Sonex/Rotax Engine Bed
Posted: Sat Dec 16, 2023 5:15 am
by Skippydiesel
Have just installed the latest Sonex fix for excessive Rotax engine movement.
Have precisely one hours flight time on the latest mod - two additional washers in each rubber stack.
Removed cowling to inspect for movement /contact signs.
Movement : may be very slight improvement - early days for signs of abrasion/polishing. The exhaust tail pipe has contacted the cowling (as before washer fix). Have used “witness” paint on all previous signs - most good.
Possible bigger problem: Both rear engine mounts - bottom rubber (lowest in stack) has become displaced sideways - right side the most obvious.
Front rubbers: As installed, ie nothing unusual.
Your advice/comments will be eagerly read (Is it okay to go flying?)
Re: Sonex/Rotax Engine Bed
Posted: Sat Dec 16, 2023 10:04 am
by Ercoupechris
Sorry to say it but until someone comes up with a ring mount engine mount or rigid connection at engine and resilient isolators on the firewall, like most 912 engine installs are done, you will continue to be R&D
Re: Sonex/Rotax Engine Bed
Posted: Sat Dec 16, 2023 11:33 am
by Kai
Ercoupechris wrote:Sorry to say it but until someone comes up with a ring mount engine mount or rigid connection at engine and resilient isolators on the firewall, like most 912 engine installs are done, you will continue to be R&D
During our development work getting the Edge engines into the Sonex airframe, we looked at this. We quickly came to the concusion that the ring mount was the only way to go, and developed an engine mount for the Sonex A accordingly: look up Sonex turbo on YouTube. However- making a welding jig and making the mount was a LOT of work! And unless you had a certified welder that was willing to work for free, costs would be close to astronomic in a shoestring operation. There was no way we would be able to recover some of the expenditure, not to mention the glaring absence of paying customers. So the rather voluminous welding jig was dismantled when nobody showed any interest: one chapter closed!
Having said that; there are industrious people who have had the fortitude to successfully go down that road, so it can be done. I know of one guy in Sweden and one in Argentina. I am sure there are more.
Anyhow, what you see below, is what Edge came up with. If memory seves me right, the basis for this taildragger mount was a Sonex product for the Aerovee. After all these years, it is still flying.
Re: Sonex/Rotax Engine Bed
Posted: Sat Dec 16, 2023 4:48 pm
by Skippydiesel
I am seriously considering obtaining firmer rubbers - I know they are available.
What I don’t know is, what the pros/cons may be in fitting firmer rubbers - what think you?
My Sonex Legacy has the thinner, than B model, bolts connecting the Sonex/Rotax adapter. There are 4 of these, in shear and they just don’t “look” to be adequate. The reason I mention this, are my concerns that stiffer engine mounts may put additional pressure (vibration/twisting force) on these bolts - comments?
Re: Sonex/Rotax Engine Bed
Posted: Mon Dec 18, 2023 2:40 am
by Ercoupechris
Skippydiesel wrote:I am seriously considering obtaining firmer rubbers - I know they are available.
What I don’t know is, what the pros/cons may be in fitting firmer rubbers - what think you?
My Sonex Legacy has the thinner, than B model, bolts connecting the Sonex/Rotax adapter. There are 4 of these, in shear and they just don’t “look” to be adequate. The reason I mention this, are my concerns that stiffer engine mounts may put additional pressure (vibration/twisting force) on these bolts - comments?
I would try to get a hold of Casey Cooper as I believe he is using the Rotax rails that Sonex provides. I could be wrong but I seriously doubt there’s more than a handful of those things (Rotax rails) actually flying in the fleet right now. The design that Sonex decided to go with was a compromise mainly surrounding their thoughts on the high cost of using the Rotax suspension ring. They could’ve gone with the alternative of resilient mounting the engine mount to the firewall and picking up the four mounting points on the rear of the Rotax engine rigidly. Those who don’t use the Rotax suspension ring almost always go with this alternative method where cost is a concern.
This is one area where they should’ve gone with the best solution, not the least expensive one. It’s my belief that people that are spending the kind of scratch that it takes to put a Rotax on one of these airplanes, would rather have the better solution. I did a little research and the best I can tell, the Sonex design closely mimics, but is not exactly, what the Czech sport cruiser bed mount uses.
Re: Sonex/Rotax Engine Bed
Posted: Mon Dec 18, 2023 5:41 am
by Kai
The issue with those confounded iRMT´s, is that they very often have a point: several points, as a matter of fact. The advantages of the vertical suspension layout for the Rotax 912 is no exeption, and those who feel that the Rotax ring is on the pricey side, have new mounts for the Sonex keep popping up all over the place.
