MUCH remains to be desired in the vibration characteristics of present crankshaft-propeller systems, in the opinion of the author.
Discrepancies between torque-stand and flight measurements of torsional vibration on the same engine may explain propeller fractures due to the vibration of flexure. Recent fatigue fractures of crankshafts, differing from those due to torsional vibration, must be attributed to longitudinal vibration.
Degrees of freedom are discussed with a graphical summary of vibration frequencies. Vibration forms, sources, stresses, and resonances are subjected to mathematical analysis.
Three roads open to effective measures against vibration are given as: direct elimination of sources; subsequent destruction or damping of existing vibrations; and changing the pitch of the vibrating system, or displacing the resonance points to fields outside of the operating range. Of these methods the last is believed to be the most promising.
It is proposed to separate the crankshaft and propeller through the interposition of a flexible spring connection to obtain a crankshaft-propeller system that would be vibration-free to a large degree within the operating-speed range. Such construction would permit decreased crankshaft dimensions and weight.