Aileron Control Interference

[racaldwell]

I have had several occurrences of being in a 45 deg bank and move the stick to level the wings but nothing happens initially then slow movement back upright. Now I know why. Yesterday while thermaling with a passenger, I heard a metal on metal clunk at the base of my stick and the Xenos first seemed to want to stay banked but then slowly came back level. Looking at the aileron deflection, I could see it was moving maybe 50% travel if that. The stick was not moving any further. I could keep banging it but it was not changing. Back on the ground, I was able to recreate the interference.

The seat pan can deflect down so the stick cutout in the seat pan will catch on the welded steel bar on the link rod that connects the two sticks together. This link is not constructed like the one shown on the plans. Mine has the corner of that welded bar sticking up above the steel tube so the corner of the bar can catch on the seat pan if it happens to be deflected down just enough. Both the left and right corners of that link on mine had the paint chipped off where it had been hitting. Here are pictures.

My fix today was to grind off the corner of the welded on bar and radius it so as to be below the top of the round tube. I also used my sheet metal edge roller to turn up the edge of the seat pan cut out in that location. I am wondering about a seat pan reinforcement to support it.

My Xenos has the lowered seat pan design and the flat bottom of the seat rests on the floor channels underneath. The stick openings have been modified with a larger opening than the plans shows so that the stick does not hit the edges with full back stick. The front bend at the spar tunnel turned out about 3/16" short of the 2-45/64ths called out on the plans. The location of the hinge on top of the spar tunnel is located to fit the seat pan, thus it is about 5/16" back from the front of the spar tunnel.

Rick Caldwell
Xenos 0057 62 hrs

Aileron Link on the plans

Aileron Control DWG Sm.jpg (116.79 KiB) Viewed 8371 times

Seat pan interference

Aileron Link Left Side Interference Sm.jpg (78.13 KiB) Viewed 8371 times

Chipped paint on the exposed corner

Aileron Link RT Side Interference Sm.jpg (86.21 KiB) Viewed 8371 times

Link corners removed and seat pan edge beveled

Aileron Link Modified Sm.jpg (97.3 KiB) Viewed 8371 times

[Bryan Cotton]

I should have posted my safety wire stuff here. I have stuff that has not been approved by mods yet over in lessons learned.

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.

Edit: 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.

seat sling tubes.jpg (33.33 KiB) Viewed 8358 times

Good post and a great reminder of why the safety and clearance checks are so important.

[racaldwell]

That is a good idea to gain some additional clearance.

I am currently thinking of a support up from the floor channels to support the seat sling from underneath between the two stick cut outs. Mine currently has a crease there from someone's foot. Several people have asked to sit in my Xenos to see how it fits them. Not being the builder, they would not know the seat is unsupported on the sloped portion. A foot can easily be placed there and I can't possibly watch every passenger's footstep. I'll sit on this idea for a while and see if there is any rubbing of the link on the sling. In the meantime, I'll put a bar of plastic on top of the spar tunnel between the cut outs to raise it up following your idea.

Those corners sticking up on the welded bars placed at an angle on that link rod have no useful purpose. Those should be ground away if you have not already done so.

Rick Caldwell
Xenos 0057 62 hrs

[bvolcko38]

I had the same issue with 2 aboard. The tab for the trim spring rubbed on the seat pan. I made a blister for the seat pan. I can't find my picture of it. Works perfectly and under the cushion it can't be felt.

[Bryan Cotton]

I wanted to share with the group that 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:

scrapes on the seat pan.png (387.07 KiB) Viewed 7666 times

As I was working my fix, I also noticed a scrape on the elevator pushrod between the stick mount and the idler:

scrape on elevator pushrod.png (500.73 KiB) Viewed 7666 times

I fabricated a hat section with the angle that I expect the seat pan to follow:

tapered hat section.png (468.94 KiB) Viewed 7666 times

I rested it in place, put the seat pan on, and evaluated. It seems good and I am going to rivet it in.

hat section in place.png (483.62 KiB) Viewed 7666 times

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!

Stay tuned...

[brian_rebbechi]

A critical feature of the aileron control interference arises if the Dynon autopilot servos are installed. With the standard Xenos seat pan the roll servo lever arm is very close to the underside of the seat pan on the right hand side. The same thing happens in a Sonex if lowered seat option is used, as the lowered seat for Sonex/Waiex is the standard seat pan for the Xenos. And if the lever arm gets trapped under the seat, then the shear pin built into the servo is of no help, as it is the rod end that is stuck. The simplest solution would be to not use a lowered seat in the Sonex, and copy the standard Sonex (non-lowered) seat layout to use in the Xenos. Even better would be to build in some of the features of the newly-released dual seat option for Sonex/Xenos, as it appears much stiffer than the older layout, with a transverse beam.
The use of stiffening along the seat pan edges may not be such a good idea, as if these permanently deform with a heavy passenger planting their foot in the mid-span of the seat pan, that could then cause the aileron rod to get stuck.

Brian Rebbechi
Xenos 0058

[Bryan Cotton]

I'd like to have a non-lowered seat pan. I think I'm down to 5'7" and not growing any more.

[brian_rebbechi]

I'm similarly just on 5' 7" and no need for a lowered seat pan either. I initially built the Xenos seat pan exactly as per the drawings, not realizing that this was the same as the Sonex/Waiex optional lowered seat pan. Much later with the help of a Sonex builder here, I figured this out, and built another seat pan according to the standard Sonex one (its Sonex drawing F-08). The Xenos seat pan is 2.5" lower, at its lowest point, than the std Sonex one. And there is another subtle difference in that unlike the std Sonex seat pan, which is tight between the front and rear piano hinges, the 'lowered' seat dips below the font and rear piano hinges, so it can readily bend down further than the drawing would indicate.
Incorporation of the standard Sonex seat pan simply needs a new seat pan made up; the airframe piano hinges are in the same location.

Brian Rebbechi
Central Vic
Australia
Xenos 0058

[pappas]

The seat pan interference is something I have seen in almost every legacy Sonex. I bet it is the main reason the B model has seat pan ribs. A really good change to the plans. If I were building a legacy now, I would fab up seat ribs and use them.

[daleandee]

The seat pan interference is something I have seen in almost every legacy Sonex.

I know you to be a quality builder but I'm gonna toss a flag on that statement. My legacy Sonex taildragger (Corvair powered) doesn't have any concerns with aileron interference and the VW powered nose roller Sonex I had before this one didn't have that concern. I've never heard this complaint until recently on this thread. I believe if this had been a safety issue there would have been a service bulletin from Sonex concerning this. Perhaps I'm missing something and this is only concerning the lowered seat mod.

When I installed the servo for my A/P I had to be very careful to make sure there was not interference and admittedly when I tried to use the hole in the triangle (center stick) that is the tube for the aileron stops I did have a rub between the servo rod and the seat pan. The fix was to connect the servo rod to the aileron connection that is lower down on the triangle mount.

But as far as the standard seat in the model-A Sonex being a problem ... I just haven't seen it.

Respectfully,

Dale
3.0 Corvair/Taildragger