See these two mounts. The black one is from some genius Down Under, the other one flies in Sweden. And a chap in Argentina refined my own crude work by making a sculpture mating an Aerovee mount to the R912
Re: Sonex/Rotax Engine Bed
Posted: Mon Dec 18, 2023 3:28 pm
by achesos
Hi Skippy,
For what it’s worth, I used to work at a motorcycle manufacturer that used rubber mounts for engines with a fairly significant imbalance…
That said, my caution for changing the durometer (stiffness of rubber) of an engine isolator will also cause a change in the energy transfer from the rotating engine likely causing some vibration level into the frame of the aircraft. Stiffer isolators increase the energy at higher frequencies. Softer ones damp the vibrations at lower frequencies.
The harmonics in the airframe noticed with one engine type and mount may not be observed in the same airframe with a different engine and the same durometer mount. ‘Balance factor’ is a thing. There are companies that specialize in ‘tuning’ isolators for specific installations if the budget will allow the science to do the development of the ‘best’ solution - there are always trade-offs for slightly less evil somewhere.
It really is a relatively inexpensive experiment, and maybe you won’t hear any new buzzing. Structural engineers might caution you on fatigue life. The vibration energy (excitation) has to go somewhere…
Keep us posted!
Re: Sonex/Rotax Engine Bed
Posted: Mon Dec 18, 2023 5:31 pm
by 13brv3
I’m very glad I chose to use the ring mount. My only regrets are not adding some right thrust angle, and not using a softer damper. I used Lycoming sized conical dampers, and they’re a bit too stiff.
Re: Sonex/Rotax Engine Bed
Posted: Mon Dec 18, 2023 5:37 pm
by Kai
An interesting thread indeed!
Reminds me of my own trials and tribulations when I went through this. Now I have spent the entire evening fanning around on the internet, looking for pictures and drawings for R912 bed mounts: it should be emphasized that a successfull R912 bedmount seems decidedly possible. However, what strikes me, is that these other bed mounts without exeption have their rubbers positioned far outside the circumference of the oil sump, wheras with the Sonex setup the rubbers are positioned almost on the centerline under the sump, thus robbing the design of any arms to react torque. And thanks to the psru, torque is considerable on these motors, causing deflections of a magnitude not experienced with direct drives. In addition, there is little to prevent the motor from wobbling up and down: IMHO everything on the mount is just spaced too close together.
However, that is what I feel. Others might have another opinion- comments?
Re: Sonex/Rotax Engine Bed
Posted: Mon Dec 18, 2023 5:48 pm
by Kai
13brv3 wrote:I’m very glad I chose to use the ring mount. My only regrets are not adding some right thrust angle, and not using a softer damper. I used Lycoming sized conical dampers, and they’re a bit too stiff.
Rusty- beautiful! Very nice and clean design.
Re: Sonex/Rotax Engine Bed
Posted: Mon Dec 18, 2023 6:09 pm
by Skippydiesel
13brv3 wrote:I’m very glad I chose to use the ring mount. My only regrets are not adding some right thrust angle, and not using a softer damper. I used Lycoming sized conical dampers, and they’re a bit too stiff.
I second all of Kai’s comment - I am particularly impressed by the size of the sockets for the rubber vibration isolators - no problems with vertical loads.
How will/is the undercarriage attached?
Re: Sonex/Rotax Engine Bed
Posted: Mon Dec 18, 2023 6:33 pm
by Skippydiesel
Thank you all for your responses.
I have written to Sonex on this topic - hope to hear from them in the next day or so.
Summarising the advice so far:
Ring Mount
This would seem to be the best solution.
I would really like to go down this route BUT just got this Sonex into the air (seem to have solved the earlier cooling issues) and need to recover from all the unforeseen/unplanned expenditure.
I dont have the knowledge or skills to build one, so am dependent on purchasing the ring from Rotax ($$$!) & having the Ring/Sonex frame fabricated by someone else($$$!).
Higher Durometer Rubber
[list=]Fitting stiffer rubbers may be the most cost effective/easier/quicker answer BUT could have unforeseen consequences elsewhere, due to transferring more of the vibration & twisting forces to the Sonex engine frame & airframe. This may be my most likely attempt at a solution.
