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).
Analysis of engine flywheel vibration and periodic speeds observed during testing.
| Identifier | ExFiles\Box 137\4\ scan0070 | |
| Date | 24th December 1929 | |
| -2- true at low speeds or when turned over by hand. We have observed this on about six engines, in the Test and Expl., Depts., and have measured it on four. The maximum deviation at the periphery in a radial direction was .008", and in an axial direction .014". Undoubtedly they are all quite true when built, so we think this deviation may be a result of straining the shaft when running on the flywheel period. If the engine be revved up to about 1,000 r.p.m. it can be seen to be running quite true, and it remains true until the periodic speed (3200 r.p.m.) is reached, when it can be seen with the naked eye to go indistinct. The Rotoscope bears this out. We have observed when using the Ashdown Rotoscope, that if this instrument be set to the correct frequency to make the rotating flywheel appear stationary, then the flywheel vibration appears stationary as well. Therefore, the frequency of vibration is equal to the frequency of rotation, and the flywheel is going round out of truth, as if the shaft were bent. We have not yet determined the phase of this relative to the last crank. Another interesting point which we have observed is that the flywheel vibrates at a speed of approx. 2,800 r.p.m. on a test bed, instead of 3,200 in a car. The particular test-bed engine we were watching had a bad mounting period at 2,500 r.p.m. at which it shook itself and the whole test bed, and we think this has affected the flywheel frequency. We think the change in flywheel period is due to the proximity of the two natural periods of the engine and flywheel, when | ||