Re: Actual Flying Rotax Installs
Posted: Fri Dec 17, 2021 12:19 pm
Skippy,
That’s interesting the previous owner didn’t want to switch. I would like to understand his reasoning.
I do want to say though, the chromoly is not failing in any way. It’s just moved about 1/16” which could easily happen just in jigging when welding up the mount and in no way is it going to cause failure. But that 1/16” over a distance from it to the propeller flange caused about a 1/4” down and a 1/4” left.
Other manufactures do a 1-2 degree thrust offset to try and manage this phenomenon the Rotax has. They’ll shim the flange up and right so that it returns to center under load. So in no way is this anything new to the Rotax community. ICP produces the Savannah, a Zenith 701 type aircraft, that’s an SLSA and they use this method just by using washers to get the desired angles. Rans uses them on the s12 bed mounts as well. After I weld in a intermediate support in the mount I’m going to monitor its flexing. If it solves it, it will very likely be standard on all the Rotax mounts. But as a temporary solution I’ve shimmed the bed mount with 1/16” fender washers (under the top bed angles between the angle and bushing) and put the flange into a slight offset and it’s been working great. The addition of washers that thin hasn’t caused any strange distortion. It still keeps the bushings at their standard compression. I’ve purposefully put the plane through g loads, high attitude and stress to try and get more movement but it’s been steady so far. It’s just steps to refining it as much as possible. As we all know, Sonex tends to over engineer and build a safe product.
That’s awesome you have a project so close to completion! If you have any pictures it would be cool to see. Everyone’s install is a little different, you might have some good ideas on the build that others haven’t thought of yet
That’s interesting the previous owner didn’t want to switch. I would like to understand his reasoning.
I do want to say though, the chromoly is not failing in any way. It’s just moved about 1/16” which could easily happen just in jigging when welding up the mount and in no way is it going to cause failure. But that 1/16” over a distance from it to the propeller flange caused about a 1/4” down and a 1/4” left.
Other manufactures do a 1-2 degree thrust offset to try and manage this phenomenon the Rotax has. They’ll shim the flange up and right so that it returns to center under load. So in no way is this anything new to the Rotax community. ICP produces the Savannah, a Zenith 701 type aircraft, that’s an SLSA and they use this method just by using washers to get the desired angles. Rans uses them on the s12 bed mounts as well. After I weld in a intermediate support in the mount I’m going to monitor its flexing. If it solves it, it will very likely be standard on all the Rotax mounts. But as a temporary solution I’ve shimmed the bed mount with 1/16” fender washers (under the top bed angles between the angle and bushing) and put the flange into a slight offset and it’s been working great. The addition of washers that thin hasn’t caused any strange distortion. It still keeps the bushings at their standard compression. I’ve purposefully put the plane through g loads, high attitude and stress to try and get more movement but it’s been steady so far. It’s just steps to refining it as much as possible. As we all know, Sonex tends to over engineer and build a safe product.
That’s awesome you have a project so close to completion! If you have any pictures it would be cool to see. Everyone’s install is a little different, you might have some good ideas on the build that others haven’t thought of yet