[/list]
Live with the current situation
[list=]In the short term, I think I will continue to fly with what I have got and monitor the situation as best I can. I should hear from Sonex soon & they may have some useful comments.[/list]
Re: Sonex/Rotax Engine Bed
Posted: Tue Dec 19, 2023 1:39 am
by Kai
Skippy,
I have to disagree- it does not have to cost a leg and an arm. Secondhand and/or surplus ringmounts for the 912 turn up on the web from time to time. Surplus Aerovee mounts for the Sonex likewise- the core weight of the Aerovee is close enough to the 912 for CG purposes. Then you make up the famous two 12mm steel (or resilient aluminium if you can get hold of it!) adapter plates, and you are in business. No welding att all.
My two bits.
Re: Sonex/Rotax Engine Bed
Posted: Tue Dec 19, 2023 4:40 am
by Skippydiesel
Ercoupechris wrote:Sorry to say it but until someone comes up with a ring mount engine mount or rigid connection at engine and resilient isolators on the firewall, like most 912 engine installs are done, you will continue to be R&D
I reckon that Sonex could easily adopt 13brv3/Rustys concept - Rotax ring mated to Sonex framework - beeeeautiful!
Re: Sonex/Rotax Engine Bed
Posted: Tue Dec 19, 2023 4:42 pm
by 13brv3
Skippydiesel wrote:How will/is the undercarriage attached?
The Onex is a bit unique for the tailwheel plane since there’s no gear sockets on the mount. It uses flat aluminum gear attached to the fuselage. Fabricating a mount with the gear sockets or nosewheel would have been more complicated for sure.
Re: Sonex/Rotax Engine Bed
Posted: Tue Dec 19, 2023 7:29 pm
by Skippydiesel
13brv3 wrote:
Skippydiesel wrote:How will/is the undercarriage attached?
The Onex is a bit unique for the tailwheel plane since there’s no gear sockets on the mount. It uses flat aluminum gear attached to the fuselage. Fabricating a mount with the gear sockets or nosewheel would have been more complicated for sure.
Thanks for that - explains, in part, why your system looks so wonderfully clean/minimalist - I have a Sonex Legacy/Rotax 912 ULS sitting on the Sonex Mk2 engine bed adapter - nowhere near as “clean” as your system.
Re: Sonex/Rotax Engine Bed
Posted: Fri Feb 09, 2024 6:05 pm
by Skippydiesel
Calling Casey Cooper
Hi Casey, as a fellow Sonex/Rotax owner, I would like to make direct (person to person) contact with you, to compare experince with the Sonex /Rotax engine bed adapters, through Forum private messaging.
Re: Sonex/Rotax Engine Bed
Posted: Sat Feb 10, 2024 8:42 pm
by CaseyCooper
Hello all,
This has always been a long winded story between Sonex and Rotax.
The original attach bar/mount Sonex sold was an attempt to finally provide an option for those that always wanted a Rotax in a Sonex.
I bought a Sonex with the whole hearted intent on having it equipped with a Rotax. Having an Aerovee or Jabiru wasn’t ever on the table for me.
On my first several flights I completely destroyed their 1st generation rails. Discouraged but determined, I began to design my own to replace theirs. I had just dumped my entire savings into a plane that didn’t work. The 2nd generation rails they now provide was my solution to the initial problem.
(Sorry to add my story time.)
As you stated Skippy, the engine moves. A LOT. Bed mounts of any kind with a Rotax tend to move quite a bit because of motor mount flex. In my opinion the 6.5” cowl opening for the propeller spacer is too small. You place a bigger prop on there and the spacer will burn into the cowling, which happened to me when I had the Sonex cowling in the beginning. I then made my own cowling with a bigger exit (about 8”) and a spinner. I have never had contact issues again. Rotax’s have a tremendous amount of torque compared to Aerovees and Jabirus, so the exit on the Sonex cowls never had to be very big. The worst thing that ever happened was the engines would sag.
I don’t know what propeller/spacer combo you’re running but you may benefit from the propeller spacer Sonex developed for the 912 to help this issue.
Another issue is where the engine finally resides when run up. The motor mount structure will eventually “settle”. To bring back some alignment and provide some resistance to the torque over, I’ve used fender washers between the tops of the Barry mounts between the rubber and upper attach angles to essentially “shim” the engine into alignment. The Barry mounts are already the hardest ones they offer. I don’t believe it’s the rubber compression so much as it is the flexing of the chromoly structure. I now have about 350 ish hours I guess with that setup with no issues.
