Re: Concorde's Engines

Date:         10 Jul 99 02:33:42 
From:         Steve Lacker <no@spam.thanks>
Organization: Applied Research Laboratories - The University of Texas at Austin
References:   1 2 3 4 5
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Gregory Travis wrote:
> The inlet doesn't produce thrust.  Thrust is produced, as it always is,
> by expanding air by heating it (by burning fuel) and directing that
> expanded air out rearward.

Thrust F  is produced by causing a mass  M of air to undergo an
acceleration of A meters/second/second in a direction toward the rear of
the airplane.  F=MA.  Burning and heating, are not strictly required at
all. releasing compressed air from a scuba tank ( or a balloon for that
matter) produces thrust, and the only thing happening there is expansion
and cooling. However, since sustained thrust requires a constant energy
input, it is much more convenient to burn the fuel on board the airplane
than to store all the energy in compressed air prior to flight
... at least for everything except toy water rockets ;-)

If the inlet structure and its capturing of the shockwave from the
moveable spike causes an acceleration of air within the intake
structure, then I see no reason why it couldn't be regarded as
"producing thrust." True, you must have an engine running behind the
intake to drive the process, but if the rearward acceleration of air
occurs within the inlet, then I see no reason not  to say "the inlet
produces thrust." This does NOT imply that I understand the physics
behind it :-)

-- Stephen G. Lacker
slacker at arlut dot utexas dot  edu
sglacker at texas dot net