Locz wrote:

I think this is a good discussion.

Basically, the concept here is: Can *something* be placed into the
cavity to increase the safet margin of the leading edge.
goals:
1) very lightweight
2) durable
3) not burn up
4) not transfer heat from the leading edge and further into the wing
5) increases the flight safety margin of the wing leading edge

I agree with several people here that a conventional foam filling
would be inappropriate. Aerogel satifies #1-4 (its perhaps the best
thermal insulator known). But I doubt aerogel would do much to enhance
the safety margin. Why? Well if the leading edge were pierced, the
*very fragile* aerogel would likely also be pierced by the same very
same event. And even if it were not pierced and did not have its
aerodynamic shape ruined, its fragility in a 15,000 mph windstream
would cause rapid erosion and loss. Here is a very good refernce page
on aerogels so everyone could stop speculating:
http://p25ext.lanl.gov/people/hubert/aerogel/

I think a better solution to 1-5 would be to insert an inner
"secondary" RCC curved leading edge within the hollow area of the
primary RCC. My concept would be conceptually similar to a
double-hulled ship.

Why not just make the thing thick enough to withstand accidental
strikes? It would have higher heat capacity and weight, But it seems
like the trade offs are worth it.
Jim Davis.