World's Fastest Airliner
Copyright ©2011 by Paul Niquette. All rights reserved.
There were two. They were contemporaries and rivals. Their respective developments commenced in the sixties, during an extraordinary era for technology worldwide. A prototype of a supersonic airliner, the Tupolev Tu-144, built in the USSR took its first flight on New Years Eve in 1968, followed 32 months later on September 4, 1971 with the first flight of Concorde, which was developed and built in a collaboration between Aérospatiale and the British Aircraft Corporation.
The US had been conducting studies for a "supersonic transport" (SST) since the early fifties. Boeing's Model 2707 won a design competition in 1964 against Lockheed's L-2000 for an American SST, but the development program was terminated in 1971 in recognition of the lead already enjoyed by the Tu-144 and Concorde.
The challenges of supersonic flight are immense. Upwards of 50 tons of engine thrust are required to drive 200 tons of hardware through the sky, overcoming drag, which increases abruptly as the plane accelerates toward what is popularly called the "sound barrier"...
Air friction heats the skin, expanding the airframe by as much as a foot in length. Indeed, the nose tip temperature can reach 260 °F (127 °C) at Mach 2. Then too, there are pesky aerodynamic complications to deal with for enabling the world's fastest airliner to fly slow -- like at take-off and approaching to land.
As the technical problems are common, resemblances between the Tu-144 and Concorde are striking (delta wing, drooping nose cone), but there are significant differences in their designs, too (for pitch authority at low speed: a canard in one, shifting fuel inside tanks along the fuselage in the other).
Try to imagine this: Concorde was forbidden to fly at supersonic speeds over inhabited areas! Note the exclamation point, the only one in this puzzle. The thought must have been that by flying high enough, an SST would avoid the most troublesome environmental impact -- sonic boom.
The expression sonic boom is misleading. "Sonic" has nothing to do with it. "Over-pressure boom" would be more to the point. Over-pressure followed by under-pressure in quick succession -- but far below the frequency of ordinary sound waves.
In the sketch above, we see the characteristic "N-wave" produced by Concorde flying at twice the speed of sound. An abrupt rise in pressure at the nose results from compression of the air and an abrupt fall in pressure at the tail results from the air returning to its undisturbed state.
At supersonic speeds, Concorde streaked across the sky unheard on the ground, with its passengers inside unaware that objects and people were being hammered by a pair of unwelcome shock waves -- "baboom" -- along a swath of ground. Flying high was doing little to attenuate the intensity of the detonations, only increasing the width of the swath and thus the area impacted.
What remedies for the sonic boom would you propose that might enable the world's fastest airliner to fly at supersonic speeds over inhabited areas?