From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Torsional oscillation tests on a B.60 No.4 engine fitted with a Wraith spring drive.
| Identifier | ExFiles\Box 124\1\ scan0088 | |
| Date | 28th April 1939 | |
| Rm{William Robotham - Chief Engineer}/JRS.1/JH.28.4.39. TORSIONAL OSCILLATION TESTS ON B.60 No.4. (Wraith Spring Drive). This test was carried out to discover the effect of the Wraith spring drive on the vibrations of the B.60 crankshaft. The friction of the spring drive was set at the standard figure of 15 lbs. at 1 7/8" radius. The vibration amplitude speed curve for this engine is shown and for comparison the curves obtained from the Wraith III with a similar spring drive, and the B.60 with a B.80 damper set at 219 lbs.ft./degree are included. Comparing the Wraith and B.60 with the spring drive shows that there is very little difference between the two except above 2900 r.p.m. where the amplitudes occurring with the B.60 are from .05 to .15 of a degree less. On examination of the two B.60 curves, one with spring drive and one with B.60 damper, it is found that up to a speed of 3200 r.p.m. the spring drive gives amplitudes up to .1 of a degree less, but above this speed the B.60 damper shows up the best, having a maximum of .5° against .65° for the spring drive. The two curves for the spring drives show that the high power head of the B.60 is not aggravating the torsional vibration conditions, indeed the third harmonic of the torque curve must be less than for the Wraith. The two B.60 curves show that on the whole a slight reduction of amplitude is given by the spring drive if the speed range is limited to below 3700 r.p.m. The quieter running of the engine with the spring drive compared with that with the B.60 damper is explained by the fact that with the spring drive the camshaft gears are not oscillating to the same extent as the crankshaft and consequently gear noise and vibration in the camshaft driven auxiliaries are greatly reduced. Rm{William Robotham - Chief Engineer}/JRS. | ||