Steve Jacobs wrote: > I am looking to do Mark L style sandwich wing skins - glass on both > sides of the skin core. The logistics of shaping the material aside - > can Styrofoam be used to the same good effect? The theory says that the > strength of a composite sandwich increases almost exponentially with > thickness.
Without digging up a bunch of charts for the various materials you mentioned, I'll just give you my uneducated opinion. You could use the (normally blue) kind of foam that doesn't look like little beads (and I think that is the Styrofoam you mention, made by Dow) just fine in your wing, if you aren't going to get fuel anywhere near it. I'm pretty sure that the skin would stick to it even better than urethane foam (well it'll stick to both, but the urethane fails earlier in tension), but it is maybe twice as time consuming to sand for that same reason. Sanding the wing foam to shape is not something that takes a lot of time anyway though, in the big scheme of things. And the neat thing about Styrofoam is that you can hotwire the inside (and the outside, if you're careful) pretty quickly. So Styrofoam will get you there, and your skin would be less likely to separate from the foam on the top surface after years of flying. I think Mike Mims used Styrofoam on his wings, since he was a former canard builder (see http://www.fortunecity.com/marina/anchor/270/wing.html , and make sure you see all three pages). To me, Lastofoam (Clark foam, whatever) is an improvement over urethane, especially for wing skins, because it's stronger and will bend further without breaking (not as brittle), and is pretty easy to sand too. Again, none of this is based on any kind of numbers that I got from anywhere, just experience having used them all to make composite shapes from... Those double skin wings probably cost me another 5 pounds per wing, but man are they stout! I sit on the wings to work on the back side of the panel (and rewire the radio), and I don't worry for a second about damaging anything. If I ever have to put it down in a cotton field, I'm going to be choppin' cotton! Mark Langford, Huntsville, AL N56ML at hiwaay.net see KR2S project N56ML at http://home.hiwaay.net/~langford -----
