be an option for some builders wanting to try and go that route. Are you intending on installing a Rotax in your Sonex?

Re: Actual Flying Rotax Installs

Posted: Fri Feb 05, 2021 1:30 pm

by 13brv3

All great points. I would buy a 912 mount from Sonex in a heartbeat if they made one for the Onex. Maybe if I keep putting mine off they’ll make one

One thing I don’t understand is why they’re moving a lighter engine aft? It looks like the goal might have been to keep the prop in the same place for cowl purposes, but I’d think for CG purposes you’d want to move it forward. It must work out OK for CG purposes on the Sonex, or they wouldn’t do it of course.

Rusty

Re: Actual Flying Rotax Installs

Posted: Fri Feb 05, 2021 5:11 pm

by Zack

Kai, thanks for the details! I spoke to Kerry today and they said they were aware of one customer with issues, but he didn’t have any updates. He asked me to email him and he would keep me posted.

Re: Actual Flying Rotax Installs

Posted: Sat Feb 06, 2021 11:18 am

by Kai

Herraripower wrote:Kai,
If you put the prop flange where Sonex suggests for a Rotax, you do not have to modify the cowl. They want it positioned back with a propeller spacer. I used a 2” to save any issues. As I understand it, you had some input in the design of a ring mount Rotax in a Sonex? That would be helpful if you had any pictures of your input or process of helping move that along. That might be an option for some builders wanting to try and go that route. Are you intending on installing a Rotax in your Sonex?

My experience with prop shaft spacers is strained, to put it mildly- that also goes for the R912: so no spacer here.

Intending to install a Rotax in my Sonex?! No, not any more, as it has been sitting in the airframe since last summer.

If you look at the first page of this thread and my posting of August, you’ll find two pics of my installation.

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Thu Feb 11, 2021 9:27 am

by Brett

13brv3 wrote:

One thing I don’t understand is why they’re moving a lighter engine aft? It looks like the goal might have been to keep the prop in the same place for cowl purposes, but I’d think for CG purposes you’d want to move it forward. It must work out OK for CG purposes on the Sonex, or they wouldn’t do it of course.

Rusty

As mentioned early in this thread. I moved the prop hub on mine forward 1 " of the Aeovee position using a bed mount I made. I flew also with the Aerovee turbo that felt balanced perfectly but obviously changed to the Rotax. I can’t imagine how they plane feels to fly after moving the Rotax back as far as the factory mount places it. My plane is within W+B specs but feels a bit tail heavy . I’d probably not enjoy flying a Jab 4cyl one with 2 x ppl, min fuel and an overnight bag.

Have about 100 hours now on the Rotax and flew about 105 hours with the Aerovee turbo. One thing I do miss with the Aerovve turbo is the Stall turns I used to do all the time… Been a bit dubious to even attempt one with the standard Rotax carbs.

Re: Actual Flying Rotax Installs

Posted: Tue Feb 16, 2021 2:45 am

by Kai

Bett,

Hm- I have the same reflections.

The prop flange face of my R912/EP (without any spacer) is 35mm forward of the Jab 33 face with the shortest flange. Because of the lighter R912/EP compared to the Jab33, I did not dare move it further back. I am still a bit away from the session with scales and CG calculations, but I have an additional 10USG seat back fuel tank so my inital stomach feeling is presently calm.

An interesting aside turned up in the latest edition of Light Aviation, the publication of LAA: they were actually fight testing a Sonex Legacy with a Jab 33. In a few hours the test pilot found out the same as I with my 560 hrs in my Sonex (!). The LAA has a mandatory requirement to put 10 kilo’s of ballast in the luggage compartment should the single pilot weight in with less than 80 kg’s. As far as I can understand this means that they feel the plane is on the nose heavy side with the J33? Maybe this is why Sonex moves the Rotax backwards? I have never noticed anything of this nose heavy thing myself, however with my 5’9 I passed 80 kgs 25 years ago…

For 25 years I have been chairing the Tech. Dept. of the SLA section in our national airsports federation. The carb and fuel pump issues with the R912 have aged me prematurely, so I went EFI.

Thanks
Kai
Sonex Legacy #0525, SG, DS
Formerly Jab 120HP
560 hrs

Re: Actual Flying Rotax Installs

Posted: Wed Feb 17, 2021 2:20 am

by CaseyCooper

As far as CG calculations go, and feel of the aircraft in the real world instead of on paper, my Sonex is very well balanced. My cg calculations full forward, and aft, fall right in FAA standards, and within Sonex limits. Solo with full fuel I’m actually just aft of the forward limit by .20”. In flight when solo and full fuel I have to barely apply nose up trim to maintain straight and level flight. I weigh 180 lbs.
I know you might think, well how can that be? A lighter power plant all the way up there and still on the edge of the forward limit?
It really pretty simple. I’m running one of the heavier props you can get, and a three blade at that. As well as a 2” billet spacer. So it may be a lighter power plant, but my moment arm with a considerable amount of weight compared to a Sensenich like most people run on Aerovees and Jabirus, makes a difference. It’s an easy way to move your CG without just adding weight to the front. In the pre-flight stages I was actually considering using a 4 blade prop, with shorter blades, to move my cg even further forward. But with some calculations prior to choosing my propeller I found out that wouldn’t be necessary.
In my opinion spacers are nothing to be afraid of. People use them for good reason and they allow for assistance in these instances where we might need a little more clearance or help elsewhere.

Brett,
I wouldn’t worry about issues during spins or wing overs with your Rotax. As long as you are coordinated and keep positive G’s you won’t have an issue. It’s only a problem if you’re negative for more than a few seconds which is the same with most aircraft without an inverted fuel system. I’ve seen plenty of people do spins, I’ve seen 7 full rotations, and not have an issue. The 3300’s use just a larger version of the 912’s and they perform just fine as well. Although I do recommend operating with an electronic fuel pump as back up, or ON prior to any “aerobatic” maneuvers.

Rotax’s are pretty easy when you get down to the peas and carrots of them. The carbs are nothing to be afraid of, as long as you know how to properly tune them, or have someone who does, they’re wonderful. As most of us know, in the experimental category we can do whatever we want with our aircraft (almost) which means we can run stuff indefinitely if we so choose. But replacing the mechanical pump every 5 years per Rotax specifications will keep things happy.

Re: Actual Flying Rotax Installs

Posted: Wed Feb 17, 2021 3:18 am

by Kai

Well,

As far as the Bings on the R912 go, Europe has been fighting the float issue for at least the last 7-8 years. I am out of count as to how many float SB’s Rotax have issued.

Part of the problem is undoubtedly the universal authority imposed bioethanol (10-15%) content in our 95 octane (RON) mogas. It dissolves the plastic in the floats and they loose buoyancy. The result is that the engines start running rich. Add to that carbs out of synch, props out of ballance, ignition issues, and leaking fuel pumps. It is not a very short list, and a considerable number of running engines shake like wet dogs: easily felt in the airframe.

The operation of a factory standard R912 over here require that you are very much on the ball when it comes to inspection and maintnance, with a much increased frequency.

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Wed Feb 17, 2021 12:03 pm

by CaseyCooper

Kai,
Floats can definitely be an issue but not unmanageable. On each condition inspection you should be taking down the float bowls and inspecting at a minimum as it is. Allow the floats to dry, and weigh them to make sure they’re within spec and give them a shake by your ear and make sure you don’t hear any liquid inside. Also a misaligned float arm can cause issues, as well as old float needles not sealing from old age. Which most the time I’ve found it’s a misaligned float arm or needle causing the issue. I find most people tend to run their carb parts too long and don’t take them down and take the time to maintain them. One, because it’s not cheap to kit both carburetors, and two, people are afraid of them. Then put them back together and re sync them.
I find it VERY rare to find a prop imbalance, leaking fuel pump, or ignition issues. A lot of these come through our doors and it’s not a common issue. But one in a while, we’ll have an ignition issue with a module or stator. But like you say, you have ethanol fuels, and here in Arizona that’s all we can get also unfortunately. Which means more attention to the fuel system and rubbers that may come in contact with the fuel. But it’s a better evil than running avgas in my opinion. As long as you’re flying often, circulating the fuel, and not flying fuel more than a month old, it helps keep things conditioned. Fortunately, and unfortunately, we put on close to 2,000 hours just on our trainer in 3 years which means lots of maintenance, love and care.

ArchiveBot · August 1, 2020, 5:03am

Re: Actual Flying Rotax Installs

Posted: Wed Feb 17, 2021 3:37 pm

by Kai

So- all is well, then?

It has struck me that there always seems to be some genereic fault with our engines.

The R912 issues have already been mentioned. The Jab gen 1-3 brand has been fighting its top end issues since conception. We have had our fair share of broken cranks on VW type 1 aeroderivatives. And so further, and so forth.

Fairly new on the market is UL-Power; too new for anything to chrystalize. Let’s hope it fares better.

I have a 2007 year 100HP Yamaha 4-stroke outboard on my boat, close to 900 hours TT. It is run much like an aircraft engine: a fairly hard pull to get the boat up on plane (t/o and climb), and then a long stint with a little reduced rpm on cruise. So far I have replaced the oil each fall, the timing belt once, and the plugs twice. No one touches it during the winter months lay-up. First start up each spring is a non event, and it runs happily all summer.

Why can’t they engineer and build our engines to a standard like this??

Tailwinds
Kai

Re: Actual Flying Rotax Installs

Posted: Wed Feb 17, 2021 3:59 pm

by Scott Todd

I agree Kai. My dad ran a marina for 20 years in the 90’s and 00’s. I serviced lots of outboards that were totally abused and usually kept running. I was always impressed with them. I’ve been flying a Rotax 912 for the last 25 years. While its a nice engine, I think it has too many maintenance issues and the prices have gone crazy. Modern technology should be able to make an affordable engine that lasts 1000 hours with oil changes and basic maintenance. Oh wait, we already do for cars and boats, like yours. I know every few years someone comes out with a car engine conversion that is supposed to be the next best thing since sliced bead but I really have my eye on the Aeromomentum guys. They have run their engines for thousands of hours in air boat operations building data and confidence. As my Rotax nears overhaul time, I might seriously consider one.

Re: Actual Flying Rotax Installs

Posted: Thu Feb 18, 2021 7:50 pm

by cj1711

I have the sonex 912 engine mount also, the engine has just been fitted. After reading some of the posts about the rubber bushings I am concerned that they are not strong enough. I have chrome moly penny washers (home made) on the outside of the bushings and inserted a close fitting chrome moly bush an 1/8" narrower through the rubber bushings, so that there is some pressure on the rubber when the nut and bolt are tightened. Would like to know how long they are lasting in installations that are flying.

cj1711.

Re: Actual Flying Rotax Installs

Posted: Thu Feb 18, 2021 11:37 pm

by CaseyCooper

Cj,
As far as I know I’m the only one on this thread that’s flown them. Jake has done some ground testing. As mentioned earlier in the thread there has been a few issues with a both of us and a lot of discussion into it. I’ve been working with Mark at Sonex to find a solution and they’re working very diligently to solve the issues at hand.

Re: Actual Flying Rotax Installs

Posted: Fri Feb 19, 2021 2:08 am

by cj1711

Herraripower
I like the the mounts you have made, I’m sure that would fix the issue because the engine is mounted in a bed, which is well supported by the Barry mounts. Are you not happy with mounts?

Re: Actual Flying Rotax Installs

Posted: Fri Feb 19, 2021 2:16 am

by CaseyCooper

Cj,
I’m very happy with the mounts I made! More vibration isolation and more support. I’ve been flying them a few times a week since I made them with no issues. I think a mount system like that is the way to go in combination with the current Rotax mount from Sonex

Re: Actual Flying Rotax Installs

Posted: Fri Apr 02, 2021 3:10 am

by Kai

Anybody with factual CG findings?

I did the excercise on the scales last week: plane on the scales with the upper cockpit longeron level.

To refresh your memory, I have a R912 clone sitting in Sonex standard gear #0525 now. The face of its prop flange is 35mm further forward compared to a Jab33A with the shortest one. To the prop flange is bolted a Sensenich fp prop originally intended for the Sonex with a R914 plus the usual scull cap spinner. Different from most other taildraggers is that there is a 10 gal seat back tank in the fuselage, made up of 1/8’’ Al 6060T6 sheet. I speculate the empty weight to be some 15 lbs.

It came out heavier than expected. Total empty weight is 682 lbs, with 39 lbs on the tail wheel and 643 lbs on the mains. As far as I am able to find out, this puts the empty weight CG at 22% MAC. I am surprised the empty weight CG is not further forward.

Comments, anyone?

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Fri Apr 02, 2021 8:42 am

by sonex1374

Kai,

This probably doesn’t apply to your situation, but it’s a good time to remind everyone that the weight and balance measurements need to be collected while the plane is in a level attitude (upper fuselage longerons horizontal). This will make a surprising difference in the weight on the tail (up to about 5-8lbs more tailwheel weight when tail-down vs level position). Calculating the resulting CG for both sets of measurements, the tail-down CG is approx 1.5 inches further aft than the actual CG when level (or about 2% of MAC difference). This is the same effect as loading the baggage compartment with 40 lbs to get a rearward CG shift of 1.5", so it does make a significant difference.

The change in tail weight when you’re tail-up vs tail-down is easy to see next time you pick up the tail of your plane to move it. You can sense the difference even without using a scale, and even a simple bathroom scale will measure the change. If anyone is not sure how they performed their W&B measurements and think they may have collected the weights in a tail-down position, I’d encourage you to re-do the W&B. It really does matter.

Jeff

Re: Actual Flying Rotax Installs

Posted: Fri Apr 02, 2021 1:37 pm

by CaseyCooper

I agree with Jeff. A good weight and balance is key. Mark and I have been working together on compiling data/information for Rotax powered Sonex’s, every build will be different of course meaning more/different data. But, more people flying them, means more results. Which will benefit everyone in the long run.
I ran a weight and balance with Mark just to be certain of figures and this is what we came up with. I’m at the forward limit for my weight and full fuel, but have no way of going further forward. As fuel burns off, with passengers baggage etc., it still remains in range quite well.
In my opinion, weight and balances don’t always match up on paper vs real world. Rigging comes into play (flaps up or down slightly for example will move your center of lift forward or aft), and of course slight irregularities in measurements, etc. It happens!
One of my intentions of running a 64” Warp Drive, which is solid carbon fiber, extremely durable, but consequently heavy, was to get my cg forward. Being a 3 blade it puts more weight in the front, which was a benefit of offsetting the lighter power plant weight. Also I’m running a 2” spacer the same diameter as the prop flange.

I’ve been attempting to upload a picture of the weight and balance we compiled but the website isn’t letting me. So I’ll try again later!

But for now here are some basic figures I have;

Empty weight: 666 lbs.
Empty cg: 16.85%
Max Forward with 180 lbs pilot and 96 lbs fuel: 20.31%
Max Aft with 180 lbs pilot 170 lbs passenger 38 lbs baggage 6 lbs fuel: 31.21%
Full Gross with 180 lbs pilot 170 lbs passenger 38 lbs baggage 96 lbs fuel: 27.61%

Obviously these percentages can vary given different weights and their location, and also different aircraft with different configurations.

Re: Actual Flying Rotax Installs

Posted: Tue Apr 06, 2021 2:45 am

by Kai

All,

Good points and well taken! Of course I can’t disagree with any of them.

