Doug... wrote in message ...
In article ,
says...
When I looked at the video of how they simulated the foam block
colliding with the reinforced carbon carbon leading edge of the
shuttle, I noticed that behind the leading edge (which is a thin sheet
of RCC) there was nothing.

Isn't this highly irresponsible, in other words stupid? Any
homebuilder of kit airplanes knows that filling the cavity with foam
would greatly enhance the strength of the leading edge without
increasing the weight of the structure. The carbon fibers comprising
the composite sheet are strong in tension/compression but can be bent.
This lack of support from the inside was the direct cause of the hole
that the foam block punched in it.

I know several people have responded to you in a rather sneering fashion,
Zoltan, but they're correct. Not only is there not a material that
wouldn't be unreasonably heavy, the thermal issue is what kills the
concept.

The RCC panels don't just sit there at room temperature as the leading
edge of the wing rises beyond 2000 degrees Fahrenheit. The panels get
hot, first along the outside surface and slowly throughout. They don't
get as hot on the inside as the outside, but they still get very, very
hot on the inside surface.

During most of the descent, the panels aren't in contact with much of
anything that could conduct that heat into the structural members of the
wing. They only contact the bolts and fittings that hold them in place,
and those are made of inconel, which takes a long time to heat up. By
the time the inside of the wing starts getting hot, you're on the ground
and the RCC panels aren't being heated anymore.

If you fill up the space behind the RCC panels with foam or anything else
that can conduct heat, that material will get really hot, really fast.
And it will conduct the heat into the interior of the wing. This is
exactly what you're trying to prevent.

It might not make sense to you in a common-sense world, but the Shuttle
enounters temperatures and stresses, and operates in environments, with
which you don't have any common-sense experience.

What about a carbon based foam that weighs 3lbs/ft3 and has a 97% void
volume? This reticulated vitreous carbon(rvc)looks like it might
work:

HOW CAN RVC BE USED?
· Porous Electrodes--for electrochemical processes that require very
high current distribution areas, low electrical or fluid flow
resistance, and minimal cell volume loss to electrodes.

· High Temperature Insulation--for inert gas and vacuum furnaces
where its ease of fabrication, self-supporting nature, low density,
low outgassing, low heat capacity and excellent K value combine to
improve efficiency and reduce costs over conventional insulating
materials.

http://www.ergaerospace.com/rvc.htm

This company also makes an aluminum foam and a ceramic foam.