[ExI] Skylon- a plane that can fly anywhere in under four hours!

[spike]

>... On Behalf Of Keith Henson
Subject: Re: [ExI] Skylon- a plane that can fly anywhere in under four
hours!
>
>>... John I am not going to get too excited by this until I see that they
can make that precooler perform the way they say it will.  I did the numbers
on this a few years ago and they suggested that this precooler would need to
be higher performing than any heat exchanger we have.  If the Brits get it
to work, then I will offer a Jolly good show, chaps, jolly good.

>...Spike, they did.  And indeed the performance is better than any previous
heat exchanger.  The tubing is so fine that the things look like fabric.  I
have seen them up close.

Cool, Keith that gives me confidence in those calculations I did.  It looked
to me like they would need something like that to get sufficient heat
transfer.  In general a pressure tube wall thickness is proportional to its
inner diameter, which makes sense if you look at the equations for hoop
stress in a cylinder.  Greater heat transfer means smaller ID tubes, thinner
walls, and so forth.  My single-digit BOTECs were suggesting a heat
exchanger that would do the job would need tubes smaller than anything I
have seen, which makes them very delicate and subject to leakage.  

The next trick they must have solved is figuring out how to make this heat
exchanger stand up to a shock wave.  Now that's technology indistinguishable
from magic.

...

>...What amazed me was that these things, with thousands of brazed joints,
don't leak helium.  Keith
_______________________________________________

Ja, helium wants to be free.  That stuff is hard to contain.  Any tiny crack
or imperfection in any joint or anywhere and it's game over man.

spike