However, my intentions were to get your comments om my actual empty weight CG.

Wih the 912- should one aim for an e-w CG on front of the 20% MAC mark?

I am scratching my head here. Originally my Sonex had a Jab 22A up front. Its e-w CG was at 24% MAC. Takeoff from a grass field with a full tank, pilot and passenger, was an exercise only for the very interested ones. With the 912 I am at 22%.

With the 912 conversion one of the goals was to fully exploit the MTOW of 1150 lbs.
What do you say: go or nogo?

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Tue Apr 06, 2021 10:24 am

by sonex1374

Kai,

My Jab 3300 powered plane weighs 675 lbs empty, with an empty weight CG at 20% MAC. This works out very well over the entire range loading configurations. Solo with full fuel I’m at 21%, with a passenger and baggage and low fuel (flying to camping) I’m at 30%. If the E-W CG was further aft then I could run into a situation where I was very close to the aft CG limit when flying with baggage and low fuel.

My tailwheel weight is 34 lbs, and playing with my CG numbers if I increase it to 39 lbs (like yours) I also would have a E-W MAC of 22%, and this would cause my MAC to change to 31% in my passenger+baggage+low fuel scenario (but still within limits).

I think you’re probably in the sweet-spot with your current W&B (E-W CG MAC of 20%-22%), and I wouldn’t change anything.

Jeff

Re: Actual Flying Rotax Installs

Posted: Tue Apr 06, 2021 12:07 pm

by CaseyCooper

Kai,
I think you’re right on track. The only thing I would possibly worry about is if you’re at full gross, with your aux tank full and baggage, you might fly out your aft end if you don’t burn your aux fuel early in the flight.
With my empty cg of nearly 17% it’s allowed me to operate in all conditions safely without falling out the forward or aft end with fuel minimum and max gross of 1150 with a max aft of nearly 32%.
But with your calculations I would say you still have room to operate well in range. Like Jeff says, I wouldn’t worry. It looks good!

Re: Actual Flying Rotax Installs

Posted: Tue Apr 06, 2021 3:13 pm

by Kai

Guys,

Thanks- both of you.

Much appreciated!

Rgds
Kai

Re: Actual Flying Rotax Installs

Posted: Tue Apr 06, 2021 5:27 pm

by garyb

Hi all
My empty weight CG is 21% MAC at 645lbs I often fly it at 1150 lbs gross with no problems. The CG does track on the fuel cut off line maybe a bit over. I don’t know how others with the Rotax engines get such Fwd empty weight CG’s. I tried to keep the tail light.
Cheers

Re: Actual Flying Rotax Installs

Posted: Wed Apr 07, 2021 5:21 am

by peterp

Hi all,
Mine has prop flange 1" forward and 3/4" up with a ring mount. 650 lb empty and 21% mac. Fly’s just fine. Cheers Peter

Re: Actual Flying Rotax Installs

Posted: Tue Apr 20, 2021 12:30 pm

by CaseyCooper

I’ve posted this on Facebook but I realize not all of us are on there. I made a short video of an evening flight. Details of the days flight are in the description including performance figures. I’m going to make another video of my install with ins and outs that might help other pilots/builders. Once I get used to hearing my own voice on camera. Ha!

Re: Actual Flying Rotax Installs

Posted: Tue Apr 20, 2021 12:35 pm

by CaseyCooper

Also for other builders as an update! Mark and I have been working together after the noted issues with the attachbars. We took my design, modified it slightly, and put together some new bars. These will come anodized and pretty like the original bars and Sonex will be releasing them very soon. I’m going to test a pair to ensure they operate the same as my design, then Sonex will be getting them out! Big thanks to Mark and John for their help and support!

Re: Actual Flying Rotax Installs

Posted: Wed Apr 21, 2021 10:08 am

by 13brv3

Thanks for the update and video. Hopefully future 912 users will appreciate your contribution to a better mount.
Rusty

Re: Actual Flying Rotax Installs

Posted: Wed Apr 21, 2021 11:46 am

by Zack

Thanks for the update!! I’m waiting for the updated mounts to continue with my build.

Re: Actual Flying Rotax Installs

Posted: Thu Apr 22, 2021 1:25 am

by Kai

Good news!

As long as the new design only loads the isolators in compression and tension, this should be fine. However, bear in mind that prop traction too will load the isolators installed horizontally under the engine in shear, for which they are not designed. So this has to be taken into consideration the design of the new bars.

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Thu Apr 22, 2021 12:16 pm

by CaseyCooper

Roger that!
That’s why in my design I did away with any horizontal bushings. That’s what caused the issue in the first place! It’s all just a bed mount now where the engine rests in a cradle with vertically positioned bushings and adapt perfectly to the original tube structure mount. The only change basically from the new ones, and the ones I designed is we got rid of the middle isolator bushings so there’s 4 sets instead of 6 sets.

Mark is shipping them out this week, next week I’ll install them and get some pictures on here sometime next week

Re: Actual Flying Rotax Installs

Posted: Thu Apr 22, 2021 4:15 pm

by Kai

In engineering, there is always a better way…

Why Rotax in the first place could not design their 900-series with a vertical flange mount for the isolators to sit horizontally, thus always loading them in compression/tension like Camit, Jab, UL, VW, LyCon, D-Motor, etc etc have done for ages, is a mystery. Of course Rotax has their bolt-on ring mount solving all issues, but it is heavy and shockingly expensive.

And, as many have discovered, once the ring mount is in place the issue with the water pump inlet elbow has to be dealt with, as the ring mount effectively blocks any possibility to hook up a hose. It forces the builder/installer to design and weld up an alumimium inlet elbow with a 35mm long neck.

So the question remains- which evil to choose? The engine has to be cooled and overloading the isolators must be avoided.

Preferences, preferences…

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Wed May 12, 2021 10:37 pm

by CaseyCooper

Hey guys,
So I received the new mounts, installed them, and I’ve been flying the new mounts a bit. I wanted to try them out for a while before I came back with any news. But the news is, they work fantastic. I don’t know if anyone has had a chance to look them up on the Sonex website, but they’re nearly identical to my originals. I hope those considering installing a Rotax are not detered from the previous mounts.
The only issue there might be is that I’m having too much fun flying this thing.
Next on the list, I’m designing toe brakes for the Sonex hydraulic brakes. But that’s for a different thread.
It’s been awesome talking to you guys, Ive enjoyed your ideas and insight.

Re: Actual Flying Rotax Installs

Posted: Wed May 12, 2021 10:47 pm

by CaseyCooper

https://www.sonexaircraft.com/new-rotax-mounts-050521/

Re: Actual Flying Rotax Installs

Posted: Thu May 13, 2021 1:11 am

by Kai

Great!

I’m happy your work with Sonex solved this issue. Blueskies- Tailwinds!

I notice you fly behind a ground adjustable Warp Drive prop.

Could you elaborate about the rpm settings- wot static ground? And with this setting how much rpm does the engine pick up at wot cruise?

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Thu May 13, 2021 1:32 am

by 13brv3

Good to hear that it’s working well, though I still like the ring mount better. I’m assuming the picture on their web site with the red anodized mounts installed is not your plane. The oil pickup should not be on the front of the engine on a tractor, and I’m hoping it was just an engine they had laying around to use for a picture. The prototype picture above it is likely yours, with the oil pickup where it should be.

Cheers,
Rusty (almost done with engine install)

Re: Actual Flying Rotax Installs

Posted: Sun Jun 27, 2021 2:34 am

by Kai

Finally got old #0525 in the air again.

This time with a 120 HP EdgePerformance EP915ECI powerplant (R912ULS refinement)

First impressions:

I am too hamfisted on the throttle when on the ground: very little goes a long way!

On the ground the coolant quickly boils: get your finger out! But airborne oil and coolant temps drop like stones: they are FAR too low.

Engine torque is at least double that of the Jab 33A: will take some practice getting used to. It turns hard left on the ground and needs a boot full of right rudder. Climbs like there is no tomorrow, is at least as fast as with the 120HP Jab. Prop is a Sensenich 64x82 fixed pitch.

Somehing funny going on with the VSI gage- the pointer is all over the place. Static???

We’re getting there!

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Sun Jun 27, 2021 2:59 pm

by SonexN76ET

Congratulations Kai! Well done!

Jake

Re: Actual Flying Rotax Installs

Posted: Fri Jul 16, 2021 2:44 am

by Kai

All,

Further to my previous posting, I believe I have solved the static issue.

Old #0525 originally had the cheapy ASAS pitot/static tube- I’ve had my suspicions about this one for a long time.

I decided to relocate the static pickup point to the inside of the rear fuselage cone. Problem solved. At 1500’ amsl on a windless afternoon now both the gps and the asi correspond to within a few knots. I speculate that relocating the static to behind the panel under the glareshield, just as Sonex does with the factory prototypes, would give similar results.

Question: will plugs with out of spec gapping result in poor idle?

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Fri Jul 16, 2021 12:22 pm

by killerfish72

Nice! Any pics from the front? I’ve been considering a B Model build with an Edge Performance Rotax. Would like to see how you did your cowl.

Re: Actual Flying Rotax Installs

Posted: Sun Jul 18, 2021 6:15 am

by Kai

Sorry,

I’ve tried to upload a photo, but the system won’t let me. If you pm me, I could mail some pics to give you an idea.

However, you should know that this sheet thing came about because I hate composit work, and not because of any issues with the cowling Sonex supplies. In addition, I am not using the Sonex engine truss for the R912. This is because of cg worries since I am using a 40l seatback fueltank. In addition I had to make space for my twin radiator cooling setup. Further I far too late in the finishing process realized that Sonex is using a 2” prop flange spacer in combination with their own cowling.

I am therefore perfectly confident that it is entirely possible to use the Sonex supplied composite cowling without too many changes provided a more standardized setup is selected.

Thanks.

Re: Actual Flying Rotax Installs

Posted: Sat Aug 07, 2021 4:16 am

by Kai

All,

There are a little more vibrations in the airframe than I appreciate, and the indications are I should probably move my prop a little further forward- say 1” or so (?).

Anybody knows where I could get hold of a prop spacer? (ASAS is out of stock).

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Sat Aug 07, 2021 9:28 am

by 13brv3

Warp drive list some, but no idea if they’re in stock.
https://warpdriveinc.com/propeller-accessories/

I think Saber is the one who makes most of the extensions, so maybe try them as well.
https://sabermfg.com/extensions

Rusty

Re: Actual Flying Rotax Installs

Posted: Sat Aug 07, 2021 5:44 pm

by WesRagle

Hi Kai,

The Sonerai I’m working with has Saber extension on it. Beautiful piece.

I think the guy that makes them is local to me at 0TX0.

Wes

Re: Actual Flying Rotax Installs

Posted: Sat Aug 07, 2021 7:33 pm

by Murray Parr

Kai,
Answer to your Question: will plugs with out of spec gapping result in poor idle?

Plugs not firing properly usually show up as engine missfire at light engine loads, usually just above idle. The reason for this is there is not as high voltage being supplied. If you have missfire at heavier engine loads it could be the plug wires or connectors or even the coils. Do you have the idle mixture set up correctly?

Murray

Re: Actual Flying Rotax Installs

Posted: Sat Aug 07, 2021 8:50 pm

by 13brv3

WesRagle wrote:Hi Kai,

The Sonerai I’m working with has Saber extension on it. Beautiful piece.

Wes

Indeed they are. I have a 3" Saber on my Onex, which I may or may not need. It was from the previous installation of the 912, so I’ve just left it there for now. If I don’t need it, I may just set it on my desk so I can look at it all day

Rusty

ArchiveBot · August 1, 2020, 5:03am

Re: Actual Flying Rotax Installs

Posted: Thu Aug 12, 2021 11:22 pm

by CaseyCooper

Hello all!

I’ve been out and about so I haven’t been on the forums. I’m very happy for you Kai! It’s a world of difference flying a Rotax in a Sonex compared to the other power plants! Your plane looks wonderful. Warp Drive definitely has spacers. They sell Sabre spacers. As far as your roughness, being that your plane was switched to efi might have something to do with it, but unlikely. Especially an Edge engine. They all run like a top. I would definitely check your plugs first, ensure proper gapping, maybe just throw in a new set for giggles and see if the problem goes away. New doesn’t always mean good! I’m very excited to see your progress and what kind of figures you’re seeing and maybe we can compare!

This last month I flew my Sonex to Airventure! It was a wonderful adventure. Interesting weather made things fun but there was no mechanical issues whatsoever with the plane. I managed to put on 36 hours of flight time and 3,500 miles under me on my trip

Next year Sonex is providing a Waiex for the One Week Wonder. They will be building it with a Rotax Is and they are currently working on a Sonex B with an Is in the shop. Some standardized equipment will be coming out for the Rotax installs as well

Re: Actual Flying Rotax Installs

Posted: Fri Aug 13, 2021 1:52 am

by Kai

Good to hear from you!

Issue numero uno, even more worrysome than the slight airframe vibrations, is cooling.

During my Jab days I was constantly fighting high cht’s- nothing I did seemed to finally solve the cooling issue.

Now, with the Edge, I am still fighting them!

But now they are FAR too low. On a good hot quiet summer afternoon at 3500’ amsl I can see 75C oil temp. Coolant never rises above the high sixties. It’s going to look like the north pole in there when winter comes………

I have a split coolant radiator setup. Right and left hand cylinder bank flows are separately collected in small manifolds I made up and routed to their separate radiators- it should be possible to make this out in enclosed photo. Below the radiators the oil cooler (not shown in the photo) is sitting- it’s the biggest Rotax recommends: the EP has an oil jet cooling the underside of the piston crowns (piston cooling, insurance against detonation), so considerable heat from internal components is handled this way.

If I could find a smoothly operating three way flow valve with ø1” hose barb connections, a 50% reduction of the cooling capacity during flight would be possible- but as yet no such luck!

Perhaps in the US?

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Fri Aug 13, 2021 11:38 am

by CaseyCooper

Kai,
I experienced the same issues. I’m actually in the process of redoing my lower portion of my cowl to reduce and streamline my cooling system. I was expecting high temps since in the summer we operate up to 120f (48c) at max and I set it up too well. I’m running a stock 912 radiator and a aftermarket oil cooler in succession in my scoop. When flight testing in December, 65f (18c), I would see 130f (54c) cht and 100f (38c) oil. Which surprisingly a lot of people run those numbers all winter long here. Not saying you should! But people do. We always want around 200f (94c) right? So all I did for a temporary solution was put duct tape across my radiators to bring my temps up. During that time I bought a oil system thermostat that operates at 10% capacity until reaching 180f (82c), then it opens accordingly to maintain temps. I installed it and removed my tape and that in turn brought up my cht’s and they remain an equal temperature to each other in either summer or winter. As a plus, my warm up times went down to about 5 minutes total, when before I would sit for about 10-15 to warm up. I still need it warmer, we want to see 200f (94c) every once in a while to steam off the water and impurities in our oil. So my new cowling should help bring those temps a little higher, I’m also going to install adjustable louvers just to fine tune in flight with changes in atmosphere and terrain.
As a recommendation to you, so you don’t have to manipulate your mechanical integrity, I would do a pass of duct tape on each radiator and go fly it and add or remove tape until you see temps reaching where you’re happy. Then once you’ve reached your happy medium, bend some removable aluminum dams (like a c channel) that you can clip on your radiators just to block some airflow. We have to do that here with our oil coolers on some of the experimentals to bring the temps up in the winter. Then in the summer we remove them to allow the engines run a little cooler. It’s cheap, easy, and affective, without producing points of potential failure in the system. I do like your idea of a split system to help each bank. You could also consider installing a in-line thermostat in your coolant system. You can get a thermostat like mine in either 180f (82c) or 200f (94c) that will restrict the flow down then maintain temp. I would rather dam up my radiators but those are options I see. It would at least get things constant and in the meantime if you wanted to design some baffling to regulate your cooling system, you could still fly happily while improving your system

Re: Actual Flying Rotax Installs

Posted: Fri Aug 13, 2021 11:42 am

by CaseyCooper

Kai,
I read your last post and failed to see that you wrote you had an oil cooler, you could also do as I did! It greatly helped and it was not an expensive or difficult addition. It took about a half hour to install a oil thermostat. In using a oil thermostat it also helps keep your oil temps slightly higher than coolant temps. Which I would prefer

Re: Actual Flying Rotax Installs

Posted: Sat Aug 14, 2021 3:06 am

by Kai

Herraripower,

Thank you for your c/f conversion! It takes the calculator out of my reading

Testing with aluminium tape over the radiator grid is indeed an accepted method to get an idea og cooling efficiency. I have been doing so since these motors appeared on the market. But the coolers themselves are not the issue- the cowling is the culprit. Flow through the coolers during ground operations is insufficient- upstairs there must be a virtual storm in there. And I hate tape.

