Cavity behind the RCC leading edge

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.

Derek Lyons wrote:

"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.

The heat is going to go *somewhere*. So the question is, how does the
RCC stand up to a prolonged heat pulse, from the front *and* the back?


Why should it need to go anywhere? Where does the heat at the
surface of a tile go? If the RCC is stable and structurally
sound at the maximum temperature it's expected to experience,
why not insulate behind it? It can't get any hotter, can it?
I only ask because I truly don't know the answers to these
questions.

JazzMan

--
***************************************
Please reply to jsavage"at"airmail.net.
Curse those darned bulk e-mailers!
***************************************

In article ,
(Zoltan Szakaly) wrote:

snip

From reading the responses here it sounds like you guys are the same
ones that designed the leading edge without the foam filling.

Practically the foam would have no appretiable weight so that point is
mute.

"Moot".

The foam inside would not be exposed to the heat of the outside.

RCC is not a great insulator. It's used because it can *withstand* the
head, *not* because it doesn't conduct it.

As for flight qualifying the foam thats a ridiculous burocrat's
statement. All kinds of airplanes are made using composits and there
are fire resistant foams in common use.

How many of them fly to an altitude where the air pressure is
essentially 0?

My original point stands.

As mute (n.b. correct usage) testimony to your ignorance?


Zoltan

--
Alan Baker
Vancouver, British Columbia
"If you raise the ceiling 4 feet, move the fireplace from that wall
to that wall, you'll still only get the full stereophonic effect
if you sit in the bottom of that cupboard."

In article ,
ElleninLosAngeles wrote:

I thought this was odd, too. I'm surprised what with the woodpeckers
pecking holes in the foam that they didn't get birds building nests in
there or mice building habitrails. I wonder if they ever stuck a
flashlight up there to check.

IIRC, there's been a lizard taken for a ride on the ET before...

--
-Andrew Gray

"Andrew Gray" wrote in message

IIRC, there's been a lizard taken for a ride on the ET before...

That would have been an interesting one to see up close in the ETCam. It
might have added a bit of drama.

Might have been fun for the lizard, too ... until he couldn't keep his grip
and met ... the *plume*:

"Wheeeeeeeee Pfffft!"

:-\

Jon

In article , -pc-
dot.org says...
"Andrew Gray" wrote in message

IIRC, there's been a lizard taken for a ride on the ET before...

That would have been an interesting one to see up close in the ETCam. It
might have added a bit of drama.

Might have been fun for the lizard, too ... until he couldn't keep his grip
and met ... the *plume*:

"I wonder if it's friendly...?"

--

Do not meddle in the affairs of dragons, for | Doug Van Dorn
thou art crunchy and taste good with ketchup |

"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

I realize this thread is old by now but what the heck...

Just a little backgrounder on impact damage. There are two main failure
modes going on that take place in different time scales.

If the impactor is moving fast enough, it can cause a shock wave in the
material that travels laterally through the thickness, originating from the
point where the impact occurs. This is obviously a compression wave . What
"fast enough" means is that the speed of the impactor is fast compared to
the wave speed in the material. I don't know what the wave speed in RCC
might be but in metals it's on the order of 11,000 mph, so I doubt this was
part of the Columbia failure mode. At any rate, what typically happens is
the compression shock reflects off the back face of the material and turns
into a tension wave which rips the material apart.

The other mode is usually called global structural response. That is, what
happens to the structure as a whole when it gets loaded by the impact. In a
"slow" impact the response is quasi-static, whereby the structure responds
(for example, local plate bending) as it would if you simply pushed on it
with a force equal to the peak force seen in the impact. At higher speeds
(smaller time scales) you can see dynamic structural effects, like plate
bending waves, rippling outwards from the impact location. This is usually
the killer.

Focusing on the plate-bending mode, depending on the shape of the bending
waves the induced bending stresses can be very high. Obviously the long lazy
waves will induce small stresses but a "fast" impact might give you a sharp
wave shape with astronomical stresses that purée your material.

So, what would a foam backup do for you? If you have a really fast impact
that causes a compression wave, obviously nothing since the modulus of foam
is always orders of magnitude less than primary structural materials, and
you are still going to get the reflected tension wave.

