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Trim tab misadventure

Bill Boyd

Well Known Member
My 10 has had a heavy right wing since first flight. I've countered it with left roll trim as needed and trying to burn the right tank off first. Since it sometimes required all the left roll trim available with the factory spring trim setup, I decided to add a trim tab wedge under the left aileron to reduce the trim requirement. This served well on the test flight I made last week - neutral roll trim was right where I needed it to be.

This morning on takeoff for a cross country with the wife and a suitcase, the AoA started b*tching at us with "Angle, Angle - Push!" during climb out. I am accustomed to hearing this briefly in ground effect when I rotate at 60kts, but once reaching about 80 it stops alerting in a normal departure climb profile (I have mountains dead ahead of my home runway so max performance climbs or S-turns are expected with most take-offs if I'm not solo). Some time during the "what the heck is this thing squawking about - I'm at 100 KIAS with a normal-looking deck angle and it's showing one red chevron and saying I'm about to stall into a mountainside - not comforting..." I noticed as well that the plane was pulling very hard to the right. I circled back to the airstrip to land and sort things out and then saw the trim tab hanging off the TE of the aileron. I had attached it (tapered maple wedge) with aluminum HVAC tape fore and aft, and apparently the forward strip of tape had let go and the wedge was hanging on by the aft tape. It produced a pronounced downward force on the aileron in this configuration, exacerbating the heavy right wing.

During the left 270 to final, the AoA continued to chant and show just a couple of red chevrons most of the way to the threshold despite a normal looking descent profile and adequate airspeed on final (80 bleeding off to 65 over the numbers). I hopped out, tore off the trim tab, and re-launched. The AoA fussed a little bit but not as excessively as before, and began to indicate as expected during the cruise-climb phase. It also indicated as-expected when we flew the pattern at our destination airport.

I'm a little weirded out by this combination of occurrences and will examine the pitot tube closely when I get back to the field tomorrow for the return leg. The aileron trim wedge clearly needs permanent attachment now that I know it's the right size - I'll seal it with varnish and attach with E6000. The idea that I was somehow mushing along in a near-departure-stall needs further investigation and I intend to do that.

Full disclosure: I washed the plane last evening with a hose and wash mitt - nothing out of my normal routine but I suppose water in the static line or in the pitot is a possibility. Static tubing was routed with no inadvertent P-traps to collect water so I am discounting this possibility for now. Will check for bugs/nests carefully tomorrow before departure. I'd appreciate any thoughts from the hive in the mean time.
 
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Q: so is your AOA pitot based? Like a Dynon pitot mast with two ports?
Some details of what equipment you have would be useful. Many AOA units out there.
 
Sorry about that. AFS avionics suite with Dynon AoA pitot. Standard fuselage side static ports. Calibrated per the manual and performing normally for 100 hours.
 
I am not sure how old is your Dynon Pitot, but they had some issues with them some years ago that the drain hole did not work as intended and Dynon finally replaced those. I had one in my 7 which was replaced.
 
I'd check the AOA, Pitot, and Static lines for leaks. Seems like the system is seeing a big discrepancy somewhere. I just did a bunch of work where the builders had put in the push type connectors (nice), but didn't trim the plastic line ends square... rather just hacked them off. As a result they didn't seat in the o-rings properly and it leaked everywhere. Something like that could work loose over time I suspect.

I thought I had them all licked only to find they simply shoved the hard plastic line over the aluminum tubing coming off the pitot mast.
 
Have you checked the aileron height?
Steve Smith (-10 wing airfoil designer) has a post here on VAF concerning ‘heavy wing’ and the vertical height of the aileron. He suggested:
1. Place ailerons in neutral (this will require clamping the elevator neutral too).
2. Stand in front of the wing, looking aft. Sight down the top aft section of the wing, and note where your line of sight hits the aileron. You can also do this measurement with a steel (unbending) straight edge.
3. Ideally you should just barely see the aileron, the same, both sides.
4. If you see one but not the other, the unseen side will be the heavy wing. You need to find a way to vertically raise the aileron. 1/16” makes a big difference.
 
Appreciate the feedback, on all sides.

I know there are better ways to deal with the aileron rigging problem but was trying to take the lazy way out, for now, and avoid dismounting the control surface and enlarging holes or replacing brackets.

I'm puzzled whether the aileron trim tab coming loose and trailing behind the aileron could cause sudden issues with the AoA, but the likelihood IMO is that it's two separate issues happening on the same flight by chance.

I will report back as the story plays out.
 
Yep. Been through that drill already with my 6A a couple decades ago. There's no squeezing the TE on a -10 aileron.
 
Yep. Been through that drill already with my 6A a couple decades ago. There's no squeezing the TE on a -10 aileron.

Ah, my bad :)

How’s the rigging look - one aileron a little higher/lower in trail? Same question on the flaps.
 
As for the AOA, I would first look for bugs or debris in the AOA hole in the pitot or a smashed bug on the 45* slash cut face, as that will create turbulence and bad readings.

On my 6, one day the AOA started reporting me having yellow chevrons in the climb and red on very aggressive climbs, which was quite unusual. Did a few stalls to test and it was still dead on. I was stumped for a couple of months, but after 900 hours flying in harmony with the plane, I just knew it wasn't accurate. Fast fwd to my pitot static check and we had leaks. While I was under there, I pulled the AOA line off yhe AHRS. The GRT uses the 1/8 NPT for P and S, but only gives a barbed fitting for the AOA. Found that the rubber had softened and stretched around the barb and addressing the leak that it caused stopped the climb issue. Moral of the story is that a leak in the AOA tubing can give perfectly accurate stall warning consistent with the actual stall, yet give false readings in the lower angle regions, like climb out. I do not believe that a tab hanging off the aileron could have ANY effect on either the AOA reading or the actual AOA of the wing.

Only answer for heaving wing is move the offending hinge hole or put on a tab.

Larry
 
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As for the AOA, I would first look for bugs or debris in the AOA hole in the pitot
Larry

You, sir, win the chicken dinner.

Mud dauber larvae.

Stay tuned for update on aileron rigging and heavy wing. And a report on a near mid-air on landing today.
 

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You, sir, win the chicken dinner.

Mud dauber larvae.

Stay tuned for update on aileron rigging and heavy wing. And a report on a near mid-air on landing today.

“A biologic…”

You do cover the pitot tube, plug the static ports and fuel vents when parked —- anywhere, and for any length of time….right?
 
Spitballing

Just Spit Balling here, but I would check the wing incidence and make sure the left and right wings are the same. The fuselage does not have to be level, because I think all that matters are that they are the same. JMHO
 
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