My Rotax Mount for a Onex

Rotax 912 series discussion.

My Rotax Mount for a Onex

Postby gcm52 » Tue Mar 20, 2018 3:16 pm

I just mounted my Rotax 912ULS onto my Onex. The mount was designed by me based on other mounts I have seen, I created a jig based on an EAA video, cut the tubing using a coping cut program on the web, and had an FAA certified welder weld it up. Everything fits well. Photos attached, also added a photo of my toe brakes. If you are going to buy a Rotax engine, I recommend you sign up for the Rotax service tech course. This is a two day course where you learn all the ins and outs of Rotax engines. After you complete the course, you can get a discount on Rotax products, so this pays when it comes time to buy the engine and all the accessories. I took my course at Leading Edge Air Foils in Wisconsin and it was great. People came from as far away as Oregon to take this class.
Onex Brakes.jpg
Onex engine mount 4 .jpg
Onex engine mount 3 .jpg
Onex engine mount 2.jpg
Onex engine mount 1.jpg
George Mueller
Halfway through a Onex
gcm52
 
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Re: My Rotax Mount for a Onex

Postby Marrahm » Tue Mar 20, 2018 8:13 pm

Well done! the factory mount looks like a bed mount — is there a benefit of one style over the other for this application?

Mike
Sonex 1713B (and leaning towards Rotax when the day comes..)
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Re: My Rotax Mount for a Onex

Postby lgsievila » Tue Mar 20, 2018 10:07 pm

Hi George,
Your install looks good and I believe you will be very happy with your Onex with that engine. Just curious as to how far you moved the engine forwar for CG as your Rotax is lighter than the AeroVee. I had to add 7 inches to the mount when I went to a CAMit 2200 from an AeroVee. Looking forward to hearing your performance numbers when you get flying.
Loren Sievila
Conventional Gear Onex33
CAMit 2200
Dynon Skyview
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Re: My Rotax Mount for a Onex

Postby WaiexN143NM » Tue Mar 20, 2018 10:22 pm

Hi George,
Wow! Bravo! Looks great that mount and the toe brakes set up on your onex . Yep the onex is just begging for more engine options. I’m sure Sonex could sell a lot more onex kits with some other engine options, UL260, rotax 912, jab 2200. At least a factory mount. The builder would have to due their own fwf from there.
Keep us updated.

WaiexN143NM
Michael
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Re: My Rotax Mount for a Onex

Postby Waiex 49 » Wed Mar 21, 2018 1:11 am

Nicely designed and executed Rotax installation!

I think you will be very happy with this engine and airframe match up.

Please post more updates as you move forward with your project!

Fly safe,

Don Bowen
N49YX
Outlaw Viking Waiex
Waiex 49
 

Re: My Rotax Mount for a Onex

Postby gcm52 » Wed Mar 21, 2018 9:59 am

Mount 3.jpg


Regarding the bed mount versus the ring mount, a Rotax mechanic explained the benefits of the ring mount to me a long time ago and I can’t remember what he said, but the ring mount is considered a bit better than the bed mount. Even so, due to lower cost (the ring mount for the Rotax is $700) I initially was going to use the Sonex bed mounts and more or less adapt the Sonex engine mount to the Onex. I called Sonex to see if I could look at one of their Rotax engine mounts (I live just an hour away from the factory) but they make them to order and didn’t have any in stock. I did order the Sonex rail mounts that bolt to the side of the engine but then discovered that these mounts conflict with the new Rotax factory exhaust system. The Sonex mounts might be compatible with the old Rotax exhaust system, but Rotax now offers this new system which is fully welded up and requires less work than the old (less expensive) exhaust system that they still offer. It would not have been a big deal to weld a 1” extension into two of the rear exhaust pipes of the new system to get it to fit but at that point I thought the universe was trying to tell me to go to a ring mount so I bit the bullet and ordered the ring mount from Rotax and went that route. By the way my Sonex rail mounts are for sale in the classified section here.
As far as the CG considerations for the Rotax, I did move the engine forward 7 inches.
If anyone is considering making their own mount, this program is very helpful in cutting the tubing to fit all the weird angles:

http://www.metalgeek.com/static/cope.pcgi

The program outputs a paper template that you tape on the tube that shows you how to cut it to get the correct angle. I cut the tubing with an angle grinder.

I also found a video on the EAA site that shows how to jig the engine mount. The attached photo shows the jig. The threaded rod set-up allows very minute adjustments to the mount, and is strong enough for a one-off welding job.

I had an 80 horse Rotax 912UL engine in a Zenith 701, and I grew quite fond of that engine. It gave me zero problems, just flew and flew.
George Mueller
Halfway through a Onex
gcm52
 
Posts: 50
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Re: My Rotax Mount for a Onex

Postby Concorde » Wed Mar 21, 2018 11:30 am

Very nice .
What prop are you going to use ?
Ben
Sonex # 1684
Tri-Gear, Dual Control
Rotax 912uls
N379BS reserved.
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Re: My Rotax Mount for a Onex

Postby gcm52 » Wed Mar 21, 2018 4:06 pm

Concorde wrote:Very nice .
What prop are you going to use ?


I am leaning toward a Sensenich three blade ground adjustable. THey have a "pin indexing" mechanism for setting pitch that really looks neat. What prop are you using? Are you flying? What kind of performance are you seeing? By the way I increased the length of my nose strut by 3 inches to accommodate a bigger diameter prop for the Rotax. My understanding is that anything below a 62" prop creates cavitation on the takeoff roll.
George Mueller
Halfway through a Onex
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