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).
Crankshaft periods and torsional vibration in V-S engines.
| Identifier | ExFiles\Box 63\4\ scan0087 | |
| Date | 6th October 1929 | |
| To R.{Sir Henry Royce} from Hs{Lord Ernest Hives - Chair}/Tsn. c. Sg.{Arthur F. Sidgreaves - MD} c. WDR. Rg.{Mr Rowledge} c. A.{Mr Adams} EY. X 4499 Hs{Lord Ernest Hives - Chair}/Tsn5/AM.6.10.29. CRANKSHAFT PERIODS IN THE V-S ENGINE. x4499 x634 From remarks in RL/19.10.29, 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 phaseand 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 set their propeller hubs on fire in the air. | ||