Re: Concorde's Engines

Date:         24 May 99 01:52:41 
From:         "P. Wezeman" <pwezeman@blue.weeg.uiowa.edu>
Organization: The University of Iowa
References:   1
Next article
View raw article
  or MIME structure

On 12 May 1999, Bill Herman wrote:

> I don't regularly read this group, so sorry if this has been asked
> previously...
>
> Do the Concorde's Olympus engines use some form of afterburner while flying
> supersonic?  A friend of mine doesn't think so, but I don't see how that
> plane can fly at Mach 2 without reheat.  I thought the F-22 was considered
> to be a great technological achievement because of its ability to fly beyond
> Mach 1 at military power (no afterburner).  It's hard to believe that a
> plane designed 20+ years prior to the F-22 already had that capability.

	The Concorde uses its afterburners to takeoff and to accelerate to
cruising speed, but maintains its cruising speed without them. The
exhaust velocity of a straight turbojet like the Concorde's Olympus
provides very good propulsive efficiency at Mach 2. A great deal of
the progress in jet engines has been in making them shorter and
lighter for the same thrust. A fighter plane with supersonic cruise
without afterburners could have been built in the 1960's if they had
chosen to do so; it would have been like a de-rated SR-71 or
F-108, both of these being Mach-3 jets designed at that same time.
Such a plane would of course not have been anything like as effective
as the F-22. The weight of the engines would have cut into the useful
load and without stealth technology it would have been more vulnerable
to missiles. Still, it could have been done, but the planners at that
time did not realize how much of an advantage it would be to have
a tactical plane that could carry out its entire mission at, say,
Mach 1.5, slow enough to maneuver but fast enough that opposing
aircraft would need afterburners to keep up, and thus quickly
use up their fuel. The closest to this was probably the Canadian
Avro Arrow which would have probably gone about Mach 1.5-1.8 at
full military power with the Orenda Iriquois engines originally
intended for it. This was a dedicated interceptor rather than a
maneuvering fighter.
	Note that the F-22 uses a low-bypass turbofan rather
than a straight turbojet, the turbofan being more efficient at its
cruise speed of Mach 1.5.

                        Peter Wezeman, anti-social Darwinist

                             "Carpe Cyprinidae"