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I was fussing with my aileron trim springs and ran across a post on using RC clevis rods rather than safety wire to set the slack length...

First I carefully measured the spring force for a couple of new springs; it is about 1 pound per inch but is not quite linear.

I picked up two small metal clevis with threaded rods for 1.05 each at a local hobby shop. They are much easier to measure, adjust, and instal.

 

[eddieseve]

Great idea Stephen, can I steal it from you, I had real trouble getting the safety wire locked off properly in that area.

Cheers

 

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Post and share

Post and share... VAF

 

[DaAV8R]

Suggestion

The metal clevis you show is a Kwik-link clevis. As a precaution against the clevis coming off the horn, or in your case the spring, we use a piece of fuel tubing cut about 3/16" long over the clevis. This prevents the clevis sides from separating which would allow the clevis to become disconnected.

If you wish to install some tubing, disconnect and remove the clevis. Slide a short piece of RC fuel line on the rod. Re-connect the Kwik-link and slide the tubing up the Kwik-link about half way to the pin.

All old modelers have lost a model due to a failed connection. We take every precaution to make all connections 110%. It is good training for maintenance on our full size airplanes.

Edit: One other note. These Kwik-links and rods come in 4-40 and 2-56 threads. I would recommend 4-40 for an application with constant load. I have had many failures of the 2-56 connections over the years.

 

[RV7Guy]

4-40

The metal clevis you show is a Kwik-link clevis. As a precaution against the clevis coming off the horn, or in your case the spring, we use a piece of fuel tubing cut about 3/16" long over the clevis. This prevents the clevis sides from separating which would allow the clevis to become disconnected.

If you wish to install some tubing, disconnect and remove the clevis. Slide a short piece of RC fuel line on the rod. Re-connect the Kwik-link and slide the tubing up the Kwik-link about half way to the pin.

All old modelers have lost a model due to a failed connection. We take every precaution to make all connections 110%. It is good training for maintenance on our full size airplanes.

Edit: One other note. These Kwik-links and rods come in 4-40 and 2-56 threads. I would recommend 4-40 for an application with constant load. I have had many failures of the 2-56 connections over the years.

This a great idea!!! As mentioned above, I wouldn't use one without secondary securement. I've gotten into the habit of using heat shrink on the clevises of my models. That really locks things down. I would also recommend the 4-40 size used on larger models. I used the 4-40 on my flap position sensor linkage.

Sullivan and Great Planes both have linkages that have a small tab that will lock the pin on the clevis in place.

 

[Eddie P]

Just wanted to back up the previous posts and ensure you heed the warnings (not to rain on the parade of good thinking and problem solving). Be sure to keep the clevis pin inserted properly at all times. The clevis used has a weakness in design in that the clevis pin can shear fail under vibrations even in relatively small loadings if the clevis pin comes unseated from it's closed and locked position. Even the strong metal 4-40 ones. There are small metal parts called "clevis keepers" that are snap on metal parts that fit over the small groove in the end of the clevis pin that ensures they stay seated. While fuel tubing also works to keep the clevis closed, it might be a good idea to use both techniques to ensure the clevis stays closed. It's a great option just with it's own minor caveats.

Might also want to use a jam nut and a dot of red lock tite - the jam nut threaded onto the pushrod and then locked up against the clevis intersection to make sure your threaded pushrod does not wear and strip at the clevis due to vibration, loading and temperature shifts. That might be overkill but I tend to jam nut all clevises to keep them solid.

 

[Closterman]

Thanks a lot for the idea ! I have just make some improvement by using 2 ball link and a tork link. Impossible to disconnect like that and it's possible to make some fine tuning adjustment with the tork link !

 

[carlrai]

How about safety wire on the clevis?

The clevis is a great idea.

Fuel tubing or heat shrink may crack or split over time. I never lost a model due to the failure but have discovered it on older models when doing a PM check on the controls.

Would a few wraps of small diameter safety wire make for more secure insurance?

Ball link looks like the ticket! Secure with little chance of failing.