Aluminum leading edge installation
I am working on a Kelly D project (Rotec R3600 engine) -- my question is on the installation of the aluminum leading edge of the wings which are wood with 1/4 inch plywood ribs. On the Biplane Forum some months ago I saw comments about the aluminum warping when the plane was parked in the sun -- the solution to that was to install the edge in approximate 3 foot pieces so it could move some. I am after to any suggestions/installation procedures that have worked for you guys. If it's installed in pieces, how is the lap configured, etc. Any comments would be appreciated.
I own an Acrobatic Category Pitts S-2A biplane. Construction is similar to your airplane with aluminum leading edges over wood ribs and spars. On my airplane, I will note that there are a very few nails through the aluminum to keep the nose ribs from moving and coming loose. My airplane sits in the sun at contests and I have never seen a problem with the leading edges due to the sun heating up the aluminum. I can hear some shifting, but no change in the leading edge is visible.
I would build to the plans and not worry about it.
Best of luck,
Last edited by WLIU; 06-05-2012 at 02:19 PM.
Stan, I think you're worried about nothing. Putting the leading edge on in sections will cause problems with your fabric when things shift around underneath. Is the leading edge held in place with nails or a slot in the rib? How do you plan on covering the wings? Blanket or envelope?
I responded to this on <BiplaneForum> but I'll cover it again. There is also a how to on installing the leading edge there under "Handy Resources". The leading edge can be installed in one piece with good results. You need to install the aluminum in the sun with a coat of rattle can black on it. Use the cheap stuff so it can be easily removed with a little acetone. The idea is to put it on in the expanded state so it won't buckle later. I first heard of this years ago from an old A&P/IA then again recently from Kevin Kimball. Use 5/8" 20ga. nails and only in the spars. Nail spacing is about 1". Use an awl to pierce the aluminum for the nails. This leaves a nice little indentation for the head of the nail. Make sure the aluminum extends back past the spar about 1/4" so it can be bent down a little to keep the sharp edge off the fabric.
I didn't do the black paint in the sun thing on mine but I did install them when it was 105 in the shade. That has to be better than installing during the winter in a dimly lit 40 degree shop.
Last edited by Neil; 06-05-2012 at 09:46 PM.
How thin are the AL leading edges that you are using?
My Pitts was rebuilt two winters ago in a shop that was running in the high 60 degree range. My leading edges are not having any problems in the sun. Does the aerobatic aircraft use thicker AL on the leading edges due to the higher VNE (202mph)?
Pitts also run into the problem that snap rolls cause the leading edge ribs to wiggle, and after many hours we see some airplanes have a glue joint fail and a rib start floating around inside. As a result, some rebuilders put one nail into the front of the rib using the method described in the last post. Appears to cure the problem. Oh, another hint. Tap your nail in halfway, squirt some CA glue on it, then drive it home. Won't loosen up.
Best of luck,
Gentlemen, thanks for the response. With what you guys have said, I'm going to install the edge in one sheet -- it is 0.020 material per the plans -- but will do it in high temperature conditions as you suggested. I did find the installation guideline in "Handy Resources" this morning -- have been following most of the steps shown there, 4 foot sanding block, etc. This plane will not be used for aerobatics so high stresses should not be an issue. The leading edge will be nailed to the spar and covering will be a blanket approach -- plan on using the Stewart System. I am considering 3 or 4 spots of epoxy on the ribs as I saw this morning -- that would be easy to do and should give it extra support.
Again, thanks for the comments -- I'll welcome anymore that you have.
I'll think you'll be happy with that Stan.