From: bowers@rigel.dfrf.nasa.gov (Al Bowers)
Subject: Re: Aurora - fast new toy from skunkworks
Organization: NASA Dryden, Edwards, Cal.
Date: Mon, 14 Dec 1992 19:48:52 GMT

In article <Bz5oJs.Lqx@news.cs.andrews.edu> maierj@edmund.cs.andrews.edu (Joey Maier) writes:

>Earlier, somebody posted that CNN had said  something about a fast (Mach
>8?) new aircraft, and someone else posted that this may be the result of
>project Aurora at Lockheed.

Still a lot of speculation on this from a number of fronts.  See
below...

>        What kind of propulsion would something like this be likely to
>use?  Ramjets?  Recently, I've heard some aviation buffs talking about
>*external* combustion engines.  The rumor goes that they would function
>by dumbing fuel on the exterior of the fuselage, where it would ignite
>from the heat of friction.  The walls of the combustion chamber would be
>the fuselage and the shock wave of air comming off the nose.

It's been a while since I wrote this old report (and it will probably
never get published), but below Mach 3 to 4 you are most efficient
using turbojets and hydrocarbon based fuels (kerosene based stuff like
JP-4 or JP7).  Between that Mach number and about 5 or 6 you are best
off with a ramjet (long pipe).  Above that you are best off with a
supersonic combustion ramjet.  Most scramjet designs use the afterbody
of the fuselage for a combustion/propulsion surface.  Go do a
literature search and you'll see what I mean.

>Is this for real?  I don't think so.  It seems to me that the pressure
>of the propulsive expansion of the ignited fuel-air mix would have more
>pressure than the shock wave.  It would disrupt the shock wave.  Net
>result:  the plane doesn't move forward.

not.  The flow behind the shock is slower than freestream, but it
isn't subsonic, and so downstream pressure disturbances can't move
forward to disturb the bow shock.

>Could someone out there with a little more knowledge on the subject tell
>me if I'm crazy.  I just don't think this sounds real possible.

It's real, and possible.  A recent flight experiment to test bed
boiler plate the idea in flight was recently shelved, the test bed was
an SR-71.  One application of this reduces base drag, but if you do
efficiently enough, you produce net thrust.

Look up anything by Fred Billig, Grif Andersen (LaRC) or Dr Paul
Waltrip (John Hopkins APL).  These guys are the high gurus of external
burning and scramjet combustion...

About Aurora.  Some folks in the flight test community believe it.
Others are highly sceptical (like me).  My position is: If such a
thing existed, we'd know of the people dissappearing into weird
places, like when the F-117 was flying in the early '80s.  We didn't
know _what_ was going on, simply that something was and _it_ was
probably a stealth airplane (keep in mind that flight test is a small
community and the F-117 was a very small operation).  This time I
don't see folks dissappearing into the woodwork, so I don't think so.
But the folks who _do_ believe something is going on cite the `sonic'
booms and the sightings.  I dunno.  Maybe, maybe not.  I'm still a
sceptic.

--
Al Bowers                       bowers@rigel.dfrf.nasa.gov
NASA F-18 High Alpha Research Vehicle, Lead Aero
NASA, Dryden Flight Research Facility, Edwards, California