Trim stuck

[DannyDot]

I have stuck trim (full nose up) on a BC12-D. The cable over the pullies looks good. I suspect the problem is inside the left elevator. The problem started right after washing the plane. Any ideas on how to proceed? Could pushing on the tab while washing have done something?

[Dick Smith]

Re: Trim stuck

Try reading through this gathering of info:

http://vb.taylorcraft.org/showthread.php?49-Trim-common-problems&s=&highlight=problems%20trim

Rob Lees worked it up from comments on the forum.

Dick

[M Towsley]

Re: Trim stuck

Don't forget while operating the trim that you pull the yokes back a little so the elevator is near neutral so it relieves the tension on the trim cables.

[Hank Jarrett]

Re: Trim stuck

First thing, DON'T FORCE anything. You might want to first remove the fin covers so you can get to the aft pulley and see if it is moving at all. Also disconnect the tab push rod from the tab and be sure the tab itself will move. If it isn't the tab or handle, work your way back from the trim handle GENTLY rocking it back and forth to see if the cables are actually shifting tension from one to the other. If you have small fingers you may be able to GENTLY rock the pulley (assuming the cables actually are trying to move the pulley) and feel for a jamb in the shaft or the pulley wheel between the elevators. If they aren't jammed, the next thing is the threaded shaft. It is a B***H to get to the threaded shaft, so jump over it to the crank and push rod to the tab. If everything is free you are toast, the threaded shaft is stuck. You are going to need to get in and turn the threaded shaft. You can turn one end from the pulley (hope those fingers are small AND strong) but you will be twisting the pin to the bell crank to pop it loose (the threaded shaft is probably jammed at one extreme position).
Now the follow on problems. You are not allowed to unhook the trim system connections (OK, ANYONE can unhook them, but you need to get the re-assembly signed off). You have violated the control system and it is going to have to be looked at by someone who can sign your plane off as airworthy again. You may even have to cut the elevator open to get to the parts inside. If so, PUT AN ACCESS COVER ON over the bell crank (your mechanic can cover the paper work on that too). Snap in covers are supposed to go on the POSITIVE pressure side of a surface. Bad news, BOTH sides of the elevator can be positive side. My plane has a cover held with screws.
I hope you find what is stuck without going through the whole system. To prevent this kind of thing NEVER turn the trim handle with the elevator far from neutral! Also, if you EVER feel resistance to the trim handle turning, stop. If you push it and the threads are at the ends, you can jamb the system. The Taylorcraft trim system isn't the best one I have ever worked with. It works, but is a little delicate and can be damaged with just a little too much enthusiasm. Treat it right, and it will work great for decades. Once it is working, be sure to lube the threads and where the shaft runs in the elevator.
Hank

[jdoran]

Re: Trim stuck

Danny,

I would bet that the soapy water is acting as a lubricant, and the cable is slipping in the rear pulley.

Don't keep doing this, or the vee in the pulley will wear, and the cable will never grab the pulley right.

My suggestion is to get a helper to turn the front pulley in the direction that does NOT pull the spring. The helper should only apply pressure to the crank, not force it allowing the cable to slip. You go to the rear of the plane and try to manually turn the rear pulley at the same time, but do this with the elevator in the neutral position (in line with the horizontal stabilizer). Make sure you are both turning in the same direction so you aren't working against each other. This should get the thing turning again.

Rob Lees suggests buying a block of violin resin and applying it to the trim cable to give it better grip.

Last thing, you will probably need to re-sychronize the cable so that the cable stops are "midway" between the stops when the elevator is in neutral.

[flyguy]

Re: Trim stuck

IF...your trim cable has a spring on it you should be able to decrease the tension on the pulley by pulling on the top cable (just in front of the top of the rear pulley.) Then you can rotate the pulley with your other hand and center the tab.

That should get the gear in the actuator freed up (the jam is usually caused by forcing the gear past its limit.)

Using this method and repositioning the crank handle up front, then adjusting the tab position as above a bit at a time should get everything matched up again.

At some point you may want to remove some fabric and check the gear to make sure it is installed correctly. It is possible to install the gear in such a way that the the lever arm will not swing through an even distance/arc in both directions. (as John says) The BC12 I have now had that problem.

DC