Mach 1: Assaulting the Barrier- page 4 | History | Air & Space Magazine
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.)

Mach 1: Assaulting the Barrier

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

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(Continued from page 3)

The solution to the problem was to design wings with greater rigidity. The English Electric Lightning, although sounding like a household appliance, somehow achieved adequate rigidity despite an enormous amount of wing sweep: a 60-degree angle between the leading edge and a line perpendicular to the fuselage centerline. Only a single Soviet fighter—the Sukhoi Su-7—and delta-wing aircraft such as the Concorde ever equaled or exceeded the Lightning’s arrow-shaped sweep.

Even fewer have equaled the Lightning’s ability to go supersonic in level flight without using afterburner, a talent so rare, in fact, that it wasn’t until September 1989, 35 years after the Lightning first flew, that an experimental F-14 Tomcat with a special engine demonstrated “supercruise”—supersonic cruise without afterburners—for the first time. And that happened only after the aircraft was boosted past Mach 1 on full burner.

In 1953, one year before the English Electric Lightning did it, the North American F-100 Super Sabre became the first fighter in the world to fly faster than sound in level flight, though by benefit of an on-or-off afterburner that in a single unthrottleable torrent of kerosene raised the engine’s thrust by half. The pride of the U.S. fighter fleet in the mid-’50s, the F-100 demonstrated how little could even then be taken for granted about supersonic flight.

North American was desperate to get the F-100 into production, so when Air Force test pilot Pete Everest turned down the Super Sabre as having some unacceptable handling qualities, North American put the brute in the hands of a group of young tigers from the Tactical Air Command. They all thought it was neater than a wet T-shirt contest and far more exciting than the F-86s they’d been flying. The Air Force’s claque outvoted Everest, and F-100s started coming off the production line.

In 1954 they also started coming apart, killing five pilots, including the North American factor test pilot who’d okayed the airplane in the first place. It turned out the original F-100A Super Sabre had such a long, heavy fuselage atop short, heavily loaded wings that it wanted to go sideways or tumble—or preferably to do both at once, called “yaw coupling.” And when it inevitably did, the resulting force tore off the vertical tail. Later models were given a larger and considerably stronger tailfin.

THE TRANSOCEANIC regime was still a mysterious one in the 1950s. Airplane builders confronted it by equipping their machines with enormous engines and afterburners, and designers expanded wings into full deltas or shrank them into short, skinny vestiges of wings like those on the F-104 Starfighter, Lockheed’s missile-with-a-man-in-it. But sometimes even this combination of brute force and creative extremes was not enough to wrest speed from an unwilling atmosphere, and in 1952 Richard Whitcomb discovered why.

Whitcomb, one of the most productive transonic aerodynamicists in the world, would go on to develop Whitcomb winglets—the vertical wingtip extensions seen on advanced transonic aircraft from the 747-400 to recent Learjets—and would play a major part in the development of the supercritical airfoil for more economical transonic cruise. As Adolf Busemann, the German inventor of the swept-wing concept, once said of Whitcomb, “Some people come up with half-baked ideas and call them theories. Whitcomb comes up with a brilliant idea and calls it a rule of thumb.”

Shock stall—the effective loss of lift caused by supersonic perturbations on the wing—is one of the two Katies barring the door to supersonic flight. The other is wave drag—the increase in air pressure, or resistance, against the entire airframe shouldering its way through transonically compressed air. Vintage aeronautical engineering had concerned itself almost entirely with airfoil cross-section, as though the wing was the only significant part of an airplane and was simply a three-dimensional extension of a two-dimensional curve. As airplanes began to probe the transonic region, designers realized the wing had to be studied as a whole—that its sweep, shape, structure, and aeroelasticity all had to be considered together.

And now, as true supersonic flight revealed a whole host of unexpected control, flow, and drag problems, designers discovered that every external component of the airframe—wings, fuselage, tail, engine pods, intake ducts—affected the others so strongly that the entire vehicle had to be studied as a single entity.

Whitcomb’s Area Rule was the first major outgrowth of this revelation, and the need for it was demonstrated by one of the great slips ’twixt aviation’s cup and lip, the Convair F-102. The F-102, the first U.S. pure-delta design put into production, was based on some German World War II research and wing tunnel data on components. Unfortunately, the wind tunnel data was incomplete—“perhaps the most outstanding case in the history of aviation of full-scale drag proving to bear little relation to drag measured in the wind tunnel,” says writer Bill Gunston. There was no way the supposedly supersonic F-102 could get anywhere near Mach 1.

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