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Thread: PA 22/20 Elevator Trim

  1. #1
    Join Date
    Mar 2007
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    Atascadero
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    Default PA 22/20 Elevator Trim

    I ordered a new jack screw and yoke from Univair. THe A&P stated it was hard to install and the elevator bound when the control wheel was moved. He removed the new yoke and screw and measured the old and new yoke and found quit a bit of difference in width and hole spacing. Has anyone else ran into this problem? Thanks

  2. #2
    Join Date
    Nov 2006
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    Mason, Ohio
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    There are a number of thing to be concerned about when doing this repair. The first is to be sure the yoke is install with the correct side up. The first time I installed one, I got the yoke upside down. Everything worked, but the elevator travel and trim was way out wack. Refer to drawing 12989 on the drawing CD so see how these parts should be installed. On the second installation, I rigged up some tie wraps to hold the large trim pully in position while I removed the yoke and screw. This way I didn't have to reroute the trim cable once the yoke and screw were installed. Take a look at drawing 11825 on the CD to make sure the elevator bungee and the link tube assembly are correctly installed. Finally, the part numnbers for the yoke and screw are the same for the Tri-Pacer, the Pacer, the PA-18 and most of the old Pipers so you should not see any dimentional difference between what you took out and the new one.

    Tom Anderson

  3. #3
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    Mar 2007
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    Atascadero
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    Thanks for the info Tom. I will review the drawings.

  4. #4
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    Mar 2007
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    I have the new unit installed per drawings and previous pictures. Now I notice that the cable from the top of the yoke screw pulley (left side looking aft) to the idler pulley is resting on the cable that comes from the front of the plane to the top groove on the yoke screw pulley (right side looking aft). I did not take note of the condition before it unit was removed. Are they supposed to touch? That does not seem to be a good situation.

  5. #5
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    Nov 2006
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    Mason, Ohio
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    No the cables should not touch, although they do come very close to each other. Is it possible that when you installed the cables on the pulley that you got the grooves reversed? Attached is a photo that Frank Rush included when he wrote the Rigging CD presentation that shows how he routed the cables.
    Attached Thumbnails Trim Pulley rigg
.jpg  

  6. #6
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    Mar 2007
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    Atascadero
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    Thanks Tom -

    I have before and after photos of the assembly. The A&P matched the original installation. However it appears that my cables are reversed from the photo you sent. I will get with the A&P and discuss. Thanks again.

    Dale

  7. #7
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    Nov 2006
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    Mason, Ohio
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    Dale,

    I have seen installations with the cable as shown in the photo and with it reversed. I will try and check my plane later tonight to see which way the cable is installed and verify they are not rubbing at the crossover point.

    Tom

  8. #8
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    Nov 2006
    Location
    Mason, Ohio
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    Dale,

    I checked my plane and the routing of the cables is opposite of what is shown in the photo I sent. And, the cables are very close to touching if not touching. After taking another look at the photo I sent, I'm not sure changing the routing will change the amount of contact at the cable crossover point. Even in the photo, it appears that the cables are touching. It's been a number of years since I installed the new jack screw, but I recall changing the routing to try and minimize the contact and wound up with it opposite of the photo. If the contact is very light I would be inclined to go with it the way it is and just keep an eye on the cables. I see no wear on mine and it's a real bitch to change the routing as you well know.

    Tom

    Tom

  9. #9
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    Mar 2007
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    Atascadero
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    31

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    Tom -

    The A&P told me that he swithched the cables and got the same result at the crossing. I guess that is the way it is. The next time a see a PA 22 I will talk to the owner to see if I can get other information. I haven't seen any on the California Central Coast. Thanks again for going the extra mile on this issue.

    Dale

  10. #10
    Join Date
    Feb 2010
    Location
    Texas
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    17

    Default

    The cables should not touch. They will wear prematurely and are a real pain to replace on a covered airplane. Something is probably installed incorrectly. Here are two threads with installation diagrams, detailed parts descriptions and pictures.

    Last edited by Garry; 04-30-2012 at 03:24 PM.

  11. #11
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    Mar 2007
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    Thanks Cathy -

    The exhibit showing the exploded view is great. It appears that when the previous owner re-installed the yoke and jack screw he reversed the position of washers; 7 & 10. Correcting that will lower the pulley on the jack screw about a 1/32". I will switch them to match the exhibit. Hopefully that will provide space between the cables.

  12. #12
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    Feb 2010
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    Texas
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    Great, that is what i suspected.

  13. #13
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    May 2006
    Location
    Ont
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    Thxs Cathy (Steve sitting right beside you, smile ;-D)

    This job could be one of the more demanding tasks that we could work on with the Short Wings.

    Steve, your links to the above are very good and JohnW explains the how to very well, I will take the liberty to copy what he said.

    "If you have the original PA-16 trim system installed then you have single-groove sheaves for your system. There are several of us "here" that have installed the double-sheave [2nd generation PA-20] and ] PA-22 system. Steve's pics will make the job "possible". It's pretty easy to have the endless cable "wound" (routed) incorrectly. It's easier yet for whomever NOT to do an Ops Check and confirm everything works right!!! Shame, shame!