I had a Jab motor seize on me once because the oil thermostat failed and blocked flow; since then I have been a little reluctant to embrace them. But it would indeed solve my cold oil issue.

A thermostat on one of the coolant cirquits is acceptable as long as it does not block full flow through the heads, so an inline unit (even with an internal 10% bypass) is nogo for me. I would need a 3-way unit, sending either full flow coolant to the radiator, or through the full flow bypass back to the pump inlet (as is done on all car engines). As yet, I have not been able to find one. I know BMW made one a long time ago, but because of outlet positions it would be difficuilt to incorporate into my system.

You would not happen to know of another one, do you?

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Sat Aug 14, 2021 4:29 am

by Paul Johnson

Kai,

I have been researching something else but came across a Thermo-bob, I do not know if it is suitable for what you want but here is a link.

https://watt-man.com/new-shop/thermo-bo … -fittings/

Regarde

Paul.

Re: Actual Flying Rotax Installs

Posted: Sat Aug 14, 2021 12:16 pm

by aripilot

With Laminova oil cooler you get engine temperatures to flying range fast.

Aripilot

Re: Actual Flying Rotax Installs

Posted: Sat Aug 14, 2021 4:13 pm

by Kai

aripilot wrote:With Laminova oil cooler you get engine temperatures to flying range fast.

Aripilot

Yep- no argument there!

However, you need to make absolutely sure that the cooling capacity of your radiator (which then has to cool everything; oil and coolant) is sufficient to handle the additional heat load. I have seen installations with an oil/coolant heat exchanger where an additional radiator was needed to handle it (!)

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Sat Aug 14, 2021 10:15 pm

by CaseyCooper

Kai,
I personally do not know of any thermostats that would be suitable in the coolant system that you’re wanting to achieve, but I’m positive they exist!
Another option, and it may sound silly, but hear me out. The 912’s are water, air, and oil cooled by the principle that air helps keep cylinder head/coolant temps low, coolant helps keep oil temps low, and the dry sump oil can keeps the oil temps lower. So, with that being said, 912’s are not required to use oil coolers but people use them in applications where needed. So, you could take your oil cooler out of the equation completely and just remove it. Or just bypass it with a solid line from your can to your pump, and see what your temperatures do as a test. You may not even need an oil cooler. Your overall engine temps will come up and even out. During this time of year would be about your highest outside air temperatures the engine would see. Im 100% certain with temps your seeing that your engine wouldn’t overheat anyway. If it works, you wouldn’t have to do anything, you may even save a few pounds removing the cooler and extra oil it takes on.
Again, there’s a million ways to skin a cat. But I see that as another possible alternative.
I’ll keep an eye out though for something that may work for you. If not, at least you have some options!

Re: Actual Flying Rotax Installs

Posted: Mon Aug 16, 2021 3:09 pm

by Kai

Herrari,

No- not silly: just been there done that!

First option was just your suggestion: no oil cooler. The result was the oil temp almost went to the moon.

Second option was to install the cooling air side outlets. The result was now the ISS (MIR)

Third option was to install a Laminova oil/coolant heat exchanger. Results better, but the coolant still boiled- this time most likely because the cooling grids in my radiators just have 10% more cooling area than an original Rotax: they could not handle the added heat load.

./. Note (again): this motor has piston cooling. A lot of internal heat is added to the oil. A Laminova will dissipate this heat to the coolant.

Fourth option was to discard the Laminova and replace it with the biggest oil/air cooler Rotax suggests. WOW!! I still have to proceed fairly smartly on the ground before t/o, but once in the air the temps now drop like stones to the values described previously. This leads me to conclude that thermostats on both coolant and oil are a dire neccessity.

But now on a Rotax forum I read that actually there are no lower operational temp limits for the coolant!……. I don’t know what to believe. After all maybe this aircraft engine thing is not for me!

Thanks
Kai
(I can already hear the wailing siren of the vehicle with the nice man in a long white coat and a large hypodermic needle inside)

Re: Actual Flying Rotax Installs

Posted: Sun Aug 22, 2021 4:33 pm

by Zack

Hey guys, I just wanted to update you on how my firewall forward is proceeding. I’m using an MT propeller with a 13" spinner, so my cowling needed radical work to accommodate this. I had a local university scan my firewall forward so I could digitally design the cowling. If anyone is interested in the file please let me know. There was a cost involved in getting the scan.

Re: Actual Flying Rotax Installs

Posted: Sun Aug 22, 2021 4:37 pm

by Zack

I noticed the 912iS has different oil return line crankcase locations than the 912ULS. Please see page 195 of the ULS installation manual and page 156 of the iS installation manual. The mounts will interfere with a standard AN fitting into the crankcase. I told Sonex Tech support and I’m sure Kerry and Mark weren’t too pleased I don’t have a solution to this yet.

Update: This is what Mark and Cris at Sonex had to say "The banjo fitting is a Vibrant Performance 11535 - It’s a 16mm x 1.5 banjo bolt to -8 AN. Here’s the link to Summit: https://www.summitracing.com/parts/VPE-11535 "

Re: Actual Flying Rotax Installs

Posted: Sun Aug 22, 2021 5:35 pm

by Zack

I did some research on oil coolers, and compared the large Rotax oil cooler to some Made in the USA Earl’s oil coolers (Earl’s coolers are cheaper than the stock cooler). I thought my research might help others. The Earls have a roughly square design like the stock Rotax, plus two long and short coolers that have that have >35 sq in of area and may work. I figure slightly larger can be fixed with tape over the fins. I compared the large size oil cooler because the 912iS runs leaner than the 912ULS. The 912iS installation manual identified how much heat the radiator and oil cooler must reject, measured in Kw and BTUs. One of their BTU conversions is incorrect, I forget which one. The Earls coolers say they reject less heat than the Rotax, despite being 33 percent thicker. I can only assume this is a function of the average airflow in the aircraft versus a car.

Rotax large oil cooler P/N 886 015
Width (mm / in): 180 7.09
Height (mm / in): 131 5.16
Depth (mm / in): 40 1.57
Frontal Area 23580.0 36.5844

Earl’s UltraPRO Oil Coolers 361-219ERL
Width (mm / in): 163.5 6.438
Height (mm / in): 146.1 5.75
Depth (mm / in): 50.8 2
Frontal Area 23882.9 37.0185

Earl’s UltraPRO Oil Coolers 361-413ERL
Width (mm / in): 282.6 11.125
Height (mm / in): 100.1 3.94
Depth (mm / in): 50.8 2
Frontal Area 28279.0 43.8325

Earl’s UltraPRO Oil Coolers 361-810ERL
Width (mm / in): 358.8 14.125
Height (mm / in): 76.2 3
Depth (mm / in): 50.8 2
Frontal Area 27338.7 42.375

Update: Mark and Cris at Sonex are going to experiment with an oil cooler in the nose and dual radiators in the side exit air vents. I’m also going to go with the nose location, but a centerline radiator.

Re: Actual Flying Rotax Installs

Posted: Mon Aug 30, 2021 4:43 pm

by Kai

I’ve finally got some cruise numbers.

Airframe: Sonex Legacy #0525 standard gear dual stick, first flight may 2005; accumulated flight hours presently 605.
Engine: Edge Performance EP915ECI (Rotax 912 ULS refinement), max output 120HP/5800 rpm/29,92”Hg. A/F ratio 12.8-13.2, presently 12 hrs tt. Engine is still loosening up and rpm readings very slowly creep upwards.
Cooling: Split radiator up front, on each side of red gear housing, combined grid size as for R914. Oil cooler- the largest size Rotax suggests- installed centrally up front, below gear housing. Cooling air exits under cowling as per plans, plus side outlets.
Prop: Sensenich wood/glass 2 blade fp 64x82 with conical hub for Sonex. Standard Sonex scull cap spinner.

Note: Sensenich prop first had to be dynamically balanced. It is a true cruise prop, at climbout from home field it allows the engine to turn 5200 rpm with initially 29.92”Hg MP (remember:efi- no venturi pressure drop.) VSI then reads 1500’/min. WOT static ground home field 5050 rpm/29.92”Hg MP.

Combo weight: 309 kgs plus 40l fuel and one fat flier. CG empty at 20% aerodynamic chord (forward limit)
Note: very quiet late afternoon, little or no convection, headwind component apprx 5 kts.

Ambient field temp: 24 centigrades
Ambient field pressure: 1022 mbar.
Field elevation: 38’ (!) amsl

Track: 45 degrees magnetic
Altitude: 3000’ amsl.

Rpm: 5050. Mp 22”Hg
ASI: 126 kts (gps gs 122 kts)

Rpm: 5550. Mp 27”Hg (wot)
ASI: 147 kts (gps gs: 143 kts)
Note: it has been explained to me that this would translate to apprx 152 TAS at wot.

Note: I hate TV screens, so the panel only sports steam gages- brand is Aviasport. The tach, however, does not promote exact readings: too fat markings.
Note: while barely acceptable for hot (scandinavian) summer conditions, the cooling system as a whole will be outside Rotax specs during winter. As of present day, oil temp will not rise above 70C. Coolant stops at 65C. What will happen at -10C ambient, keeps me awake!

This original posting has been edited, and will be again as further numbers become available.

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Wed Sep 08, 2021 11:07 pm

by Zack

Thanks for posting those number Kai!

Re: Actual Flying Rotax Installs

Posted: Fri Sep 10, 2021 3:04 am

by Kai

Further to the oil cooler research above, I would like to chip in with the following:

Most automotive oil coolers are designed with passages intended for pressure feed. This makes the passages fairly narrow. The Rotax recommended brand is adapted for suction- the oil pump sucks the oil through the cooler; wider passages. The pressure drop through an ordinary automotive oil cooler could become an issue (oil pump cavitation).

Most automotive oil coolers are designed with a cooling grid intended for airflow generated by dynamic air pressures attained by cars. This results in grid spacings which are narrower than desirable for the faster aircraft. This again could result in cooling efficency issues. To overcome this the Rotax recommended coolers often have wider grid spacings than several makes intended for cars.

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Sat Sep 11, 2021 1:49 pm

by Zack

I wanted to share an update on my cowling. I’m going with a MT propeller with a large 13" spinner, and the stock cowling with the “skull cap” style cowling would have required a lot of custom work. I visited a composite shop in Kansas that walked be through the process of design, gantry CNC mold cutting, fibers, resins, the whole works. It was very fascinating and I learned a lot, but unfortunately that shop was unable to help me. I found another, Mace Aviation in AZ, that was willing to take on the job and was understanding regarding my budget. I contacted a local university who came out and did a 3d scan of the firewall forward plus a foot or so of the windshield and fuselage. This cowling is based on that scan, and it should be adaptable to any B series Sonex or Waiex.

The radiator is fully ducted. We selected a forward tilt to give us room in the rear for an exhaust. I’ll be using the standard Sonex side cowling vents to create negative pressure for the air inlets and oil cooler. Mark from Sonex is currently planning on two radiators in the side cowling vents instead of this approach. It will be interesting to compare the results when we’re done. The other thing Mark is thinking about is a NACA duct to feed engine intake air. I had planned to pull intake air from inside the cowling, but I could retro fit the NACA duct later if I choose.

Re: Actual Flying Rotax Installs

Posted: Sat Sep 11, 2021 2:07 pm

by Zack

The larger spinner and redesigned cowling will really change the profile of the aircraft. Mace Aviation created a 7 page PDF slide show I can share with other views, but I’m not sure the best way to post it.

Re: Actual Flying Rotax Installs

Posted: Sat Sep 11, 2021 2:38 pm

by Zack

Kai, that was very helpful information regarding the oil coolers. One thing that confused me was that the Rotax oil coolers dissipated more heat energy than the automotive coolers. The Rotax cooler dissipates 34,121 BTUs/hr (calculated) while the comparable Earl’s cooler dissipates only 13,000-17,500 BTUs/hr (published). Perhaps this is due to the slower air the automotive cooler is exposed to, and it would be higher at aircraft speeds? In any case, after doing the research I settled on the Rotax oil cooler. I thought the research could be helpful to others considering different options. One thing that could have fooled me was unit conversion. Even Rotax goofed there!

Re: Actual Flying Rotax Installs

Posted: Sat Sep 11, 2021 9:51 pm

by Skippydiesel

Kai wrote:Casey,

When replacing the oil in the tank we are supposed to do this with the aid of compressed air: do not exceed 1bar/15psi!, the manual says.

T

Remember : Murphy lives!

Thanks
Kai

Incorrect - I have been changing the oil in my Rotax 912 ULS for 11 years - the only time additional air pressure is required, is when you do a crank case (complete system) oil removal. For all other changes you, Burble/burp your engine by hand, just drain/replace the tank oil (nominal 3 litres), check for oil pressure (short non ignition crank) - that it.

Re: Actual Flying Rotax Installs

Posted: Sun Sep 12, 2021 2:36 am

by Kai

All,

Regarding the use of compressed air when replacing the oil in the tank: I stand corrected!

Kai

Re: Actual Flying Rotax Installs

Posted: Sat Sep 18, 2021 1:43 am

by Skippydiesel

Herraripower wrote:So with some work I have completed the install of my Rotax with the Sonex mount. With some tweaks to the water pump, elbow replacement and orientation, the Sonex mount works. I had run my engine for the first time today. It’s not yet synced and tuned but it started right up. Currently going to run it for an hour on non synthetic 10w-40 Castrol oil and a Fram filter to break in, tune, and collect all the crap, then I’ll be doing an oil change to the standard Aeroshell and Rotax filter. It’s a 912 with 84mm pistons and cylinders. I had tigged up an exhaust into duals, made a scoop that houses my radiator and oil cooler, and a few other things. I’m running a 64” 3 blade taper and nickel tipped Warp Drive. Right now this is what I have and it’s about ready to be flown. I have a DAR appointment this next weekend to get my airworthiness.

