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Endurance Tests of a 22'' Diameter Pulse Jet Engine with a Neoprene Coated Valve Grid

Thrust-stand tests were conducted at high thrust outputs to
determine the operating life of a 22-inch-diameter pulse-Jet engine
equipped with a neoprene-coated valve grid. The results of the
endurance tests show that through the use of the neoprene-coated
grid the operating life of the pulse-Jet engine, as limited by
valve deterioration, was extended to more than 164 minutes, as
compared with 30 minutes for the standard uncoated grid. The
average Jet thrust (not deducting the momentum drag of the entering
air) developed by the engine was 855 pounds at a simulated ram
pressure of 58 inches of water and a fuel flow of 2800 pounds
per hour; no decrease in thrust was obtained during the entire
164 minutes of operation. This get-thrust value represents a slight
reduction in performance from the average 890 pounds of thrust
obtained with the standard valve grid under similar operation condi-
tions.

At the request of the Air Technical Service Command, Army Air
Forces, and of the Bureau of Aeronautics, Navy Department, an inves-
tigation is being conducted at the NAGA Cleveland laboratory to
improve the performance and extend the operating life of the pulse-
Jet engine. As a part of this investigation, thrust-stand tests
were conducted to determine the seaqlevel performance of a
22-ineh-diameter pulse—Jet engine at simulated ram pressures of 0,18,
40, and 58 inches of water over the entire fuel-flow operating range of
the 3st engine (reference 1).

The results of reference 1 and of tests conducted at wright
Field (reference 2) indicate that the Operating life of the pulse-Jet
engine, as limited by valve deterioration caused by the repeated impact
forces imposed on the valves in closing during operation, is approximately
sgtginutes, after which a rapid reduction in engine-thrust output is
o ined.

Attempts to increase valve life through change of valve material
and thickness have been unsuccessful, oral reports from'Wright Field,
obtained subsequent to the tests reported herein indicate, however,
that the time of satisfactory operation can be increased to about
1 hour by careful selection, honing, and.finishing of the valves.