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).
Methods to reduce torsional vibrations and booming, focusing on engine mounting and frame design comparisons.
| Identifier | ExFiles\Box 137\4\ scan0256 | |
| Date | 13th March 1931 guessed | |
| (2) ing the frame and the body. It should be realised that the sources of torsional vibrations cannot be reduced by any known means except by increasing the number of cylinders. Bentley and all of us must be alike within very small limits and we can only dull their energy by soft mounting of the engine in the frame, and the body on the frame. Now this brings us to another reason for the variation of booming, which although appreciated may be of more importance than we think - i.e. the body mounting on the frame. (i) We ought to get the same improvement by changing the power unit as we do by changing the entire chassis - i.e. if the engines vary in their smoothness. (ii) It is so extremely well known that very definite difference can be made by altering the tightness of the scuttle insulation (always getting worse as the scuttle is made more solid). This suggests that if the entire body and scuttle could be mounted on soft rubber we might get a definite improvement. We have tried to make this possible with our under-frame construction and mounting this on soft rubbers at the front. (iii) I am sorry that I repeat myself so much but it comes about from the fact that the points I repeat have not been satisfactorily cleared up, but the engine mounting that I thought would prove satisfactory is the 4 arm scheme and rear central support with soft rubber (thick) under and above the rear feet. It is still not decided (as far as I know) whether the rear support requires rubber mounting. We think that it does not for torsional vibrations, but it may do for lateral ones, which brings us to the next important and oft repeated point. If our designs are wrong compared with Bentley it can only be in 2 points - i.e. (a) the whirling of the flywheel, (b) the bending of the crankchamber. The analysis of these modification have been in hand for many months and should have been cleared up by the experiments suggested soon after the faults were thought to exist - (a) Stiffening and tightening the flywheel including its mounting on the crankshaft - i.e. more bolts and stiffer flange as well as back plate which should definitely put up the period if there is one, as is very generally believed by most of us. (b) The crankshaft was to have balance weights - 4 - so as to reduce the couples tending to bend the crankchamber. Une feels that this is not our trouble, but should be proved. (a) may prove to be of great importance and fairly easy to find but costly to cure in back numbers, though easy to avoid in the immediate future as I hope and expect has already been done. I will write another memo. on Mr. Evernden's suggested | ||