Hot Speed Record

A North American F-86D Sabre jet "broke 700" last week: i.e., established a new official speed record of 715.7 m.p.h.* The previous official record, also held by a Sabre jet, was 699.9 m.p.h. To turn the trick, Lieut. Colonel William Barnes, 32, flew his Sabre jet at the most favorable spot: the hot desert that surrounds the Salton Sea in Southern California. A Sabre jet is built to fly at mach .91, i.e., 91% of the speed of sound. Above this speed, it runs into a sharp increase of air resistance that is called "compressibility drag rise." Since sound moves faster at high temperature, the best place to try for speed is a hot desert.

The Salton Sea has another advantage: it is 236 ft. below sea level. Its air is denser, which slows an airplane a little, but this disadvantage is more than made up for by the increased thrust that a jet engine develops in denser air.

To establish his record officially, Barnes made two passes in each direction (to average out the wind) over a three-kilometer course marked with smoke generators. He flew with his afterburner roaring (for maximum thrust) at an altitude of 90 ft. (to fly in the hottest air). The rules required him to fly level so that he could gain no speed out of diving, and his Sabre jet carried a simulated military load, representing rockets, radar, etc. During the tests, shortly after noon, the temperature near the ground reached 104DEG. In air as hot as this, the speed of sound is 797 m.p.h. (it is 764 at 60DEG), so that theoretically the Sabre jet could have done 725.3 m.p.h. Barnes's record (715.7 m.p.h.) is only 9.6 m.p.h. less than that theoretical maximum. Said he after the flight: "It seemed about fast enough."

* The fastest manned aircraft are rocket planes like the Bell X-1 and the Douglas Skyrocket (1,238 m.p.h.), but these experimental jobs fly under rocket power at altitudes where the air is too thin for the oxygen-breathing engines of operational planes. Their flights do not count as official records, which must be made over a measured course close to the ground.

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