Foam Airfoiled Wings and Their Balsa "Partners"

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BigRiJoe

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https://www.flyingfoam.com/

I came across this site looking for pre-airfoiled balsa.......anyone have any ideas how to apply this technology to boost gliders, and does any manufacturer sell pre-airfoiled balsa wings? I never seem to be able to sand a decent airfoil when I use balsa.
 
I think SIG may offer airfoil balsa sheet. If so it will be in limited sizes. As for the foam, you can sheet it with thin balsa using any number of adhesives or glass them with light cloth and epoxy. I noticed they offer different densities of foam. Get one stiff enough and you won't need any laminate at all. Worth considering. Thanks for the heads up.
 
I made some RC glider wings from a foam core with fiberglass skins some years back. The same techniques can be downsized for rocket boosted gliders, though I don't know how much weight saving there might be in that size range.

The basic technique is to cut a foam core from blue or pink foam as you would find in the insulation section of a building supply store. The white foam in the link is lighter and may crush under vacuum.

You make up a set of "transfer sheets" from mylar sheets. Basically, these are four panels (top/bottom left/right) hinged with peel ply or tape along the dihedral joints so that you have one hinged panel for the lower surfaces and one for the upper. These are waxed and buffed out. You can spray Krylon onto the transfer sheets to give color to the finished wing if you like.

You need a pair of hinged boards that you can set to the dihedral angle. Onto these, you place the bottom "shucks" (the bottom half of the foam blocks from which the cores were cut). If you got CNC machined cores like the web site showed, there will be no shucks and you will have to improvise some sort of cradle to hold the wing panels at the proper dihedral angle and in and untwisted condition.

Glue the cores together at the dihedral joint and allow to dry.

Lay one or more layers of glass cloth of an appropriate weight onto the upper and lower sheets and roll laminating resin into the cloth with a foam paint roller. You want this to be completely wetted out, but no excess epoxy. Apply any desired extra layers of cloth to the dihedral joint and wet out. The cores are now laid onto the bottom transfer sheet and the top is laid on top of that (glue sides in) an the dihedral joints are aligned. It can be helpful to tape all this together so it doesn't slip.

The resulting sandwich is slipped into a mylar vacuum bag and laid in the cradle. You may want to lay some breather on top of the top transfer sheet to distribute the vacuum. Seal the ends of the bag and connect to a vacuum source. As the air is removed from the bag, pull out any wrinkles. After curing, the transfer sheets should pop off leaving the wing blank to be trimmed. This technique gives a pretty ratty leading edge which must be hand shaped and smoothed.

This is a lot of work and takes a lot of practice. The first glider wing I produced was heavy as a rock and survived an impact with football goal posts without a scratch. The fuselage sheared off and did a javelin dive and did not fare nearly so well. If you are not careful, you will overbuild. In larger sizes, there is a definite weight reduction by using this technique providing you don't get carried away and use too many layers of glass cloth. I'm not sure that the benefits will carry through to smaller sizes.
 
Back in the 60s and 70s there were some rocketry vendors who sold foam wing panels that were already airfoiled. I think I have one somewhere, still in the original packaging, buried in one of my boxes.

About the only time I ever found a BG or RG wing to give any significant benefit when airfoiled was when I built the old GroundHog designs (swing-wings). Otherwise, it was always a PITA to trim a rocket for boost with an airfoiled wing trying to turn it over, no matter how well it glided.
 
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