Cavity behind the RCC leading edge

Chuck Stewart wrote:

Hmm?... but what about heat conduction via carbon strands in
contact with both RCC and wing structure? It might not be much, but
it'd be there.

It needn't be zero, it need only be less than the heat transmitted
by radiation.

There are already inconel radiation baffles behind the RCC to reduce
the radiative heat transfer.

I'll note that carbon aerogel would have the problem of eroding
rapidly if exposed to high temperature air. A combination carbon/SiC
aerogel might get around that problem.

Paul

"Chuck Stewart" writes:
Er... send in the Rover after it's made the coffee?

If this was to be seriously done then the aerogel would be in
pieces that would be lifted out chunk by chunk... each chunk
individually cut to a precise specification different from every
other chunk, and requiring serious overhead in record-keeping,
handling and storage while maintanence was underway.

Not really... Aerogel works quite well as a filler material, either as
loose chunks, or you can actually grind it down to a powder with
virtually no loss in thermal performance (and, interestingly enough,
it's *very* difficult to grind it down to the point where it's density
increases---the granule size is still way larger than the void size,
so the density is unaffected)

I actually work with this stuff, as insulative material for cryogenic
superconductors---while you can actually buy slabs of it and machine
it (on an a standard milling machine, even), it's usually much easier
to break it up and use it as fill if you are just insulating with it,
since it really is quite fragile stuff---And I have a few chunks of it
in the office and I've lost more than a few pieces by people picking
them up and squeezing them, which fractures the chunk into a gazillion
little bits that disappear instantly into the carpet.

As far as using it as RCC filler? I'm not sure it would do much
good---While it's a great insulator, it's really not much of an
improvement over a good vacuum gap with some radiaiton shielding.

--
Richard W Kaszeta

http://www.kaszeta.org/rich

In article ,
Richard Kaszeta wrote:

"Chuck Stewart" writes:
Er... send in the Rover after it's made the coffee?

If this was to be seriously done then the aerogel would be in
pieces that would be lifted out chunk by chunk... each chunk
individually cut to a precise specification different from every
other chunk, and requiring serious overhead in record-keeping,
handling and storage while maintanence was underway.

Not really... Aerogel works quite well as a filler material, either as
loose chunks, or you can actually grind it down to a powder with
virtually no loss in thermal performance (and, interestingly enough,
it's *very* difficult to grind it down to the point where it's density
increases---the granule size is still way larger than the void size,
so the density is unaffected)

I actually work with this stuff, as insulative material for cryogenic
superconductors---while you can actually buy slabs of it and machine
it (on an a standard milling machine, even), it's usually much easier
to break it up and use it as fill if you are just insulating with it,
since it really is quite fragile stuff---And I have a few chunks of it
in the office and I've lost more than a few pieces by people picking
them up and squeezing them, which fractures the chunk into a gazillion
little bits that disappear instantly into the carpet.

As far as using it as RCC filler? I'm not sure it would do much
good---While it's a great insulator, it's really not much of an
improvement over a good vacuum gap with some radiaiton shielding.

And remember the whole point of the original poster - he wanted to fill
the cavity with foam NOT for thermal reasons at all, but to distribute
impact loads on the RCC and structurally reinforce it.

--
Herb Schaltegger, B.S., J.D.
Reformed Aerospace Engineer
"Heisenberg might have been here."
~ Anonymous

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.

In article ,
(Locz) writes:
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:
snip
alternate proposal...

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.

Not sure about this one, but I'll float it, anyway.

How about beginning by making the first structural member behind the
leading edge out of titanium? Perhaps this just plain can't be a
retrofit, but could it have worked on a new orbiter?

A second swizzle is some sort of cooler (not necessarily cool) air
path from within the fuselage into the leading edge space - possibly
fans, possibly even passive flow. Note I didn't say cool, maybe it's
even a few hundred degrees. But the idea is to change out the gas
content inside the leading edge space. A flaw is that I'm not sure
where to get that cooler air, but possibly an air path through the
cargo bay and blown out through the leading edges. The cargo bay
has to 'leak' somehow, and is presumably chilled from orbit. (What
is its working orbital temperature?)

Might the combination of a titanium structural member behind the
RCC combined with some sort of airflow have saved Columbia, or at
least kept intact until it was low enough for bailout?

Dale Pontius

"meep" wrote in message u...
http://www.cockeyed.com/inside/foam/foam.html

"Zoltan Szakaly" wrote in message
om...
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.

Zoltan


---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.512 / Virus Database: 309 - Release Date: 19/08/2003

First of all I apologize for calling NASA irresponsible and stupid. I
unfortunately have had first hand experience and found common sense
lacking. I guess I could have better packaged my message or sugar
coated it or made it more politically correct.

The filling in a cavity like the one under discussion is important to
prevent the thin composite shell from breaking the exact way that it
broke in the test.

For filler material I can think of two candidates, one might be glass
sphere filled epoxy (microballon filler, bondo makes it) the other
candidate might be divinycell foam. During takeoff the foam would be
cold and it would support the RCC skin. During reentry the foam would
heat up and it would not provide support but it would be still better
than nothing. The epoxy and glass would probably take the heat
especially because it is already protected by the RCC skin. Both could
be applied through any small hole as a liquid and would solidify once
in the cavity.

Whatever else is being done to make the shuttle safer this cavity must
be filled before another flight is made. This is a no brainer.

An alternative protection method would be to coat the leading edges
with the same or similar foam on the outside. This could be sprayed on
before flight and it would cushion any impact during ascent and later
burn off during reentry.

Zoltan

Paul F. Dietz wrote:

Chuck Stewart wrote:

And any "foam" behind [the RCC] would conduct the heat even faster
than the void that is currently behind
the leading edges.


It's not clear this is the case. Heat is being transmitted from
the RCC to the wing structure by radiation. Interposing an opaque
material (for example, carbon aerogel) could actually reduce this.

Paul

What's carbon aerogel? I Thought the only type was silica and
some other silicon / metal based materials.

On Fri, 29 Aug 2003 07:00:49 +0000, Paul F. Dietz wrote:

Chuck Stewart wrote:

Hmm?... but what about heat conduction via carbon strands in
contact with both RCC and wing structure? It might not be much, but
it'd be there.

It needn't be zero, it need only be less than the heat transmitted
by radiation.

There are already inconel radiation baffles behind the RCC to reduce
the radiative heat transfer.

I'll note that carbon aerogel would have the problem of eroding
rapidly if exposed to high temperature air. A combination carbon/SiC
aerogel might get around that problem.

Your replies have been quite interesting, Paul, and I don't know
how it would work out. My original aerogel response was not meant
seriously, but the subject makes for interesting reading and
research

Now I must go and beat up on Zoltan again...

Paul

--
Chuck Stewart
"Anime-style catgirls: Threat? Menace? Or just studying algebra?"

Paul F. Dietz wrote:
jimmydevice wrote:

What's carbon aerogel? I Thought the only type was silica and
some other silicon / metal based materials.


Use google on "carbon aerogel".

Paul

Heh, I did 2 seconds after I posted that note, and killed it after I saw
all the references. Do'H, guess you got it before the kill did.
Jim.

jimmydevice wrote:

Heh, I did 2 seconds after I posted that note, and killed it after I saw
all the references. Do'H, guess you got it before the kill did.

And not all news servers respect cancel messages.

BTW, I note some of the google hits are to papers or abstracts on
application of carbon aerogels to reentry thermal protection systems.

Paul