Where to buy balsa for molding?

[soholingo]

Looking to do some molding and I would like to get sheets of balsa that are 10x36 and relatively thin.

Let me know where you are buying your balsa.

[davidfee]

I don't think you'll find 10"x36" sheet balsa at acceptable prices. Normally you will have to join two or more "normal" width sheets. Superior Balsa and Lone Star Balsa are good sources. You want to ask for 4-6 pound balsa, sometimes called "contest" balsa.

This is one reason many modelers have gone to the various foam cores... it is easy to get consistency with composites, while balsa is a natural product and varies drastically.

-David

[hayman]

Hey Soholingo,

If foam is an option then watch Phil's video again, if you still have it. Disc 2 "Slabbing Foam". Get your self some Hi-load 60 or Formular 400 and make yourself some wide sheet balsa substitute sheeting. You can make up any thickness you want up to 4' x 8'....

Bill

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[soholingo]

wait a second... are you guys saying to use foam for the sheeting of a molded wing? That isn't a half bad idea but won't the wing be heavy? I am in the process of getting my supplies together to make a fully molded sailplane/hotliner by next summer. I want a 62"-66" plane to weigh in at around 15-18 oz. empty. And it needs to be strong enough to do egg beaters...

[davidfee]

Most foams will be much lighter than balsa, and they absorb less epoxy (so you can use less of it), which also makes things lighter.

Regular blue DOW styrofoam (or the specific products Bill mentioned) can be sliced very easily into thin sheets using a hotwire. The foam is in the 2-3 pound/cubic foot range, whereas the lightest balsa is usually at least double that. Right off the top, you've cut your core weight in half.

However, also important is the compressive modulus of the foam. For this reason, more advanced foams are often used. Rohacel is an example, but there are several others. Most of these foams can not be cut with a hotwire (melting point is too high, they ignite and/or toxic fumes are emitted), so you purchase them in pre-sawn sheets. These foams are often more expensive than balsa, so I'd practice with blue foam first.

Block up the hotwire 1/16" (for example) above the table and just slowly slide the block of foam under it. Instant sheet foam. :)

-David

[SoarNeck]

I've thought about using foam in this way, but I think it would be difficult to get ANY sort of ding resistance out of it. Rhoacell is much denser than most blue/pink/green foams, and even that is much poorer than balsa at stopping dings.

[davidfee]

Rohacell comes in several densities, of course. However, the densities range from 2 lbs/cu.ft. to just under 7 lbs/cu.ft. Compressive strength ranges from 58-435psi.
http://www.nfgsales.com/rohacell_A.htm

End grain balsa does have better compressive strength, but it is rarely used in wing skins. I don't know about the compressive modulus across a sheet. Finding meaningful engineering data on contest balsa is difficult.

[MikeC]

A friend of mine use to make molded F3B sailplanes. Initially he used balsa, and when he switched to Spyder foam, he found that he had to use a stronger (heavier) spar system, or the wings would break on launch. Lone Star has very low prices on balsa, and their wood is consistently excellent. I would not use regular blue foam.