Very interesting; I have just checked out the information printed on my Aeroshell Oil Sport Plus 4 oil containers - no mention of viscosity at all. In fact very little information about the oil. Googled it & learnt a bit more - its a 10W/40 semi synthetic (blend mineral & synth). One particularly important feature is its compatibility with the gear box.

So wondering what is your rational for selecting a Castrol non synthetic 10W/40 and a Fram filter.

Re: Actual Flying Rotax Installs

Posted: Sun Sep 19, 2021 2:49 am

by Kai

Flying Rotax with AeroVee hydraulic brakes:

Any of you Sonex flying R912ULS guys with the standard Aerovee brakes as supplied from Sonex in your plane?

Previously, with the Jab, my Aerovees would hold the plane amiably during static runup and mag tests. However, with the R912, this happy situation is a thing of the past: there is no way the brakes will hold much above 3000 rpm with that enormous paddle blade thing up front: not enough for the mag test.

Perhaps I should start looking for a master cylinder with increased capacity? If so, does anybody know where I could get one?

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Sun Sep 19, 2021 4:21 am

by garyb

I am running the Sonex standard brakes with the machined drums and also only hold up to 3000 RPM. I only really use them for Taxing and occasionally on short fields and find that they deteriorate quite rapidly when they get hot.

Re: Actual Flying Rotax Installs

Posted: Sun Sep 19, 2021 4:25 am

by Skippydiesel

Try the ATEC catalogue page 11-12

https://www.atecaircraft.eu/storage/app … omplet.pdf

Re: Actual Flying Rotax Installs

Posted: Sun Sep 19, 2021 10:49 pm

by CaseyCooper

Skippydiesel,

My Rotax in my Sonex isn’t new. It was sent to my friend Ronnie who is a iRmt and teaches Rotax maintenance courses, works the Rotax booth at Airventure, and produces aftermarket big bore kits and additional components for the Rotax series so I don’t question a word he says. I ran the oil and filter for. break in/cleaning period since the engine was torn down and reassembled with new components. In that period of time I just used it as a flush procedure which he does on every engine he breaks Into just to collect the crap, then throw in new Sport 4 and a Rotax filter.

Kai,

I’m using the Aeroconversion hydraulic brakes. I’m using toe brakes I designed I’m conjunction with 1/8” brake lines with 1/2” bore master cylinders. For all my mag checks I perform them at 3,500 rpm and they hold just fine. If you’re having issues you might try a new master and/or lines and fittings to help provide better braking force.

Zack,

Mark and I at Sonex were taking about that exact issue with the sump on the iS at Airventure and the banjo was the best option. Another that I had found that might work well is at Specialty Flightlines they produce a stainless banjo with about a 30 degree bend that would work wonderfully. They produce Teflon aircraft lines for whatever application. You just send them whatever measurement you have on line length, what fittings you’d like to use, and they make up the lines for you. The nice thing is they’ll last the lifetime of the engine anyway. As far as your cowling your on the right track with a bigger spinner. Because of the torque the Rotax produces, it should have a bigger cowl opening at its disposal. Mark and I had talked about. Blister that they may offer to Rotax users to integrate into their cowling for simpler installations. And as far as the radiators, he had mentioned installing them on the side next to the vents on the B cowls and the exhaust on the bottom. Because I have a vertically split cowl (and makes a molded in scoop complicated) and have found out just how well my plane cools, I’m redesigning my scoop so it’s more aerodynamic and restricts a position of the airflow to bring the temps up. I already have a mock up that recesses my radiators in flush and all in the one scoop. I’ll be making it out of carbon fiber to increase strength and durability. I’m also working on some other aerodynamic components, airframe related, that will hopefully help refine the plane further. I’m eager to see how your install comes along! Looks like you’re right on track with some great ideas.

Re: Actual Flying Rotax Installs

Posted: Sun Sep 19, 2021 10:55 pm

by gcm52

I installed Sonex hydraulic brakes on my Rotax 912 ULS powered Onex. They would not hold at 3000 rpm for the run-up which is supposed to be done at 4000 rpm. I looked for a replacement for the Sonex brakes. I liked Berringer brakes when I looked at them at Sun and Fun, but the cost would be north of $2000. I looked at O’Keefe brakes but they would not respond to phone calls or emails. I ended up installing Matco brakes for about $800 for the wheels and brakes and they work very very well. They basically will hold for a full power run-up and I could flat spot my tires if I put full braking power on during the roll out. ( I have dual toe brakes by the way) They offer a complete brake and wheel kit for the Onex which includes custom machined spacers that were very nicely done.

Re: Actual Flying Rotax Installs

Posted: Tue Sep 21, 2021 12:39 am

by Kai

I mentioned the holding power of the Sonex hydraulic brakes installed in Rotax powered aircraft for Sonex Tech. They had little to suggest.

However, they made it abundantly clear that their brakes were intended for the direct drive engines they support, and not a geared powerhouse like the R912. That the brakes let go at around 3000 rpm did not surprise them at all. But they emphasized that any changes to their original design should ensure that these had no chance of putting a standard gear plane on its nose.

It seems I’m on my own here, so right now I’m toying with the idea of installing a second master cylinder as Sonex supplies- separate brake lines for each wheel caliper, operated by an identical hand lever.

Comments?
Kai

Re: Actual Flying Rotax Installs

Posted: Tue Sep 21, 2021 3:11 am

by Skippydiesel

Kai - did you check out the parts catalogue I mentioned above ? - two different hand/master cylinder options.

Re: Actual Flying Rotax Installs

Posted: Tue Sep 21, 2021 9:20 am

by DCASonex

Kia,
I have Great Plains (now O’Keef) brakes with custom differential toe pedal operators and came much too close to pulling my CAMit 3300 powered tail-dragger over on its nose when a stray gust of wind at end of runway of our hill top airport lifted the tail. MUCH TOO CLOSE! Now only do full power run-ups with tail tied to something immovable.

David A.

ArchiveBot · August 1, 2020, 5:04am

Re: Actual Flying Rotax Installs

Posted: Tue Sep 21, 2021 3:05 pm

by Kai

Skippydiesel wrote:Kai - did you check out the parts catalogue I mentioned above ? - two different hand/master cylinder options.

Yes- I did. Thanks for letting me know!

However, they come with a hefty price- I will probably have to get a little more desperate before I decide to contact them.

Kai

Re: Actual Flying Rotax Installs

Posted: Tue Sep 21, 2021 3:11 pm

by Kai

DCASonex wrote:Kia,
I have Great Plains (now O’Keef) brakes with custom differential toe pedal operators and came much too close to pulling my CAMit 3300 powered tail-dragger over on its nose when a stray gust of wind at end of runway of our hill top airport lifted the tail. MUCH TOO CLOSE! Now only do full power run-ups with tail tied to something immovable.

David A.

David,
That can’t have been much fun! And compared to the prop dia that goes for the CAMit, the 64 inches on my own Sensenich would only make it much worse. Only emphasizes to heed the dire warnings from Sonex Tech.

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Wed Sep 22, 2021 8:43 am

by DCASonex

Kia, I installed my hydraulic brakes before Sonex offered their own version. Back then they were telling one and all that any change from their wonderful mechanical brakes would end up tipping your plane on its nose. I have never come close to pitching my plane forward when applying them while still moving following landings, Just use common sense. I see no need for Full power run-ups prior to flight. If there is any problem when applying full power it will likely show up early in the run with time to abort.

David

Re: Actual Flying Rotax Installs

Posted: Fri Sep 24, 2021 3:01 am

by Kai

All,

I have learned that the size of lever operated MCP master pump Sonex supplies in the Aerobrakes kit, is 3/4”. As mentioned previously I am toying with the idea of replacing it: either with a single 7/8”, or install a second 3/4”- one master for each caliper.

Now, my knowledge of hydraulic brakes is limited: so what would you suggest?

Thoughts? Comments?

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Sat Sep 25, 2021 6:18 pm

by Murray Parr

I have learned that the size of lever operated MCP master pump Sonex supplies in the Aerobrakes kit, is 3/4”. As mentioned previously I am toying with the idea of replacing it: either with a single 7/8”, or install a second 3/4”- one master for each caliper.

Kai,

Larger diameter master cylinder will decrease the braking force to the slave cylinder (calipers) and the brake lever will travel less. You actually need a smaller master cylinder bore size to increase the force applied to the slave cylinders but that will increase the travel required on the lever. Think of it as changing the mechanical (hydraulic) advantage ratio. Not sure if you can buy much smaller than 3/4" and if you can, it might need to have a longer stroke. A simpler way of increasing force would be to change the mechanical advantage with the linkage geometry however, you are now potentially applying more force to the master cylinder than the designer intended.

Murray

Re: Actual Flying Rotax Installs

Posted: Sun Sep 26, 2021 2:53 am

by Kai

Murray,

Much obliged for your comments- but not what I was hoping for!

I know of one Sonex standard gear flying in this country with the original Sonex puck calipers. After testing with the original single 3/4’’ MCP master the owner informs it was replaced with two pcs 7/8’’ Hegar hand lever operated master pumps- one pump for each wheel. At least- that is what he says. Maybe they were 1/2’’?

I tested this setup- the improvement was startling! That is why I thought of trying something similar.

So what you are basically telling me is to downsize: what about two handlever operated 1/2’’ masters?

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Sun Sep 26, 2021 3:59 am

by Skippydiesel

Hi Kai,

Just wondering how easy it would be to use two hand levers (independent main wheel braking).

Have had a short fly in a Europa, configured as a conventional tail dragger and fitted with two hand brakes - not so easy to use when landing. Once down, did help with tight turns at taxi speed.

I am experienced with one lever, mounted on the control/joy stick, operating both mains - does a good job but does not facilitate tighter turns.

Trained in an aircraft fitted with independent toe brakes - also works well but great care needed to avoided doing a ground loop.

Re: Actual Flying Rotax Installs

Posted: Mon Sep 27, 2021 2:37 am

by Kai

Skippy,

Yes- you do have a point!

As long as the levers are short, such as a dual Hegar setup, it is definitely doable- at least I don’t seem to recall any paricular problems.

However, playing two long levers like on the Sonex setup, might be something else- I am far from sure I want to go down that road!

I see that Hegar can provide a 1/2’’ master with a button on the stem, intended for floor installation and heel operation. What about two of those, one for each caliper?

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Mon Sep 27, 2021 11:57 am

by CaseyCooper

Kai,
Murray is absolutely right.
A larger bore will decrease your overall brake pressure, a smaller bore will require a little more effort, but much more pressure. On my Sonex I’m using 1/8” line and 1/2” bore Hegars on my Sonex brakes and if I try and land short and apply hard pressure, I have to back off sometimes because my tail will rise and the plane will nose over. They are toe brakes so I am able to apply a good amount of pressure. They do provide adequate stopping power. Differential definitely makes a difference in control and stopping ability. Now I don’t need a parking lot to make a u-turn. Hegar makes a quadrant of dual masters and handles you could install. Also you could install 2 handles on the stick, I say that because my other aircraft with Hegar brakes have them set up on the handle and they work awesome. I just alternate with my fingers and I don’t have to take my hands off any controls. Only difference between the 2 planes is I have Hegar disk brakes on one, and Sonex on the other. Lines and bore sizes are all the same. I would shy away from heel brakes in my opinion. Or, just make some toe brakes!

Re: Actual Flying Rotax Installs

Posted: Mon Sep 27, 2021 4:33 pm

by Murray Parr

Kai,
I ran the numbers for the master cylinder sizes. The Sonex standard setup (if the master cylinder is 3/4") has a hydraulic advantage of 8.99:1 If you change the master to 1/2" you get a 20.28:1 advantage (which would require less effort but further brake handle travel) or if you use 2 of the 1/2" masters supplying individual brakes you get a 10.14:1 advantage which is a 13% better than factory and most likely a good combination. A single 5/8" master gives a 12.95:1 advantage. The factory brake handle gives a mechanical advantage of 8.93:1 so if considering a change in geometry this should be considered as well. I am toying with the idea of dual brake handles with 1/2" cylinders mainly because it would be easier than fabricating toe brakes.

Murray

Re: Actual Flying Rotax Installs

Posted: Tue Sep 28, 2021 3:06 am

by Kai

Guys,

Thanks- excellent info: a lot to consider!

Two lever operated 1/2” Hegars, one master for each wheel caliper, seems an acceptable way to go. I am a little unsure if I should either adapt the long Sonex brake handle, or put in a complete Hegar setup. Your thoughts on this?

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Tue Sep 28, 2021 6:19 am

by Murray Parr

Two lever operated 1/2” Hegars, one master for each wheel caliper, seems an acceptable way to go. I am a little unsure if I should either adapt the long Sonex brake handle, or put in a complete Hegar setup. Your thoughts on this?

Thanks
Kai

My thoughts would be to try them as supplied and if you need to change the handle geometry you can do that during testing.

Murray

Re: Actual Flying Rotax Installs

Posted: Tue Sep 28, 2021 5:10 pm

by Kai

Murray,

Duly noted: I guess I’ll have to start somewhere! I’ll order the setup from Hegar to set the wheels in motion. The installation will probably be a winter project- at least one wing will have to come off for access.

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Sat Nov 20, 2021 10:48 am

by Zack

Zack wrote:The larger spinner and redesigned cowling will really change the profile of the aircraft. Mace Aviation created a 7 page PDF slide show I can share with other views, but I’m not sure the best way to post it.

Here is the cowling attached.

Re: Actual Flying Rotax Installs

Posted: Sat Nov 20, 2021 10:50 am

by Zack

Zack wrote:Here is the cowling attached.

This is the front view. Oil cooler up top and ducted radiator below.

Re: Actual Flying Rotax Installs

Posted: Sat Nov 20, 2021 5:50 pm

by 13brv3

That does it. I’m never posting a picture of my cowling

Rusty (Frankencowl)

Re: Actual Flying Rotax Installs

Posted: Wed Nov 24, 2021 4:46 am

by Skippydiesel

Zack wrote:

Zack wrote:The larger spinner and redesigned cowling will really change the profile of the aircraft. Mace Aviation created a 7 page PDF slide show I can share with other views, but I’m not sure the best way to post it.

Here is the cowling attached.

I am just at the stage of using;
The Sonex supplied vertical split cowling, suitably modified to fit my set up
OR
Making a cowling from scratch.

My Sonex has a Rotax 912 ULS driving an an Airmaster CS 3 blade prop (large spinner/back plate).
Coolant radiator is mounted just below lower firewall and will be cooled by cowling exit air - cowling will need to be a good fit to facilitate cooling system.
Oil cooler mounted directly behind right cowling inlet(may over cool)

Size of inlets will be critical to achieve adequate ground ops cooling while not creating undue drag in flight.

Any additional information you can supply will be very much appreciated

Re: Actual Flying Rotax Installs

Posted: Mon Nov 29, 2021 10:58 am

by Zack

Skippydiesel wrote:I am just at the stage of using;
The Sonex supplied vertical split cowling, suitably modified to fit my set up
OR
Making a cowling from scratch.

My Sonex has a Rotax 912 ULS driving an an Airmaster CS 3 blade prop (large spinner/back plate).
Coolant radiator is mounted just below lower firewall and will be cooled by cowling exit air - cowling will need to be a good fit to facilitate cooling system.
Oil cooler mounted directly behind right cowling inlet(may over cool)

Size of inlets will be critical to achieve adequate ground ops cooling while not creating undue drag in flight.

