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 torsional vibrations and critical speed based on diagrams at various engine speeds.
| Identifier | WestWitteringFiles\P\2July1926-September1926\ Scan135 | |
| Date | 4th September 1926 guessed | |
| contd :- -8- and the amplitude is greater. The amplitude on these diagrams being represented by the height from the 'crest' of the wave to the 'trough'. The diagram at 3350 r.p.m. we designate the critical speed, and assumption pretty safe owing to its intensity being far more severe than any of the other vibrations and additional proof which we will state later. This diagram is not as good as the others due to the breaking of the apparatus before we could repeat, but we see that there is evidence of only three complete oscillations per rev. Therefore at this speed the frequency is the same as either the inertia torque impulses or the explosion pressures - i.e. three per revolution. The lever arms of the scriber were reduced for this test consequently the amplitude considered on the same basis as the other diagrams is nearly 3 1/2 times greater than the one at 1600 r.p.m. The rather distorted diagram at 800 r.p.m. is caused by running on to the natural period of the spring driven fly-wheels. This we proved afterwards by using lower rated springs when the diagram became 'single track' like the others and distortion was obtained at a lower speed - approx. 500 r.p.m. Nevertheless we are able to pick out indication of torsional vibrations even from this diagram and see that there are twelve complete oscillations per rev. Oscillations of the frequencies shewn exist over quite an appreciable number of revs. about 100 to 150 - but the amplitude naturally decreases before coming on to the other frequency. Therefore the speeds given are approx. those giving contd :- | ||