Two Worlds of Speed

Even as it rolled out toward take off, its fuselage had the swift, forward-straining look that is a jet-age hallmark. But its wings stuck almost straight out from its sides with the leisurely air of an old-fashioned puddle jumper. The contradiction is designed to make General Dynamics' slow-fast F-111A fighter-bomber the forerunner of a whole new breed of military aircraft operating in two worlds of speed.

The F-111 had already demonstrated its airworthiness--but only with its wings in a slow, takeoff position. This was the time to test the wings' ability to move, to sweep backward so that the plane could switch to high-speed flight.

Novel Control. At 10,000 ft. over Carswell Air Force Base near Fort Worth, Test Pilot Richard L. Johnson began the critical maneuver that is the F-111's reason for being. In the instrument-crammed cockpit, he reached for a novel control: a pistol grip that can be moved backward and forward like a trombone slide. He pushed it forward, and the wings responded by folding backward. He moved them first to 26 degrees of sweep, then 43 degrees, at last to 72 degrees. In this highspeed condition, the F-111 looked like a schoolboy's folded paper dart.

During its hourlong flight, the F-111 climbed to a modest 27,000 ft. and flew at only 450 m.p.h., which is less than one-third of its planned 1,650-m.p.h. speed. But the revolutionary wing mechanism worked perfectly, and the airplane handled easily with wings in all positions. Before landing, Pilot Johnson pulled the trombone control backward. The wings extended again, and the plane touched down lightly at moderate speed. Many more flights will be necessary, but the crucial wing-sweeping maneuver was wholly successful, and it was completed 24 days ahead of official schedule.

Massive Mechanism. The details of the wing control mechanism that changes the F-111 from a low-speed, easy-landing airplane to a dartlike, deadly, high-altitude speedster, are mostly classified. But all parts must be unusually strong to resist the giant forces of high-speed flight. Massive screw-actuated jacks pull the wings against the racing air. A new lubricating system had to be developed to make the pivots work freely.

For a while, pilots and engineers argued about the wing control. One faction held that when the pistol grip was pulled backward, the wings should fold backward in concert. Others insisted that since all pilots are trained to push engine throttles forward when they want more speed, they might get confused at a dangerous moment if they were compelled to pull the wing control backward for the same effect. The second faction won. Now, with a plane that can fly to any place in the world in a single day, F-111 pilots will still be handling controls as familiar and reliable as modern engineers can make them.

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