SonexBuilders.net

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

Nose gear extension of 1 inch using rubber donut and 1 inch extension with internal reinforcement.

Jake

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.

Here are the custom exhaust pipes going down to the muffler on the Rotax.

Jake

Here is the oil tank mount I made for my Sonex

Jake

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

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.

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

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!

Looks awesome! We sure would like to have you show it off on the virtual fly in........open slot tomorrow.