Preparation for Covering

[arun 0]

Thinking ahead a bit here, but what methods would you recommend to prepare a wooden airframe for covering? Is it worth applying a sanding sealer (brand recommendations please!)? Anything else I should do before attempting to cover?

 

Current state of the wing for my SLEC Fun Fly is:

 

[Trevor 25]

I have never used sanding sealer so I dont know whether it would work or not. Assuming you intend to use heat shrink covering, I usually make sure the wood is dust free (wipe with a damp cloth not too wet just enough to lift any dust), let it dry thoroughly then use Balsaloc or similar around the extreme edges to give the lower covering a good purchase. Cover the lower side first then overlap the upper covering over the lower. The covering only really needs to be fully stuck down round the edges. Cover top and bottom before final shrinking then shrink both evenly to avoid warping.

[arun 0]

Thanks Trevor, that sounds like great advice. I'll take that approach... great point about warping - looking back on my last attempt at covering I think this may have been the reason why the tail-plane of my Micro Fusion warped (it was an open structure which was true at the time of removing from the board!). Thanks again.

[Martin 0]

Another thing that can cause warps is if the joints are not totally flush before gluing. This shouldn't be the case with laser-cut parts, but can be when cutting all the pieces by hand. If the wood doesn't quite fit together cleanly (say, you've sanded the end of a cross-piece at slightly the wrong angle) then it may not have as much strength as it should.

 

As Trevor says, shrink things evenly, but also do just check things as you go. If things are warping as you shrink, then twist it flat (or even very slightly beyond), and shrink the covering until the wrinkles caused by your twist disappear. That should fix the warp. It's best to shrink the covering with an iron, not with a heat gun, which is too fierce.

 

I've just had to do this to set the wing of my new indoor model (Stevens Aero 1918 Hergt), which is covered on the top only and has almost no torsional stiffness (presumably it gets away with this due to having no ailerons). I had to not only fix a warp in the right wing, but also introduce my own in order to have the correct degree of washout. I did this by holding the correct twist in the wing with one hand and shrinking the new wrinkles out of the covering with the iron with the other. (On a larger model this would be more than a 2-handed job, unfortunately.)

[arun 0]

Thanks Martin, good points. Let's see a few build photos of your model!