VAF Forums

VAF Forums (https://vansairforce.net/community/index.php)
-   RV-7/7A (https://vansairforce.net/community/forumdisplay.php?f=7)
-   -   elevator rigging (https://vansairforce.net/community/showthread.php?t=86707)

LettersFromFlyoverCountry 07-05-2012 06:39 AM

Quote:

Originally Posted by Flying Scotsman (Post 676305)
Installing elevator pushrods tomorrow...just to confirm that there is no measurement other than "vertical" on the elevator bellcrank? I believe that on the -8 there is a measurement called out somewhere, but I couldn't locate any such measurement on the -7 plans.

Correct, there's no measurement other than vertical on the elevator bellcrank. The elevator, of course, should be in trail at the time this is set. No other measurement needed in this case.

The other thing here is there should be NO way for any rod end bearing on that push tube to come off if more than half the threads on each rod end bearing are engaged.

Flying Scotsman 07-05-2012 07:57 AM

Quote:

Originally Posted by LettersFromFlyoverCountry (Post 676344)
Correct, there's no measurement other than vertical on the elevator bellcrank. The elevator, of course, should be in trail at the time this is set. No other measurement needed in this case.

Thanks...that's what I needed to know.

Quote:

The other thing here is there should be NO way for any rod end bearing on that push tube to come off if more than half the threads on each rod end bearing are engaged.
Yep...see my post #10 just above :)

LettersFromFlyoverCountry 07-05-2012 08:09 AM

Also make sure that the jam nuts are tight before you drop the pushrods in. Not so much with the big rod but with the smaller one that goes forward, it's a giant pain in the neck to get a wrench in there to do it once it's been installed.

I know this is a "duh" advisory, but it's surprising how many times DARs and others find these particular jam nuts loose.

Smilin' Jack 07-05-2012 11:45 AM

ROd ends
 
It should almost be impossible for any pushrod on a Vans aircraft to unscrew it's self since all the rod ends are threaded like a normal bolt and not like a turnbuckle. You can not turn the pushrod and have both rod ends loosen up.
Smilin' Jack
Ever wonder if you've been building too long... and now might have an answer :)

rvbuilder2002 07-05-2012 01:10 PM

Quote:

Originally Posted by Smilin' Jack (Post 676446)
It should almost be impossible for any pushrod on a Vans aircraft to unscrew it's self since all the rod ends are threaded like a normal bolt and not like a turnbuckle. You can not turn the pushrod and have both rod ends loosen up.

Actually it is possible (just not in the way you think).
Since both rod ends are threaded as you describe, if they are both loose and rotating, the push/pull rod would be threading further onto one while it is threading further off the other. The way RV push/pull rods are designed, they should always bottom out onto the jamb nut of the one threading further in, before they fully unscrew off the rod end that is threading out.

Mel 07-05-2012 05:30 PM

Never say Never!
 
Quote:

Originally Posted by Smilin' Jack (Post 676446)
It should almost be impossible for any pushrod on a Vans aircraft to unscrew it's self since all the rod ends are threaded like a normal bolt and not like a turnbuckle. You can not turn the pushrod and have both rod ends loosen up.

Anytime you think something can't be done or is "almost impossible", I promise, SOMEONE will prove you wrong.

Flying Scotsman 07-06-2012 04:02 PM

Quote:

Originally Posted by rvbuilder2002 (Post 676474)
Actually it is possible (just not in the way you think).
Since both rod ends are threaded as you describe, if they are both loose and rotating, the push/pull rod would be threading further onto one while it is threading further off the other. The way RV push/pull rods are designed, they should always bottom out onto the jamb nut of the one threading further in, before they fully unscrew off the rod end that is threading out.

This depends critically on the length. I was a) careful to make all pushrods to the *exact* length per the plans and b) double-checking each pushrod as we assemble the systems to check for possible backing-out problems (none found so far).

rvbuilder2002 07-06-2012 08:06 PM

Quote:

Originally Posted by Flying Scotsman (Post 676971)
This depends critically on the length. I was a) careful to make all pushrods to the *exact* length per the plans and b) double-checking each pushrod as we assemble the systems to check for possible backing-out problems (none found so far).

I guess I should have clarified that if built correctly per plans, it should not be possible.
My post was in response to the comment that it wasn't possible because of the way the rod ends thread, but in reality, if the push/pull rod is of incorrect length, with the wrong amount of thread engagement of the rod ends, it is possible for the tube to thread to one end and separate from the rod end at the other end.

LettersFromFlyoverCountry 07-07-2012 08:39 AM

Quote:

Originally Posted by rvbuilder2002 (Post 677052)
I guess I should have clarified that if built correctly per plans, it should not be possible.
My post was in response to the comment that it wasn't possible because of the way the rod ends thread, but in reality, if the push/pull rod is of incorrect length, with the wrong amount of thread engagement of the rod ends, it is possible for the tube to thread to one end and separate from the rod end at the other end.

I would be very careful about assuming that just building the tube to the exact dimension will eliminate a problem. There are other factors here including how the elevators horns are installed and drilled, for example. If you're off by a 1/8", that pretty much negates the safety of the cut-to-plans push tube. Same with the bellcrank (although I can't recall if that's pre-drilled or not).

There's a reason why in dealing with rod end bearings -- of any kind -- the wisdom has always been make sure AT LEAST half the threads are engaged at both ends. That's the only foolproof guarantee, and it's just good building practice.

That's not to say other methods don't include a margin of safety.

Jimzim 12-30-2012 08:50 PM

Interference
 
So the large and small pushrods are of the correct length, bellcranck verticle, etc... Problem is,the stick hits the instrument panel when full forward!! Not good...what to do?? Shorten sticks, extend elevator stop, or ??? Anyone else have this issue?
Jim


All times are GMT -6. The time now is 08:09 AM.