Elevator trim tab question

[Freemasm]

Originally Posted by PilotjohnS

If the jam nut is loose,I think it could cause the threads inside the clevis to wear. This could lead to a sloppy fit between the clevis and the cable. If it gets really bad, then the cable and clevis could slip a few threads.

I would check the cable and clevis threads for excessive wear. If any is found, then it might be prudent to replace both. JMHO

...and then some. If the jam nut is loose, you can easily get a reversing load on the threads; never a good idea. They will wear and fret away or even fail from fatigue. In quick summary, their purpose is two fold.

[sahrens]

Could this be a chaffed wire grounding somewhere? The trim motors are reversible based on grounding through the trim switch. Perhaps it’s a loose connection or a frayed wire. That’s where I’d start searching; maybe start where the wire passes through the elevator to the horizontal and into the fuselage.

[Roadjunkie1]

While you are under there.....actually has to do with checking your log books: make sure SB 06-9-20 was complied with. That has to do with WD 415 which is the welded fitting your cable passes through visible through the hole in the elevator. There is a better designed WD 415-1 that has welds on both sides of that nut the cable fitting passes through. When I was replacing mine, the welded nut on the original WD 415 actually snapped off Pretty happy I replaced THAT!
Van sells the new -1 for just over $8. Worth it. Hopefully the previous owner replaced it. It is a little bit of a PITA to replace the thing.....

[Everwild]

Very informative video on the subject of rod end bearings as they apply to aircraft.

The answers related to reversing loads and wear on threads are correct. Most installations wont let the rod end unscrew by design.

https://www.youtube.com/watch?v=foyZLBneV08

[ronrapp]

Originally Posted by Freemasm

If the jam nut is loose, you can easily get a reversing load on the threads; never a good idea. They will wear and fret away or even fail from fatigue. In quick summary, their purpose is two fold.

That does not sound good. I do not have the construction documents for the airplane; is there a place where I could find a torque value for the jam nut? Do people put torque seal on this nut?

Thanks for the info!

--Ron

[ronrapp]

Originally Posted by sahrens

Could this be a chaffed wire grounding somewhere? The trim motors are reversible based on grounding through the trim switch. Perhaps it’s a loose connection or a frayed wire. That’s where I’d start searching; maybe start where the wire passes through the elevator to the horizontal and into the fuselage.

I suppose anything is possible. I'll as much of the wiring as I can get access to and see if anything stands out as worn, chafing, etc.

The behavior of the motor is interesting. Once it starts to trim nose up -- and it's always been nose UP -- it just keeps running until I disconnect the autopilot.

--Ron

[ronrapp]

Originally Posted by Roadjunkie1

While you are under there.....actually has to do with checking your log books: make sure SB 06-9-20 was complied with.

Thanks for the information! There is nothing in the logbooks about this SB having been completed on the airplane (first flight in '97), so I probably have the single sided weld. For $8 it's hard to go wrong.

--Ron

[ronrapp]

Originally Posted by Everwild

Very informative video on the subject of rod end bearings as they apply to aircraft.

The answers related to reversing loads and wear on threads are correct. Most installations wont let the rod end unscrew by design.

https://www.youtube.com/watch?v=foyZLBneV08

Thanks, David. I learned quite a bit about rod end bearings from that vid. It certainly clarified the role of the jam nut. What I'm still not 100% sure of is how to ensure the jam nut is tight enough. At the very least, it's something I'll be checking closely in my preflight inspections.

--Ron

[lr172]

Originally Posted by ronrapp

Thanks, David. I learned quite a bit about rod end bearings from that vid. It certainly clarified the role of the jam nut. What I'm still not 100% sure of is how to ensure the jam nut is tight enough. At the very least, it's something I'll be checking closely in my preflight inspections.

--Ron

one wrench on the flat area of the clevice and the other on the jam nut.

[RV7A Flyer]

Originally Posted by ronrapp

I suppose anything is possible. I'll as much of the wiring as I can get access to and see if anything stands out as worn, chafing, etc.

The behavior of the motor is interesting. Once it starts to trim nose up -- and it's always been nose UP -- it just keeps running until I disconnect the autopilot.

--Ron

Does it *ever* run away when the autopilot is NOT on?