1939-01-01

Permissible Amplitudes of Torsional Vibration in Aircraft Engines 390160

ACTUAL computation of the vibratory crankshaft stresses, although a laborious process beset with many difficulties, should offer the best chance for an intelligent evaluation of the crankshaft torsional-vibration characteristics in aircraft engines and of whether the amplitudes are dangerous or within safe limits, Mr. Masi concludes. In a discussion of the various methods used, their relative merits, and allied problems, he shows that the simple expediency of using fixed allowable amplitude limits, for certain classes of engines, determined from experience, is likely to lead to erroneous conclusions.
A novel method, which has been used on numerous engines by the Naval Bureau of Aeronautics, is suggested by Mr. Masi. It consists of determining the twist of the crankshaft with the application of rated engine torque and basing the allowable vibration amplitude on the amount of the twist. This method, he reports, lends itself to rapid routine check of a variety of engines and gives reliable data for conventional designs.
In the light of present knowledge, he concludes, propeller vibration must be considered a separate and distinct problem peculiar to each engine-propeller combination, and requires separate and individual consideration.

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