Aileron Control Interference
Posted: Sat Dec 31, 2022 7:39 pm
by 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 8015 times
Seat pan interference
Aileron Link Left Side Interference Sm.jpg (78.13 KiB) Viewed 8015 times
Chipped paint on the exposed corner
Aileron Link RT Side Interference Sm.jpg (86.21 KiB) Viewed 8015 times
Link corners removed and seat pan edge beveled
Aileron Link Modified Sm.jpg (97.3 KiB) Viewed 8015 times
Re: Aileron Control Interference
Posted: Sat Dec 31, 2022 10:17 pm
by 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 8002 times
Good post and a great reminder of why the safety and clearance checks are so important.
Re: Aileron Control Interference
Posted: Sun Jan 01, 2023 4:50 pm
by 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
Re: Aileron Control Interference
Posted: Mon Jan 02, 2023 11:27 am
by 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.
Re: Aileron Control Interference
Posted: Sun Aug 06, 2023 1:20 pm
by 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 7310 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 7310 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 7310 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 7310 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…
Re: Aileron Control Interference
Posted: Tue Aug 08, 2023 8:51 am
by 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
Re: Aileron Control Interference
Posted: Tue Aug 08, 2023 9:28 am
by 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.
Re: Aileron Control Interference
Posted: Tue Aug 08, 2023 8:13 pm
by 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
Re: Aileron Control Interference
Posted: Wed Aug 09, 2023 6:41 pm
by 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.
Re: Aileron Control Interference
Posted: Wed Aug 09, 2023 7:21 pm
by daleandee
pappas wrote: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
Re: Aileron Control Interference
Posted: Wed Aug 09, 2023 7:43 pm
by Bryan Cotton
Dale,
I think this is a lowered seat problem. I wish they had put the standard seat option in my Waiex plans.
Re: Aileron Control Interference
Posted: Wed Aug 09, 2023 9:44 pm
by pappas
I’ll buy that, flag noted. To clarify, “The seat pan interference is something that I have seen in almost every legacy Sonex”.." that I have seen". Exceptions could be for lightweight pilots but not this 200 lb lump!
Re: Aileron Control Interference
Posted: Wed Aug 09, 2023 10:30 pm
by daleandee
pappas wrote:I’ll buy that, flag noted. To clarify, “The seat pan interference is something that I have seen in almost every legacy Sonex”.." that I have seen". Exceptions could be for lightweight pilots but not this 200 lb lump!
No harm, no foul. Bryan indicated that these were on the lowered seat mods but IIRC that pretty much became a standard part of the build early on. No doubt that there isn’t a lot of room under the seat pan.
BTW, for whatever difference it may make both of the ones I referenced were center stick models without a lowered seat and that might make a difference as to the lump in the seat. Might be different with dual sticks and the “lump” sitting right on top of the control instead of next to it.
Cheers,
Dale
3.0 Corvair/Tailwheel
Re: Aileron Control Interference
Posted: Wed Aug 09, 2023 11:56 pm
by Bryan Cotton
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:
three piece half installed.png (557.06 KiB) Viewed 6914 times
I screw the other side down, and then put the top in. Those clecoes will become nutplates and #6 screws.
hat section 2 trial.png (564.28 KiB) Viewed 6914 times
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.
Re: Aileron Control Interference
Posted: Sun Aug 13, 2023 6:38 pm
by Bryan Cotton
Here is my finalized seat structure. This adds 0.6 lbs at 75".
It seems like I have plenty of clearance now.
Edit: all the parts are made from 2024-T3 alclad. The right rib has a duct tape shim on top, to make everything coplanar.
Re: Aileron Control Interference
Posted: Fri Aug 18, 2023 11:25 am
by Bryan Cotton
I’ve flown twice since I completed this. Once dual, once solo. I can really feel the seat pan is supported better and the controls are free. If I ever build another legacy Sonex with the lowered seat pan I will add this structure from the start.
Re: Aileron Control Interference
Posted: Fri Aug 18, 2023 11:47 am
by Area 51%
I raised the back of the seat by an inch and made it out of .040. Never had a problem.
Re: Aileron Control Interference
Posted: Fri Aug 18, 2023 11:59 am
by Bryan Cotton
Area 51% wrote:I raised the back of the seat by an inch and made it out of .040. Never had a problem.
Sort of sounds like the non-lowered seat pan. Your solution also sounds like a good option.
Re: Aileron Control Interference
Posted: Fri Aug 18, 2023 5:33 pm
by Area 51%
Bryan Cotton wrote:
Area 51% wrote:I raised the back of the seat by an inch and made it out of .040. Never had a problem.
Sort of sounds like the non-lowered seat pan. Your solution also sounds like a good option.
I purchased an un-started, 10 year old Sonex fuselage sub-kit last Feb., just to get the ball rolling on this build. The plans show the common variety “raised seat” installation. It’s amazing how much difference there is between that install and the “lowered seat”. Not simply a relocation of the hinge half.
I didn’t raise my seat to clear the control tree, but to clear the floor supports it was coming in contact with. I have pictures. bubblesinbpfl@yahoo.com
Just got parts back-ordered since November in the mail…gotta go…Area 51% .