Any additional information you can supply will be very much appreciated

This cowling is for a 13" spinner with a 1.5" distance to flange. The airmaster AP332CTF-WWR64W (if that’s what you’re using) can use spinners of the following sizes according to the website: 8.3, 9.0, 9.5, 10.3, 11.2, 12.2, 13.0in. I don’t know the distance to flange of the airmaster, but with spacers you should be able to fit this engine / prop / spinner combination without modification.

I’m having the exhaust fabricated next week. The bed mount will make this challenging and I haven’t selected a design yet. 2-1 out the sides, 4-1 or 4-2-1 out the bottom will be largely determined by available space. I’m working with a motorcycle exhaust fabricator and will use in-line mufflers instead of the standard Rotax log muffler. I’ll provide another update on this in a few weeks.

The oil cooler is mounted just under the propeller and will create positive cowling pressure.

The radiator is inside, with two ducts to keep airflow separate from the air inside the cowling. This will be neutral to cowling pressure. I will tune the outlet size to give the necessary cooling without added drag.

The front air inlets and oil cooler will be vented using the stock Sonex side vents. Since the radiator airflow is self contained, I will undersize these side vents so I don’t have excess drag.

I spoke to Mark and Sonex is planning a split radiator Rotax installation using the side vents to draw air through. They mentioned they are considering blisters to add to the universal cowl to accommodate the Rotax installations. My large 13" spinner would require moving the inlets in the front further to the sides. I didn’t want to do all the custom work required for the spinner, oil cooler and radiator so I started from scratch.

Re: Actual Flying Rotax Installs

Posted: Tue Nov 30, 2021 1:41 am

by Skippydiesel

Great stuff Zack. Thanks for all that. Did you manage to work out how to post the pdf file you referred to??

Re: Actual Flying Rotax Installs

Posted: Thu Dec 02, 2021 8:44 pm

by 13brv3

Getting closer… I moved the 912UL Onex to the hangar today (finally). I just got the last part for the prop installation today, and the engine just needs fuel and a turn of the key aside from that. I hate the cold, so realistically, it won’t be ready to fly until early spring.

Rusty

Re: Actual Flying Rotax Installs

Posted: Thu Dec 02, 2021 9:12 pm

by WesRagle

Hey Rusty,

Looking good! Did you put the O’Keefe Aero landing gear on it?

Wes

Re: Actual Flying Rotax Installs

Posted: Thu Dec 02, 2021 10:37 pm

by 13brv3

Hi Wes,

Stock gear. I went with the 5.00x5 tires, which gave me about an extra inch of prop clearance. Warp seems to think a 60" 3 blade will work fine for 80 HP, so that’s what I’ve got. Prop clearance will be tight, maybe 6", but I had 4" on an RV-3B with a Mazda engine, and those gear legs were really flexible. I never hit the prop, but the guy I sold it to trimmed it a bit on the runway

I’m hoping to get the wings on it tomorrow, and I’ll be really interested to see how the W&B comes out.

Rusty

Re: Actual Flying Rotax Installs

Posted: Fri Dec 03, 2021 10:31 am

by WesRagle

Hi Rusty,

Sounds good. Stay out of the gravel

Wes

Re: Actual Flying Rotax Installs

Posted: Fri Dec 03, 2021 11:15 am

by Kai

Herraripower wrote:Kai,
Murray is absolutely right.
A larger bore will decrease your overall brake pressure, a smaller bore will require a little more effort, but much more pressure. On my Sonex I’m using 1/8” line and 1/2” bore Hegars on my Sonex brakes and if I try and land short and apply hard pressure, I have to back off sometimes because my tail will rise and the plane will nose over. They are toe brakes so I am able to apply a good amount of pressure. They do provide adequate stopping power. Differential definitely makes a difference in control and stopping ability. Now I don’t need a parking lot to make a u-turn. Hegar makes a quadrant of dual masters and handles you could install. Also you could install 2 handles on the stick, I say that because my other aircraft with Hegar brakes have them set up on the handle and they work awesome. I just alternate with my fingers and I don’t have to take my hands off any controls. Only difference between the 2 planes is I have Hegar disk brakes on one, and Sonex on the other. Lines and bore sizes are all the same. I would shy away from heel brakes in my opinion. Or, just make some toe brakes!

Herraripower,

Most gratefull for all explanations given by you, Murray, and others. Should I decide to rebuild the brake system, 2 pcs 1/2” bore masters clearly seem the way to go!

I once flew some kind of Cub (I seem to recall) with heel operated brakes. They indeed took a little while to get used to. And while I don’t feel differential braking is a must operational wise (category ‘nice to have’), making up some sort of baseplate with both heel brake masters installed on them before the whole setup is secured to the cockpit floor, presently clearly seem to be the easy way out installation wise- anyhow much less physical contortions than rebuilding to toe brakes would require. And when I got this setup worked out I could perhaps install some sort of parking brake valve operated by the existing standard wheel brake lever.

But- am I missing something? It seems you probably know something I don’t: why shy away from heel brakes?

Thanks
Kai

Re: Actual Flying Rotax Installs

Posted: Sun Dec 05, 2021 9:51 am

by Zack

Skippydiesel wrote:Great stuff Zack. Thanks for all that. Did you manage to work out how to post the pdf file you referred to??

I would reach out to Ryan Mace at Mace Aviation for details, he could also provide you the PDF. https://www.maceaviation.com/ It has multiple 3D views, some transparent that really help you visualize the cowling. Here’s one page:

Re: Actual Flying Rotax Installs

Posted: Sun Dec 05, 2021 10:58 am

by Zack

Next week is exhaust week, I trailered the plane to the exhaust fabricator yesterday. My goal for the exhaust was equal length primaries and a 4-1 merger into a secondary, all at appropriate lengths for engine size, rpm etc to maximize power between 5400 - 5900 RPM range. I purchased a program called PipePRO that allows you to enter the engine characteristics and it would calculate the ideal pipe length, diameter etc. The end result would look like some of these systems: https://www.kitplanes.com/firewall-forw … t-systems/

Unfortunately the space constraints won’t let that happen. The biggest issue is the Sonex bed mount verses the more typical ring mount. In addition to the mount, the radiator and oil cooler are also on centerline. If I wanted to merge the exhaust from each pair of cylinders it would have to happen behind the radiator close to the firewall. This won’t leave space for any length after the collector, it would have to drop out of the cowling immediately. I would need to use inline mufflers before the collector. Finally, running the exhaust along the entire bottom of the firewall would add a lot of heat where my ECU, fuel pumps, fuse box etc are mounted. Not an ideal situation.

Thanks to the wider firewall on the B-Model, I do have a lot of room on the sides. We are planning to do a 2-1 design with two exits, one on each side. I considered the sides of the cowling first, but I don’t want the exhaust exiting directly in front of the leading edge of the wing, and higher up I have two of Peter’s NACA vents and I don’t want CO poisoning. So out the bottom it is.

Based on my research, and the PipePRO program, I should NOT step up the pipe diameter after the merger / collector on a 2-1 system like I would for a 4-1. I’ll be using 1.2500 OD tubing (the factory exhaust sockets measured 1.1895 OD). The ID is 1.1300 versus the 28mm / 1.100 the Installation Manual calls for. I will try for 11th harmonic 8.8" to 11.9" equal length primaries with 7-15 degree merge angle, then an inline motorcycle style muffler and exit out the bottom between the landing gear legs and the radiator exhaust duct.

The Rotax installation manual states: “Distribution of the exhaust system into 2 separate systems is not recommended. Individual mufflers on either side cause power loss and increased engine noise.” but it also says “The shape and configuration of the exhaust system is essentially determined by the free space available in the aircraft.”. I’m disappointed there wasn’t space for a 4-1 system. Looking back, the only way that would work is if I had ring mount and / or split the radiators, one on each side.

The graphic I shared in the previous post should help visualize this. I’ll take photos this week and share later.

Re: Actual Flying Rotax Installs

Posted: Mon Dec 06, 2021 3:19 am

by Kai

Zack wrote:Next week is exhaust week, I trailered the plane to the exhaust fabricator yesterday. My goal for the exhaust was equal length primaries and a 4-1 merger into a secondary, all at appropriate lengths for engine size, rpm etc to maximize power between 5400 - 5900 RPM range. I purchased a program called PipePRO that allows you to enter the engine characteristics and it would calculate the ideal pipe length, diameter etc. The end result would look like some of these systems: https://www.kitplanes.com/firewall-forw … t-systems/

Unfortunately the space constraints won’t let that happen. The biggest issue is the Sonex bed mount verses the more typical ring mount. In addition to the mount, the radiator and oil cooler are also on centerline. If I wanted to merge the exhaust from each pair of cylinders it would have to happen behind the radiator close to the firewall. This won’t leave space for any length after the collector, it would have to drop out of the cowling immediately. I would need to use inline mufflers before the collector. Finally, running the exhaust along the entire bottom of the firewall would add a lot of heat where my ECU, fuel pumps, fuse box etc are mounted. Not an ideal situation.

Thanks to the wider firewall on the B-Model, I do have a lot of room on the sides. We are planning to do a 2-1 design with two exits, one on each side. I considered the sides of the cowling first, but I don’t want the exhaust exiting directly in front of the leading edge of the wing, and higher up I have two of Peter’s NACA vents and I don’t want CO poisoning. So out the bottom it is.

Based on my research, and the PipePRO program, I should NOT step up the pipe diameter after the merger / collector on a 2-1 system like I would for a 4-1. I’ll be using 1.2500 OD tubing (the factory exhaust sockets measured 1.1895 OD). The ID is 1.1300 versus the 28mm / 1.100 the Installation Manual calls for. I will try for 11th harmonic 8.8" to 11.9" equal length primaries with 7-15 degree merge angle, then an inline motorcycle style muffler and exit out the bottom between the landing gear legs and the radiator exhaust duct.

The Rotax installation manual states: “Distribution of the exhaust system into 2 separate systems is not recommended. Individual mufflers on either side cause power loss and increased engine noise.” but it also says “The shape and configuration of the exhaust system is essentially determined by the free space available in the aircraft.”. I’m disappointed there wasn’t space for a 4-1 system. Looking back, the only way that would work is if I had ring mount and / or split the radiators, one on each side.

The graphic I shared in the previous post should help visualize this. I’ll take photos this week and share later.

Re: Actual Flying Rotax Installs

Posted: Mon Dec 06, 2021 4:19 am

by Kai

Zack wrote:……..The Rotax installation manual states: “Distribution of the exhaust system into 2 separate systems is not recommended. Individual mufflers on either side cause power loss and increased engine noise.” but it also says “The shape and configuration of the exhaust system is essentially determined by the free space available in the aircraft.”. I’m disappointed there wasn’t space for a 4-1 system. Looking back, the only way that would work is if I had ring mount and / or split the radiators, one on each side……..

Zack,

Eighteen months ago this was me.

After intense and exhausting activity of my mental capability I came to the same conclusions as you: INCREDIBLE! I HAVE ACTUALLY DONE SOMETHING RIGHT! But there is always some nagging doubt, so thank you for this confirmation. Hence my decision not to fall for the temptation to use the easy way out and go for the Sonex bedmount. Instead I slightly butchered my Jab 6 mount, fabricated two 12mm steel adapter bars for the rubber isolators to go between the Jab mount and the Rotax ring, and went for a split radiator setup. Pictures of the installation was posted on this forum a good while back.

This setup allows more free space for the exhaust setup, but my Legacy cowling is even more restrictive than your B-type, so the selection of an exhaust system caused many sleepless nights. I finally decided to go for the Rotax 914 setup- piping, flanges, brackets, and muffler. As a replacement for the turbo I had a stainless pipe connector elbow tig welded up with inlet- and outlet turbo flanges on the exact same positions as the turbo housing. The final result is good suppression of the characteristic Rotax exhaust noise, with an aggressive, dark, undertone. Super!

The split radiator setup required some additional work, as overcooling even in high (for us) ambient temperatures could only be harnessed with the addition of tw BMW V12 thermostats, one for each radiator cirquit. Finally coolant temps stay pegged at 80C’s during operations.

Thx
Kai

Re: Actual Flying Rotax Installs

Posted: Tue Dec 07, 2021 11:41 am

by Zack

Kai,

You made a sound decision. My philosophy on this project is to take things one step at a time. In this case my previous decisions have limited my exhaust options. Looking back, I think I’d still chose the Sonex bed mount simply because I’d want an engineered ring mount, I don’t have those skills, and finding others that could engineer and fabricate the ring mount would be expensive. I do wish Sonex would ditch the bed mount though, it’s been a source of frustration.

The 2-1 design should have some advantages, it’s simple, light, and easy to install. The PipePRO program identifies primary and collector pipe lengths based on the harmonics. Like a trombone changing length for different notes, you can tune your exhaust lengths to give you a negative pressure pulse as the exhaust valve opens, to improve airflow through the cylinder head. Here is the output of the program for the 2-1 header (Rotax 912 engine specs but for a 2 cylinder instead of a 4). Caveat: the inputs I supplied to the program were to the best of my ability!

— Primary Tube Specs : Race Header • Single Tube diameter size —
Peak TQ Diameter Range = 1.213 -to- 1.338 Best Length = 32.524 -to- 34.924 inches
Best Mid-Range Diameter = 1.338 Best Length = 32.524 -to- 34.924 inches
Peak HP Diameter Range = 1.338 -to- 1.463 Best Length = 32.524 -to- 34.924 inches

— Primary Tube Harmonics — ( One-End-Closed Tube = Odd Numbered Harmonics )
1st Harmonic = 97.573 to 99.973 inches long … typically never used ( too long to fit any Vehicle )
3rd Harmonic = 32.524 to 34.924 inches long … highly recommended , best Torque and HP Curve
5th Harmonic = 19.515 to 21.915 inches long … shortest recommended ( Shorty or very Hi-RPM Header )
7th Harmonic = 13.939 to 16.339 inches long … shortest recommended ( Shorty, Hugger, or Log Style )
9th Harmonic = 10.841 to 13.241 inches long … shortest recommended ( Log Style or Cast-Manifold )
11th Harmonic = 8.870 to 11.270 inches long … shortest recommended ( Log Style or Cast-Manifold )

— Collector Specs : Straight Tube Collector • or Straight with a slight Merge shape —
Peak TQ Diameter Range = .923 -to- 1.048 Best Length= 21.312 -or- 42.624 inches
Best Mid-Range Diameter = 1.048 Best Length= 21.312 -or- 42.624 inches
Peak HP Diameter Range = 1.048 -to- 1.173 Best Length= 21.312 -or- 10.656 inches

— Collector’s Harmonics — ( Both-Ends-Open Tube = Odd and Even Numbered Harmonics )
1st Harmonic = 170.494 inches long … longest recommended with Mufflers and TailPipes
2nd Harmonic = 85.247 inches long … longest recommended with Mufflers and TailPipes
3rd Harmonic = 42.624 inches long … greater Low RPM Torque -to- Peak Torque RPM
4th Harmonic = 21.312 inches long … highly recommended , best Torque and HP Curve combination
5th Harmonic = 10.656 inches long … reduced Peak Torque , higher RPM HP gains possible
6th Harmonic = 5.328 inches long … reduced Low RPM Torque , even though Tuned Length

Best TQ + HP Tuned Collector Lengths= 5.328, 10.656, 21.312, 42.624, 85.247, 170.494 inches long
Worst TQ + HP Loss Collector Lengths= 7.992, 15.984, 31.968, 63.935, 127.871, 255.741 inches long

Collector definition: from the Primary Tube’s ending inside the Collector -to- Atmospheric exit point
Note : all Tube Outside Diameters are based-off your Header Tube Thickness choice’s value

These lengths are similar when calculated for a 4-1 system, but the collector diameter is larger. 33 in / 84 cm primaries and a 21 in / 53 cm collector would never fit in a Sonex cowl. Even if that large exhaust header fit, it would be heavy and put off a lot of heat to be managed. That squashed my dream of an ideal tuned 4-1 system and made my compromise 2-1 system easier to accept. We’re targeting 5th Harmonic = 19.515 to 21.915 inches long primaries right now. Once we tack that up today or tomorrow we’ll figure out the collector.

