Control Pushrod Adjustment

I helped look over a not yet flying, brand new -6 today, and found something which seems to be quite common in initial setups. I do not know if this applies to the -4 or -8 or 10, but it applies to the 6's, 7's and 9's. It has to do with the rotational adjustment of the rod end bearings of the lateral aileron pushrods. Because of the nature of the design, the inboard connection of the lateral pushrods will rotate in the pitch axis when the stick is moved fore and aft. The aileron bellcrank in the wing of course does not rotate in the pitch axis. Each rod end bearing only allow for a limited amount of rotation, and the two rod ends on the lateral aileron pushrods must be carefully adjusted relative to one another so that in no case is there torque on these pushrods.

To check for this, one needs to put the stick in all four corner limits, and verify that in each position the lateral aileron pushrods can be rotated slightly back and forth. There is very little room for error in this adjustment, and adjustment can be a pain in the neck. There is some trial and error, because the act of tightening the jam nut will move things slightly.

This same check needs to be performed on the fore/aft aileron pushrods as well. In fact, all pushrods should allow for slight rotation back and forth as described above.

In the case of today's plane, the aileron pushrod was a de-facto elevator travel limiter, as the rod end bearings were jamming before the elevator stop limits were achieved.

Interesting!

I've inspected literally hundreds of RV-6s and not seen this phenomena. Yes, the rod end bearings need to rotate in several directions but I've never seen it as a problem.

What it boils down to is that all of the rod end bearings in the system need to be very close to neutral (i.e. able to rotate in both directions) when the controls are neutral.

If (for instance) both of the rod end bearings on the big push pull in one wing are already at their limit, you'll have a control system jam in one direction in pitch.

Not a good thing.

Control throws and fully installed hardware are two of the most important things to check during final assembly.

Interesting. I've seen it on about half of them around here that I've looked at. I haven't looked at that many aircraft, but this adjustment is not difficult, but takes time. I would guess that there is only a couple degrees of play on the lateral pushrods when at the corners of the stick travel.

The easy way to do a rough check of the aileron push pull's is to hold both the stick and the ailerons neutral. Then, reach through the access panel on the wing and see if you can rotate the push/pull equally in both directions.

Then do the other wing.

Yes... they did bind.....

Mel said:

I've inspected literally hundreds of RV-6s and not seen this phenomena. Yes, the rod end bearings need to rotate in several directions but I've never seen it as a problem.

Click to expand...

Mel... IIRC this was a problem on the early models (-6s and probably -4s), and Revision 9 to RV-6 Drawing #40 (Jan 1995) added a washer 5702-75-060 next to the bearing at the control stick.

This small diameter washer (about the diameter of the end of the heim bearing) allows more rotation of the push rod without any binding occurring.

It must have been causing problems for Van to actually change a drawing....

Perhaps you are looking at later RV models where the washer is standard..... or all your builders had later plan versions....

gil in Tucson

UPDATE

Revision 4 on RV-6 drawing 19a (same date - Jan 1995) added these same 5702-75-60 washers to the other end of the aileron push rod at the wing bell crank end - more rotational tolerance added....

Mine was built between '89 and '93. I don't remember having this problem. I'll go back and check my plans. I've been inspecting since the came out in the '80s. Of course back then you were expected to make necessary adjustments on your own. These weren't "assembly" kits.

This is particularly interesting to me since I just finished rigging my ailerons last week and removed both wings for final fuse assembly today. I hadn't noticed there being a problem with binding but will now be watching closely when I reassemble my 7. Thanks for the heads up.

Just to confirm, this is still a potential problem on newer models. I had this exact thing happen on my 7A when I tightened the jam nuts on the aileron push tubes. I was about to leave for the night when I decided to mess around with the stick. I discovered I could no longer make the elevator hit the down stop. Took me a while to figure out what was going on. Adjusting and re-tightening the jam nuts fixed the problem.

I can confirm that this same issue (see first post in this thread) exists in the -9 models. Let's just say we found it in a 200 hour RV9A here in the neighborhood. Indeed, a loose (or is it lose? inside joke, sorry) jam nut was also discovered earlier in the same plane.

It seems to be more the norm than the exception, based upon my inspection of perhaps 12 side by sides. Maybe people are not exercising the corner extremes of the stick when they check this? I.e., full forward, full right stick.

Guilty as Charged

I was in the midst of the the annual when I told Alex that I had a jamb nut come loose (yep, that's the one) at the bellcrank, breaking the torque seal.

We maxed the stick in all 4 corners and found some binding. Messed with the end bearing for a few minutes, snugged the jamb nuts and then re laquered the thing.

I don't recall this check specifically called out in the instructions and several of us missed it prior to first flight last year.

Easy check, and worth doing IMHO.

Having a smart hangarmate is great - Thanks Alex

Alex
To clarify your set up procedures. Did you start the bearing adjustment with the stick in the neutral position first or begin with one of the corner stops and then proceed to check the other stops fine tuning the adjustments as needed? Thanks for the info, probably would have never checked it.

Oldgeezer
RV9A Finishing

Another data point

I had the same issue at first with my -7A. It takes a little bit to figure out what is happening.

Another thing along the same lines, be sure your elevator is NEUTRAL when rigging the ailerons to center.

After rigging ailerons to center with elevator neutral, center the ailerons in trail and then move the elevator up and down and watch the ailerons. They will show some roll as you move the elevator up and down on the side by side planes. If you were to rig the ailerons to center with UP or DOWN elevator, they would not be in trail with each other with elevator at neutral.

Not much, but noticeable.

Geezer - Nice Avatar

We started with the stick in a corner and then just adjusted till the bearing had some side to side play in each corner. Then tightened the jamb nut and checked it again.

Maybe that is really "Oldgeezer's" picture, Pete. How insensitive!

I think you answered the questions, Pete.

MY apologies, Oldgeezer

Sometimes I can be a real looser........

Thats ok, sonny. I don't feel as old as I look. One Viagra a day does wonders for my vitality and rivet banging. Once I get past that first bit of forward motion, you would have a hard time catching me and the girls think I'm cute for being hairless.
Living the Dream
Oldgeezer
RV9A

Giddy Up OG!

Keep it Up! <groan>

I didn't know.

Oldgeezer said:

One Viagra a day does wonders for my vitality and rivet banging.

Click to expand...

I didn't know that Viagra would be prescribed for that kind of banging.

Kent