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Trim Misery

cplne

Registered User
Hey All

i made a post on the STOL fourm regarding the trim on my newly acquired PA12. At cruise the airplane will not trim nose down, it feels like the cable is slipping but I’m still trying to sort it out. One member suggested installing the Supercub trim system with a double pulley. The plane has PA18 tail feathers by Ron Sullivan, O320 with extended wings, PA18 gear. I observed the annual and the mechanic lubed, lubed and lubed the trim jackscrew, it worked in the hangar. Once I left I was unable to trimmuch if any at all. I simply set the trim for cruise on the ground and headed home. Frustrating as the purchase included an airworthy airplane. She’s going to get some love before I take her to her new home. Any and all thoughts on how I should approach the repair. If you think the Super Cub double pulley system is the way to go where do I find the parts and any guidance installing greatly appreciated. Other than that the plane flew great.
 
The PA-18 double pulley system is the final fix, but you can also see if the cable can be adjusted for now. Theres an adjustment to tension the cable at the tail by adjusting the idler pulley. In the PA-18 system the idler pulley is under constant spring tension. Also check if the worm gear and tail feathers are rigged properly. If not they will bind. Many fuselages are slightly twisted and you have to find a point of adjusting the brace wires to where everything is a working compromise. You might also check if the front pulley is worn to the point of where it hasn't got enough diameter to fit snugly against the cable. That's the short non-technical answer, but I've gotten by for many hours with some maintenance, before a rebuild and install of the double pulley system.

Also check that the rear stabilizer tube is free to rotate, and has been lubricated through the little hole in the rear fuselage support tube. This tends to get neglected. A drop of Marvel Mystery Oil work wonders. A welded on grease fitting at rebuild is even more wonderful.

These trim systems were made for original engines, and new planes in 100% original configuration. Like original brakes being replaced by Clevelands, other mods need to be added as the planes age and are modified. I wouldn't blame your IA necessarily. The forces change in flight and this can be a time consuming "fiddly" job.
 
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I've has good luck cleaning any oil on the cable off and rubbing some of this on the cable where it touches the pulleys. Like pine tar on a baseball bat

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Glenn
 
I've had the same experience....excess lube or oil from the jackscrew can flow down and over the trim pulley below allowing the cable to slip. Depends on the lube and if it's warm. My fix was to unlube the pulley and cable with solvent, clean the jackscrew with same, and apply a very thin layer of moly grease (like common CV joint grease) to the screw and work the trim and yoke up and down. That takes very little lube. Also oil applied to the trim crossbar and rear frame to stabilizer rotating slip joints can help them move if they're sticky. Not a mechanic but I'm the one that gets to make it work for me. If it's real cold then use low temp grease on the jackscrew.

Have someone crank the trim and see what's not working right and fix.

Gary
 
Check the idler pulley tension in the tail. You may be able to tighten it up and fix the issue. Simple if that works.

MTV
 
After installing a 150 on my 12 it aggravated a slipping trim problem. Tried some of the tricks above like lubing the jackscrew, tightening the tension but to no avail. Considered replacing the drive single groove pulley but decided money would be better spent on a known fix. (Double Pulley). With the installation of a Borer Prop and 18 tail feathers I decided I needed something that actually works. Researched the threads here and a lot of good information. Particularily Mike @ MCS Repair post on installing trim in a covered 12 using clamps. With my mechanic we did just that with most parts purchased from Dakota Cub, Tony Cesare and the clamps from Aircraft Hardware. Cut an access on the right rear side of the fuselage to install a clamp supported idler pulley in the rear. Fabricated brackets and welded to the clamps for the idler pulleys. Simple cover closes the access. Cut the inside fabric to install the idler pulley below the drive pulley. An ugly patch covers that.
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Works perfectly. It is so great to have a trim system that actually works. Only problem was a 4 month wait for field approval grounding me for all of last winter's ski flying. Hope this helps...Rod
 

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Dakota and the magic of Tony Cesare tying little dinky pieces of wire together. Amazing. Sure cured my trim ailment a few years back. Works beautifully.
 
Double groove PA-18 system is the way to go. During my lengthy rebuild I asked MANY questions of more experienced folks. They left no doubt that double groove was the answer. So glad I listened as it performed flawlessly. Was lucky to find a fellow with many 18 parts available---geezer Dan
 
A poor mans fix, while trimming just push in on one side of the cable in the area just prior to the crank pulley as you turn the trim crank, adds tension to the pulley stopping it from slipping, same effect as adding the dual pulley.
 
A poor mans fix, while trimming just push in on one side of the cable in the area just prior to the crank pulley as you turn the trim crank, same effect as adding the dual pulley.