We were planning to use an inline motorcycle style muffler as part of the collector. Has anyone had experience with straight pipes on a Rotax, are they really loud or obnoxious?

Re: Actual Flying Rotax Installs

Posted: Tue Dec 07, 2021 12:02 pm

by Kai

Zack,

Depends a little on what kind of straight through muffler you are planning to use.

We have experimented a little with what Tony Bingelis defines as a ‘swiss muffler’. It’s a fairly long outer tube, a perforated inner tube, the space between inner and outer filled with absorption material.

This layout was not a success for the high revving Rotax. To tame the Rotax bark we needed a very long (almost as long as the fuselage) unit. It worked so-so to start with, but after a short while the thing got louder and louder: the absorption material disappeared out of the muffler!

We came to the conclusion we needed something with chambers/deflectors.

Thx
Kai

ArchiveBot · August 1, 2020, 5:06am

Re: Actual Flying Rotax Installs

Posted: Wed Dec 08, 2021 6:54 am

by Skippydiesel

Slightly pessimistic words of caution:

The manufacturer of the engine (Rotax) has gone to great lengths (money, science, experience/testing) to design a machine that will give reliable (safe) service over an extended operational life - what makes you think that you can do better?
The development of the engine exhaust system (extraction pipes & noise attenuator), is but one aspect of a complex relationship with other components & systems - have you considered the negative impacts/benefits if any, of your “enhancements” ?
The internal combustion engine can be likened to a pump. Air & fuel in/burnt fuel & gases out. You are modifying the burnt fuel/gases out side of the plumbing (gas flow) - what, if any changes, have you made to the inlet side ?
With the exception of a relatively small group in society, the noise emitted by a poorly muffled or straight through exhaust system is considered to be unpleasant & anti social - have you considered the noise impact, of your modifications, on those living within earshot ?

To make any significant gain in the power output of a given engine, you must increase the volumetric efficiency (the ability to process fuel/air). No simple task. In doing so you will inevitably increase, the amount of heat developed by the engine and the pressures being exerted on almost all internal components. These will need to be managed by other changes ( eg increased cooling capacity, greater oil flow, stronger/heavier components) if the engines expected in service life & reliability/safety is not to be significantly reduced.

Re: Actual Flying Rotax Installs

Posted: Wed Dec 08, 2021 9:22 am

by Scott Todd

“Rotax bark” ? They tend to be pretty quiet with the stock muffler. No sense re-inventing the wheel.

Re: Actual Flying Rotax Installs

Posted: Wed Dec 08, 2021 11:00 am

by builderflyer

Skippydiesel wrote:Slightly pessimistic words of caution:
With the exception of a relatively small group in society, the noise emitted by a poorly muffled or straight through exhaust system is considered to be unpleasant & anti social - have you considered the noise impact, of your modifications, on those living within earshot ?

My old Jabiru 3300 powered Sonex has the original and rare one piece 3 to 1 collector exhaust. (not the later Jabiru supplied four piece collector exhaust system). My Sonex exhaust sound could be described with only one word,“loud”. However, the one universal comment I get from almost everyone who has heard my airplane fly, and repeated over and over again until I’m tired of hearing it is, how great my airplane sounds. In 16 years of flying my Sonex, I have not received one negative comment on how it sounds, loud or otherwise. But I know you are correct in that my Sonex would be banned from the skies in certain other countries, just not here in the USA.

Art,Sonex taildragger #95,Jabiru 3300 #261

Edit: come to think of it, however, there are some airports in some communities here in the USA whereupon departing from those airports may trigger a nasty letter regarding noise. This happened to me many years ago when I was flying a Bellanca Super Viking out of Torrance airport in southern California, as I recall.

Re: Actual Flying Rotax Installs

Posted: Wed Dec 08, 2021 8:47 pm

by Skippydiesel

[…]

My old Jabiru 3300 powered Sonex has the original and rare one piece 3 to 1 collector exhaust. (not the later Jabiru supplied four piece collector exhaust system). My Sonex exhaust sound could be described with only one word,“loud”. However, the one universal comment I get from almost everyone who has heard my airplane fly, and repeated over and over again until I’m tired of hearing it is, how great my airplane sounds. In 16 years of flying my Sonex, I have not received one negative comment on how it sounds, loud or otherwise. But I know you are correct in that my Sonex would be banned from the skies in certain other countries, just not here in the USA.

Art,Sonex taildragger #95,Jabiru 3300 #261

Edit: come to think of it, however, there are some airports in some communities here in the USA whereupon departing from those airports may trigger a nasty letter regarding noise. This happened to me many years ago when I was flying a Bellanca Super Viking out of Torrance airport in southern California, as I recall.[/quote]

Hi Builderflyer,

I have little doubt that the admiring listeners (to your Jab) were predominantly aircraft/field people.
I too like a good throaty sound from an exhaust, however those non aircraft obsessed persons, living in the vicinity of an airfield, are all too often not so delighted by the sound of aircraft engines.
It behoves all pilots to “fly friendly” that is with consideration for the non aviation persons (the vast majority) in the community.
My little local grass strip, has self imposed noise & overfly limits due to neurotic community members who are convinced the noise of a small aircraft passing overhead, is but the precursor to the same aircraft crashing through their roof.
Do not forget they (the majority) have the voting power to have all sorts of restrictions imposed on aircraft movements and even have an airfield closed (happens here in Australia).
I try my best not to “prod” the beast (the voting community) least they form a committee to close us down.

Re: Actual Flying Rotax Installs

Posted: Wed Dec 08, 2021 9:27 pm

by Zack

Kai wrote:We have experimented a little with what Tony Bingelis defines as a ‘swiss muffler’. It’s a fairly long outer tube, a perforated inner tube, the space between inner and outer filled with absorption material.

This layout was not a success for the high revving Rotax. To tame the Rotax bark we needed a very long (almost as long as the fuselage) unit. It worked so-so to start with, but after a short while the thing got louder and louder: the absorption material disappeared out of the muffler!

Kai, thanks for that input! I am indeed planning for a “swiss muffler” (I had to look that up https://www.piteraq.dk/flight/muffler.html) I hope it will be more robust! Do you happen to know how far the muffler was from the cylinder head? I may ask for an alternative straight pipe section to be included with the exhaust and try them both out. This is who I am having fabricate the exhaust: http://www.stradafab.net/exhausts You can see on the website the mufflers he fabricates for motorcycles. He perforates the inner pipe, then wraps it in steel wool then fiberglass absorption material before sliding a carbon fiber tube over it.

Skippy, I appreciate the words of caution. I don’t have much choice, the stock system won’t fit.

Re: Actual Flying Rotax Installs

Posted: Thu Dec 09, 2021 4:33 am

by Skippydiesel

Zack wrote:

Kai wrote:…
Skippy, I appreciate the words of caution. I don’t have much choice, the stock system won’t fit.

Just checking - this is a Rotax 912 being fitted to a Sonex??

If yes, then I would draw your attention to, the now significant number of 912/Sonex, that have Rotax mufflers hidden within Sonex engine cowl.

Mine - yet to be cowled , painted & fly, should have no difficulty accommodating the Rotax standard muffler (hope I am not being overconfident).

Re: Actual Flying Rotax Installs

Posted: Thu Dec 09, 2021 5:46 am

by Kai

Zack,

You are probably better than we were- but our swiss muffler experience was not a success. Actually, to our astonishment, because we have something similar on our club 180 HP O360 sailplane tug, where it works fairly well. Our R912 issues were insufficient noise attenuation, as well as the ‘stuffing’ disappearing. We first tried with glass wool, then with steel wool, and finally with stainless steel wool. We also tried a few diffrent lengths. Nogo

Selecting the radiator and the oil cooler, their ducting, and their position, mainly governs the layout of the exhaust system. If you start looking on the web, I’m sure you can find a Sonex with the muffler under the cowling. I would not be surprised if the coolers are then either side mounted, or up front behind the cooling air intakes. And I have actually approved an installation where the cooler went behind the seat with a scoop à la a P51 and outside pipes to the engine (It never flew: destroyed during the final build stage in hangar fire).

Thx
Kai

Re: Actual Flying Rotax Installs

Posted: Thu Dec 09, 2021 7:52 am

by Skippydiesel

Well most of the Rotax 912 installations, I have viewed, have the coolant radiator on the left rear side of the engine bay, oil cooler in front and muffler below the engine. There are other variations - my newly acquired, almost complete Sonex, has the oil cooler front left, muffler below and coolant radiator lower centre. The idea being that all the air entering the cowling exists through the radiator. Interesting concept, yet to be proven.

Re: Actual Flying Rotax Installs

Posted: Thu Dec 09, 2021 10:41 pm

by Zack

Exhaust update: We’ve started mocking up equal length primaries.

Exhaust Fabrication 1 small.jpg (58.68 KiB) Viewed 35203 times

We spend 90 minutes studying the available space and I’m happy to report we have come up with a compromise plan. We have a lot more room than we thought behind the radiator after we moved the wiring out of the way. We’re going to run the mufflers at an angle back towards the center rear of the cowling near the firewall, behind the radiator. The exhaust will have one exit, directly downstream of the radiator exhaust duct. This new routing has a few advantages. It will allow for a larger diameter muffler for more sound attenuation. The distance is a “tuned” distance of approximately 21". I’ll only have one exhaust exit in the cowling, not two. Finally, it will exit in the turbulent air from the radiator duct instead of clean air, leaving the airflow along the sides of the bottom fuselage undisturbed for hopefully a small decrease in drag.

Exhaust available space small.jpg (62.09 KiB) Viewed 35203 times

The area in light blue is available, further up the firewall is full with iS stuff (ecu, fuel pumps, fuse box etc). I also have a good 5-6 inches between the engine mount and the radiator exhaust vent. The fabricator feels confident in the durability of the “swiss style” muffler. He wraps the perforated core in stainless steel wool, then fiberglass. If this isn’t durable, I have the space to do a “toucan” style exhaust muffler with a right and left entrance and a center outlet, and the primaries will already be in the right place. http://toucanexhaust.com/

The stock Rotax exhaust muffler will likely fit, but custom primaries will be needed. Maybe a turbo if you want to go wild.

Re: Actual Flying Rotax Installs

Posted: Sun Dec 12, 2021 8:00 am

by Skippydiesel

Turbo charging a naturally aspirated engine, without significant & costly modifications, can only lead to a truncated service life.

If you ned high altitude performance, purchase a Rotax 914 - it will also give you improved take off & climb while giving Rotax reliability & durability.

Your aftermarket exhaust system & mufflers is unlikely to do much more than make an impressive sound - if this is your aim/expectation, go for it (& pay the cost).

The standard Rotax muffler and exhaust pipes will fit & give good service.

Re: Actual Flying Rotax Installs

Posted: Wed Dec 15, 2021 10:29 am

by 13brv3

I won’t be in the “actual flying” category for another couple months probably, but first run was yesterday and there were no surprises. There should be a big asterisk by the “first run”, because this engine had 670 hours on it when I bought it a few years ago, and I had it on a previous plane that I hated, so we already have some history. I guess it’s just first run on this plane. My first pitch guess was 13 degrees, and it hit 5540 rpm on full power static.

W&B came out great. 618 lbs minus wheel pants, and the CG is such that anyone from 100-300 lbs could fly it from full to empty fuel and stay in balance.

Rusty

Re: Actual Flying Rotax Installs

Posted: Wed Dec 15, 2021 7:41 pm

by Skippydiesel

I like it!

Re: Actual Flying Rotax Installs

Posted: Thu Dec 16, 2021 2:03 am

by CaseyCooper

I have not been on this page in a while so I’m doing my best to catch up!

Kai,
I’m just not particularly fond of heel brakes. If I had a choice I’d either have a handle on the stick or toe brakes before I had heel brakes. The coordination between heel brakes and rudder pedals can be tricky and a pain (in my opinion). But like all things, with practice, comes proficiency. You might be able to design a great heel brake mod that works! But I just went with toes. On one of my other planes I made dual handles on the stick and they work awesome.

Zack,
I’m going to try and offer as much information to you as I can, which hopefully other people will learn from as well. As stated previously in the forum I finished my install last year almost 200 hours ago. I destroyed the original Sonex mounts in just hours. I then designed the new bed mount they’re using (the aluminum bracket system) to adapt to the chromoly structure to solve issues at that time. The problem I experienced am experiencing now is a motor mount flex or sag if you will in the chromoly structure. Really the proper mount to have is a ring mount. It would allow for better room for components, it would be lighter, and discourage certain characteristics of a bed mount. Plus a ring mount would allow for turbo charged models, like the 915, which requires the exhaust/turbo system to remain standardized so it would not work with the current bed mount.
With all that being said, my left side parallel bar that the aluminum mount bars attach to (your left side when sitting in the plane), has slightly sagged due to a lack of support. Only about a 1/16” but that translates to a bit at the propeller flange. In talking with Mark, I’m going to do a field upgrade to my motor mount to remove the sag, increase support strength, and hopefully solve the issue. Being that my plane is the only one flying with this mount system and the steady accumulation of hours, it has kind of been turned into a test monkey fortunately/unfortunately. So I will be doing some further modification and I will let everyone know how it goes. With your current set up, your propeller flange WILL NOT, and I’m not saying this to be a Debby downer, stay centered in your cowl and you will end up with an off center spinner. (Low and left if sitting in the plane) and it will look more pronounced with your set up. Your cowl setup is gorgeous. I just don’t want to see it potentially be damaged or have problems. My original cowl for my plane was made with the intention of seeing what worked and what doesn’t, and I’m now in the process of refining the cowling.
I work on Rotax’s everyday and have many hours behind and in front of them. My friend who overhauled my engine before I put it in is a performance Rotax builder, iRmt instructor, mans the Rotax booth at Airventure and one the go to (if not the go to) guys in the U.S.
We’ve talked a lot about Rotax “do’s and don’t s.” The 912uls/ul (carbureted) lends itself well to dual exhaust set ups, or 4 into 1 set ups. As long as you have proper tuning (as you’ve stated) you’ll be fine. You just don’t want any pulses canceling or a surplus of back pressure to keep the engine from breathing properly. After all, an engine is an air pump. It only pulls in as much air as it can push out, it is an exchange for energy. You ideally want a pulse to be accompanied by the next pulse at the proper rate to help cycle air through the engine properly.
However, on the 912is you absolutely have to use their stock exhaust (muffler). Being that it’s computer controlled the exhaust plays a big roll in its operating parameters (o2). So in modification to the exhaust system, it must be “tricked” into thinking its stock but just simply tuning it to stock parameters. Which you are attempting to do so kudos. The problem with your current setup is that the way to do that is to fit a muffler under the mounting truss but now you have radiators in the way. (Which I do also, my radiators are in the exact spot yours are). So that’s a factor to account for. I know at Sonex they’re mounting their radiators to the side allowing for the side ducts on the cowling to provide cooling, then using the under space for the exhaust. Your current exhaust work is a thing of beauty. The only thing I worry about is on hard starts or killing the engine, a Rotax bucks a bit because of its high compression and usually a large propeller up front. So I worry about your exhaust slapping the support it’s directed around. I’m not saying it will, but it’s possible.
Again, I offer my experience just as that. I have no intention of belittling anyones project. Yours definitely is being built with some care. Keep it up!

