Eliminating Crankshaft Torsional Vibration in Radial Aircraft Engines 360105
CRANKSHAFT torsional vibration has become a serious problem in aircraft engines. Thanks to much experimental work, we now have a good working knowledge of the two phases of the problem, the elastic and inertia characteristics of the crankshaft-propeller combination and the forces to which this system is subjected.
Methods used in the past to reduce vibration have been to change the elastic characteristics of the crankshaft, or to incorporate direct damping or some form of vibration damper of which the Lanchester and the resonant damper are examples. All of these methods have serious limitations. An interesting device which is capable of eliminating vibration in constant speed machinery is the undamped absorber. For variable speed machinery this absorber is of no value. By arranging an undamped absorber so that the restoring force varies with speed, it is possible, theoretically, to eliminate vibration in certain variable speed machinery. A pendulous weight rotating with the crankshaft of an engine can be constructed so that the restoring force has the desired variation with speed. The device is simple and has a number of outstanding advantages, chief of which is the extraordinary effectiveness of a comparatively small device. The principle has been utilized in a device applied to the Wright “Cyclone” series radial aircraft engines.
Torsiograph records taken on this engine show complete freedom from vibration with the device functioning.