1942 - 0076.PDF

£ LIGHT JANUARY 8TH , 1 94 2 SHOCK D MPERS om Interesting Results of Tests on a Gipsy Engine Crankshaft with Rotating Pendulum Torsional Vibration bsorbers c Gipsy-Six crankshaft with torsion dampers opposite each crank throw. p . 182, of the neers^ 3fc therefore lOTATING pendulum vibration absorbers were first introduced as standard equipment on aircraft engine crankshafts in 1936, when one of the crankshaft counterw eights on the Series " G " Wright Cyclone radial engine was used as a rotating pendulum vibration absorber. Service experience soon revealed that the device had succeeded in smoothing engine vi' tion to such an extent that quite important reducti' of wear of engine components and of controllable-pitf airscrew mechanism s were being obtained. Indeed, results were so encouraging that in the case of the G.ioo Cyclone engine, introduced in 1939, both crankshaft counterweights were used as rotating pendulum torsjp»«rr in r vibration absorbers, with the result that a higher take off speed was found to be permissible and that even with this higher speed there was a reduction of airscrew stress due to reduced torsional vibration. published jn Vol. 143, Institution of Mechanic^ Iroffeedihis 01 the specially ^welcome attentif perf artic f\me when so much s of increasing engine presents the subject in be , tory theory orber practical manne in this country of the rota ults unicatjo'ns on this c.I.Mech.E., p. 223 ^ description 's carried .out by theT)e Havilland Aircraft The Theory Explained Until quite recent times the real principles under lying the operation of rotating pendulum torsional vibration absorbers were not generally understood, and there is little doubt that in many instances where these devices failed to give satisfaction the fault was due to an imperfect understanding of their mode of action. A paper entitled "The Elements of Pendulum Dampers," by R. W. Zdanowich and T. S. Wilson, crankshaftjajted with he ani»ffgernent of the sorjaers are shown are designed to ordejirfrjrquey<?ariation. There are on a corresponding •anged that an absorber each of the six crank also function as crank web a useful relief of main-bearing ly lightens the duty required from of si Company on rotating pend crankshaft a: in the photogr reduce the/Major 3rd six absorber assembl number of cr; mass is diamej pins. Thus the counterweights, loading, which n these bearings bujt' also improves the internal balance of the forces acting on the crankshaft and crankcase. The latter consideration is of great importance from the point of view of crankcase design, since it enables lighter scantlings to be employed without the danger of fatigue cracks developing, at points of local stress concentration, due to the distortions which would otherwise be caused by the centrifugal forces originated by the rotation of the revolving parts of individual crank throws. Each absorber mass consists of two steel rings case-hardened and ground in the bores and on the side faces. These rings are quite free to roll on a case-hardened steel pin which itself is free to roll in a case- hardened steel bush pressed into a carrier arm forged integrally with the crank web. The special feature One of the shock dampers assem

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1942 - 0076.PDF