13brv3,
I’m eager to see you fly that thing! Looks awesome! You may want to dial your pitch in a little more. At WOT at straight and level flight you want to be as close to 5,600 rpm as you can. With your current pitch setting you’ll blow passed that, likely passed the max recommended. Static of 5,300 will get you right where you want to be and give you some more top end.

Someone also asked about the Rotax exhaust growl. My plane I intentionally made it LOUD. I wanted a hot rod and one that sounded like it. I get complements all the time on it’s noise. But in the cockpit it’s no louder than a 3300 or VW. But, you can sure make a 912 whisper which is wonderful in a completely separate way.
I’ll copy the link to an old video but at 11:38 in the video I do a low pass during testing and it gives a good indication of what it sounds like.
https://youtu.be/5lCcuGX2KLc

I’m going to try to keep up to date on my current cowling crusade. I’m switching from the dreaded vertical split cowl to horizontal split with a new look and new exhaust and radiator placement. As well as some aerodynamic devices to be added to the plane to clean it up a bit.

I’m so excited for all these builds! They’re all looking awesome. I can’t wait to sit back and see what comes out. I’ll be flying my plane to Airventure again next year, maybe we’ll get one or two more Rotax powered Sonex’s to show up

Re: Actual Flying Rotax Installs

Posted: Thu Dec 16, 2021 10:36 am

by 13brv3

Herraripower wrote:13brv3,
I’m eager to see you fly that thing! Looks awesome! You may want to dial your pitch in a little more. At WOT at straight and level flight you want to be as close to 5,600 rpm as you can. With your current pitch setting you’ll blow passed that, likely passed the max recommended. Static of 5,300 will get you right where you want to be and give you some more top end.

Thanks for the comments. My target RPM is 5200-5300 for static, and 13 degrees was just a first guess. I haven’t settled on a spinner yet, and there’s plenty of prop fiddling to do. I do worry that at some higher pitch the blades will be partially stalled, so that would give a false high RPM static reading.

I definitely recommend the ring mount. They’re expensive, and not without their own challenges for routing hoses, but it frees the most space possible for everything else you need.

I definitely share your approach to cowling. I’m hesitant to show pictures of mine now

Rusty

Re: Actual Flying Rotax Installs

Posted: Thu Dec 16, 2021 11:37 am

by CaseyCooper

Rusty,
I know how it goes! It’s all the little odds and ends that add up. I particularly like your exhaust. I’m building a brand new Kolb M3xtra for a customer to take to Mexico and fly off the beaches and I installed that exhaust on his engine. It’s convenient because you can rotate those mufflers around the cylinder heads to position them exactly where you want. Plus the exit tubes can be trimmed and manipulated. The guys who make those really did a nice job.
On my plane I have a 64” Warp tapered 3 blade and I’m running 17 degrees of pitch. I tried a 64” 2 blade square tip and had 20 degrees in it to try and load the engine properly and that goes outside the realm of acceptable for me and had exactly that, stalling blades. I have a 68” 2 blade I’m going to give a try but that means 3 point take offs and landings. I should theoretically have the space for it. Props are an interesting science.

Re: Actual Flying Rotax Installs

Posted: Thu Dec 16, 2021 5:51 pm

by Skippydiesel

Herraripower;

The engine “sagging” you referred to; are you using the first Sonex ( 2 piece parallel rails) Rotax adaptor or have you moved to the second (4 piece angle)?

Re: Actual Flying Rotax Installs

Posted: Thu Dec 16, 2021 7:55 pm

by 13brv3

Herraripower,

The Toucan exhaust is certainly a convenient package. The guy who makes them now is not the original guy who came up with it. He bought the business some time back. People worry about the comments in the Rotax manual about not using dual mufflers, but the original Toucan exhaust was developed to satisfy all of the Rotax requirements at the time. It was designed for the 80 HP engine, so maybe all bets are off when you go over that.

As for props, I’m starting with a 60" 3 blade Warp Drive. This is for 80 HP with the lower numerical 2.27 ratio gearbox. I’m thinking you’re running 100 HP from the diameters and pitches you mentioned. 60" gives me 5.5 " of clearance at level attitude, but with no pilot or fuel. I never wheel land, and I won’t be starting now Warp said we can go lower than 60" and stay with 3 blade, but we decided to carefully try the 60" with full square tips, then use the flight data to decide if they should be tapered, or if they can be shortened.

Everything is an experiment, and that’s the part I like. I tend to get rid of planes after I get done tinkering, so it’s best to build planes that will require long term tinkering

Rusty

Re: Actual Flying Rotax Installs

Posted: Thu Dec 16, 2021 10:06 pm

by CaseyCooper

Skippy,
I’m not using the original attach bars. I only used them for about 10 hours before the failed. I designed the new mounts and have put almost 200 hours on them since. I’ve done pretty extensive measuring and found the flexing in the chromoly structure. So hopefully the field upgrade will prove fruitful. The Rotax is just a powerhouse of torque so it works on materials a little differently than the Jabirus and Aerovees like Sonex is used to.

Rusty,
Well one thing is for sure, it’s easier to say don’t do something and have people comply than it is to leave people the option to tinker and potentially cause issues. Kolb exclusively uses the toucan on all their 912uls installations and I’ve seen them on other planes. I’m sure they work just as great.
When I had my 912 gone through I actually had the 2.27:1 gears installed. I wanted a little more speed if I could get it. I know the uls comes with 2:43:1 but they do offer the option for 2.27:1. I actually know a few people who have changed from the 2.27:1 in the ul to a 2.43:1 with a slipper clutch and they love it.
But I wish you luck with your testing! I’m sure that Onex will be a ball of fun. Kelly at Warp is a great guy and he always goes the extra mile to take care of his customers.
I hear ya! Experimentals keep the mind working and ideas original. But sometimes that isn’t always a good/bad thing, but I always find they keep everybody learning.
How close are you to flying?

Re: Actual Flying Rotax Installs

Posted: Fri Dec 17, 2021 1:12 am

by 13brv3

Herraripower wrote:How close are you to flying?

A year ago I would have told you “just a few months” Winter will be my biggest delay now, since I hate trying to work in the cold. There really isn’t that much left to be done though. I’ll be shooting for the first warm days of early spring. I figure that gives the pilot a chance to not be cold, and gives the engine the best chance of not being hot.

Rusty

Re: Actual Flying Rotax Installs

Posted: Fri Dec 17, 2021 1:56 am

by Skippydiesel

Herraripower

“Skippy,
I’m not using the original attach bars. I only used them for about 10 hours before the failed. I designed the new mounts and have put almost 200 hours on them since. I’ve done pretty extensive measuring and found the flexing in the chromoly structure. So hopefully the field upgrade will prove fruitful. The Rotax is just a powerhouse of torque so it works on materials a little differently than the Jabirus and Aerovees like Sonex is used to.”

I hope I am in the final months of building - partial build aircraft came to me fitted with the original two piece Sonex / Rotax adapter.
Previous owner reluctant to action the Sonex offered swap to the newer design 4 piece design (no idea why).
I dont much like the look of rubber isolator’s “in shear” - the new design where they are in compression, makes much mores sense.
I am about to start on the engine cowling installation, so will have to purchase the new design ASAP, so as to accommodate any small changes in engine & prop alignment .
Its a bit of concern that the Sonex chromoly engine frame is flexing - any changes since the new mounts were installed ?

Re: Actual Flying Rotax Installs

Posted: Fri Dec 17, 2021 12:19 pm

by CaseyCooper

Skippy,
That’s interesting the previous owner didn’t want to switch. I would like to understand his reasoning.
I do want to say though, the chromoly is not failing in any way. It’s just moved about 1/16” which could easily happen just in jigging when welding up the mount and in no way is it going to cause failure. But that 1/16” over a distance from it to the propeller flange caused about a 1/4” down and a 1/4” left.
Other manufactures do a 1-2 degree thrust offset to try and manage this phenomenon the Rotax has. They’ll shim the flange up and right so that it returns to center under load. So in no way is this anything new to the Rotax community. ICP produces the Savannah, a Zenith 701 type aircraft, that’s an SLSA and they use this method just by using washers to get the desired angles. Rans uses them on the s12 bed mounts as well. After I weld in a intermediate support in the mount I’m going to monitor its flexing. If it solves it, it will very likely be standard on all the Rotax mounts. But as a temporary solution I’ve shimmed the bed mount with 1/16” fender washers (under the top bed angles between the angle and bushing) and put the flange into a slight offset and it’s been working great. The addition of washers that thin hasn’t caused any strange distortion. It still keeps the bushings at their standard compression. I’ve purposefully put the plane through g loads, high attitude and stress to try and get more movement but it’s been steady so far. It’s just steps to refining it as much as possible. As we all know, Sonex tends to over engineer and build a safe product.
That’s awesome you have a project so close to completion! If you have any pictures it would be cool to see. Everyone’s install is a little different, you might have some good ideas on the build that others haven’t thought of yet

ArchiveBot · August 1, 2020, 5:06am

Re: Actual Flying Rotax Installs

Posted: Mon Dec 20, 2021 11:06 pm

by Zack

Herraripower wrote:Zack,
I’m going to try and offer as much information to you as I can, which hopefully other people will learn from as well. As stated previously in the forum I finished my install last year almost 200 hours ago. I destroyed the original Sonex mounts in just hours. I then designed the new bed mount they’re using (the aluminum bracket system) to adapt to the chromoly structure to solve issues at that time. The problem I experienced am experiencing now is a motor mount flex or sag if you will in the chromoly structure. Really the proper mount to have is a ring mount. It would allow for better room for components, it would be lighter, and discourage certain characteristics of a bed mount. Plus a ring mount would allow for turbo charged models, like the 915, which requires the exhaust/turbo system to remain standardized so it would not work with the current bed mount.
With all that being said, my left side parallel bar that the aluminum mount bars attach to (your left side when sitting in the plane), has slightly sagged due to a lack of support. Only about a 1/16” but that translates to a bit at the propeller flange. In talking with Mark, I’m going to do a field upgrade to my motor mount to remove the sag, increase support strength, and hopefully solve the issue. Being that my plane is the only one flying with this mount system and the steady accumulation of hours, it has kind of been turned into a test monkey fortunately/unfortunately. So I will be doing some further modification and I will let everyone know how it goes. With your current set up, your propeller flange WILL NOT, and I’m not saying this to be a Debby downer, stay centered in your cowl and you will end up with an off center spinner. (Low and left if sitting in the plane) and it will look more pronounced with your set up. Your cowl setup is gorgeous. I just don’t want to see it potentially be damaged or have problems. My original cowl for my plane was made with the intention of seeing what worked and what doesn’t, and I’m now in the process of refining the cowling.
I work on Rotax’s everyday and have many hours behind and in front of them. My friend who overhauled my engine before I put it in is a performance Rotax builder, iRmt instructor, mans the Rotax booth at Airventure and one the go to (if not the go to) guys in the U.S.
We’ve talked a lot about Rotax “do’s and don’t s.” The 912uls/ul (carbureted) lends itself well to dual exhaust set ups, or 4 into 1 set ups. As long as you have proper tuning (as you’ve stated) you’ll be fine. You just don’t want any pulses canceling or a surplus of back pressure to keep the engine from breathing properly. After all, an engine is an air pump. It only pulls in as much air as it can push out, it is an exchange for energy. You ideally want a pulse to be accompanied by the next pulse at the proper rate to help cycle air through the engine properly.
However, on the 912is you absolutely have to use their stock exhaust (muffler). Being that it’s computer controlled the exhaust plays a big roll in its operating parameters (o2). So in modification to the exhaust system, it must be “tricked” into thinking its stock but just simply tuning it to stock parameters. Which you are attempting to do so kudos. The problem with your current setup is that the way to do that is to fit a muffler under the mounting truss but now you have radiators in the way. (Which I do also, my radiators are in the exact spot yours are). So that’s a factor to account for. I know at Sonex they’re mounting their radiators to the side allowing for the side ducts on the cowling to provide cooling, then using the under space for the exhaust. Your current exhaust work is a thing of beauty. The only thing I worry about is on hard starts or killing the engine, a Rotax bucks a bit because of its high compression and usually a large propeller up front. So I worry about your exhaust slapping the support it’s directed around. I’m not saying it will, but it’s possible.
Again, I offer my experience just as that. I have no intention of belittling anyones project. Yours definitely is being built with some care. Keep it up!

Wow, that’s a lot of great feedback, thank you. I’m disheartened to hear the mount is sagging and needs further refinement. Could you please share details of the field modification so I can leave space available as I locate things? Is this issue serious enough to cause you to ditch the bed mount in favor of the ring mount? I have a lot of sunk cost and time working around the bed mount, and I need to decide if I should pull the plug. It’s very frustrating that Sonex advertises a Rotax mount and universal cowling when issues keep cropping up.

Regarding the exhaust, we did our best to follow the 912iS Installation Manual during the design. They have a section titled “If a genuine Rotax exhaust is not used” and states: “The shape and configuration of the exhaust system is essentially determined by the free space available in the aircraft.” This is where I find myself, and I haven’t yet seen an un-modified stock exhaust on the Sonex bed mount. Because of the sloping firewall, you actually have quite a bit of space behind where I mounted the radiator. It’s just that you need a custom routing to get there, and the price of the custom work (I don’t weld) and the stock Rotax muffler to modify isn’t a sound financial choice when you can just build your own. We had to compromise on the “ideal” length of the primaries from the rear cylinders to route around the trusses. We placed the EGT probes per the Installation Manual. IIRC, the ECU is a closed loop EFI with the EGT sensor a key input instead of an O2 sensor. I too worry about rocking motion of the engine in the mount, and have designed in some clearance. I hope it’s enough.

Re: Actual Flying Rotax Installs

Posted: Mon Dec 20, 2021 11:14 pm

by Zack

Here is a picture of the nearly completed exhaust off of the aircraft. You can see the mufflers and EGT mount locations. We’re going to merge these into one outlet on the centerline downstream of the radiator exhaust. I should have picture of it completed this week.

