Mach 1: Assaulting the Barrier

In 1947, no airplane had ever gone faster than the speed of sound.

The Douglas D-558-2 Skyrocket (shown here at Edwards Air Force Base circa May 1949) pushed past Mach 2 on November 20, 1953, beating an advanced X-1 to the record. (US Navy via National Air and Space Museum. Photo SI A-5168-C.)
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What was creating the unexpected drag, it turned out, was a considerable mismatch between fuselage and wing. Whitcomb’s brand-new Area Rule said that if you graphed the area that an airplane presented head-on to the air, along an axis extending from the tip of its nose to the end of its tail, the resulting line, a measure of square footage at each point, should come out as a smooth curve. Spikes in the curve, created by the sudden addition of a wing to the cross-section just where the fuselage was fattest, say, meant enormous drag.

The easiest way to flatten such spikes was to locally decrease the fuselage cross-section if that’s where the wing needed some breathing room. The result was the grotesque wasp-waistedness of the hastily modified production F-102 and its far faster successor the F-106. The similarly Coke bottle-shaped Grumman F11F Tiger was the first airplane to be designed from inception to take advantage of the Area Rule and as a result was the first Navy line aircraft to pass Mach 1 in level flight.

IN AN ERA WHEN prosperous airline passengers can fly at twice the speed of sound, aerodynamicists have learned a lot about supersonic flight. But even if the sound barrier is down, the lift spoiler remains. It limits the practical flight speeds nearly as firmly as did that imaginary sonic wall. To fly faster than sound—to achieve lift despite shock spikes and to shove aside wave drag—requires massive doses of power or fuel or money. Or, more likely, all three.

In the 1960s, brute force and extreme airframes vastly boosted fighter speeds, and soon everybody—French Mirages, Swedish Viggens, Soviet MiGs, U.S. Century Series jets, even bombers—was routinely doubling the Mach. But after it was discovered that airplanes could fly at two, three, even four times the speed of sound, a strange thing happened: For the first time in the history of flight, designers applied the brakes. Today we are flying slower than we were 20 years ago.

The cream of our military crop, although capable of much higher speeds, clusters on the classic transonic band, cruising and maneuvering at between Mach .8 and 1.2. For commercial aviation, the infrastructure is already far behind the airplane. The complexity of air traffic control, the congestion of runways, the limited access to airports, and the economics of what is becoming a 21st century mass-transit system have made supersonic flight with foreseeable technology irrelevant for all but the most limited and premium applications.

The need for speed seems to have been satisfied. Perhaps. But maybe this is just a Mach .8 plateau, where we rest and await the development of aircraft shapes that create comfy little low-drag shock ripples rather than waves; of airfoil curves that produce lift without sonic drag; of airplanes that reflect all their booming shock-created energy up, toward noiseless space.

A well-known aerodynamicist and aviation entrepreneur who is either laughably optimistic or an unrecognized visionary recently insisted all this was possible. Then he told the story of an orphan he adopted some years ago. When he first met the child, he asked what the boy wanted to be when he grew up. “Oh, I can’t tell you that,” the boy said. “It might not have been invented yet.”


What’sAckeret 1?

Ernst Mach, the man whose name has become synonymous with high-speed flight, never saw an airplane that traveled much more than one-tenth the speed of sound, for he died in 1926. Mach published the work that resulted in the concept of “Mach number” in 1887, 15 years before the airplane was invented. He hadn’t the slightest interest in aircraft and was actually studying the flight of artillery rounds when he did his pioneering work on quantifying the speed of sound—and was doing it largely as an outgrowth of some photographic laboratory techniques he had developed to study sound wave propagation from meteorites, explosions, and projectiles.

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