    You're "on the right track". But you need to evaluate the WHOLE LENGTH of the cable before you get all the way down inside there. You need to hold a rag loosely around the cable itself and have someone operate the trim handle so that the cable slides through the rag. Make sure you run the WHOLE LENGTH through the rag, because the cable CAN actually "slide along" and slightly change it's position around the sheaves and you are looking for broken strands in the cable. So you may have to reposition the rag at different places to check the whole endless loop. You are only gonna wanna go down in there on this job ONCE in your lifetime of ownership on THIS airplane, and once a strand or two is worn through, it will unwind itself, bind up, fold over, and wreak havoc... making a genuine MESS that is a cryin' shame to correct. You can "pass the cable" through your fingers (or "closed fist") if you don't want to hunt up a shop towel, but even ONE of those teeny cable strands is a MEATHOOK and you will not like it! Better they should hook the rag, than your own personal meat.

    It's not an "easy task" by a long shot, doing it INSIDE the airplane. However, while it IS frustrating, sometimes "puzzling", and could easily be called akin to what Houdini went through chained and padlocked inside a locked "coffin-like" box after being dropped into the Hudson and sunk to the bottom... But it is not "impossible" (although you may think so after the blood all goes to your head).

    And with that thought in mind...raise the tail of your Clipper onto a horse (or similar) so that you won't be "head DOWN' inside there. First, there is the "blood going to your head" thing, but after a while it gets worse... you will find that crawling UP feet first out of that Hell-Hole is MUCH worse -and closer still to "impossible"- than going IN. You ain't the first to do this (I've gotten this task prb'y TWELVE or so times over the last 3+ decades, and I'm pretty sure the "I'm gettin' too old for that crap, any more" excuse is going to keep me out of any more, if I can help it!).

    Nonetheless, "Enjoy". It's a bear. But, it's worth it. Don't EVER whine to anybody about it...nobody but someone that has actually "been-there, done that" can ever understand what a tribulation it actually IS. Point being, when it's done, just file it away in the "I'm under-appreciated" folder and be secure in the knowlege that "if everybody could do it, then everybody WOULD (but most CAN'T and never will)".

    That said, the tough part is being in such a tight space for as long as it takes to get the job done. Let me add just one more "suggestion"...you will NEED to have someone outside the airplane willing and able to quick-step over to the tools to fetch something you'll need when you are in there. Getting out and back in more than once is REALLY very tedious, and once you find the one or two "acceptable positions" that you can wait in, you'll relish every thirty second break you can get.

    Oh, and I guess while I'm at it...to take the cotter pin out at the top of the jack screw, take in with you about a two foot long hunk of .040 stainless steel safetie wire and a set of safetie wire twisters. Once you get the bent legs of the cotter pin SOMEWHAT straightened out, you can thread the wire through the cotter pin eye, then twist it about a foot long, or so. With the twisters clamped on the end, you can then (by having your Helper twist rotate the trim handle until you can) manage a straight pull FORWARD (along the line of flight) on the cotter. Then ya make a little hanging loop in the twisted wire (by pushing lightly towards the cotter pin) and *YANK* the wire, snapping it tight. You might have to repeat a time or two and you'll pull that cotter pin out like a bad tooth. Slicker'n [you know what] in a mitten. "Conventional methods" for removing a cotter pin don't take into consideration the tight working area, or the fact that you are balancing on one elbow, or that there is FABRIC nearby that you do not want to "slash" when you pop off the pin (and it DOESN'T COME). This method is easier and quicker than the time it will take to rebend the new cotter pin legs when you are done.

    And...don't "overtighten" the nut on top of this screw when you re-install it. You don't want too much drag on the trim system cable, and you should notice that there is a washer, and another washer, under the nut...reason being that these two washers ride against each other on a slightly loose installation. Check out these washers for excessive wear, and replace one or both, IF NECESSARY. Because of this wear point, many yoke/jackscrews are mistaken replaced for being "worn out", when in fact, the softer of these washers has worn. This lets the jackscrew "chuck" up and down, and someone of the "uninitiated many" group see the only source of such loososity as being the threads themselves. If the jackscrew ass'y was lubricated periodically, you can often remove excessive play (vertically) on the horiz stab simply by pulling the cotter pin and snugging that nut a schosch. There ARE NO "lubrication call outs" for lubing the contact surfaces of these washers, and they constantly turn (under something of a load) against each other's faces, and they DO eventually wear (putting oil or grease on them is actually counter-productive, since dust and dirt gets between them, when lubed, and ACCELERATE the wear). The Piper Assembly Drawings call for .015" max "chuck" on the front of the stab. Worn jackscrew threads are a sure thing if you have a wee bit of "loose" at this nut, AND the stab chucks more than about 1/16 of an inch. As long as with the nut not binding the turn is results in LESS THAN .015" chuck, the jackescrew is good to go.

    Are we having fun, yet?"


    Kind of wanting myself to go work on my system, I'm sure that it would need the TLC.

    PeterL

  14. #14
    Join Date
    Oct 2005
    Location
    Graham, Texas
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    838

    Default

    Peter, The above quote, though very informative, has nothing to do with the question asked. The solution lies in the illustration from the parts manual and the research done on the parts in the call out to help the installer know which part is which.

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