elevator struggle

[HansLab]

I intended to title this message 'Warp struggle' but I'm not too sure that this is my case: therefore I'm asking the Forum.
Assembling the Mark IV gave me a struggle at the elevator. I was able to get the elevator and the moving elevator-rudder together. Trying to attach the hinges, though, seemed a problem. The outboard and inboard hinge of every rudder-blade where lined-up, but the middle-one of each blade seemed to be out-line for 2-3 mm: It looked if the hinge-side of the moving rudder part was welded in a large radius.
I was able to get the two pats together, though.

But moving the movable part of the elevator now moves the whole elevator up-and-down a bit: there seems to be tension on the parts, and by moving the elevator up and down the tips of the fixed part move some 4 mms - at each side.

Is this what you call warp? What can I do? Is there something I CAN do?

Thanks for reading & answering,

HansLab

[Dave S]

Hans,

I think most of us work a bit at fit and finish to get the elevator/stab hinge working smoothly.

One thing you could do as a first step is disassemble the two and run a string/line through all 6 bearings & brackets on the Elev & Stab and also run a string along the tube on each part to best detremine where the problem is.

Kinda depends on a person's comfort quotient; but, I would have no qualms about attempting to straighten a tube if it is found to be warped a bit. 4130 steel is pretty darn forgiving in this regard.

A second thing a person could do is work a little more tolerance into the bushings. If they are misaligned at all, a snug fit on the bushings may not allow free movement. 0.001" or 0.002" tolerance on the bushings may make for easier movement. A person could get fancy with this and finish the bushing to a very slight barrel shape which could help reduce pressure due to misalignment

A third thing to consider is the finish on the surface of the steel bushings that clamp up between the bolt tabs. I found that spinning the bearings against progressively finer wet/dry sandpaper ending with 600 grit did a lot to reduce friction. A coarse finish equates to increased friction.

Getting the bearings to move effortlessly is as much art as science. Good luck and let us know how it works out.

Sincerely,

Dave S

[HansLab]

Dave, thanks for your suggestions.
The 'warp' is too much for working out the tolerance, unfortunately.
And bending the tubes would be a solution - but the bunch has been covered, already.

So, I think that might be where the problem is: I guess I pulled the cloth too tight round the rudder: shrinked it some more, and presto.

Anyone had that, before?

If I can't think of anything else, I intend to make an incision along the front tubes (where the bushings are). That should take the tension off of it. After that I could repair it with 2" wide PolyFibre. Tough operation, so I'm hoping for a miracle..

[HighWing]

Do you have a friend with a lathe? I think that by making new bushings of delrin and drilling the holes offset using a four jaw chuck might create enough of an offset to line everything up satisfactorily.

I would be happy to help if you can't find someone locally. Drop an email and we can talk.