World's Fastest Airliner -- Puzzle

World's Fastest Airliner

$Description: C:\G Drive\niquette\images\cnd-illl.jpg$ 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.

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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.

Meanwhile, something else was taking center stage. The Soviet Space Program had been scoring a steady stream of technological firsts since Sputnik in 1957. The "giant leap for mankind" on Mare Tranquillatis took place 201 days after the Tu-144 first flew. Eyes were glistening with pride on both sides of the Iron Curtain. From that point forward, there would be no problems that could not be solved by technology. "Bring on cancer," someone exulted.

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Video Comparison: Tu-144 versus 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"...

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$Description: C:\G Drive\niquette\images\cnd-illl.jpg$ Air friction heats the skin, expanding the airframe by as much as a foot in length. 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).

World's Fastest Airliner(s)
Airliner	*Tu-144*	*Concorde* (The)
Country	USSR	UK & France
Manufacturer	Tupelev OKB	BAC /Aerospatiale
Nickname	"Konkordski"	"Speedbird"
Cruise Speed	1,320 mph	1,334 mph
Quantity Built	16	20
Take-off Weight	185 tons	205 tons
Range	4,039 miles	4,500 miles
Capacity	80 Passengers	128 Passengers
Flights	Weekly	Daily
Distinctions	Canard Brake Chute	Fly-by-Wire Trim by Fuel CG
Issues	Failures: 226 in 122 Flights	Sonic Boom Take-off Noise

$Description: C:\G Drive\niquette\images\cnd-illl.jpg$ 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.

Concorde had a service ceiling of 60,000 feet MSL. That's more than eleven miles straight up. One would surely expect that the inverse square law would apply -- that no airplane flying in the stratosphere would be found guilty of spooking farm animals or rattling school windows. Such a happy notion was demolished when test flights of the North American B-70 Valkyrie were carried out in the mid-1960s, not to mention the Operation Bongo fiasco about that time. Bummer.

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.

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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.

The speed of sound is about 1,100 ft/sec. At 200 feet in length, the fuselage of Concorde traveling at twice the speed of sound passes a given point in about 90 ms. Meanwhile, the N-wave from that point in the sky moves outward in a circular ring at the speed of sound, forming a shock cone, which diverges from the flight path by 30^o and will be experienced on the ground as a double-boom.

$Description: C:\G Drive\niquette\images\cnd-illl.jpg$ 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?

{1} Airspeed: Faster or Slower?
{2} Fuselage: Lengthen or Shorten?
{3} Wingspan: Longer or Shorter?
{4} Shape of the Aircraft: Redesign?

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