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).
Technical memorandum discussing crankshaft periods and torsional vibrations in V-8 and other engine types.
| Identifier | ExFiles\Box 137\4\ scan0037 | |
| Date | 6th October 1929 | |
| To R.{Sir Henry Royce} From Hs{Lord Ernest Hives - Chair}/Tan. C. DS. C. Wcr. Rg.{Mr Rowledge} C. E.{Mr Elliott - Chief Engineer} By.{R.W. Bailey - Chief Engineer} X 634 Hs{Lord Ernest Hives - Chair}/Tan5/AML6.10.29. X4499 X634 CRANKSHAFT PERIODS IN THE V-8 ENGINE. From remarks in Rl/M9.10.29, headed "Car Superchargers" we conclude that you are under the impression that the proposed twin-4 aero engine will not have a "top period". Actually it will, due to the fact that there are four peaks per rev. in the torque curve. Therefore there will be a 4-per-rev. torsional vibration period. The mathematical explanation is that the 4 x m frequency harmonics (8th) of the individual cylinder torque curves are in phase and add together for all the cylinders. In a twin-6 there are six peaks per rev. in the torque curve and thus no 3 x m frequency harmonics to produce 3-per-rev. periods. The highest period is the 6-per-rev. one. If however, only 6 cylinders of the 12 are firing (any 6 evenly spaced, i.e. front 6, back 6, or one bank) then the torque curve has 3 peaks and the 3-per-rev. period will occur. This is the explanation of crankshaft failures on Condors etc. when run on 6 cylinders. We know that certain V-8 engines e.g. the Hispano - gave a lot of trouble with torsional vibrations during the war, and even got their propeller hubs on fire in the air. | ||