Trim Jackscrew Binding

[PeytonM]

1989 J. 3300 hours. Hangared. I've become less dependent on the electric trim because of my own experience that I reported on MS, as well as others.'  I use the manual trim wheel when flying the airplane, especially on departure and landing.

Upon returning to my home airport after a short flight last week, I reached down to the wheel to begin trimming for the approach and landing.  I could not budge it!  I could not move it at all. I used the electric trim to set up the approach, but I could tell the trim wheel was moving much more slowly than usual. I landed and taxied back to the hangar. I tried using the manual trim to no avail. I repositioned the trim to "Take-Off" with the trim switch, closed the door and walked away!  

Please note: trim was never at either extreme of full nose up or down.

After a few calls and suggestions, I removed the belly panel, checked the trim screw and chain; they both looked a little dirty, but not bad. I cleaned them off and checked to see if that helped; it did not. In the battery compartment, I decoupled the electric trim motor from the system to no avail. I opened an inspection panel on the right side of the tailcone and removed a bolt that connects to the the trim actuator to the jackscrew. (bolt #26 on Illustrated Parts Catalog page 27-40-01) The trim wheel moved freely. I plan to fully access the jackscrew by removing the fairings and move the boot to see what I can see.

I remember back to the last times that I used the trim wheel, and it seemed stiff. I wrote it off to the single digit weather. Maybe my Mooney was talking to me and I was not listening!!

Any guesses what I'll find? Has this happened to anyone? What steps should I take to look for the problem?  I'd sincerely appreciate your thoughts and suggestions. 

[carusoam]

The last jack screw problem reported around here came from Amelia.  She had an unrelated screw interfere with the jackscrew...

It doesn't take much to bind the trim.  Misplaced tools, crusty grease, a too long sheet metal screw,  that kind of thing...

along with that thread were discussions on what to do on how to handle the mis set trim in flight...

PP thoughts, not a mechanic...

Best regards,

-a-

Edited January 17, 2017 by carusoam

[RobertGary1]

Certainly take a look at the jack screw in the tail. If it's not getting lubed correctly it can get stiff too. 

 

-Robert 

[Hank]

Two things to check on the jack screw:  is it dry, or is there grease on it? Is the grease on it (and inside) old, hard and dry? Old, hard grease inhibits movement of the jack screw.

While you're down there with the belly panel removed, check the other things suggested above. Everything is right there together.

[RobertGary1]

The jackscrew is accessed by removing the panel at the tail that slides when the tail moves near the leading edge of the tail. Either side is fine. There is a boot over it. If it's old and torn you can see around it. Otherwise there are Uber tiny screws to remove to slide it back. Accessing under that boot can be a pain and probably why it gets missed. 

-Robert

[N201MKTurbo]

The fact that it moves with the electric is interesting. It makes me think it might be the clutch in the trim servo. The Centaury servo engages with a solenoid that meshes two gears. If that solenoid is stuck then the electric motor would move it but you wouldn't be able to move it by hand except by overcoming the slip clutch.

Remove the chain from the trim servo and see if you can manually move the trim.

[carusoam]

Starting to sound like the electric trim is not behaving very well...

1) the electric trim was working slower than usual...

2) the manual trim is being hampered by it...

This is what I am seeing by reading this thread.  PP thoughts only...

Best regards,

-a-

 

[Oldguy]

I don't know if the Century has a pre-flight like the King does, but it might be worth a look in your POH to see if there is a check for proper electric trim functionality. Rich's test above would probably yield the same results, but if you need to contact someone about the problem, you might be ahead of their questions.

Like Anthony, just a PP thinking out loud.

[PeytonM]

We did decouple the electric trim and I still could not move the trim wheel; the only way I could move the wheel is when we decoupled the jackscrew. 

Today, we reattached electric trim motor and trimmed it nose up (I had to help it by lifting the tail!).  Lots of gunk on jackscrew, including what looked like lithium grease. Cleaned up what we had access to and greased. Movement is much better with electric trim and I can move the manual trim wheel.   In the middle half to 2/3rds of travel, trim wheel moves fairly easily up & down both manually and electrically, so we've made progress. However, with nose trim full up, trim wheel still nearly impossible to move.  The only long term fix is to pull the jackscrew out, replace the bearings, clean and lube the whole length of the jackscrew and reassemble and rig.  Hopefully I won't have to do this again, although it's been a great learning experience:)

[jetdriven]

It's a KP-16A bearing. I've replaced mine but the jackscrew is unbelievably difficult to reassemble where it runs freely with a load on it. 

