Port-side flap pulley in the wing root

[Battson]

Hi everyone, I have a question about the last pulley (in the wing-root) on the port-side flap cable system.

The pulley is mounted on an angle, and depending on the position of the flap drive arm, there is sometimes a noticable change in direction (of the cable-run) at that pulley. I positioned my flap drive so that the cable was straight at about the mid-point, but there's almost no other option given the tight spaces involved. Now that all the holes are drilled etc and I've been using the flaps for a while, a rubbing noise started coming from the pulley with full flap. Upon investigation, when the last notch of flap is added, the cable is being forced to change direction significantly enough that is makes contact with the side of the pulley's channel. This, combined with the very high cable tension at full flap, is causing the cable to gradually eat away at the side of the pulley (making the "rubbing" noise). Obviously this isn't ideal.

Because the plane is fully covered, wings fitted, etc - I can't repositon easily reposition the whole arrangement. I had some questions:

Has anyone else had this problem?

Would it be worth putting a stong bolt or steel rod through the pulley's mounting hole and trying to bend the mounting bracket, to re-align the pulley?

[Mark Goldberg]

The way you describe how you set it up is correct. With maybe two notches to three notches of flaps the cable should be centered in the pulley. With the flaps all the way the cable should ride on one side of the pulley, and at full flaps it should move to the other side. I have never heard of it making a noise though. And any wear on the pulley should not be noticeable for about a jillion years with the small amount of time that the flaps are used. Are you really seeing wear on the pulley already? That would be unusual. Mark

[Battson]

Hi Mark, glad to hear it's intentional. Mine works exactly as you describe. But yes, we are seeing noticeable wear on the pulley after maybe 50 operations of the flaps. Small flakes of the phenolic material can be found on the cable, and the pulley has lost a little shape on the inboard side (very minor). It will probably need to be changed after a few hundred hours of frequent landings. The noise it makes isn't loud, just something I noticed on the ground. For anyone who's inspecting it each annual, I am sure it's no risk.

[Enewton57]

Could you move the pulley outboard a bit using a couple of washers between the mount and the pulley?

[Battson]

Yes that is certainly possible and a good suggestion; the difficulty is it's rubbing on the inboard side at full flaps - but that point wasn't implicity clear in the posts above.

[Enewton57]

Oh ok, well then could you file or remove some material from the pulley mount? I would think the cable is under greater strain at full flaps than at 10 degrees so I would prefer it to rub on the side of the pulley near 10 degrees instead of rubbing at near full flaps.

[Battson]

I don't have a great deal of access behind the fabric, but your suggestion has given me an idea. The right bit on the Dremel tool might be able to get in there.

[Untainted123]

I am having a similar problem, and it looks like the weldment is at the wrong angle. I am trying to formulate ideas for how to get everything more in line. This is after shimming the pulley out away from the fuse with 4 washers. This is a video of the problem.
IMG_0348.jpg

[AKKen07]

That doesn’t look bad to me. It is an awkward angle by design. Here is mine - in a flying bh. I tried to replicate your video for clarity.

[Untainted123]

Yours looks just enough more inline to not sound like it’s grinding. The other side on mine is at a better angle and seems more like yours, this side is like the little piece of tubing that holds the bolt tubing got twisted a little more and welded in place, or maybe twisted upon cooling. I think if I can make mine “stand up” a little bit, the tracking angle will be better. I might try bending a bolt and putting it in the other way. I am afraid to try and twist where the bolt goes thru, might break the entire weld in that area?

[AKKen07]

Shucks! If you don’t want to reweld it maybe you can do what I’ve had to do to the landing gear. That is, use a torch to soften up the weld area (keep it under 1000 degrees) and use a long arm through the bolt tube to twist a bit. Not sure if that’s a good idea in your case but if it doesn’t look like it matches spec (can you verify against drawings?) maybe…

[Untainted123]

Heating and bending would have probably been the best option, but unless I want to burn down the airplane, we are far past that ? I think my best option is to put a bolt thru, bend it, and then attach pulley. The bolt should never need to be replaced, and I can replace the pulley on condition, and cut the bolt off and pull it back out worst case.

[Nev]

Is there any room to move the flap torsion tube towards the wingtip, thereby allowing the flap arm that the cable attaches to to sit closer to the apex of the spar attach join ?

[Untainted123]

If understand correctly, you mean shorten or move the flap torsion bar outboard? Perhaps that might have been a possibility before closing the wings up and painting and mounting them… at this point (a few weeks from flying) I don’t have a lot of options for rework, just because everything is closed up already.

[Nev]

If understand correctly, you mean shorten or move the flap torsion bar outboard? Perhaps that might have been a possibility before closing the wings up and painting and mounting them… at this point (a few weeks from flying) I don’t have a lot of options for rework, just because everything is closed up already.

Yes thats correct.

Another method, is instead of using a shackle to attach the flap cable to the arm (which centers the cable on the arm), consider putting a bolt through the arm and attaching the cable to the bolt. This allows the flap cable to sit off to one side of the flap arm - ie the side closest to the apex of the spar attach point, for maximum clearance. It allows a straighter cable run and results in less pulley wear.

See a picture here.

[jaredyates]

The inboard-outboard location of the flap torque tube and the clocking of the angle of the inboard actuating arm are really critical. Most folks can't set this final dimension until the wing is on the plane, and you would use cues like the angle of the braided cable at the pulley to set the location. If you were to move the torque tube outboard, would it fix the problem? If so, the easiest way to fix it may be to pull the wings, replace the torque tube with a new piece, and drill it correctly. Or, see if you can get acceptable edge distance by moving the existing torque tube outboard and drilling fresh holes on the outboard end. It is always possible that the inboard-outboard alignment may not be the problem, but it's really a tricky spot.

[Untainted123]

I guess maybe I am assuming too much about the fact it is a quick build wings as far as the torque tube being correct? I was mostly going off the 2 sides being at quite a bit different angles for the pulleys. My right side seems about like AKKen’s video (normal), whereas this one has a few extra degrees clockwise twist (from the viewpoint both of our videos are shot). It seems to me just moving the torque tube outboard would help only incidentally, the pulley still wouldn’t really be at a desirable angle, it would just be rubbing the cable along the front and the back more evenly, instead of “rolling around” it like it should.

In addition, at max flaps, if the torque tube (actually the arm) was outboard more, it would interfere with the shackle/thimble/nicopress where it gets close to, and kind sits in the angle where the rear spar attach is. When I am back at the hangar I can take more pictures and kind of compare and mull over more about what I can do. I can see if Nev’s idea can buy me enough.

Jared, I really don’t see how there’s much room for error there, it would seem you make the tubes a certain length, and put the outboard bits on at the end, making the inboard part have a certain set distance from the fuselage. Both of mine seem the same. The plans seem ambiguous (DWG 14) about the pulley angle though, except “make it so it works”.

Thanks for everyone’s suggestions and help!