Hi Everyone,

I'm building a flying wing for FPV use, I run an epp one and although it's bomb-proof, my flying has got pretty solid now so I don't think that a slightly more fragile speed machine will be a problem (famous last words maybe!), I have cut the cores out of blue styrofoam and I plan to coat that with one layer of 160gsm glass cloth, does anyone have any tips on how to keep the cloth flat and to get a smooth finish as I really don't want to do too much sanding, getting a perfect finish isn't essential because i'll probably have to make a new one every few months after the inevitable!

Thanks Steve 

There is an art, or rather a knack to flying.  The knack lies in learning how to throw yourself at the ground and miss.  ~Douglas Adams, Hitchhikers Guide to the Galaxy

Hi Steve,

There are a few neat tricks you can use to cover a foam core neatly, without having to go down the coating/flatting route.  if you have a straight profile to the wing (ie single curvature) using a thin sheet of plastic (around 1mm) as a form works great, you first laminate the reinforcement flat onto the sheet and then take this and wrap it over the core, the trickiest bit of the process is holding the sheet in place; it can be done with clamps or weights, however vacuum is the easiest method as it keeps a really uniform pressure on the part. After the resin has cured simply remove the plastic and you should be left with a finish that after a trim and tidy is ready to use.

If your wings have a compound curve (curving in 2 directions) obviously the plastic sheet won't follow the profile so another method must be looked at. I would suggest laying up the cloth and resin over the foam as you normally would, after doing this if you stretch release film over the laminate and tape it securly in place this should leave you with a very flat finish. This method also allows you to see the result beneath, any small air pockets or irregularities can be squeegied out with a soft spreader.

Both of these methods would leave you with a perfectly usable part, however, there is likely to be a small amount of filling and finishing required if you were looking for a perfect finish.

Paul Statham
Easy Composites / Carbon Mods - Technical

Thanks Paul.

I've got my spar system made up now thanks to you advice I'm going to order up the stuff to cover the wings now, I'll keep you updated on how I get on

There is an art, or rather a knack to flying.  The knack lies in learning how to throw yourself at the ground and miss.  ~Douglas Adams, Hitchhikers Guide to the Galaxy

The experience I have with laminating over a closed cell foam core I learnt from surfboard building. Surfboards/skimboards are also quite complex in shape. I did it in multiple layers of 160 glass (for strength needed in the application) but always only one layer at a time. I laid the glass onto the board and then used a squeegee to apply the resin. Using the squeegee yields very nice results and the resin to cloth ratio was not bad at all. The final gloss coat however was applied with a brush. 4 layers on top and 3 on bottom yielded a very strong part.

I think if I were pursuing your application, I would go about it similarly, with the single layer as you said. My dad built his extra300 1/4 scale gasser plane like that and it came out very nicely.

Oh and btw there are plenty videos on youtube on the subject of surfboard lamination. I will have a look later for the good ones I saved a long time ago.


Hope I could help.

Cheers

I've done something similar with sport 40 wings.  I always did it the other way around.  I layed up the cloth with resin on release film then placed the foam core on top of that.  I rolled the film / glass layer around the leading edge and the vacuumed the whole lot.  I always got superb results like that.  I did find you need to do a slightly resin rich lay up to get a really good bond to the foam.