1942 - 0077.PDF
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LIGHT January 8th 1942. c . . and the same dismantled to show its few and simple parts. of this method of suspending the absorber mass, which is based on Salomon's Duplex Suspension patents, is that the motion of the absorber mass, under the action of vibratory torques transmitted from the crankshaft, is the same as the motion of a simple pendulum. The absorber rings are retained in place by flanges on the pin and lock ing bolt, the latter being secured by riveting over the end of the bolt after it has been screwed into position. The tuning characteristics of the oscillating system were determined in accordance with the method des cribed in the paper previously mentioned,* aj/d the theoretical predictions were fully confirmed by subse quent tests. The illustration shows a series of records obtained from this engine by means of the R.A.E. re- * See also W. Ker Wilson, Practical Solution of Torsional Vibration Problems. Chapman and Hall, London.) Vol. 2, Second Edition, 19+1. WITHOUT ABSORBERS 3 R a ORDER PART 3 R D ORDER PART 3 R D ORDER 5'/a ORDER 6 T H - ORDER WITH ABSORBERS 5 < /2 ORDER 6™ ORDER ENGINE R.P.M. 2700 2,500 2,000 1,750 1,600 1,050 cording torsion meter. This instrument records the amount of twist across a prescribed length of shaft at the power end of the engine. In the case of steady torques the record is a circle, of radius proportional to the transmitted torque, but if the shaft is being subjected to important torsional vibra tion stresses, the circular trace becomes distorted into a pattern representing the combined effect of the mean transmitted torque and the superimposed vibratory torque. At speeds near a resonant zone of torsional vibration, this distortion is very severe, and the circular trace breaks down into a lobed pattern in which, gener ally speaking, the number of lobes represents the number of vibratory impulses acting on the shaft during each revolution. Since the torsional stress in a given length of plain shaft is proportional to the twist over that length, these records also represent shaft stresses to some scale determined by the dimensions of the shaft and the cali bration constant of the instrument. ' nterpreting the Records The torsion meter record shows a large 3rd-ortfef torque variation at 2,700 r.p.m. in the case of the engine without the absorbers. Traces of this 3rd-order varia tion are still discernible at 2,000 r.p.m. With the absorbers in action the 3rd-order disturbance is com pletely eliminated, although traces of the 2.5th and 3.5th orders are discernible at 2,700 r.p.m. The presence of these at 2,700 r.p.m. was predicted by the tuning calcu lations, and is, therefore, a useful confirmation of the theoretical treatment employed. Additional confirmation is afforded by the presence of the 5 5th and 6th orders at 1,750 and 1,600 r.p.m. respectively, both with and with out the absorbers, since the tuning calculations indicated that the influence of the absorbers on these two orders would be negligible. + 26,000 Z+22X>00 tD ± 18,000 ui . 3 +14,000 p f-± 10,000 z o t-± 6,000 < > i 2.000 • v^ v /\ »-* 1 1 ' ' • I I 1 » • * •II I r— ' ~\ \ 1 * / / \ ' £— I600 ISOO 2,000 2.200 2.400 ENGINE SPEED R.PM. 2600 2800
Transcript of 1942 - 0077.PDF
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FLIGHT, January 8th, 1942. c
. . and the same dismantled to show its few and simple parts.
of this method of suspending the absorber mass, which is based on Salomon's "Duplex Suspension" patents, is that the motion of the absorber mass, under the action of vibratory torques transmitted from the crankshaft, is the same as the motion of a simple pendulum.
The absorber rings are retained in place by flanges on the pin and lock-ing bolt, the latter being secured by riveting over the end of the bolt after it has been screwed into position.
The tuning characteristics of the oscillating system were determined in accordance with the method des-cribed in the paper previously mentioned,* aj/d the theoretical predictions were fully confirmed by subse-quent tests. The illustration shows a series of records obtained from this engine by means of the R.A.E. re-
* See also W. Ker Wilson, " Practical Solution of Torsional Vibration Problems." Chapman and Hall, London.) Vol. 2, Second Edition, 19+1.
WITHOUT ABSORBERS
3 R a ORDER
PART 3 R D ORDER
PART 3 R D ORDER
5'/a ORDER
6 T H - ORDER
W I T H ABSORBERS
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