Light ply or basswood?

When balsa isn't enough (but you're not going to fiberglass), what do you reach for? I'm curious about which material is favored in mid power sorts of applications. It seems like basswood is probably somewhat lighter than light plywood would be, and is easier to cut in my experience. But ply would be stronger. Which would you choose?

If I'm jumping up from balsa, I go with thin light ply every time.
Basswood as a solid piece will tend to crack with the grain like any solid wood.
It is quite strong, also quite heavier.

Just be aware that there are several different grades of plywood. There's the really cheap stuff, suitable for dollhouse furniture (nope), the middle stuff that's usually used for model airplanes (usually OK for rockets), and the nice and really nice stuff that's real aircraft ply(super nice stuff). Price follows grade. I find the 3 ply aircraft grade is stiffer than the model airplane 3 ply.

YMMV, Caveat Emptor

Dont forget about balsa plywood too, iirc thats what US Rockets uses with their kits.

I have some light ply and it's really unimpressive in strength and warped like most plywood but it can be used sometimes for bulkheads reinforced as necessary. I've seen so much warped plywood in stores that I no longer consider it for fins. The good kind is good but the price is out of the question.

I like basswood and and even think MDF (Walmart clipboards are a source) is better than cheap plywood. Basswood is barely heavier than balsa for thin shapes with finished surfaces since balsa's a sponge. MDF is actually stiffer than plywood and about the same weight, more brittle but easy to repair with epoxy as the broken edges usually fit together much better than plywood.

rharshberger said:

Dont forget about balsa plywood too, iirc thats what US Rockets uses with their kits.

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Yea, that's my choice. Lite, a little soft on the surface but strong and flexible (not brittle)

I'm a basswood fan. It weighs only a bit more than balsa, definitely a lot less than plywood, and sands a lot easier than plywood.

For all my kit builds, I've stopped using the balsa fins and started using basswood, using the kit fins as a template.

The other thing is, basswood won't seriously change the CG of most low- to mid-power kits, but plywood can get heavy, and i would definitely check the CG and CP of a rocket if you are using plywood. For lighter weigts, you can use thinner plywood, but then I would be concerned about warping.

I haven't had a chance to launch much, but both my Quest Big Dog with basswood fins and my Estes Leviathan that got kit-bashed into a 3" Goblin, that I built with basswood fins, flew well last weekend (the Big dog with an E30 and the Goblin with an F50). I used basswood with the Leviathn=>Goblin esp. because plywood fins were going to be very heavy, and I wanted to make sure the CG stayed ahead of the CP on that thing.