Date: 24 May 99 01:52:41 From: "P. Wezeman" <email@example.com> Organization: The University of Iowa References: 1
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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"