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).
Letter discussing engine torsional vibrations and crankshaft performance in 6 and 12-cylinder engines.
| Identifier | ExFiles\Box 158\5\ scan0080 | |
| Date | 4th November 1940 | |
| - 2 - Cont'd.{John DeLooze - Company Secretary} However, I feel that such an analysis at the present juncture would serve very little useful purpose since the engine is already in being, and what we have to do is to make it work. We can however, give you some figures relative to your 6-cylinder engines which may give you a picture of the magnitude of the torsional with which you have to deal. The worst torsional on your 6-cylinder engine was, we believe, at about 1,900 r.p.m. and you could not run through this without fear of breaking the crankshaft. It was, of course, the 6/rev period and was produced by gas torque. If your 12-cylinder had exactly the same crankshaft and big ends weights, it would also have it's major period at 1,900 r.p.m. but the amplitude of the vibration would be twice that of the 6-cylinder engine, so that you would certainly be unable to run through it unless you fitted a very large and satisfactory damper. If your worst period is at 1,900 r.p.m. then the next bad one would be at 1400 r.p.m. but you should have no difficulty in getting rid of this one. We imagine that your "12" crankshaft is much stiffer than that of your 6-cylinder engine and in consequence both these periods may be moved up 100 revs or so. If you want to run fast there is no doubt that you have got to do some serious work on crankshaft dampers or you will never get through the sixth order vibration. Yours sincerely, | ||