How to Ride the Jet Stream

Near the base of the stratosphere, 35,000 to 40,000 ft. above the earth, the jet stream offers free west-east transportation to airplanes that can find it and stay in it. It is a hard trick to do, but last week a B-47 bomber stayed in the jet stream most of the way from March Air Force Base, Calif, to Hanscom Air Force Base, Mass., and made the 2,700-mile trip in 3 hr. 47 min. at the average ground speed of 714 m.p.h.--setting an unofficial record. Major Mont Smith, commander of the B-47, gave most of the credit to the AN/APN-66, a navigation device made by General Precision Laboratory, Inc. of Pleasantville, N.Y. The "66," said Major Smith, "put me into a 165 m.p.h. jet stream and held me there all the way across the country."

The "66" is a complex dead-reckoning system that measures the airplane's speed by means of radar pulses reflected from the ground. It also measures the sideways drift caused by cross winds and keeps track of the airplane's heading during all parts of the flight. This informa tion, combined automatically by a computer, tells the pilot continuously where he is, and as a kind of extra feature, the clever "66" helps him find the fastest wind to boost him to his destination.

To find the jet stream the pilot flies in its general direction, which can be determined by the weatherman. When the "66" tells him that his drift angle is increasing, he knows that he is getting into the jet stream and is being carried along by it. When the drift angle reaches a maximum, he turns downstream until the drift angle falls to zero. Then he knows that he is flying in the center of the jet stream. If the stream curves, as it often does, the airplane can follow it by keep ing the drift angle at zero. When the "66" is hooked to the autopilot, the airplane will follow the stream automatically, getting maximum benefit.

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