Flap alignment issue

[Mouser]

I've got one wing done minus wingtip, and its flap and aileron aligned perfectly on the first try. Now I'm working on my second wing, and it's done except for bottom skin, aileron actuation, and wingtip.

I was doing some get-ahead work on aileron actuation when I realized that the flap was not sitting "level" relative to the wing body, which is to say that the rivet line on the flap that is half-covered by the top wing skin at the inboard end is fully hidden by the wing skin on the outboard end of the flap. On the good wing that rivet line is half-covered for the entire length of the flap. I'd estimate that the outboard end of the "bad" flap is about 1/4" forward of where it is on the other flap. The result of this alignment issue is that when I try to align the aileron to the flap, it is not possible unless I rotate the flaps until the outboard nose of the flap is about 1/4" away from the rear spar. In this position, the aileron and flap align perfectly, but then the flap is decidedly not sitting on the rear spar as the instructions suggest it should be (and as it is on the good wing).

I've done a bunch of measurements on the wing body and everything seems to be square and built to plans as far as I can see, the flap looks good too. Any ideas where my problem is coming from? Anyone seen this before?

 

[jaybob]

I had a very similar sounding issue. Called Vans and they said "fly first and see what happens". Well, one wing (left) was very heavy and could not be trimmed out. I checked the rigging (very close), aileron roll springs (fine), flaps hinges (fine) and angles, using a digital inclinometer, from one flap to the other (definitely not fine).

Some other things I did... Check the hinge lines by running a string tightly through the holes to see if one hole is different than the others. Does the flap attach to all holes without binding? Do you hear rubbing while moving the flap?

The flap on the heavy wing side was definitely twisted and different than the other. I rebuilt the offending flap, slightly adjusted the travel, and can now trim out the roll with single pilot flight.

If you search around you'll find that heavy wing is a very common issue. Some folks have iterated on their rigging and/or oblong-ed aileron holes to create different behaviors. Some split the wingtips to align better. Some simply add a shim on the opposite side aileron. You really can't do much experimenting until you fly.

I'm still undecided about which things are worth trying and which are simply asking for more trouble. In addition, once you're flying, it's really hard to take everything apart unless you absolutely have to!

Good luck!

Cheers,
Jay
N433RV... It's not painted yet, but it flies!

 

[rvbuilder2002]

I've got one wing done minus wingtip, and its flap and aileron aligned perfectly on the first try. Now I'm working on my second wing, and it's done except for bottom skin, aileron actuation, and wingtip.

I was doing some get-ahead work on aileron actuation when I realized that the flap was not sitting "level" relative to the wing body, which is to say that the rivet line on the flap that is half-covered by the top wing skin at the inboard end is fully hidden by the wing skin on the outboard end of the flap. On the good wing that rivet line is half-covered for the entire length of the flap. I'd estimate that the outboard end of the "bad" flap is about 1/4" forward of where it is on the other flap. The result of this alignment issue is that when I try to align the aileron to the flap, it is not possible unless I rotate the flaps until the outboard nose of the flap is about 1/4" away from the rear spar. In this position, the aileron and flap align perfectly, but then the flap is decidedly not sitting on the rear spar as the instructions suggest it should be (and as it is on the good wing).

I've done a bunch of measurements on the wing body and everything seems to be square and built to plans as far as I can see, the flap looks good too. Any ideas where my problem is coming from? Anyone seen this before?

The most likely problem is that the flap has a twist in it. You can confirm by checking with a digital level at the inboard and outboard ends. If it's straight, the readings should be the same.

 

[Jesse]

You definitely have a twist in your flap. When you rivet the bottom skins on your flaps, they must be held perfectly straight on a perfectly flat surface/table. Any twist in that surface will give you a twist in your flap. I would recommend that you fly it first and see how much of a difference it makes. The only really fix is to build a new flap. Please don't ask me how I know, but you can ask the set of twisted flaps on my shelf.

 

[DaAV8R]

Checking for twist

A simple way to check for twist is to lay a straight edge on each end of the surface, perpendicular to the hinge line. Sight across the top of the straight edges. A couple of short levels or something similar works well. You will be able to see a fraction of a degree which is well inside the tolerance of most levels, including those that display a tenth of a degree. This technique is frequently used in the RC modeling world and also works well on the big stuff.

 

[Jesse]

The twist can be checked by what you have already done. The rivets on the soar should all line up equally with the trailing edge of the top wing skin. If they are not exact from inboard to outboard, there is twist.