Trim stuck

[Steve]

Yesterday after take-off (touch-and-go) I could not lower the elevator trim. I wasn't very far from home, but after 15 minutes of holding it down I was getting a little tired. The trim handle turns very hard, but I am able to "help" the cables. It feels like either a pulley is stuck or the cable has jumped out of the track. The trim handle is above the headliner and none of the zippers seem to allow a good view of the problem. There also isn't a good view in the tail. Before I start taking things apart does anyone have any suggestions of where the problem probably is?

[lktiller]

Sounds like the cable is too tight. This will cause the handle to be very hard to turn. Also cables will slip, but you can pull the cable as you indicated by reaching above the headliner.

1st, loosen the tension on the spring. Yep. loosen it.
2nd, rub rosin on the cable at the pulley locations.

I just recently rebuilt my entire trim system. Rebushed every pivot point. Bellcrank, pushrod, clevis, pulleys. Replaced the jackscrew. New oversize roll-pin.

Slightly over-tightening the spring will now put enough tension that I cannot turn the handle. Or if I force it the cable will slip.
With the tension just right (very little) everything works perfectly with very little effort. I didn't have to rough up the pulley grove.

Another note. I usually don't bother adjusting the trim unless I have a passenger.
Adjust it with 3/4 tank of fuel, at cruise rpm & airspeed. Then if the trim changes, I just slightly vary the RPM.
No changes on takeoff or landing.

[Chet Peek]

Check the lubrication of the jackscrew in the left elevator.

[dennispip]

Has anyone ever considered putting a sprocket and chain on the trim handle end and on the pulley mechanism at the tail. It seems that this would eliminate the slippage problem that plagues this design and still allow for the cable between the pieces of chain. It just seems like there should be a better way, especially with the new covering materials that preclude the need for recover jobs every 5 years nowadays. I have had the same problem with the trim on my '86 F21B. I wonder if they have made any changes in engineering of this weakness on the planes they are planning on producing down in Lagrange?

[yerich109]

One thing that I had thought of is to have the cable double loop around the pulleys on the ends. It would probably require a thicker pulley, but would give much more surface area of contact between the pulley and cable.

I haven't had much trouble with mine in a while. For the first year I had the plane, it slipped alot and would hang in the full nose down position. (Very unsettling). The jack screw was popping out of the sleeve and I would have to hand roll the pulley at the tail to get it re-threadded (sore fingers....). I'm very careful not to lube the cable at the pulley anymore, just the jackscrew and pulley to shaft point.

[Robert Lees]

Steve, there is a précis of Trim Common Problems at:

http://vb.taylorcraft.org/showthread.php?s=&threadid=49&highlight=problems+trim

[Steve]

Well, I need to thank everyone for the great information. The trim seems to have just been stuck in the full up position. Once I disconnected the spring and took the tension off of the system I was able to free up the pulley. The gear system seemd to move easily. Where should the spring aparatus rest in terms of position in the rear fuselage when the trim is neutral?

What this great information didn't mention was how limber one needs to be to accomplish this task. It is necessary to kneel on the seat backwards (within the very spacious Taylorcraft interior), maneuver your upper torso through the un-zipped part of the headliner, and then work on a contraption that is located above you head. The "apparatus" is spring loaded so that if you don't hold onto it (did I forget to mention that one needs to grow at least one extra appendage for this task) one end springs into the abyss of the rear fuselage and and the other through the impossible to reach headliner. I tied a rope around the spring, and put a vice-grip on the cable end which seemed to help.

I managed a beautiful hour flight in the smooth air of sunset, and it all worked well! Thanks again...

[lktiller]

kudos to you for thinking of the rope trick!!!!
And congratulations for being flexible enough to even get to the cable/spring in the first place. And being able to stay in that position long enough to adjust it!
Glad everything is working.

The spring should be moving between two cable fairleads, one almost directly behind the baggage compartment, the other a few feet furthur back.
Note: these act as stops to keep the trim tab in a certain range and the trim handle and jackscrew from reaching the overrun.

[wd6bor]

Re: Trim stuck

I'm looking for a replacement rear pulley for the jack screw. Any info on sources? Mine is showing its age.

Darrel, BC12-D