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).
Reducing high-speed engine roughness by comparing added counterweights against a stiffer crankcase.
| Identifier | WestWitteringFiles\T\November1928\ Scan121 | |
| Date | 13th November 1928 guessed | |
| contd :- -6- upper one cannot be fixed with definite certainty on a test bed. We are led to conclude that the improved smoothness lies in the stiffer support to the bearings on 1-G-1 engine, in which the bottom half has webs to the main bearings as well as the top half. We think it can be said then that the two remedies of added counterweights and stiffer crankcase would have the same effect in reducing high speed roughness. Of these two, we suggest the following reasons for preferring the former : (1) The consequent reduced main bearing loads would enable us to shorten the main bearings and lengthen the big ends. (2) If the crankshaft be restrained by a stiffer crank-case, then this is only done at the expense of increasing the main bearing loads. CRANKSHAFTS FOR HIGH SPEEDS. We think that the conventional method of calculating and thinking of main bearing loads due to piston inertia etc. as if these loads were statically applied is probably very wide of the mark at high speeds. Due to the high frequency of these large loads we think that 'elastic' effects will be much more important. Since they will probably produce small high fre-quency distortions of the crankshaft, we think it is more logical to reduce the forces by means of counter-weights than to resist the distortions by means of bearings, and that as we increase the support to the bearings so shall we increase the loads on the bearings, unless we reduce the inertia forces. Hence we suggest it is preferable that the crankshaft be so arranged by increasing its mass and adding contd :- | ||