Like Chris has said, there’s probably a handful of Sonex’s flying with the current Sonex mounting structure building time and with opinions on the setup. I currently only know of one airplane that has a substantial amount of time with the configuration, and a couple that have flown at all.
A bed mount has always been the “cheap” route for manufacturers to get away from the additional ring mount cost. However it’s ended up causing some headaches which I don’t know if they were worth the expense.
This isn’t a problem with Rotax engines. But I assure you there are solutions coming that will solve these issues and bridge the Sonex/Rotax gap once and for all.
Skippy, feel free to pm me or post on here. I was replying to you on the forum so that this may be a lesson/learning opportunity for others going this route. But I would like to see pictures of everything you’re describing. Your current set up, cowl alignment, changes you may have noticed, etc. I’ll do what I can from here to give you pointers to getting things ironed out. I’ll take some pictures too and give you information on what I’ve done to help the process. I’ll take some pictures when I’m in the shop on Monday.
Re: Sonex/Rotax Engine Bed
Posted: Sun Feb 11, 2024 7:26 am
by Skippydiesel
That was a great “letter” Harraripower - my thanks for the trouble you have gone to.
First - I have a Sonex Legacy/Rotax 912ULS/Airmaster CS /Whirlwind 3 blade prop. The prop is within Rotax weight limits but is heavy at over 11 kg.
I have recently “converted” from Sonex provided, Barry Controls 22001-13 mounts, to -14 mounts (the next stiffness up).
I have made/fitted Cupped Snubbing Washers to try and improve the resistance of the lower mount rubbers, to lateral movement.
Sonex recently sent me larger OD spacing washers, ACV-P54-06 & 07, to replace the set they sent me earlier - I have fitted these.
All of the above, made some improvement to the engine movement but I still had a contact between left rear exhaust header/pipe and engine frame.
Yesterday I removed the offending exhaust header - using a piece of tight fitting water pipe, on the side I did not want to adjust, I progressively squeezed the pipe with Vice Grips, to cause a dent/depression at the point of contact. After reinstallation, I followed up with a short engine run to 50C oil temperature and shut down in the normal way. The pipe did not contact the witness tab on the engine frame. I will do a proper flight test in about a week and report back then.
If you would like to contact me through the person to person channels, I will send you photos of my setup.
Re: Sonex/Rotax Engine Bed
Posted: Sun Feb 25, 2024 9:12 pm
by Skippydiesel
Hi Casey,
Sent you a whole heap of photos - hope you received them and they gave you further insight into my Sonex/Rotax installation (I would like to see yours).
I think my installation differs from yours, in the following ways:
Mine is a custom cowling - engine/cowl clearances were designed in from the start, so for the most part not a problem. I have had no issues with the prop clearance. Have had rubbing where the exhaust exits (fixed) and in the vicinity of the fuel pump (fixed).
My most intransigent problem has been the left rear exhaust header contacting the framework (working on it)
My current mounts are Barry Controls 22001-14
I don’t have a prop extension and think that fitting one would likely exacerbate the engine movement.
As mentioned I have quite a heavy prop. In one of the photos I sent, showing the (original) rear Barry 22001-13 mounts, the lower rubber donuts, show significant lateral displacement/distortion. The front mounts were fine. I believe this displacement shows the effect of the heavy prop causing a “whipping”/“pendulum” motion on shut down/start up, with the front mounts acting as a pivot point, generating a larger movement at the rear mounts. The fitting of Cupped Snubbing Washers was in large part a response to this symptom (seems to have worked)
I note with considerable interest that you have fitted the Barry Controls Mounts 22001-15 (“The Barry mounts are already the hardest ones they offer.”). I am intersted in any observations you may have regarding the different performance of the -15’s compared with the -13’s (Sonex original) .
We had a break in the prevailing weather yesterday and I have managed to do 1.8 hrs flying - two starts, 3 touch & goes and two landings. Again the tendency of the left exhaust header to touch the frame has been markedly reduced but there is still a faint touch mark on my “witness” material (soft aluminium)
What to do:
Can dent the offending exhaust header some more, to improve clearance. Easy, nil cost/minimal down time and as almost have sufficient clearance may be the way to go but what of future softening/sagging of rubber mounts?
Make a new exhaust header with better clearance - Without a doubt this is the ultimate solution - costly and with a significant down time.
Install Barry Controls 22001-15 (“…the hardest ones they offer.”) Would this give just that little bit more of necessary resistance to lateral movement? - What may be the negative impacts?
Try to fit one or more anti frame twist rods - If access allows, 1-2 rods across frame to reduce the tendency to flex - If possible, cheap, quick/no down time. What may be the negative impacts?
