Abstract: I've run into a bit of a problem with my trim system. My X has a trim wheel similar to a Cessna or Grumman, left of the throttle quadrant. The wheel turns a chain which turns a shaft that uses a worm drive gear to turn a pulley. This gear drive is directly below the throttle quadrant. The pulley has the trim cables wrapped around it 3 times. Moving the trim wheel turns the worm drive which in turn moves the pulley which moves the trim cables fore and aft, depending on which way your are trimming. The pulley has what appears to be a bronze gear on the top that meshes to the worm gear made into the shaft turned by the trim wheel. Apparently, the gear on the pulley has stripped a couple of teeth. It looks like it needed some lubrication, but didn't get it. I have a skip in my trim now just forward of the neutral trim position. It's still flyable, but I need to do something with this before it gets worse.
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Thread : Trim system problem
Started at 26th-September-2010 12:15 AM by John Lawton
Visit at http://forum.xopa.org/showthread.php?t=88
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Date : 26th-September-2010 12:15 AM
Thread Title : Trim system problem
It appears that the gear on the pulley could be rotated 180 degrees and that would be a temporary fix. The gear only turns about 270 degrees in the normal trim range I fly with. So, if I turned the gear so that the opposite side is used it where it meshes with the worm gear it would temporarily fix the problem. Certainly not a very easy fix, though. It's going to be quite a task just to get to it. Ultimately, I'd like to replace the gear entirely if I'm going to go to the trouble of taking the trim system apart. My parts catalog doesn't show an exploded diagram of this particular part of the trim system. I don't know if this is an Aeromot part or something they sourced from others. As I mentioned, the trim wheel and chain drive part are very similar to what I've seen in other production airplanes.
Anybody ever seen this before and if so, what was the fix?
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Date : 27th-September-2010 05:10 PM
Thread Title : Trim gear pictures posted
I posted pictures in my gallery of my trim gear that is missing some teeth. The first photo shows what the gear is supposed to look like. The second shows the missing/worn teeth.
I think it might be a Boston Gear product, but I need to remove it, check for a part number and do some measurements to confirm. Chuck is checking for me, too. I'll post more once I know more. I think the moral of this story is grease this part at every annual.
UPDATE 9-29-10: I managed to get the gear out yesterday. Six teeth are completely worn off the gear, but there appears to be no wear at all on the worm. The gear appears to be brass and the worm bronze. I think that might be part of the problem. Plus, it is quite difficult to get to, so it likely hasn't been getting proper lubrication. I'm headed out this morning to try and find a suitable replacement.
UPDATE 10-2-10: No joy finding a production replacement for this gear. Both the gear and the worm are apparently custom made by Aeromot. The gear has a DP of 32 with 28 teeth. The closest gear I can find with a DP of 32 has 34 teeth. Looks like this gear will have to be made. I put up three new pictures showing the gear and the worm in my gallery if anyone is interested.
UPDATE 10-17-10: Found a guy in NJ who fabricated an exact replica of the gear in question. Got it installed and signed off yesterday. It works beautifully! Much, much smoother and with much less effort to trim than the original. $300 for two (one as a spare). The teeth on the new gear are slightly deeper than the original and I think that is why it works more smoothly. That, and this time it has some lubrication on it. Very difficult job, though. Not for the faint of heart.
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Downloaded from XOPA Forums (http://forum.xopa.org) at 16th-February-2012 08:41 PM.
Recommended Comments
There are no comments to display.
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.