Aileron push tube length? ...Has anyone had problems?

Hi RV-7 builders,

I've been putting off cutting my large aileron push tubes because I heard rumours that the plans were giving dimensions that were a bit too short.

The plans call for the tube to be 65 25/32" long (69 9/32" from bolt to bolt). Has anyone found their push tubes to be too short using these dimensions? Was there a mistake on the plans before a revision?

Would there be any harm in making each one 1/4" longer?

Using thirty seconds of an inch accuracy for this piece seems a bit silly when there are threaded rod bearings on both ends that can be adjusted. Of course my fear is that I will not have enough threads left when assembled.

Thanks in advance.

Steve Wolfe

Making them longer would only require that the rodend be screwed in with more threads in the rodends and less showing. That's a good thing. If they are at max entry with all threads inside the rodend all you have to do is shorten it a little to meet the required dim on the bellcrank in each wing to the neutral position. Don't know what that dim is for a 7 but there is one for the 6 and the 4 so I assume there is one for the 7 also. Being too short requires more threads showing and the possibility that your wire will go through the witness hole and that is a BAD thing

This is how many threads I have after mating the wings and adjusting ailerons to fuse. I used the plans measurements to the .001 in. For the tube length.

After reading about all of the issues here I decided to make mine a little bit longer. I can't remember the exact amount longer without checking my log, but I think I just added about 1/4" or I might have just rounded to the next larger standard increment. I agree that a length measurement to 1/32" is a little silly. This is something that I wish would be changed in the drawings since I like you wasn't sure what to do about the length.

What are most of you using to achieve these measurements? I hate to use an old tape measure.

I started a thread on this after finding my pushrods too short. I built a 2nd set almost 3/8" longer.

They're perfect now:

Bret, looks like a lot of thread showing... did you try mounting your pushrods, and as a test, loosening the jam nuts all the way, then twisting each pushrod fully in one direction, then the other, to see if one end fell out? Even if one end didn't quite come out, but was wobbly (only a thread or two still holding), I'd be a little concerned.

bret said:

This is how many threads I have after mating the wings and adjusting ailerons to fuse. I used the plans measurements to the .001 in. For the tube length.

Click to expand...

Let's add a bit of process to the mix. Take the length of the end-bearing threads and subtract about 5 threads worth of length. Then divide the remainder in half. That is the length that should be showing when everything is assembled. I think for the RV6 it was 5/16 inch including the nut being in place. That gives you an equal amount in or out. Next pin the bellcrank in the "neutral position". Support the stick in the vertical position by using block(s) of wood and some clamps. Now with everthing as it should be, take a tape measure and measure the length of the tube. It is best to have the rod-end bearing with the conical tube end on both the stick and the bell crank, but you can certainly measure from pivot bolt to pivot bolt. Measure both left and right wings to see that they are the same length. Then prepare the tube. If you want to be more conservative, cut the length 1/4 inch longer, install one rod end bearing holder with rivets and then insert again to test. You will probably cut the 1/4 inch off. Certainly, any accuracy near 1/16 inch will be enough as the threads will allow adjustment.
The job doesn't take very long.

Greyforge, thanks for calling me on my set up. Thank you! Here is a pic of the same rod. I would have to agree the plans are inaccurate, there is not enough thread. The rod is too short. I cut it to plans but it is not long enough. So, do we call Vans and call them on this mistake? There is enough thread to hold the load but not if it were to unwind. Thought, what if I, me only me were to add another nut to decrease the amount of thread that the rod could come down to?

You're quite welcome Bret! Vans knows that many people end up with the rods too short, but maybe plenty are the correct length, so they don't want to change the plans. I think it takes a lot to update the plans. Maybe significant additional R&D to ensure the changes are good, so they need to weigh the benefits.

But I wonder how many people have the amount of thread in the rods that we did and are flying.

I considered adding another jam nut, but ended up being paranoid and building another set of rods. On yours, it looks like another jam nut would ensure you have maybe 3 or 4 threads left in the rod when turned all the way one way. But testing would be the best way to check. Stack on a 2nd nut on each end, screw both pairs as far towards each bearing as possible, install to the correct length and try the turn test again. Once it's all the way towards one end, leave the bearings as they are, remove the assembly from the plane and unscrew the rod end bearing that's already most of the way out, counting turns, until it comes off. Hopefully, the number of turns/threads is a value you're comfortable with.

Regards,
Russ

I have seen some use bushings over the threads between the jam nut and the end of the threads towards the end bearing, which would allow less unthreading yet, in the case that both jam nuts became loose.

It is also important to not make the pushrods so long that the pushrods itself hits the bellcrank arms, creating a binding control stop. I know this can be a problem in the -10. I'm not sure about the other models, but I wouldn't be surprised.

As a side note, I make a point, every chance I get, to grab the pushrods and twist them back and forth to verify a good solid stop as each rod end bearing hits the side of the bellcrank arms. It needs to rotate some freely, then needs to have a good solid stop. Good peace of mind.