From: rbw3q@rayleigh.mech.Virginia.EDU (Brad Whitehurst)
Subject: Re: what the little bird told Henry
Organization: University of Virginia
Date: Tue, 15 Dec 1992 20:29:35 GMT

In article <ewright.724441300@convex.convex.com> ewright@convex.com (Edward V. Wright) writes:
>In <1992Dec14.161903.327@murdoch.acc.Virginia.EDU> rbw3q@rayleigh.mech.Virginia.EDU (Brad Whitehurst) writes:
>
>>Promoting the first X-30 as a "real" space-plane was not a good idea.
>>We work on SCRAMjet technology (not the actual engines) and can tell
>>you that there is a lot of work yet to do to really understand the
>>physics of fluid flow and combustion in that environment.  Unless you
>>want to spend seriously painful sums making and breaking engines
>>(these puppies AIN'T easy to test!), we need detailed info on the
>>physics so that what is built has a higher chance of success.  
>
>Interesting NASA and the US Air Force were quite ready to test
>a scramjet-powered plane (the X-15C) during the 1960's, except
>that Congress wouldn't appropriate the money.  But today, we 
>can't even try without developing a lot of new physics.  Guess
>somebody must have misplaced a lot of data in the last 30 years.
>(Or maybe just misplaced his cajones....) 
>
>
	I know about the scramjet test article flown on an X-15, but
I'd never heard of a serious attempt to propel an X-15 with
scramjets.  I've read a fair amount of the NASA papers from '67
forward on scramjet research, and believe me, they had (have) a ways
to go before they could actually propel something.  The diagnostics
were crude in the extreme, and the computational models were in their
infancy.  Aside from issues of ignition and flameholding, mixing and
combustion efficiency, there were more practical issues of chamber
materials.  Plus, if you assume a M=2 flow into the combustor
(representative of conditions in the engine at a flight M of 5-8), 1)
the stagnation air temperature is around 2000 K--before you burn
anything! and 2) the mixing and burning lengths are such that the
combustor/nozzle combination would likely be much longer that the X-15
engine bay.  At those temperatures and Mach number, the inlet air is
moving about 1000 m/sec.  Unless you provide large lower speed areas
in the chamber (which is inefficient and leads to large losses),
you'll need several meters to complete combustion.  This is why there
is so much interest in so-called "external" combustion and nozzles, to
reduce the structure required for the engine (among other things).
	In short, it is not a matter of just "cojones".  That attitude will
get you nothing but dead planes, programs, and pilots.  According to
Yeager, one of the reasons he was successful as a test pilot was his
aptitude for understanding the hardware and why and what it was
doing.  Yes, the pilots need courage to face the unknown, but reckless
bravado will never replace good, careful engineering.  The laws of
physics don't give a shit how much testosterone is flowing in your
veins!  Now, a little intestinal fortitude in the halls of Congress
would be heartily welcome to support this work!
-- 

Brad Whitehurst    |   Aerospace Research Lab
rbw3q@Virginia.EDU |   We like it hot...and fast.
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