Jet Reversers

A problem that worries the designers of jet bombers and airliners is how to make them stop quickly enough on short or slippery runways. Propeller-driver ships merely change the angle of their propeller blades and use the reversed thrust to kill their speed. A jet has no propeller, and a drag parachute broken out of the tail in the landing run is a cumbersome solution.

This week Boeing Airplane Co. told about its experiments with certain gadgets to reverse the thrust of a jet engine. The type that finally worked best for Boeing is a divided, clamshell-like contraption that normally fits snugly around the end of the tailpipe. When the airplane has touched the ground, the halves of the clamshell swing backward and inward, cutting the blast of hot gases and partially reversing its direction.

The result, says Boeing, is that the engine exerts more than 40% of its thrust in reverse, thus braking the airplane in the same manner as a reversed propeller. When not in use, the apparatus is completely out of the gas stream and so has no effect on the engine's operation. It weighs about 200 lbs. per engine, 800 lbs. for a four-jet airplane.

Another jet-reversing system will be manufactured by Aerojet-General Corp. under agreement with the French owners of the patent. It has no moving parts, only a cylindrical stock of rings behind the end of the tailpipe. In normal flight, the gases pass through the center of the rings. When the pilot wants to stop quickly on landing, he opens a valve, and a blast of air from the engine's compressor shoots down a pipe running through the tailpipe and is released at about right angles into the center of the stream of gases. This diverts the gases into an expanding cone and makes them hit the rings, which are shaped to catch them and reverse their direction. Aerojet says that its device, which has already been flight tested, gives up to 50% of reversed thrust.

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