Elevator Friction

[Randy]

Now that I have everything flight ready on the empanage, (or so I thought), I am noticing considerable resistance to movement of the stick fore and aft. I know it is too stiff and must be loosened up as it requires much more force than the normal RV controls that nearly glide from stop to stop with very little resistance.

I would sure like to hear about what others have done to remedy this condition.

Mine seemed pretty decent until I did the final tightening of the AN3 bolts at the hinge points. My neighbor is having the same problem with his and has had it apart a few time in an attempt to get free it up, but no joy.

Ideas and or cures appreciated!

Randy C
RV7A, wings on, getting close...

 

[dan]

Are your rod end bearings on the elevators (where they attach to the HS hinges) aligned? If they're out of alignment that could be one possible cause.

A half turn of one rod end could make all the difference in the world.

 

[Norman CYYJ]

The problem you having is probably caused by misalignment of the elevator horns. Remove the bolt that connect the push tube and see if the friction goes away. Then check each elevator by itself. If all is free the elevators are not lining up properly and the bolt in the horns is pulling them out of alignment causing the friction. You may have to re-drill one of the horns.

 

[JonJay]

You are probably tightening the bolts down too much. Take the nut down until there is no space between the washer and bolt head on the outside of their respective brackets. Or, loosen all of the bolts. Tighten them down one at a time backing each one off until the controls are free. Repeat this for all four.
You do not need to tighten them anymore than that. If you torque these to "specifications" they will be way too tight.

 

[Randy]

Easy Fix!

Hey, backing off on the torque freed it up just fine. I am really surprised at the difference. I did not realize that putting a squeeze on those rod end bearings would bind up the elevators that way. It makes me consider putting new bolts in with castle nuts and cotter pins so I can keep them loose and not be concerned about their security.

Thanks to all for the input.

Any more ideas would probably be appreciated by my neighbor. I am sure he will be checking the torque on the bolts right away but I suspect he has been there and done that.

Randy C

 

[JonJay]

Hey, backing off on the torque freed it up just fine. I am really surprised at the difference. I did not realize that putting a squeeze on those rod end bearings would bind up the elevators that way. It makes me consider putting new bolts in with castle nuts and cotter pins so I can keep them loose and not be concerned about their security.

Thanks to all for the input.

Any more ideas would probably be appreciated by my neighbor. I am sure he will be checking the torque on the bolts right away but I suspect he has been there and done that.

Randy C

I am not concerned about my nylon nuts. They have worked on thousands of RV's without any problem. Also, there are no forces that could allow the bolt to capture and the nut to turn in one direction, or vice versa. I make it a preflight ritual to check those bolts, and always will. Worse case scenerio, you miss preflighting a few dozen times, one of the nuts falls off, the bolt then works itself out. If it was the outer bolt, maybe you would have an issue, but maybe not even at that. If it was an inner bolt, doubtful anything would happen. Just my two cents.

 

[Kevin Horton]

When I did my trial elevator fit, I found that I needed exactly the right thickness shims at bolt where the pushrod attached to the elevator horns. At first, I didn't have a shim there, and when I tightened that bolt it pull the two elevators towards each other a tiny bit, and that put a side load on the elevator bearings, which produced unwanted friction. I was very relieved when I figured out what was causing it.

I would tighten the hinge bolts with the two elevators not connected together. Make sure both elevators swing freely, then join them at the horns. If suddenly there is friction, you know it has to be a problem where they are bolted together, or it is because the hinges aren't all in a line.

 

[szicree]

Hey, backing off on the torque freed it up just fine. I am really surprised at the difference. I did not realize that putting a squeeze on those rod end bearings would bind up the elevators that way.

I'm confused about what is binding. Those little spheres in the rod ends seem pretty hard, so I can't imagine them smooshing out of round. Also, it should be noted that the bolts, bearing centers, and hinge brackets should all remain stationary. You don't want things rotating around the bolt, you want the bearing rotating around its center sphere.

 

[dan]

I'm confused about what is binding. Those little spheres in the rod ends seem pretty hard, so I can't imagine them smooshing out of round. Also, it should be noted that the bolts, bearing centers, and hinge brackets should all remain stationary. You don't want things rotating around the bolt, you want the bearing rotating around its center sphere.

Yeah, sounds like his horns were getting pulled by the center hinge bolt.

I would definitely lean toward shimming it properly rather than UNDER TORQUING!!!

 

[Ironflight]

I strongly agree with Dan - if it is binding with the proper torque on an AN3 bolt (which is very small), then you need an extra shim to bring things into alignment...or something. Find the real problem, don't leave the nut loose. I very rarely give "advice", but anything wrong in a control system gives me the willies....

Paul

 

[Randy]

"Yeah, sounds like his horns were getting pulled by the center hinge bolt.

I would definitely lean toward shimming it properly rather than UNDER TORQUING!!!"

I hear what your getting at Dan. I remember each individual elevator moved freely, and then after bolting the horn in they still moved freely. Only when I did final assembly and torqued the nuts down at the hinges did it bind up. I will definitley do some more testing via tightening and loosening various fasterners, including the horn to make sure some shims are not needed somewhere.

Since putting a squeeze on those bearings should not actually be causing the binding, I suspect the final tightening is putting a pull on something, and I will have to get to the bottom of it.


Still it is surprising to see how they freed up just by but backing off a bit on the torque. I may have had them over torqued a bit. With things swigning freely, I still have the correct amount of threads showing through the nuts, with the normal thickness washers in place.

Randy C