Rotax Sonex
Posted: Thu Apr 09, 2020 9:38 am
by SonexN76ET
I received my new Rotax 912 ULS engine in January from Lockwood Aviation. Right up front I will tell you installing the Rotax is about ten times more complex than was the installation of the Aerovee I had previously. I am using the Sonex supplied Rotax tri gear engine mount. The Sonex engine mount for the Rotax is very high quality and is a bit beefier than the previous Aerovee mount. So far the biggest challenge has been the fabrication of the exhaust system and deciding where to mount the radiator. I am using a 63 inch three blades ground adjustable propeller with a 2.25 inch prop hub extension. As such I had to extend the nose gear by 1 inch which in turn raises the prop hub about two inches to give me the required 7 inches of ground clearance. I simply added a 1 inch thick rubber donut above the nose gear spring and put a one inch extension to the top of the nose gear which is where the nose gear steering arm attaches. Here is a photo of the engine mounted to the airframe along with the oil tank.
Jake
Re: Rotax Sonex
Posted: Thu Apr 09, 2020 9:51 am
by SonexN76ET
Nose gear extension of 1 inch using rubber donut and 1 inch extension with internal reinforcement.
Jake
Re: Rotax Sonex
Posted: Thu Apr 09, 2020 10:17 am
by SonexN76ET
Initial fitting of exhaust and muffler. I had purchased the Zenair exhaust system for a Zenith thinking it would be the perfect fit. Unfortunately I have had to modify each exhaust pipe extensively in order to clear the engine mount and nose gear.
Re: Rotax Sonex
Posted: Thu Apr 09, 2020 8:16 pm
by SonexN76ET
Here are the custom exhaust pipes going down to the muffler on the Rotax.
Jake
Re: Rotax Sonex
Posted: Thu Apr 09, 2020 8:18 pm
by SonexN76ET
Here is the oil tank mount I made for my Sonex
Jake
Re: Rotax Sonex
Posted: Sat Apr 11, 2020 9:21 pm
by 13brv3
Thanks for the photos. Looks like maybe that’s 3/4" tube instead of 5/8"? The 912 looks pretty close to the firewall. Does it appear that the CG of the 912 is farther foward than the Aerovee, or did they make the mount so the prop ends up the same place?
It seems like the 912 is a bit lighter, even when you consider all the stuff that goes with it, so I would have expected the engine to be farther forward than the Aerovee. I’m studying the mount options for a 912UL on a Onex, and I’ll be making a custom mount pretty soon. I was planning to move the CG of the 912 4" forward of the Aerovee CG, though I know that makes the cowl a nightmare.
For the real question, did you happen to weight the Aerovee vs the Rotax? It would be really nice to have real numbers, vs what’s published.
Thanks,
Rusty
Re: Rotax Sonex
Posted: Sun Apr 12, 2020 8:41 am
by gyroron
I think its going to be a great plane.
Rotax 912 series engines should NOT be the most reliable, being that they are actually a somewhat complex engine compared to the simple design of a aerovee or Jabiru… air, oil, and water cooled. Dry sump oiling. Dual carbs. radiator. Geared drive. Lots of hoses, and connections to possibly fail. Pistons, valvetrain, etc… all spinning at nearly twice the speed of a direct drive engine. BUT… Rotax has those little engines dialed in. Extremely reliable. Smooth. Good low fuel burn. Quiet. I would be much more happy if my sonex had a 912 over the Jabiru.
Re: Rotax Sonex
Posted: Thu May 14, 2020 1:00 pm
by SonexN76ET
Oil cooler and radiator mounted. I had to fabricate mounts and brackets for each. I am modeling the basic layout with those used on the Bristell LSA which is a redesign of the Piper Sport/Sport Cruiser.
With the larger prop spinner and narrower engine my cowling will be made significantly narrower and more streamlined than it was with the AeroVee.
I will not re weigh the aircraft until I am done with everything.
Jake
Re: Rotax Sonex
Posted: Thu May 14, 2020 9:25 pm
by MichaelFarley56
It’s looking great Jake! You’re doing a great job and I can’t wait to hear how things go as you finish the project!
Keep up the good work sir and let us know how how things go as you finish up the project!
Re: Rotax Sonex
Posted: Fri May 15, 2020 5:46 pm
by Sonex Foundation
Looks awesome! We sure would like to have you show it off on the virtual fly in…open slot tomorrow.
Re: Rotax Sonex
Posted: Sun May 17, 2020 12:15 am
by Brett
studying the mount options for a 912UL on a Onex, and I’ll be making a custom mount pretty soon. I was planning to move the CG of the 912 4" forward of the Aerovee CG, though I know that makes the cowl a nightmare
Wow Rusty 4" ???
