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 crankshaft vibrations, focusing on frequency, amplitude, and stress under various conditions.
| Identifier | WestWitteringFiles\P\2July1926-September1926\ Scan136 | |
| Date | 4th September 1926 guessed | |
| contd :- -9- the maximum amplitude and should be within about approx 50 r.p.m. If we multiply together the r.p.m. and the number of oscillations on these diagrams, we get the frequency or oscillations per minute. It will be found from the diagrams that this is roughly a constant for all those given being between 9600 and 10050 oscillations per minute or 160 and 167.5 oscillations per second. The difference could be accounted for by slight error in the speed giving the maximum amplitude. This is good evidence that the crankshaft is vibrating with its natural period and quite in accordance with the statement that the amplitude will depend upon the relation of the frequency of the disturbing force and the free period of the crankshaft. Another point observed is that the speeds giving the most vigorous vibrations bear roughly the ratio 1/2, 1/3 and 1/4 to the critical speed. Before passing from this we see that at speeds of 500 and 2000 r.p.m. there are no appreciable vibrations also at other speeds but no diagrams are given. With regard to the amplitude of the oscillations we estimate from the diagrams by considering the lever ratio of the scriber that the 3350 one has an amplitude of approximately 3° 49' or 1° 54½' each side of its mean position. From a crankshaft deflection curve, which follows, we see that this deflection would give rise to the static stress produced by a torque of ±540 lbs.ft. at the end of the crankshaft. The actual stress would be higher than the static due to contd:- | ||