Check Your Autopilot Servo Arm Screws!

[L.Adamson]

Originally Posted by az_gila

....plug for having your local EAA Technical Counselor make detailed inspections as you build... and especially in the final stages of construction...

I never needed the technical counselor. And I never called Van's either!

Between the Matronics list (in the old days) and this site, as well as numerous builder websites..............I found everything I needed to know; and got it right!

But then I read a heck of a lot..

L.Adamson ---- RV6A

[cytoxin]

Originally Posted by Rick6a

Since the screw issue arose, I had no choice but to post an early detail photo to illustrate the potential fix I was thinking about. I could not find a decent photo of the correct washer orientation, and I was not to keen to drive out to the airport, open up the baggage compartment then crawl back there to take a picture. Nothing gets past the good folks at VAF! Well...almost nothing. I'm surprised no one has mentioned the lack of torque stripe on the jam nuts at both ends of the pushrod.

I figured as much, but you know when something doesn?t look right you feel obligated to point it out at the risk of being ridiculed. I hope others would view my pics with the same scrutiny...but then that?s why I love this place . It the only place a not flying yet airplane can get a conditional inspection....

[chrispratt]

A sidebar to the servo inspection discussion for RV-8 owners (If you're not an RV-8er you can pass on this post).

I inspected the servo screws in my RV-8 this evening and all is okay. While it took an hour or so to unscrew the front floors, inspect and re-install, the elevator inspection was a breeze thanks to the battery inspection door I installed. If you haven't put one of these in you might want to consider it. I only need to open the hatch, reach inside and feel the screw on the servo arm. There is a separate thread on this site describing the door install that shows several variants. Below are few snapshots of mine:

First is the rear baggage area with the access hatch door closed:




Next with the access door open:




And lastly you can see the bellcrank and servo area. Easy to see and reach from here without taking the entire baggage area out.




Chris

[Rick6a]

Chris,

This is the first time I've seen the mod, an excellent idea and one that I am sure to copy!

[dmeloche]

Just checked my servo arms. The roll servo screw was barely finger tight and had no evidence of locktite. The pitch servo was tight and the screw clearly had been loctited. I've removed both servos and the attaching linkage and pulled the fuse for the control head. Until a means of positively locking these screws in place (not loctite) is developed I don't feel this is a airworthy installation. I like the looks of the Dynon more and more.

CHECK THOSE SCREWS!!

Doug
RV6

[RV6JOY]

I have two of the TT servos so have followed this thread with interest.
A point that does not seem to have been mentioned is that the Arm retaining screw and the C/S screws that hold the motor mount plate on are both "NOT ABLE TO BE CHECKED FOR SECURITY" i.e. there is no way of confirming that they are secure!
Visually you cannot tell whether they are Loctited or not, nor done up or not.
If you test them with a screwdriver you will break the Loctite seal, so that is out. A proper dual control inspection as required for certified aircraft cannot be done.
The mount plate can be made visibly secure by inserting a couple of short AN3 screws in the thread in the body and then lock wiring them but the only really secure, inspectable answer to the arm retaining screw would appear to be the solution used by Dynon. Threaded shaft and nut.
Hopefully these will turn up soon!
Brian

[Davepar]

I'm just finding out about this issue a bit late. Good reason to stay in touch with the VAF.

One thing I haven't seen anybody mention is a caution about reinstalling the servo shaft screw. For people that have been removing the screw to check for Loctite, or just cranking on the screw to make sure it's not loose, DO NOT OVERTIGHTEN THE SCREW!! The whole purpose of the shear screw is to break if the motor jams for some reason. If you tighten down the motor shaft screw excessively, the arm will not be able to move independently of the motor, thus defeating the whole purpose of the shear screw.

[RV7AV8R]

I looked at my arm last night and it has a nylon washer on the shaft screw, this should help prevent over torquing to the point of locking the arm. The screw was originally set with locktite. Some one suggested torque paint on this screw after it is reset with locktite. This will help the next time you inspect it. The RV7 and 9 and probably the 6 look less likely to get in a "locked" up elevator mode if the arm falls off. I looks like it would fall down and just hang there (assuming you are positive Gs when it falls off). The photos of the RV8 appear to have more hardware there to hang up on.

[MNForrest]

A basic question that goes somewhat along this thread: Why not AP on the electric trim? Avoid the potential for this issue all together. Am I wrong, or is that the way my Father's C172, C210, C340 were all set up?

Thanks,

Forrest

[penguin]

Originally Posted by RV6JOY

A proper dual control inspection as required for certified aircraft cannot be done.

Brian, FWIW, duplicate inspections of flying & engine controls don't exist in the US. The concept is not even recognised. Only the English speaking world seems to insist on them. Pete