Aileron help needed...

[airguy]

So I'm working on my right aileron, and it's not adding up. I've confirmed all the parts are the correct part numbers, and tried the left versus the right hand aileron parts thinking I had one bad part somewhere, no joy.

The problem I'm having is that the nose skin appears to be ever so slightly too short, as well as being under-bent for the leading edge, with the result that it distorts the spar when clecoed or riveted (already riveted the right aileron). The distortion is such that the ends of the spar are pushed aft, with the center of spar pulled forward, which causes the main skin behind the spar to wrinkle and wave severely. It's distorted enough even at the spar location that the nose skin itself is wavy and won't lay flat on the spar.

My initial thought was the under-bent condition of the nose skin was causing too much spring tension (up and down respective to the aileron surface) which would have the effect of pulling the flange on the spar up or down, thus causing the spar web to try to bow in the flange direction to allow the flange to flex slightly outward - exactly as if the flange had been fluted, and "tightened up". I manually overbent the nose skin a little more to remove some of the spring, and reclecoed it, with no change in the situation. The spars (both of them) by themselves with nothing clecoed on them actually have a forward bend, and the spring of the nose skin pulling the flanges outward overcomes this, plus some.

Anyone else had this problem? Any suggestions?

Here are some photos of what I'm talking about, large size for easy viewing.

This first photo shows a straight edge along the spar, with a measured 1/8" gap in the center due to the aft flexing. This is of course multiplied considerably on the main skin, causing all sorts of waving and bunching on the trailing edge.


This next photo is the aileron spar, actually upside down, showing the gaps between the nose skin and the spar. The gap you see on the bottom of the spar is actually the top skin of the aileron, and there are a couple other spots just like that.


This next photo shows a straight edge laid inside the aft of the spar, with the edge along the top flange. There is a gap between the straight edge and the flange in the center of the spar that measures 1/32" - not enough to worry about for riveting here, but enough to cause the geometry of the skins and trailing edge to be completely out of whack due to the induced aftward bow of the spar.


This last photo shows the trainwreck that is the trailing edge as a result of the spar bow.


My thoughts for taking the bow out of the spar were to add several nose ribs between the counterbalance tube and the spar which would force the middle of the spar aft (away from the tube), and/or use 7 ribs instead of 14 stiffeners for the main skins, thus pulling the main skins in better alignment and putting more tension on the skin-spar rivet line to keep it straight. I also considered bending the spar flange inward a little more so that the nose skin spring actually returns it to the 90-degree position and thus maintains a straight spar - but that's a tricky target to hit, and easy to screw up.

[Spike]

Hey Greg,

Sorry it took me so long to read this post. I have my ailerons for my 9A finished and I think I see what you are talking about. If you spar is bent such as I think you are describing its really a game stopper (IMO).

If you lay the spar on that really flat surface they have you build (flanges down), does the spar not touch the surface all the way across its span? Your description sounds like there may be a bow in it such that you have a high spot in the center. If so, how much? It should be lying perfectly flat on that surface sans skins or counterbalance. Actually it needs to lie completely flat (+/- 1/32" or so) with the counterbalance on it as well. That is how you make sure there is no warp once you skin it.

The last photo makes me think you spar might not be acceptable in its current state. The nose skin is always a PITA, but you should be able to cleco the top and bottom skins to spars with zero bucking at the spars. Until you rivet the trailing edges together, the skins themselves will be very wavy, but they should have no problems sitting flat at the spar flanges.

If the spar is bowed I wonder if it got bent some how. You might be able to measure flange edge to flange edge across the length at different spots to see if the flanges have been pulled out or pushed in at any given location. Maybe you can straighten it.

Get us a picture or let us know what that gap measurement is when sitting the spar on a flat surfaces flanges down.

Spike

[airguy]

Spike - the spar by itself when laid on a flat surface actually has a slight bow in it, ends forward. When clecoed to the counterbalance tube, still the same. When clecoed to the nose skin, the springy nose skin pulls the flanges (aft facing) up and down respectively, which has the same effect as fluting the flanges and overcomes the forward bow of the spar ends, and reverses it to an aft bow - resulting in the 1/8" gap in the center.

I solved the problem today as copied below from a post on VAF, by limiting the ability of the spar to move forward in the center and transferring that load to the counterbalance tube via two additional nose ribs.

Update on the aileron issue - problem solved!

I decided to try the additional nose rib installation, since if it worked I would only be out a couple of bucks for 4 additional nose ribs to use on the other aileron, and if it didn't work I was going to have to wait for parts anyway, so there wasn't much to lose.

When the aileron spar was bowing aft at the ends due to the flanges being pulled outward by the nose skin, the distance between the spar and the nose counterbalance tube was decreased in the center of the aileron. By fixing that distance across the aileron with additional nose ribs, I did away with the ability of the spar to move forward under tension, and removed the bow, or at least the large majority of it. I riveted it all up this afternoon, and the aileron came out looking not quite perfect, but very very good - definitely airworthy. Maximum vertical deviation from a straight edge is less than 1/8" on the trailing edge.

Here is the nose rib and doubler that I installed, one already in place with the second ready to rivet on the front side of the spar.


Here's the finished right aileron.

[Spike]

Congrats!!