I moved my prop hub 1 " forward of the origional Aerovee turbo position and found the CofG ok… could maybe have gone furthur but it flies fine and weight and balance was ok…
With two heavy guys, low fuel and a little bit in the back is on the aft limit and feels a bit funky but still is ok.. I think 4" forward could be an overkill… I have no idea about the W+B on a onex but just food for thought.
Re: Rotax Sonex
Posted: Sun May 17, 2020 9:38 am
by 13brv3
Brett wrote: studying the mount options for a 912UL on a Onex, and I’ll be making a custom mount pretty soon. I was planning to move the CG of the 912 4" forward of the Aerovee CG, though I know that makes the cowl a nightmare
Wow Rusty 4" ???
I moved my prop hub 1 " forward of the origional Aerovee turbo position and found the CofG ok… could maybe have gone furthur but it flies fine and weight and balance was ok…
With two heavy guys, low fuel and a little bit in the back is on the aft limit and feels a bit funky but still is ok.. I think 4" forward could be an overkill… I have no idea about the W+B on a onex but just food for thought.
I’ll calculate this a few more times before cutting metal, but I’ve seen others mention 6-7 inches forward, which seems like a lot. Basic engine weights are 160 VW and 122 Rotax. Rotax probably has a few extra pounds of accessories, but the oil and reservoir will typically be on the firewall, and not out at the center of the engine. I’ll make the best estimate I can, and lean toward slightly nose heavy if there’s any doubt, since that’s easier to correct.
Rusty
Re: Rotax Sonex
Posted: Wed May 20, 2020 9:32 am
by 13brv3
Jake (originally said Brett, sorry)
It will be really interesting to see how the W&B compares with the previous Aerovee installation. Sonex was nice enough to send me some measurements between their Aerovee and 912 mount, and it appears that they moved the CG of the 912 aft about 3" to keep the prop in the same location. A lighter engine, mounted farther aft will have to move the CG aft, but maybe not enough to be a problem on the Sonex, or I’m sure they wouldn’t have done it that way. It doesn’t look like I can take that approach on a Onex.
Cheers,
Rusty
Re: Rotax Sonex
Posted: Thu May 21, 2020 6:24 pm
by Brett
I haven’t seen any Sonex myself personally with the Rotax factory mount. I’d have probably given it a go but with the Austalian dollar as it is and freight it was going to be well over $4000 to obtain one.
Id imagine with the factory mount my cowling would have come out nicer. So much to shoe horn in there with the Rotax. My firewall clearnace though was great.. Heaps of room for everything except the radiator. I didnt have room to sing it underneath as hoped. I don’t know of anyone either trying to fit one to a Onex but like you say will be interesting to see the final CofG. Maybe with the motor a bit furthur back the radiator and oil cooler would have room to be placed furthur forward so negating the weight issue. If so would definitely ease the installation I think.
Re: Rotax Sonex
Posted: Fri May 22, 2020 9:49 am
by 13brv3
Sorry Brett. My last post should have been directed toward Jake, since he said he was using the factory mount. Do you have a link to any pictures of your installation? I fully expect a challenge packaging all the necessary bits into a Onex size cowl, but it should be interesting to try.
Rusty
Re: Rotax Sonex
Posted: Sat May 23, 2020 7:17 am
by Brett
I have quite a few pictures on my blog but I basically lost interest in it so it’s not fully up to date. Will paint a reasonable picture though of what I did for the install. Hope this can be of help…
Re: Rotax Sonex
Posted: Sat May 23, 2020 8:56 am
by 13brv3
Thanks Brett. Those pics bring back good and bad memories of a previous custom install project. I can’t tell you how many hours I’ve spend holding various objects (radiators, oil coolers, etc) around in different spots to try to find where they will fit.
Thanks,
Rusty
Re: Rotax Sonex
Posted: Sun May 24, 2020 3:00 pm
by gcm52
I just did a weight and balance for my completed Rotax Onex. I moved the engine 7 inches forward, which turns out to be the max you would want to move it as the most forward weight and CG is just inside the forward limit by a quarter inch. That is with no baggage, full fuel and a 195 lb pilot. The CG will move aft as fuel burns off. So moving the Rotax say 5" forward on a Onex might be better. I included some pictures to show how I did the FWF.
Re: Rotax Sonex
Posted: Mon May 25, 2020 10:04 am
by 13brv3
Thanks for the excellent info George, and congrats on being this close to finished. I do have a few question though.
When you say you moved the engine 7 inches forward, where are you measuring? Are you saying the 912 prop flange is 7 inches forward of the Aerovee flange?
