Re: How Rockets Differ From Jets

in article 1130451029.522933.221880@xxxxxxxxxxxxxxxxxxxxxxxxxxxx, tomcat at
jlavine@xxxxxxxxxxxxx wrote on 10/27/05 3:10 PM:

> George Evans wrote:
>
>> in article 1130417515.983141.215480@xxxxxxxxxxxxxxxxxxxxxxxxxxxx, tomcat at
>> jlavine@xxxxxxxxxxxxx wrote on 10/27/05 5:51 AM:
>>
>> <snip>
>>
>>> I just wish they would ask 'real' questions regarding the
>>> engineering/construction of a spaceplane, not jeer, leer, and carry on.
>>>
>> If I might make a suggestion, you might try dishing out your ideas is bite
>> size pieces instead of coming across like you have the blue prints all drawn
>> up for the whole project.
>>
>> For example, nanotube technology is cool so you might ask if incorporating
>> nanotube cloth instead of rayon in the construction of RCC panels would be
>> worth the cost. Ask something that we can chew on instead of immediately
>> jumping to light speed.
>
> Nanotube fabric is so new that I have to back off a bit. It is still unknown
> when it will be in mass production, though many of the details have been
> worked out, or how expensive it will be when mass produced. Reference:
> University of Texas at Dallas.

And there are so many other questions like how does it behave in a composite
matrix? It's always being compared with steel, but how does it compare with
2422 Aluminum or whatever is the strongest alloy?

> Brad Guth has pointed out that basalt fabric is very strong and fairly heat
> resistant as well. Burt Rutan used graphite epoxy and carbon fiber in his
> Spaceship One.

I don't pay much attention to Guth but I do to Rutan. My dad built a Long EZ
and we are both working on a Lancair IV, not a Rutan but carbon fiber
construction. I am curious how much strength improvement nanotube fibers
provide over regular carbon fiber. I'm assuming, since they are just
differently arranged carbon atoms, that they would be similar and that they
could be used the same in composite materials.

<snip>

> If carbon nanotube cloth lives up to expectations it would certainly be a good
> replacement for rayon in RCC. Nanotubes are inherently very strong, light,
> almost indestructible nanoscale tubes of carbon. Current reports are 100 times
> stronger than steel at 1/6th the weight. BTW, CNT fabric is extremely
> electrically and thermally conductive.

Is that 100 times stronger in tensile strength for an equal cross section?
And is that 1/6th the density of steel? Remember a pound of feathers isn't
1/6th the weight of a pound of lead. So how do those figures stack up to
carbon fiber? I would build an aircraft out of steel.

> I envision creating LH2 fuel tanks by having them fabricated out of titanium
> by a subcontractor. Then nanotube fabric could be laminated onto the titanium
> tanks using graphite epoxy, greatly increasing the tanks strength. In turn,
> this would allow for the slushing of LH2 in the huge tanks putting double or
> triple the amount of hydrogen into the tanks than otherwise would be possible.

LH2 slush means solid hydrogen in liquid He. This is *very* cold stuff, so
how does Titanium do at those temperatures, and how would a nanotube/
graphite epoxy composite? Also it is quite a trick to bond to metal, no
doubt even more so at the temperature of liquid He. Have you done any
testing?

I notice you said that CNT is extremely thermally conductive. This doesn't
seem conducive to keeping things cold.

> The outer hull, however, should be composite only. Titanium, despite it's
> 2000 deg. F. meltpoint, is just too meltable. RCC might be a good way to get
> strength and rigidity to prevent ceramic flexing and breaking.

Here again, the extreme thermal conductivity of CNT is a drawback. Everybody
mocks the TPS tiles on the shuttle but they really are amazing. If they are
banded to a CNT/graphite epoxy composite structure, those fillers you are
concerned about probably wouldn't be necessary.

You will notice I snipped out some other things that got stuck to the bite
sized piece. It's just like spaghetti with you isn't it? :-)

George Evans

.

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