Pushrod/ball link query

[Dan Berry]

I am seeking guidance from the collective wisdom here.

The plane is a Vector 40 , LA 46 for the front end.
I have cf tube pushrods and ball links with L/R fittings from Russ at Okie Air.
The qustion is what does everyone consider the minimum length for threads into the ball link. Obviously more would better. I'm looking at having about 5/16' , maybe more threaded into the link. This is the elevator rod.

Is that enough or do I need to lengthen the pushrod?

[Ken Culbertson]

I am seeking guidance from the collective wisdom here.

The plane is a Vector 40 , LA 46 for the front end.
I have cf tube pushrods and ball links with L/R fittings from Russ at Okie Air.
The qustion is what does everyone consider the minimum length for threads into the ball link. Obviously more would better. I'm looking at having about 5/16' , maybe more threaded into the link. This is the elevator rod.

Is that enough or do I need to lengthen the pushrod?

I don't know it this is collective or even wisdom but I had a Twister that had a "short" rod and I only had about 1/8" to 3/16" in to the ball link.  It was a tight 3/16" and stayed that way for two years.  It defeats the point to have the threads go all the way to the bottom.  My guess, backed up by about five hundred or so flights on one showing no ware, that 1/4" is plenty.

Ken

[redout]

Hello.

I asked this very question about a week ago of an extremely experienced r.c. flyer who works in the local hobby shop. He said about twice the diameter of the threaded steel rod, is the minimum thread insertion into the ball link. This was for the Dubro plastic ball links which self-thread as you screw in the rod but I think his advice sounds right for all ball-links.

[Mark wood]

I like my baseline to have the end of the threaded rod be about half way in to the hole. That will give about plus minus 1/16" adjustment. If you half both LH and RH ends that would make an overall adjustment of 1/8".

[Tim Wescott]

I go by Mark Wood's rule -- thread that halfway into the hole.  Two rod diameters is probably a good figure of thumb, too.

Usually with fasteners you're just interested in clamping two parts together.  That's not really the case here -- you're asking the threaded connection to locate the ball link along the length of the rod and keep it pointed straight along the rod.  It's that "keeping it pointed straight" that, I think, would be the first thing to cause problems.  If the link can wiggle and rock on the threaded rod, then it'll wear, and then every bad thing that can happen with wear might happen.

So I'd ask if the fastener is going to have a chance to wiggle in the hole, or in the case of those plastic shanks, will the shank bend.  If the answer is "yes", then you need more thread engagement.

[Dan Berry]

I understand the ideal is halfway in. My pushrod is made- recycled from another plane.
That's why I'm asking about reality rather than theory.

[Mark wood]

 I know you're trying to use an existing rod but I would be thinking about that rod while I was flying it.

YMMV
Motorman

Me too.

[Joe Gilbert]

Dan if you are asking for a number ,I would seven full turns in is least you should ever use.

[ray copeland]

Honestly, if someone came up with and produced a heavy duty version of the dubro e z pushrod connector i would never use another ball link on a pushrod. Those things work so great on 1/2a's !! So easy to adjust and i have never had one slip!

[Mike Griffin]

Dan if you got them from Russ, I would guess that the system was the same one that Tom Morris sold.  I never got real technical about how far I screwed the threads into the ball link but as a rule of thumb I screwed them in half way.  Never had a problem.

Mike

[Dan Berry]

Dan if you are asking for a number ,I would seven full turns in is least you should ever use.

I’ve got eleven threads on them.

[Ken Culbertson]

I’ve got eleven threads on them.

On a 4-40 that is about 3/16"

Ken

[Dan Berry]

On a 4-40 that is about 3/16"

Ken

About 5\16. Close enough to half depth to call it half.

[Ken Culbertson]

About 5\16. Close enough to half depth to call it half.

My bad - I was using the 7 threads from Joe's post.  You are right.

Ken

[Brett Buck]

All this sounds about right, but one warning - don't ever let the pushrod "bottom out" in the link. They generally get pretty tight as you screw them in, so it is pretty hard to tell when it hits the bottom. If you go a little too far, it will do significant damage without it being readily apparent just from looking. Then it may break later on.

    Brett

[Ken Culbertson]

I just got a bulk pack of heavy duty DuBro links in today.  Thought it would be interesting to see hist how deep the pocket is since it has not been part of our discussion.  Well, it is 1/2".  That would make 10 turns center on a 4-40.  I intend to tap them instead of letting the rod self-tap.  I may be wrong, but I think it will be stronger that way.

Ken