Re: Actual Flying Rotax Installs

Posted: Tue Dec 21, 2021 12:33 am

by CaseyCooper

Zack,
Believe me, I know how disheartening it is. When I originally flew my plane after the engine install (with the very original attach bars) there was fiberglass burning smells, vibrations, all sorts of things that made me wonder if I made the right plane choice (all in under 10 hours). Every flight it seems like I had to tweak things. I originally talked with Sonex and found out they had never installed a Rotax, they just produced the mount, so I was on my own. That’s why I went on to design/produce the updated mounts and test them myself. They were very receptive and eager to help after presenting them with my issues and proof of concept for some changes. But I’m not going to ditch the bed mount just yet. I’m going to try the field upgrade and see what happens. If it doesn’t work, I’ll probably throw in the towel and design a ring mount. I’m trying my best to try and refine it so future people have a successful experience. Sonex is finally about to finish building their first Rotax Sonex and begin their flying and testing fortunately.
As far as the your exhaust, that is a thing of beauty. I can’t believe how good it looks! I’m sure you’ll have success with it. I’d definitely be interested in seeing how it turns out. I’m sure Sonex would too. They’re stuck (last time we spoke) on the exhaust
Please keep us updated! It’s a very nice build you have going.

Re: Actual Flying Rotax Installs

Posted: Thu Dec 23, 2021 7:33 am

by Skippydiesel

HELP!!!

I have tried 4 times to post photos of my Sonex engine installation - every time my whole post disappears, to who knows where?

Re: Actual Flying Rotax Installs

Posted: Thu Dec 23, 2021 9:12 am

by GraemeSmith

Skippydiesel wrote:HELP!!!

I have tried 4 times to post photos of my Sonex engine installation - every time my whole post disappears, to who knows where?

Resize pictures to 1,000 pixels or less on long edge and give them captions in simple text with no punctuation - seems to work best for me. Otherwise the software seems to throw a lot of errors

Re: Actual Flying Rotax Installs

Posted: Thu Dec 23, 2021 5:24 pm

by Skippydiesel

Thanks GS

Re: Actual Flying Rotax Installs

Posted: Wed Dec 29, 2021 1:18 am

by Skippydiesel

Engine to cowl clearances ??

What are measurement are people using for their Rotax to interior of cowl clearance ??

As movement is magnified the further the part is from the source - how much clearance are you giving the exhaust tail pipe to cowl ??

Re: Actual Flying Rotax Installs

Posted: Thu Dec 30, 2021 2:18 am

by Kai

I think it really depends of what kind of engine mount you’re planning to use, how hard your islolators are, and where exactly the exhaust pipe exits the cowling.

Especially on pushers with a bed mount, I’ve seen some hefty movents during startup. Concerning the bedmount in a Sonex, Herraripower should have some answers.

In my own Sonex, I have the standard R912 ring mount in combination with the isolators Sonex provides for the Jabs, as well as the standard R914 exhaust system. The cowling clearance around the exhaust exit pipe is some 3/8’’, which is ample.

Thx

Re: Actual Flying Rotax Installs

Posted: Thu Dec 30, 2021 8:17 am

by Skippydiesel

Kai wrote:I think it really depends of what kind of engine mount you’re planning to use, how hard your islolators are, and where exactly the exhaust pipe exits the cowling.

Especially on pushers with a bed mount, I’ve seen some hefty movents during startup. Concerning the bedmount in a Sonex, Herraripower should have some answers.

In my own Sonex, I have the standard R912 ring mount in combination with the isolators Sonex provides for the Jabs, as well as the standard R914 exhaust system. The cowling clearance around the exhaust exit pipe is some 3/8’’, which is ample.

Thx

Engine mount is Sonex adapter for Rotax installation. Currently the two bar obsolete model, however I am working towards obtaining the latest 4 bar (probably a bit “stiffer”/less engine movement)

As the Sonex adapter utilises the bottom 4 Rotax mounting options, I expect most movement top side of engine, in the lateral plain and at engine start/shutdown.

As for the exhaust tail pipe, it exits at a shallow angle, in line with firewall. As you illustrate, I expect this part of the system, being furthest from the “pivot” point to exhibit the greatest movement. Your 3/4 inch, is that 3/8 in on each side ? (this would be so much easier in metric).

Would love to send a photo but so far have had no luck in uploading photos

Re: Actual Flying Rotax Installs

Posted: Thu Dec 30, 2021 10:29 am

by Kai

Yup,

Apprx 3/8” all around. It is excessive, though, for taking care of all engine movement on the isolators during both flight and start. However, a little extra clearance for the exhhust tailpipe is needed to get the verical split cowling on and off.

However, there is one other big however, I have seen R912 installations (especially pushers) where the motor is only supported on its four crankcase supports. They exhibit a lot more movement than my own installation.

Thx

Re: Actual Flying Rotax Installs

Posted: Fri Dec 31, 2021 1:58 am

by Skippydiesel

Kai wrote:Yup,

However, there is one other big however, I have seen R912 installations (especially pushers) where the motor is only supported on its four crankcase supports. They exhibit a lot more movement than my own installation.

Thx

My guess - the ring mount, with its widely spaced rubber isolators, will control rotational movement, very well but may be subject to “droop” over time. The latest Sonex adapter looks to allow upper engine rotational movement but is unlikely to droop at the prop.

Re: Actual Flying Rotax Installs

Posted: Fri Dec 31, 2021 3:06 am

by Kai

Don’t guess- make sure!

Hang your engine mount on some kind of support, and attach the complete engine on its rubbers. Check the crank cl dimensions, front and rear to a flat ground surface. Let it sit there for a while, and check again.

Any sag will show up immediately. Should it sag just sitting there, it will certainly sag in operation.

Thx

Re: Actual Flying Rotax Installs

Posted: Sun Jan 02, 2022 4:54 pm

by Skippydiesel

Kai wrote:Don’t guess- make sure!
…
Any sag will show up immediately. Should it sag just sitting there, it will certainly sag in operation.

Thx

The design of the latest Sonex /Rotax engine mounts would suggest that “sag” is unlike.

My concerned is the engines lateral/rotational movement, that is likely to be most pronounced at start up & shut down, & the clearance, to inside of cowling, to accommodate this movement.

From the few responses received, it would seem that 10mm (about 3/8ths of an inch) is a generous allowance for front “rocker box” clearance and fuel pump - a little more (?) may be required at the exhaust tail pipe.

Prop spinner clearance looks like it could be reduced to 5mm (1/4 in)

Because my cooling system requires that as much air as possible exits via the coolant radiator, my exhaust pipe will have a flexible seal around its cowling exit. I will design the seal so as to allow for any increased movement in this area.

Re: Actual Flying Rotax Installs

Posted: Mon Feb 14, 2022 6:34 pm

by 13brv3

I’m one step closer to being in the “actual flying” category. My Onex now has an airworthiness certificate now The 912UL engine has been running really well on the ground, and I had it flying in another plane previously. The untested cooling configuration will be the only engine related concern, assuming you don’t count keeping the prop from hitting the runway. I’m not in any hurry to fly it, and have a few other things to tinker with. Maybe in 2-3 weeks when it warms up a bit more.

Rusty

Re: Actual Flying Rotax Installs

Posted: Fri Mar 04, 2022 9:13 pm

by 13brv3

It’s official. Onex 085 made it’s first flight today with a Rotax 912UL and Warp Drive 3 blade 60" prop. It was only about 20 min, just enough to do a few laps at 4000 ft, with a stall, then a landing. No significant issues. The engine was excellent, with nothing out of limits for cooling (purely amazing). Biggest issue is the prop is underpitched, which is an easy fix. There were a few other minor squawks to address with radio and Dynon settings, but overall it went as well as I could have hoped for. This was first flight #7 for me, and it never gets old.

Rusty

Re: Actual Flying Rotax Installs

Posted: Fri Mar 04, 2022 10:12 pm

by Zack

Congratulations!

Re: Actual Flying Rotax Installs

Posted: Sat Mar 05, 2022 9:05 am

by aschlem77

Great work,

Re: Actual Flying Rotax Installs

Posted: Sat Mar 05, 2022 10:35 pm

by CaseyCooper

So awesome! Congratulations. I’m sure it was a wonderful feeling. I’d love to see pictures, video, and any performance figures you have! I hope you start racking up those hours!

Re: Actual Flying Rotax Installs

Posted: Sat Mar 05, 2022 11:01 pm

by 13brv3

Everything is so temporary right now, I’d hate to post pictures of the cowling. I have a history of ugly cowls that haunts me even years later The engine pics are already in the thread.

I had a gopro in the cockpit, but you can’t read the instruments, which makes the flight really boring. About the only thing you can see is how far the ball is off center My biggest issue is that my Dynon D-180 is intermittently dropping out on the EMS side. RPM goes to zero, and every other measurement just freezes. That’s putting a damper on my performance data and I’m not sure how long it will take to get that fixed. Waiting to hear from Dynon, but between that, and weather the next week or so, I won’t be racking up any hours. No hurry really though.

Thanks,
Rusty

Re: Actual Flying Rotax Installs

Posted: Sun May 22, 2022 1:27 am

by 13brv3

What props are the other flying Rotax planes using? My 60" 3-blade Warp Drive has been fine on the Onex, but it’s quite a compromise. I had the pitch set toward the fine end originally, and was seeing over 1100 ft/min climb, but maybe only 115 mph in cruise. I’ve added a couple degrees of pitch since then, and climb is down to maybe 850 ft/min, though cruise is easily 130 mph TAS, and as high as 145 mph at 5750 RPM. I should really add another degree of pitch and try that, but I’m not willing to give up any more climb.

Since I require such a short prop, that rules out all the “pretty” props that are out there. They often have about a 68" min length. I’ve been really tempted to give the Ivo medium prop a try for a couple reasons. First, I’d like to see if it performs better as a fixed pitch, but it would also give me the option to go to in-flight adjustable. A 3rd reason is for some extra engine protection if my limited prop clearance ever catches up with me. Warp Drive props are practically bullet proof, which makes them great for pusher engine installations, but if I ever had a prop strike, I’d probably rather it be with something less durable.

Otherwise, the engine and Onex are doing great. I’ll be working to finalize inlets and outlets on the cowl now that we’re having some 90+ degree temps. No problem with cooling at all, but I need to make it less ugly and reduce the drag some.

Cheers,
Rusty

Re: Actual Flying Rotax Installs

Posted: Mon May 30, 2022 7:32 pm

by Zack

I should receive my M-T prop this week and be flying this fall. It’s a 62" three blade CS prop with a large (13") spinner. They were able to create a custom lengths. Thanks for reporting on your status.

Re: Actual Flying Rotax Installs

Posted: Tue May 31, 2022 12:50 am

by 13brv3

Sounds great, but I’d be afraid to ask what that cost. I ended up ordering an Ivo, and it should be here tomorrow. If it works at least as well as the Warp Drive, I’ll be tempted to add the in-flight adjustable option. I’ll try hard to resist though. I almost never fly cross country, so on the rare occasion that I do, I could easily adjust the prop for best cruise. The rest of the time it could stay on a good compromise setting for local flying.

Rusty

Re: Actual Flying Rotax Installs

Posted: Sun Jun 05, 2022 8:05 am

by Skippydiesel

13brv3 wrote:Sounds great, but I’d be afraid to ask what that cost. I ended up ordering an Ivo, and it should be here tomorrow. If it works at least as well as the Warp Drive, I’ll be tempted to add the in-flight adjustable option. I’ll try hard to resist though. I almost never fly cross country, so on the rare occasion that I do, I could easily adjust the prop for best cruise. The rest of the time it could stay on a good compromise setting for local flying.

Rusty

Somewhere in the vicinity of $15,000 Au - probably the most expensive CS you can get for a Rotax 912

Re: Actual Flying Rotax Installs

Posted: Fri Mar 24, 2023 3:18 pm

by pschwenn

Need advice on how to remove the 912iS water pump elbow that interferes with the engine mount (so that I can replace that elbow with one with a different curve.) The elbows on my 912iS are threaded into the water pump housing and then either soldered or Locktite’d in (can’t tell visually, but can see the threading.)

What is the best way to remove the elbow? Does it depend on whether solder or Loctite was used?

I have tried, without success, penetrant; and heating the housing next to the elbow - both with very high temp soldering iron, and with soldering/braising torch. I guess that the heat expansion coefficient of the elbow is much higher than the housing, so conclude that heat would only work to “destroy” the Loctite, or flow solder.

I understand that the elbows and the threading are fine and fragile enough that no substantial force should be used.

The engine mount in question is the Sonex 912 mount for legacy (not B) Sonex models (mine happens to be Xenos #32). Only one elbow is interfering. The hose could just barely clear, but with the engine running the elbow would risk destruction.

Ideas? Advice? Pointers to prior answers or other info I have missed?

Thank you

Re: Actual Flying Rotax Installs

Posted: Fri Mar 24, 2023 3:57 pm

by Murray Parr

pschwenn wrote:Need advice on how to remove the 912iS water pump elbow that interferes with the engine mount (so that I can replace that elbow with one with a different curve.) The elbows on my 912iS are threaded into the water pump housing and then either soldered or Locktite’d in (can’t tell visually, but can see the threading.)

What is the best way to remove the elbow? Does it depend on whether solder or Loctite was used?

I have tried, without success, penetrant; and heating the housing next to the elbow - both with very high temp soldering iron, and with soldering/braising torch. I guess that the heat expansion coefficient of the elbow is much higher than the housing, so conclude that heat would only work to “destroy” the Loctite, or flow solder.

I understand that the elbows and the threading are fine and fragile enough that no substantial force should be used.

The engine mount in question is the Sonex 912 mount for legacy (not B) Sonex models (mine happens to be Xenos #32). Only one elbow is interfering. The hose could just barely clear, but with the engine running the elbow would risk destruction.

Ideas? Advice? Pointers to prior answers or other info I have missed?

Thank you

It is installed with loctite 648 and needs a lot of heat to remove it. I had to re orientate all mine and one of them started to seap so I did it again and replaced the seaping one with a new elbow.

Try to direct the heat to the housing around the fitting and use a suitable dowel inside the elbow to rotate it with.

If you subscribe to Rotaxowner.com they have a video showing how it’s done, otherwise there are a few utube videos out there I think under installing a rotax on a Zenith

Re: Actual Flying Rotax Installs

Posted: Fri Mar 24, 2023 6:09 pm

by 13brv3

Murray is spot on. I had to turn a couple as well for the ring mount. I just used a good heat gun, not any sort of torch. You just have to be patient and let it soften the locktite.
Rusty

Re: Actual Flying Rotax Installs

Posted: Thu Jun 08, 2023 1:34 pm

by CaseyCooper

So it’s been about a year since my complete cowling change.. I’ve since installed a new panel as well. I just wanted to post an update. (Better late than never)
I’ll be going to Oshkosh again this summer, starting out in Tucson Arizona. It’s about a 3,500 mile round trip for me and this’ll be the 3rd time making the journey with the plane! Very excited! I saw Jake got his swap completed. I’d love to hear how it does!
I hope the rest of you guys are doing well in your endeavors

Re: Actual Flying Rotax Installs

Posted: Thu Jun 08, 2023 6:56 pm

by Skippydiesel

Hi Harraripower,

Beautifully presented Sonex.

My Sonex will be returning to the workshop, next week, for a comprehensive rethink of the cooling system (oil temps way too high).

To assist my rethink, I am trying to get as much information as possible, from Rotax drivers, about their(successful) cooling management.

To this end I would ask that you post photos of your engine /cooling arrangements (both sides and front shot) and of your cowling In & Out air vents.

Oh! and your ground/taxi, climb out & cruise temperatures with OAT would also be helpful.

Thanks in anticipation

Re: Actual Flying Rotax Installs

Posted: Thu Jun 22, 2023 3:26 am

by Skippydiesel

Hi Harraripower,

Would realy like to see some photos and get some dimensions (including your cowling belly scoop)