What about the dynamic global response mode? Hypothetically it's possible
foam could help by absorbing some of the impact energy thereby reducing the
wave amplitudes. However, this never happens, again because the modulus of
foam is so small (measured in the thousands of psi vs. millions of psi for
"real" materials.) It just isn't stiff enough to attract much load. The best
you could hope for is that the foam will survive the impact well enough to
hold some of the broken bits of the primary material in place. I wouldn't
want to be responsible for a structure that was supposed to work like that.
Not to mention that cracks in the RCC would let plasma in which would
instantly vapourize the foam, at best. At worst the gas created by the
vapourizing foam would explode and blow the whole leading edge off. No
thanks.

Patrick

"Chuck Stewart" wrote in
news
On Mon, 01 Sep 2003 02:52:22 +0000, Derek Lyons wrote:

"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.

greetings...

It seems to me that if the leading edge had some physical backup, it might
withstand abuse a bit better.
I wonder if the ceramic tile material would work? Use the rcc outer, with
tile underneath?
Certainly it would be damaged by a major strike, but might still bring the
bird home...

That carbon aerogel sounds like great stuff, but I ddin't see structural
data on it. (ok, didn't look that hard)

It seems to me, that a big thing is to prevent any plasma leakage from
penetrating the main wing. Maybe the carbon aerogel would slow the flow and
diffuse it enough to keep things alive?
regards
Jay

On Sat, 01 Nov 2003 21:45:45 +0000, jay wrote:

"Chuck Stewart" wrote in
news

greetings...

howdy

It seems to me that if the leading edge had some physical backup, it might
withstand abuse a bit better.

Yes, but that's one of the hottest parts of the ship during entry so any
structural backup material must hve extreme thermal properties as well.

I wonder if the ceramic tile material would work? Use the rcc outer, with
tile underneath?

Certainly it would be damaged by a major strike, but might still bring
the bird home...

The silica tile material doesn't have much structural strength... that's why
NASA was originally looking for _tile_ damage from the foam strike, not RCC
damage. Tile material behind a leading edge hole would be broken by the same
force that broke the RCC and worn away by plasma flow at tempertures it just
can't take.

That carbon aerogel sounds like great stuff, but I ddin't see structural
data on it. (ok, didn't look that hard)

It has no structural data
You just have to look at it and it breaks...

It seems to me, that a big thing is to prevent any plasma leakage from
penetrating the main wing. Maybe the carbon aerogel would slow the flow
and diffuse it enough to keep things alive?

Unfortunately it lacks the strength.

regards

Jay

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

This issue has been raised several times during the past 6 months. There is
a fairly large class of space-qualified materials that could be used to
protect the aluminum wing spar behind the RCC parts. They're called ablators
and have been used since the dawn of the Space Age as rugged TPS (i.e. heat
shields). My current favorite is a NASA-Ames product called Silicone
Impregnated Reusable Ceramic Ablator (SIRCA), but there are a half dozen
other ablator materials that could be used. For example, Teflon is an
excellent ablator, but is fairly dense (130 pounds per cubic foot). A
1-inch-thick slab of Teflon between the RCC and the aluminum spar would
probably add about 3,000 pounds to the orbiter weight. NASA undoubtedly
would reject Teflon on this basis since the orbiter right now has to
struggle mightly to get the heavier ISS parts up to the construction orbit
(~200 nmi altitude). SIRCA at about 30 pounds per cubic foot looks more
promising.

Later
Ray Schmitt



"jay" wrote in message
66...
"Chuck Stewart" wrote in
news
On Mon, 01 Sep 2003 02:52:22 +0000, Derek Lyons wrote:

"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.

greetings...

It seems to me that if the leading edge had some physical backup, it might
withstand abuse a bit better.
I wonder if the ceramic tile material would work? Use the rcc outer, with
tile underneath?
Certainly it would be damaged by a major strike, but might still bring the
bird home...

That carbon aerogel sounds like great stuff, but I ddin't see structural
data on it. (ok, didn't look that hard)

It seems to me, that a big thing is to prevent any plasma leakage from
penetrating the main wing. Maybe the carbon aerogel would slow the flow
and
diffuse it enough to keep things alive?
regards
Jay