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).
Engine vibration, resonance, and roughness at different speeds, with references to specific engine models.
| Identifier | WestWitteringFiles\T\November1928\ Scan117 | |
| Date | 13th November 1928 guessed | |
| contd :- -2- depend only on the magnitude of the unbalanced force and the weight or inertia of the engine unit. The effect of mounting the engine in some more or less elastic way will be to introduce a resonant speed or speeds, possibly outside the range of attainable engine revs., at which the previous constant magnitude vibration will now be magnified several times, due to resonance. At non-resonant speeds i.e., between the periods, the engine would run smoothly. We think the above remarks are borne out in experience, in particular with motor cycles and some 'small-four' cars, and also with Eagle XVI. In some motor-cycles and cars, the engine range is punctuated with periods, all pretty sharply defined, at which we imagine either of the following are occurring : (1) A resonance resulting in relative motion between the engine and the frame, or more probably : (2) A resonant period of some component on the engine or frame producing an appearance of engine vibration. Eagle XVI. which we knew to be out of balance, in the form of a long couple, had two periods at 1100 r.p.m. and 2200 r.p.m. From the above we draw the conclusion that our problem of high speed roughness is not an out of balance manifestation, since it does not appear in sharp periods, but in uniformly increasing severity roughly as the square of the speed. PROXIMITY TO CRANKSHAFT TORSIONAL PERIOD. On the 20 HP. car we find that the roughness in 3rd. gear gets progressively worse at high r.p.m. as we approach the critical period. contd :- | ||