Can you do that with one hand ???? Have a friend who only has one usable hand and flys cubs better than I can with two fairly good hands.
 
A poor mans fix, while trimming just push in on one side of the cable in the area just prior to the crank pulley as you turn the trim crank, adds tension to the pulley stopping it from slipping, same effect as adding the dual pulley.

You can put a nylon cable tie loop around one side and a spring pulling on it and do the same

Glenn
 
You can put a nylon cable tie loop around one side and a spring pulling on it and do the same

Glenn

Or a big nylon zip tie around the cable squeezing the cable together right at the entrance to the crank pulley.. wait I never did that.. I think I dreamed it
 
I wish they had left the clothes line setup like the E2 Cub had. Worked perfect and alot quicker

Glenn
 
I guess I am lucky! I have an O320 and PA-18 tail feathers on my 12 with the original trim system. My trim works great in all phases of flight. I’ll probably put in the double pulley system whenever I do a rebuild.
 
I think the best way to go is to go ahead and install the PA18 double pulley system. Parts aren’t that it looks labor intensive. Does anybody have an email for mike at mcs and Tony Cesare. Hopefully with a little guidance I can keep the labor cost down. First thing I have to do is get all that LPS and grease off the jackscrew and rear cables ug. Thanks for the advice
 
An approriately sized -0xx series o-ring in the groove on whichever puller is slipping can do wonders for a slipping single-groove trim system; these pulleys are originally designed with a v-shaped groove to cause the cable to bite, but as they wear and or get run with low tension, they slip, and every time they slip it wears the groove from a v to more of a u shape that fits the cable and allows it to slip even easier. I’ve tried reprofiling the groove back to a v with limited success; the o-ring is a much longer lasting solution. My experience is that a properly tensioned single groove system with pulleys in good shape, and/or o-rings in the pulleys, can actually function quite well and reliably, and for a lot less $$ than installing the double groove system. But if you want to spend the money and don’t want to keep an eye on the tension, the double groove is the final, forget-it fix...
 
Just out of curiosity--- how is your jack screw installed?

http://www.supercub.org/forum/showthread.php?38784-Comments-welcomed-(upside-down-trim-yoke-)


The photos of the yellow 12 are mine-- the photos of the grey 12--I photographed at new Holstein I believe. Are you able to discern the difference s of the position of the yoke and how it is attached to the horiz stab? Worse---mine was inverted. There was a gent in Mt Vernon WA who restored half dozen trim yokes and he inverted them all--apparently because that is how it is depicted in the illustrated parts break down that Piper published in the 40's. I had people at Lockhaven look at it--- people at New Holstein look at it--- no one could figure it out. By the grace of God---Pete Annis ( Skywagon) is a neighbor--and I said--hey Pete---would you come down and look at my plane and see if you can tell what is screwed up? Pete said sure and down we went. I had the both inspection plates off. I opened the hangar doors and twenty five feet away Pete said-- " Your jack screw yoke is installed ass backwards. --it's inverted--and there was an attachment issue as well. The reason why I was at my wits end is because my nose required 90% nose up trim to fly straight and level--empty. I had the necessary changes made and BINGO. LOOK at the photos in the URL
 
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BTW--the man that restored my plane in 2003--- was killed in a plane crash five years later --- PA-12 he had just restored in an apparent trim issue!
 
cleaning the cable does help some, but the main issue is usually that the "V" shaped groves in pulley have worn and are now "U" shaped and the cable can't grip the sides, you can have someone with a lathe try to recut the groves back to a "V" shape or buy new pulleys for handle and jack screw.

Also your jackscrew may be binding on yoke.... you need to adjust tail wires so there is slop on each side of jack screw/yoke connection ... use your finger at that auction and pull one side of stab up, then down, you should feel slop both ways... if not adjust tail wires till you get there... having the stabilizers level with the plane is NOT important, having a function trim is more important

and yes I got the email..
 
I like the idea of trying an oring in the slipping pulley, which on my plane is the forward pulley the trim crank handle turns, the rear pulley the jackscrew is on does not need any more tension. I wonder if its possible to slip an oring around that front crank handle pulley without taking the trim cable off?

I never heard of adjusting tail wires for slop on the jackscrew yoke, I have about an 1/8 inch slop there but its the jackscrew moving up and down, I think giving the nut securing the pulley/jackscrew a turn to tighten it will take out that slop, but I have noticed the slop is not there at the full up and down stops, so not sure how tight that should be?
 
Just out of curiosity--- how is your jack screw installed?



