Re: Concorde

Date:         21 Nov 96 03:02:20 
From:         shahid siddiqi <s.a.siddiqi@larc.nasa.gov>
Organization: as&m
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Peter Coe wrote:

> Concorde is the only plane that cruises at beyond Mach 2 without reheat.
> Yet another 30 year old invention that hasn't been bettered.
>
> On a supplemental thread, I vaguely recall that at the time of its entry
> into service, Concorde's engines were claimed to be the most effecient
> engine ever built - I presume in terms of thrust per pound of fuel.  The
> plane isn't effecient overall, because it operates in such an ineffecient
> environment.

Come come lets not get carried away - the laws of
Thermodynamics make this claim impossible. A
turbojet engine such as that of the Concorde can
never beat the fuel efficiency of a high by-pass
turbo fan such as the GE-90 or the Rolls Royce
Trent.  The thrust specific fuel consumption in
cruise for the Olympus/SNECMA engine is most
probably in excess of 0.8 pounds per hour of fuel
per pound thrust produced as compared to 0.53
pounds/hour per pound thrust produced by the GE-90.
(In afterburner it would be in excess of 1.4 and
thats why the Concorde doesn't cruise supersonic
with afterburners on it would drink all its fuel
before crossing the Atlantic).

Inmcidently the highest supersonic time pilots are
Air France & British Airways Concorde pilots
because they go supersonic for 2 hours or so
on each Atlantic trip while Air Force pilots are
barely supersonic for 5 or so at a time because
fighters like the F-15 need to use afterburners to
go Mach 2 and can only do this for dash or run out
of fuel.
The Concorde is a beautiful and reliable plane but
the nature of the compromises that have to be made
to go supersonic kill its aerodynamic efficiency.
The cruise Lift to Drag ratio of the Concorde is
approximately 7 while that of a 747-100 (same
vintage as the Concorde) is around 17.  This is
mainly due to the low aspect ratio, highly swept
wing design