Hey all,
This was posted in the old Sonexbuilders site in a thread of Rick’s called Aileron Control Interference. That thread is in this section but only one of my pictures came through. So here is a repeat.
We had significant seat sling interferences and we worked them hard during construction. One thing I did was to rivet a tube to the sling as shown, to gain some clearance on the stick. It worked well. We also had to cut a tab off the stick assembly, I think that was supposed to be for trim. I think we added the tubes after sitting in the seat and discovering the interference. You could do something similar to your already constructed aircraft and gain a little clearance.
After a year and 130 hours, I have some interference issues that have manifested themselves. I first noticed that the sticks were a lot freer when I was solo and wearing a chute. My chute is a seatpack and basically all my weight is supported by the back of the seat. So under the seat pan, I found this evidence that the stick mount was scraping the seat pan:
As I was working my fix, I also noticed a scrape on the elevator pushrod between the stick mount and the idler:
I fabricated a hat section with the angle that I expect the seat pan to follow:
I rested it in place, put the seat pan on, and evaluated. It seems good and I am going to rivet it in.
So I was super meticulous about ensuring no interference before, but with all the seat cycles and maybe Gs it changed over time. I may make a couple of similar hat sections to go on the sides.
To reiterate one of my philosophies - how much interference is allowable? NONE!
One of the issues with the dual sticks is the top tube of the stick mount is just below the seat pan. That is my interference problem. Also note that my interference is not ailerons, but the pitch axis. I thought it would be good to put in Rick’s thread because they are related.
My original tapered hat section was no good. Not enough clearance on the pitch pushrod. So, I made a 3 piece version. Here is one side installed, and one in my hand:
I screw the other side down, and then put the top in. Those clecoes will become nutplates and #6 screws.
I did a trial fit of the seat pan and it seems good. I am going to extend the other two channels as well, so it is supported more than just in the center.
Here is my finalized seat structure. This adds 0.6 lbs at 75".
It seems like I have plenty of clearance now.
All the parts are made from 0.040” 2024-T3 alclad, because I had a bunch in stock. The right rib has a duct tape shim on top, to make everything coplanar.
Ok, that post was from 2023, and it’s now 2026. 420 hours. Seat pan is still good. I think the B model design is more like what I’ve done here, probably because it was a little underdesigned in the A model. In prior discussion this was more of a lowered seat pan problem. In the old thread I lamented having a lowered seat pan because I’m 5’7” and holding, and needed boosters to see over the front. But it is perfect both with boosters or a seatpack chute when I fly aerobatics.
