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Adjusting the Aileron Pushrod?

claycookiemonster

Well Known Member
I'm trying to get the basic trim set up on my -8 wings.
With the Aileron alignment jig holding the bellcrank in neutral, and with the ailerons held neutral by the alignment of the tooling holes on the outer rib, I'm supposed to adjust the pushrod between bellcrank and aileron to fix everything in position, right? Guidance is slim in the instructions.

Should the pushrod adjust in overall length be twisting it like a turnbuckle? Mine does not, the overall length remains the same, and one rod end gets longer while the other one gets shorter.
If not adjusting the length by twisting it, then I have to disassemble the connections at either/both ends to turn the rod end bearing and then put it back together to see if it's right?
 
Correct on the fixture and tooling holes.
The rod ends are both right-hand thread, so to adjust, you have to remove one of the bolts (I used the bellcrank end) and turn one end in or out. As you said, turning like a turnbuckle just shifts it back and forth without changing overall length.

Start with the target dimension on the plans to get close and go from there.
 
Do a quick check once you"re set and before locking anything in place ... rotate the push rod until it hits the stop limit on each end. It should still be well engaged on both rod ends. That will ensure there is no normal way for the push rod to work it's way off. :eek:
 
Thanks. Yes, I checked the plans (this is a project, I did not build the pushrods) hoping there were left and right hand threaded ends, but didn't see anything about them. Ok, Dimensionally close to begin with, and then a half-turn at a time.
 
You discovered that you cannot shorten or lengthen the push tube like a turnbuckle. After you fine tune your length, I then spin the whole tube to “center” the tube between the rod ends, or count the exposed threads so it’s symmetrical.
 
Pushrod is no turnbuckle by design!

Maybe i am telling you something you already know, sorry for that.

Maybe i did not understand your question a 100% right, then blaim it as a “language barrier”…….

But:

The pushrod is designed NOT to work as a turnbuckle by design!

If, for any reason, the pushrod starts turning (loose locknut or broken safteywire), the length will not change, therefore your rigging will stay true and your aircraft controllable!
Every movement of the pushrod tube will shorten the one end for the same amount the other end is lengthened.
The pushrod will continue doing this until the rod-end-bearing beeing tightened will run out of threads. This has to happen before the other end, the rod-end-bearing coming loose, will be completely unscrewed.
Therefore rod-end-bearings in pushrods are supposed to be screwed in more than half of the threaded length.

It is a saftey feature by design!

If you could use it like a turnbuckle and the pushrod would start turning, your rigging would change. Turning in the wrong direction (both rod end bearings loosen) it could even lead to linkage disconnection of the stearing surface, leading to flutter or even more disastrous results.

In the other case you will feel nothing. On the next inspection you will find an situation on the pushrod that will be awkward to look at, but you will live to tell about it.

How likely is it that both red-end-bearings become loose at the same time?
Not very, i admit.
But you will not notice one loose end at all unless you discover it during a inspection.

And if one is already loose…..(first: there must be a reason for it that might loosen the other as well??)…….we are talking about a single failure that could lead to uncontrollability in flight.

Therefore the engineers encountered this by designing the pushrod NOT as a turnbuckle.
I would call that principle “fail-safe” (the pro’s may chip in here….)

P.s. when i was rigging my -8 a asked myself the same question. A turnbuckle-pushrod would have made rigging a lot of easier, but would have caused other issues…..
 
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