Science: Mach 1.1

Last week Test Pilot John Derry was flying De Havilland's experimental DH-108 at 40,000 feet over southern England. The weather was clear, the "machometer" (speed indicator in fractions of the speed of sound) showed Mach .86. Derry felt just right, so he opened the throttle and turned the nose down.

As the speed of the dive increased, the machometer needle crept up to Mach 1, the speed of sound. Then it went on up to Mach 1.1. The controls felt heavy, but nothing really unpleasant happened. Derry checked the speed and leveled off. He had traveled faster than sound in an engine-driven plane (the DH-108 is no rocket-ship like the U.S. Bell S-1), and was none the worse. His top speed was probably just under 700 m.p.h.

The DH-108 has swept-back wings with controls on their tips (see cut). This design may account for the fact that Pilot Derry felt none of the "compressibility" effects when flying in the transsonic speed range. But the DH-108 may have other improvements that are secret. A similar plane came apart in the air and killed Geoffrey de Havilland in 1946.

Exceeding the speed of sound in a brief power dive is not the same thing as flying continuously faster than sound in level flight. U.S. planes are rumored to have done it too. But if they have, the military has chosen to keep mum.