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.

 

[gbrasch]

part numbers

Don't mean to sound trivial, but have you double checked to make sure the top skin is top, and the bottom is bottom? I seem to remember confusing part numbers when I built mine. Hope this helps....

 

[mike109g6]

Ailerons

Call Van's support before doing anything else. I had an aileron skin that simply put was mis-punched. Talked to Bruce and he sent me new skins and stiffeners-no charge, arrived in three days. You can't beat Van's support.
Mike H 9A/8A

 

[airguy]

I fabbed up two more spar doublers and used the nose ribs from the left aileron to add two more nose ribs between the spar and the counterbalance tube at the 1/3 and 2/3 position (16 and 32 inches on a 48-inch aileron). When clecoed all together, this removes maybe 80% of the aft bow, to the point where I think the AEX wedge at the trailing edge will likely be able to keep it straight.

I will consult Vans tomorrow before riveting anything - it doesn't seem likely that this is a mispunch or a factory screwup of some type - but then again they did send me a set of misbent wing spars in the same kit, so all bets are off as far as Quality Control at this point.

 

[maspen]

Trailing wave

I just finished my trailing edge this morning. My wave on the trailing edge was huge just before riveting the wedge. More so than what I can see in your pics. I don't remember checking for bow in the nose skin/spar position along the T.E. of the nose skin. But as hard as it was to cleco the nose skin to the main skins and spar I can't imagine I wouldn't have had some kind of bow until everything was riveted. There just isn't any strength in the spar to prevent bow with the load in that direction. I would think riveting the nose skin, main skins and spar would take out most bow as the main skins are going to stay flat at the leading edge.
I pressed on with an uneasy feeling looking at the wave which had gaps from nothing to 2 inches in spots. After riveting the trailing edge it was straight as an arrow. I can't say my wave was caused from the same thing but it was big and everything worked out ok. Good Luck

Mark

 

[airguy]

Mark - thanks for the info, and

Welcome to VAF!

 

[airguy]

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 deviation from a straight edge is less than 1/8".

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.