[PeytonM]

Jet driven: Thank you for your recent posts, as well as your post back in 2012 with the same issue as what I'm struggling with.  Back then, you were hopeful that simply cleaning and lubricating would successfully correct the trim issue. I infer from your post today it took more than that? What happened?  In your post today, you said the bearing was the culprit but reassembly was a challenge.  What advice can you give?

[jetdriven]

It all went together fine, new bearings etc, but when installed, it would go about 3/4 nose up then get extremely tight then almost jam. Reassembling it again it made it better, but in our case the load from the tail makes it very hard to trim up.   I had the unit out and apart ten times.  Alll the friction is in the jacknscrew unit, not the forward gearbox, not the torque tube,  not the trim indicator cable. Idk what it is besides the jackscrew and threaded part which is like 1200$ in parts. 

Edited January 23, 2017 by jetdriven

[cliffy]

BTW  There are a couple of KA-16A bearings available. Both by the same maker. One is a commercial design and another is specific for aircraft and aviation applications. There is also a caveat that says notification to the seller is required if the application is for aviation. 

Just like our wheel bearings. Fafnir has the same bearing numbers for both commercial apps and aviation apps with the tolerances different for each, from what I read. 

So basically, you just can't order either without specifying the aviation design.

Comments appreciated. 

[PeytonM]

After you cleaned jackscrew and nut, did u notice any free-play before you greased and reassembled?  I'm told the jackscrew is hardened steel; the nut that it screws into is a softer alloy. I wonder if there is wear in that threaded nut, that would explain the difficulty in movement at the trim extreme. I'll find out today when we do the JS-ectomy! Did u ever resolve the difficulty in trim movement at extremes?

[carusoam]

Note: When machine builders select the materials for running against each other...

The one that is easier to change out or is lower cost will be the slightly softer one.  This allows for preferential wear to occur in an expected place.

in The case of the Jack screw, normal wear will occur in both directions over the travel that is most often used.  Few Mooney's ever use the maximum down trim.  Many of them use maximum up trim.

When manually trimming, it is easy to sense the limit of the up trim and top applying force....

When using the power trim, it is easy to not feel the limit of the up trim and apply excess force while it tries to jam the system into the stop.  At the extreme end for up trim, look more for damage than for wear, both should be pretty visible...

PP thoughts only not a mechanic...

Best regards,

-a-

[dooleypster]

Peyton,  a friend of mine experienced something similar..... in that his trim wheel became more and more difficult to operate over time (electrically and manually).  The mechanic was stumped after going over the jackscrew, lubrication, etc.  Finally, he surmised that the bracket which holds the chain drive in the tailcone (just aft of the battery) was twisted slightly out of position causing the chain to bind during ops.  Straighting this helped immensely.  Don't know if this applies to your situation, but it might be worth a look see.  This can be a very frustrating problem.... best of luck.

[Sabremech]

So tonight we removed the trim jackscrew from Peyton's airplane. It will get sent out for repair and then we'll reinstall it. It's a good challenge to remove.

David

[carusoam]

Fabulous photo, David!

The more we know, the better off we are.  The photo helps a bunch.

Best regard,

-a-

[cliffy]

The very thin shims between the housing and the bearing can be a bear to get back in correctly!  :-)

[TheTurtle]

is the problem that it was held together with duct tape?

[Sabremech]

20 minutes ago, TheTurtle said:

is the problem that it was held together with duct tape?

Nope! Still binding from takeoff position to full nose up. 

[cnoe]

For the curious, here's what it looks like in the plane.




Sent from my iPad using Tapatalk

[PeytonM]

It does look like duct tape!  Just a different metal alloy. 

[PeytonM]

It was a real mess! After cleanup, it looks brand new.  Looking forward to smooooth operation! Thanks Jason! 

http://www.jed-aireaviation.com/

[Mcstealth]

good luck