Hi Casey,
Sent you a whole heap of photos - hope you received them and they gave you further insight into my Sonex/Rotax installation (I would like to see yours).
I think my installation differs from yours, in the following ways:
Mine is a custom cowling - engine/cowl clearances were designed in from the start, so for the most part not a problem. I have had no issues with the prop clearance. Have had rubbing where the exhaust exits (fixed) and in the vicinity of the fuel pump (fixed).
My most intransigent problem has been the left rear exhaust header contacting the framework (working on it)
My current mounts are Barry Controls 22001-14
I don't have a prop extension and think that fitting one would likely exacerbate the engine movement.
As mentioned I have quite a heavy prop. In one of the photos I sent, showing the (original) rear Barry 22001-13 mounts, the lower rubber donuts, show significant lateral displacement/distortion. The front mounts were fine. I believe this displacement shows the effect of the heavy prop causing a "whipping"/"pendulum" motion on shut down/start up, with the front mounts acting as a pivot point, generating a larger movement at the rear mounts. The fitting of Cupped Snubbing Washers was in large part a response to this symptom (seems to have worked)
I note with considerable interest that you have fitted the Barry Controls Mounts 22001-15 (
"The Barry mounts are already the hardest ones they offer."). I am intersted in any observations you may have regarding the different performance of the -15's compared with the -13's (Sonex original) .
We had a break in the prevailing weather yesterday and I have managed to do 1.8 hrs flying - two starts, 3 touch & goes and two landings. Again the tendency of the left exhaust header to touch the frame has been markedly reduced but there is still a faint touch mark on my "witness" material (soft aluminium)
What to do:
Can dent the offending exhaust header some more, to improve clearance. Easy, nil cost/minimal down time and as almost have sufficient clearance may be the way to go but what of future softening/sagging of rubber mounts?
Make a new exhaust header with better clearance - Without a doubt this is the ultimate solution - costly and with a significant down time.
Install Barry Controls 22001-15 ("...the hardest ones they offer.") Would this give just that little bit more of necessary resistance to lateral movement? - What may be the negative impacts?
Try to fit one or more anti frame twist rods - If access allows, 1-2 rods across frame to reduce the tendency to flex - If possible, cheap, quick/no down time. What may be the negative impacts?
You have alluded to a better solution from Sonex
"...I assure you there are solutions coming that will solve these issues and bridge the Sonex/Rotax gap once and for all." I assume this is a "ring mount" of some description (many good examples in this Forum). Don't want to go to too much trouble/cost trying to make the existing mount work, if this development is iminent. Any idea when it will be available?