The photos of the yellow 12 are mine-- the photos of the grey 12--I photographed at new Holstein I believe. Are you able to discern the difference s of the position of the yoke and how it is attached to the horiz stab? Worse---mine was inverted. There was a gent in Mt Vernon WA who restored half dozen trim yokes and he inverted them all--apparently because that is how it is depicted in the illustrated parts break down that Piper published in the 40's. I had people at Lockhaven look at it--- people at New Holstein look at it--- no one could figure it out. By the grace of God---Pete Annis ( Skywagon) is a neighbor--and I said--hey Pete---would you come down and look at my plane and see if you can tell what is screwed up? Pete said sure and down we went. I had the both inspection plates off. I opened the hangar doors and twenty five feet away Pete said-- " Your jack screw yoke is installed ass backwards. --it's inverted--and there was an attachment issue as well. The reason why I was at my wits end is because my nose required 90% nose up trim to fly straight and level--empty. I had the necessary changes made and BINGO. LOOK at the photos in the URL

The issue, some Pipers the jackscrew is correct with the yoke V pointing up (inverted upside down on PA-12) The correct way I have red is if your trim is crank handle is DOWN on the side than V points Down. If your trim crank is UP over your head as in PA-20 and 22 than yoke V is UP. I have seen them installed V down when they should be up causing loss of trim control.
 
I like the idea of trying an oring in the slipping pulley, which on my plane is the forward pulley the trim crank handle turns, the rear pulley the jackscrew is on does not need any more tension. I wonder if its possible to slip an oring around that front crank handle pulley without taking the trim cable off?

I never heard of adjusting tail wires for slop on the jackscrew yoke, I have about an 1/8 inch slop there but its the jackscrew moving up and down, I think giving the nut securing the pulley/jackscrew a turn to tighten it will take out that slop, but I have noticed the slop is not there at the full up and down stops, so not sure how tight that should be?

In my experience the screw, yoke, or both wear in the range of trim normally used. They wear out metal on one or both and get sloppy enough the yoke can rock on the screw and allow the horizontal stabilizer to move up and down by hand pressure. Tighten the pulley nut and whatever washers, etc. But if it's loose in the used range then consider having someone who knows about these matters inspect the assembly. There's also some tubes that connect the front of the stabilizer to the yoke assembly and rear to the fuselage. They have to be free and able to rotate in their cavities. If not at their extreme positions then remove, clean, and lube what's there.

http://www.supercubproject.com/drawings/pdfs/SB966.pdf

Gary (not an A&P)
 

I like the idea of trying an o ring in the slipping pulley, which on my plane is the forward pulley the trim crank handle turns, the rear pulley the jack screw is on does not need any more tension. I wonder if its possible to slip an o ring around that front crank handle pulley without taking the trim cable off?
The tension is the same on all of the pulleys since the cable is one piece. It is the cable which has the tension, not the pulleys. Which system does your plane have, a single or double pulley? These pictures show a double pulley modified system. In this case there are two locations where the cable tension can be adjusted. See pictures #1 & #3. The clamps can be repositioned to pull the cable tighter.

I have about an 1/8 inch slop there but its the jackscrew moving up and down, I think giving the nut securing the pulley/jackscrew a turn to tighten it will take out that slop, but I have noticed the slop is not there at the full up and down stops, so not sure how tight that should be?I have about an 1/8 inch slop there but its the jackscrew moving up and down, I think giving the nut securing the pulley/jackscrew a turn to tighten it will take out that slop, but I have noticed the slop is not there at the full up and down stops, so not sure how tight that should be?
This sounds as though there is a washer missing at the lower end of the threads of the jack screw. Of course there is no slop at each end of the travel as the screw has reached the end of it's travel.

You should go over this with your A&P or find one who understands how it works.
 
I woulod not want to attemp to install a double groove trim system on a covered airplane. Here is an easier way to fix with an extra pulley. You drill the bracket that is already there and install the outboard pulley.
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BTW--the man that restored my plane in 2003--- was killed in a plane crash five years later --- PA-12 he had just restored in an apparent trim issue!

Sounds like youre talking about Bruce Heiner.
Crashed on the first takeoff of a totally rebuilt PA12.
Scuttlebutt was that the elevator cables were hooked up backward--
in spite of Heiner having previously rebuilt a number of similar airplanes.

Same thing happened to Roger Christianskn a few years later at KOKH,
also in spiteof several previous rebuild jobs.
 
..... but I have noticed the slop is not there at the full up and down stops, so not sure how tight that should be?


your rear stabilizer attach tube is probably seized in the fuselage, bending(and cracking) the upper longerons when you adjust the trim, also makes trim hard to turn at the extremes....
 
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