You have alluded to a better solution from Sonex “…I assure you there are solutions coming that will solve these issues and bridge the Sonex/Rotax gap once and for all.” I assume this is a “ring mount” of some description (many good examples in this Forum). Don’t want to go to too much trouble/cost trying to make the existing mount work, if this development is iminent. Any idea when it will be available?
Re: Sonex/Rotax Engine Bed
Posted: Tue Feb 27, 2024 3:01 am
by Skippydiesel
Have checked out the feasibility of installing two anti frame twist rods - seems possible.
The plan at this stage, is to fit, 2 pieces of aluminium angle(20 x 20 x 2mm), 500 & 560 mm long, to each side of the frame,. Fitted from high, close to firewall, down to near tip of Aerovee frame.
The angle will be attached to the frame using heavy duty aviation (rubber saddle) “P” clamps, sized to suit the frame tube (no cutting/welding/damage to frame).
Before fitting, I will lightly jack the frame up, to neutralise the weight of the engine.
The hope is that the additional supports will be tight (no slop). When the movement of the engine tries to twist/flex the frame, the supports will resist.
Should I have any concerns?
Re: Sonex/Rotax Engine Bed
Posted: Thu Feb 29, 2024 6:35 pm
by Skippydiesel
The addition of engine frame stiffening struts seems to have had no effect.
The struts are not ideally located for best effect, due to clearance considerations.
I marked the position of each end of struts P clamp, so that if they moved I would be able to see this. No indication of movement
Re: Sonex/Rotax Engine Bed
Posted: Tue Mar 05, 2024 6:08 pm
by Skippydiesel
FYI:
Have just received an Email from Sonex - " …a new ring style engine mount (Rotax) is being thought about for the new High Wing…the High Wing is
a B-Model type"
So owners of Legacy (A) aircraft, may not see a Sonex produced Rotax engine mount, any time soon.
Very disappointed.
Re: Sonex/Rotax Engine Bed
Posted: Tue Mar 05, 2024 7:36 pm
by BobDz
Skippydiesel wrote:FYI:
Have just received an Email from Sonex - " …a new ring style engine mount (Rotax) is being thought about for the new High Wing…the High Wing is
a B-Model type"So owners of Legacy (A) aircraft, may not see a Sonex produced Rotax engine mount, any time soon.
Very disappointed.
How possible, and or difficult would it be to make one? I’m curious about how engine mounts are designed. Specifically, how is the diameter, and thicknesses of the 4130 tubing determined. I’m actually learning TIG welding at the moment simply because I want to be able to weld 4130 tubing very well.
Sadly, I was hoping to go to Sonex today to pickup b/o parts ( AND get a sneak peak at the high wing).
Re: Sonex/Rotax Engine Bed
Posted: Tue Mar 05, 2024 8:04 pm
by Skippydiesel
Hi Bob,
Check back through this thread/Topic and you will see that some very talented builders have made their own Sonex/Rotax engine bed. The common theme is the Ring Mount. Some have made the whole system from scratch. Others have used the Rotax OM Ring Mount and adapted it to the Sonex airframe. In every case a better system that that offered by Sonex.
I admire your thinking - learn to weld properly before embarking on your own engine bed. As a retired agriculturalist , I can stick most metals together - to call this welding, would suggest a skill level well beyond anything that I would claim.
I doubt there is a Sonex/Rotax owner, using the Sonex/Rotax engine bed adapter, that would be happy with this barely adequate solution. The lack of interest/action, by Sonex, is possibly due to, what I suspect is, the low numbers of Legacy (A)/Rotax airframes using the adapter.
I wonder if there is a talented builder of a Sonex/Rotax Ring Mount, that would be intersted in building one for me???
Re: Sonex/Rotax Engine Bed
Posted: Mon Mar 18, 2024 3:29 am
by Skippydiesel
Update:
Sent the offending exhaust header, in a good strong jig, to an expert in stainless steel welding.
His brief; pipe must end up in same places & angles in the jig but needs to introduce greater clearance (all specified from known point on jig).
Cut and tack welded part returned for trial fit engine/muffler - looks good.
Fully welded pipe will be back with me next weekend - fingers crossed there will be no more contact between it and engine frame.
Re: Sonex/Rotax Engine Bed
Posted: Sat Mar 23, 2024 3:51 am
by Skippydiesel
Exhaust header has been modified & returned - looks good. Will install shortly. Test flight may take a little longer as cowl off for painting.