SonexBuilders.net

Hi everyone, I have an almost complete Waiex, just needs an engine to be mounted, instrument panel assembly and finish interior.
My plane has the aerovee engine mount from the factory kit but i recently purchased a Rotax 912ULS 100hp engine and i think it will be a better choice for my missions. And a better choice commercially (I live in Argentina, Its Rotax or nothing over here)
I will attempt to fabricate an adapter to couple the Aerovee mount to the Rotax 912. I know it can be done.... It would be really helpful for me to see photos, hear comments and ideas, or any information that you guys may consider important.

Thanks a lot, i will post pics of my conversion as soon as i start working on it.. But im still on the research phase :)

Nice looking plane. Here’s what appears to be the easy way…convert the mount you have with this kit from Sonex:

https://www.sonexaircraft.com/eshop/car ... ory_id=452

They also sell completely new engine mounts for the Rotax if you want a more elegant solution.

Good luck, looks like you’ll be flying soon!!!

Best, Gordon

The adapter concept is certainly appealing, but I'm sure no one would consider it ideal. This thread shows one adapter, but I never saw any followup about how it worked, or if it was ever even flown. In the final version, it didn't looks too bad though.
http://www.sonexbuilders.net/viewtopic.php?f=60&t=579

I was in the same situation with a Onex that already had a mount attached. My first thought was an adapter, but I ended up scratch building a new mount using the Rotax ring mount rather than the bed mount. Of course in my case, the engine mount has no landing gear, so it made the mount MUCH simpler.

Getting one from Sonex won't be cheap, but it will likely be the easiest solution. They've had some teething pains with those mounts, but now that they actually have their own Rotax installation, I'd expect any remaining issue to be sorted out fairly quickly.

One other option might be something in-between. Modify the existing mount by cutting off the tubes that go to the Aerovee, and replacing them with tubes that go to the Rotax ring mount locations.

In my opinion, you absolutely made a great decision to use the 912ULS. I wish mine was a 100 HP rather than 80, but I had the engine already, and it's actually doing quite well.

Cheers,
Rusty

My yet to fly Sonex Legacy (hope to get her of the ground within the month) is fitted with a Rotax 912 ULS and mounted using the Sonex : Rotax adapter.
The adapter looks great but was I disappointed in the fit.
Considerable "mucking about" was required, using home turned interference fit plugs, that were then drilled to suit the factory supplied engine frame - where is the QA?

Thanks guys for the information... I already read everything about Sonex+Rotax easily available.... Buying something from abroad is completely out of the table... I live in Argentina. We are having a hard time with politics and economy sucks (The last 70 years XD) So if its going to fly...Ill have to do it with my own hands

My engine arrives next week. If theres any way to make an aerovee/homemade ringmount coupling possible ill go that way... The bed mount is also tempting, but I think the ring is stronger.

The other option could be leaving the landing gear part of the mount on.... cutting the non-landing-gear part...and starting from there. Ive done similar stuff before. Im a bit anxious, want to find the solucion and fly that baby asap!!!

I don't think it would be very hard to fabricate your own copy of the Sonex : Rotax bed mount - its not much more than 4 pieces of angle aluminium. Finding the right gauge/thickness might be a problem.

The exercise of combining the Rotax 912 ULS to an already existing Sonex mount, has been successfully carried out several times. This one is manufactured by someone really in the know Down Under, and combines the 912 without the Rotax ring mount to an Aerovee engine truss. Alas, no drawings available, it was a trial and error project.

The installed engine in the airframe described above looked like this during a stage in the project.

Bearing in mind that the Rotax prop torque is massive compared to that of a VW-1 aeroderivative, I would be hesitatant to use this truss as such without some reinforcenent between the upper longeron attachment brackets in the fuselage, as indicated in the construction drawings for the Sonex A + Jab33A truss: a continuous square steel stiffener tube.

A different solution was selected for a Rotax 912 ULS with the standard Rotax ringmount installed, mating it up to a Sonex engine truss for the Jab 33A. Incidentally, the installed weight of the 912 is fairly close to that of the 33A. Hence final CG location should not be too far off.

On a side note, the Sonex mount for the 33A positions the stop flange for the isolators apprx 455,3 mm forward of the front fuselage bottom/firewall intersection (Sonex reference point). The Aerovee mount moves this plane 58,8 mm forward. The mount for the light Jab 22A moves it a total of 135 mm forward. Hence I speculate that using the 22A mount for this exercise could pose CG issues (with the R912 hanging out there, far up front), while the Aerovee mount would probably work, provided very careful design of the ring mount.

Anyhow, for this excercise 12mm thick steel (it could very well be aluminium provided you can find someone that actually manufactures 12mm 6061T6 or 7075T6) adapter plates were manufactured, which also provided for the use of the harder Sonex rubber isolators for the Jab.

I think i preffer mounting the engine from behind rather than the bed mount (i confess the bed may be easier and im still not putting out ofthe table)

Picking up my engine next week :) I will keep you guys posted on that trip.

A set of 2" rubber isolators is on its way (Jeep Cabin isolators XD... I used them in other conversions, work great and costs 40X less than Rotax rubber mounts) . I will lathe turn the housings to mount them, that way i dont have to tighten them too much. they remain soft and absorb vibration efficiently and are also stronger and less prone to ovalizing because they are radially contained.



And it will be rigged something like this... (sorry bout that paint XD...will make a 3D when i have the actual measures if you guys are insterested)