Did you also raise the thrust line, or is it the same as the Aerovee? I have to admit that I’m tempted to raise the thrust line an inch to help with prop clearance. BTW, what diameter prop is that?
I’d love to see other pictures of the FWF installation, either on the forum, or via email if you don’t mind.
Rusty
13brv3@gmail.com
Re: Rotax Sonex
Posted: Tue May 26, 2020 5:39 pm
by gcm52
13brv3 wrote:Thanks for the excellent info George, and congrats on being this close to finished. I do have a few question though.
When you say you moved the engine 7 inches forward, where are you measuring? Are you saying the 912 prop flange is 7 inches forward of the Aerovee flange?
Did you also raise the thrust line, or is it the same as the Aerovee? I have to admit that I’m tempted to raise the thrust line an inch to help with prop clearance. BTW, what diameter prop is that?
I’d love to see other pictures of the FWF installation, either on the forum, or via email if you don’t mind.
Rusty
13brv3@gmail.com
Rusty,
When I moved the engine, I moved the CG of the Rotax engine 7 inches forward of where the CG of the aerovee engine was. I tried to keep the thrust line the same. To allow a larger diameter prop, which is necessary with the Rotax, I lengthened the nose strut by three inches. I have a 64" diameter Warp Drive prop on it now. I am toying with the idea of putting on a four blade Warp Drive just for fun. I also am probably going to remove the 1" prop extension on there now as I actually don’t need it for cowl clearance. Attached are a couple more FWF photos so you can see what I did. I used a Rotax ring mount and designed a custom mount going from the ring mount to the firewall.
George
Re: Rotax Sonex
Posted: Tue May 26, 2020 5:41 pm
by gcm52
By the way I have been running the engine on the ground to adjust the prop pitch and the engine runs strong and smooth. Fires up as soon as I push the start button.
Re: Rotax Sonex
Posted: Tue May 26, 2020 8:03 pm
by 13brv3
gcm52 wrote:When I moved the engine, I moved the CG of the Rotax engine 7 inches forward of where the CG of the aerovee engine was. I tried to keep the thrust line the same. To allow a larger diameter prop, which is necessary with the Rotax, I lengthened the nose strut by three inches. I have a 64" diameter Warp Drive prop on it now. I am toying with the idea of putting on a four blade Warp Drive just for fun. I also am probably going to remove the 1" prop extension on there now as I actually don’t need it for cowl clearance. Attached are a couple more FWF photos so you can see what I did. I used a Rotax ring mount and designed a custom mount going from the ring mount to the firewall.
George
Thanks for the additional info George. 7 inches of movement for the CG is definitely out there. My best estimate shows about 3.5" of CG move, which makes the prop about 6.5" forward of the normal location. since it’s easier to fix nose heavy, than tail heavy, I’ll probably shoot for 4" of CG movement. For the tailwheel version, with standard gear, I’ll likely end up with a 4 blade Bolly (sold by Hoverhawk). I won’t make a decision until the engine is mounted and the prop clearance is known.
Thanks,
Rusty
PS- Sorry to Jake for all the Onex chat on his Sonex thread.
Re: Rotax Sonex
Posted: Fri Feb 03, 2023 8:38 pm
by SonexN76ET
Next week I will make my first flight after repowering my Sonex with a Rotax. It has taken me three years and close to 600 hours, most of which has been spent on customizing the cowling. Everything firewall forward is new. I also put the smaller nose wheel pants on the main gear and had to modify those to fit around the brakes. Once again I have the first flight anticipation.
Jake
Re: Rotax Sonex
Posted: Fri Feb 03, 2023 8:47 pm
by SonexN76ET
Side view:
Jake
Re: Rotax Sonex
Posted: Fri Feb 03, 2023 9:26 pm
by Bryan Cotton
Awesome! Good luck!
Re: Rotax Sonex
Posted: Sat Feb 04, 2023 11:24 am
by MichaelFarley56
Congratulations on finishing the swap Jake! The Sonex looks great and I can’t wait to hear how she flies!
Please let us know how the test flights go and enjoy!
Re: Rotax Sonex
Posted: Sat Feb 04, 2023 5:28 pm
by Skippydiesel
Hi Jake - Great looking cowling. I would be very interested to see some photos of how you have managed your cowling exit air.
Re: Rotax Sonex
Posted: Sat Jun 03, 2023 2:12 am
by Skippydiesel
Hi Jake,
Any cooling problems?
I would still like to see how you have managed your cowl exit air ?
Re: Rotax Sonex
Posted: Sat Jun 03, 2023 2:14 am
by Skippydiesel
Hi again Jake,
What Radiator & Oil Cooler are you using?