trim noses up during bumpy flight

[CGinSD]

Yeah, flying with one hand on the yoke and one hand on the trim wheel just doesn't sound right. 

 

I think there is an adjustable friction on the trim wheel, though.  I had the cover off last annual to clean under there and I had felt pad that rides on the left (inside) surface of the trim wheel.  It was choked with carpet fuzz.  My IPC doesn't show it, but I have a later version from the mid-70s that I think is similar.  It goes back as far as the '65C.  Take a look.  Under index 14 is listed a "BRAKE ... NI" (NI - not illustrated).  I haven't found any adjustment procedures, though. 

Your the '62B had a little different trim wheel installation.  But, since you've got a 'C' I am guessing it's similar to the attachment.

 

Ah! this sounds like a lead, thanks very much.

[CGinSD]

Wow, you learn something every day. I guess we need to tighten our brake screws a little.

It was in your neighbourhood too: SDL -> RNM via Buckeye and Blythe.

 

And um... what are brake screws?

[N201MKTurbo]

If you look at the PDF attached above you will see a screw under the chain cover that pushes a felt pad against the trim wheel. Take off the chain cover and tighten the screw until it gives you some friction. Just the right amount....

[CGinSD]

Got it. Thanks very much (in particular for the parts PDF 47U) that sounds feasible, I'll give it a try and then find another crappy day to go flying to test it and let you know.

[flyboy]

I am having the same problem in my '61-B model. I think that the problem is reduced if the airplane is loaded as tail heavy as possible. In other words, if the pressure is reduced on the trim system, then there is less need to correct the trim. Of course it is not always practical to move the CG.

[CGinSD]

Sadly this lead did not play out... it turns out that the brake screw was only added to the trim wheel in '64; 62-64 models of C, D and Es had none.

 

With a second warm body it was also fairly easy to verify the effect with one of us standing at back jiggling the tail up and down and the other observing the trim wheel rolling back at 16th of a turn per 10 jiggles. It could be stopped pretty easily and I have a strong suspicion that the brake screw was added to 64+ models precisely because of this issue.

 

Our mechanic reckons that the jack screw is just worn enough to allow the extra play necessary to wiggle the trim wheel back and should be replaced. Any thoughts or experiences? How expensive is this likely to be?

 

Anyone with a 62-63 C,D or E who wants to try the jiggle test? Had to replace the trim rods?

[carusoam]

My 65C did not have this challenge, as you have outlined above.

Good luck with finding a solution,

-a-

[carusoam]

Mark the wheel, go cruise.  If it needs to be re-trimmed, check the mark.  Did it move?

if it moves, I would guess your friction providing brake needs attention.

thank 47U for providing the drawing...

he deserves some points for supporting your part of the community.

 

best regards,

-a-

[rissacher]

Sadly this lead did not play out... it turns out that the brake screw was only added to the trim wheel in '64; 62-64 models of C, D and Es had none.

 

With a second warm body it was also fairly easy to verify the effect with one of us standing at back jiggling the tail up and down and the other observing the trim wheel rolling back at 16th of a turn per 10 jiggles. It could be stopped pretty easily and I have a strong suspicion that the brake screw was added to 64+ models precisely because of this issue.

 

Our mechanic reckons that the jack screw is just worn enough to allow the extra play necessary to wiggle the trim wheel back and should be replaced. Any thoughts or experiences? How expensive is this likely to be?

 

Anyone with a 62-63 C,D or E who wants to try the jiggle test? Had to replace the trim rods?

Looks like there were some service bulletins to add it to older Mooneys like this:

http://www.mooney.com/en/sb/M20-33.pdf