Thorp Air Command - T18.net

I was flying along the other day and readjusted my manual trim. After I took my hand off the trim wheel, I noticed that it continued to move by itself. It moved maybe a half an inch to one inch (along the circumference of the trim wheel). There is no slop or free play in the trim system, it just continues to move to another trim location after I set it where I want it. Its not a significant amount, but I fear it could become worse.

I have to admit, I don't know how to fix this. Can anyone describe what I should do? Below is a picture of my trim wheel.

I would have to know more about how the system is built to make a guess. Is it possible to tighten the axial bolt on the trim wheel. If you have built the rear per plans, it should not do that.
Cubes

I should say, I did not build my plane, but the trim system appears to be per plans.

Sounds like the flex shaft in the back is "springing". This could be due to the trim screw needing lube. If you have never had the tail apart, now is the time to do it. You might be surprised at what you find back there.

_________________
Bob Highley
N711SH
SN 835
KLAL

Is the aircraft trim really changing with the movement of your trim wheel? Is your trim wheel securely fastened and just vibrating loose? Mine wobbles a bit and I can see the trim wheel possibly coming free from the manual trim system.

I have taken the tail off in the past, and I didn't see anything out of the ordinary. I will take the tail off again before next flight and inspect/lube the jackscrew. I believe the trim is really changing with the movement of the trim wheel. There is no wobble, or looseness on the trim system.

Once any repairs are made, it may be hard do determine if I have fixed the issue without a test flight. Would you agree with that? I can not think of a way to test the trim without flight loads.

That would be the optimum way. Try to replicate the speeds/loads that made it move last time. For now, I would keep the speed down a bit just to be sure.
Cubes

I went out to the plane this afternoon and took the tail off. All good back there I lubed the jackscrew for good measure. I then moved to the control wheel. I saw an inspection panel on the right side (pax side) of the trim wheel cover. that looked like a good place to start. I removed the cover and saw a nut with safety wire. I cut the safety wire and tightened the nut about a quarter turn. The trim wheel now rotates only when I move it and with a bit more friction than before. I guess after 34 years, the nut needed a quarter turn.

I appreciate all the quick responses. I will of course approach the next flight as a test flight.