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, specifically regarding critical speeds, crankshaft flexing, and flywheel systems in various engine types.
| Identifier | ExFiles\Box 63\4\ scan0082 | |
| Date | 30th September 1929 guessed | |
| 2. gives satisfactory results. The flywheel system must surely represent conditions more closely for the amplitude of movement is not proportional to the distance from the node. I have found that in a six cylinder line engine the minor critical of the 4½ order (4½ vibrations per revolution) may be important, and the same remark applies to 12 cylinder 45° Vee engines. The effect of Vee angle and firing order in 12 cylinder Vee engines has been investigated here to some extent. Your remarks upon the relation between severity of criticals and tightness of bearings are interesting. Timoshenko shows in his recent book on vibration that the existence of clearance widens the range of speed over which a resonance peak extends and increases the amplitude of movement. My experience is that the absence of noise carries no guarantee that an engine is not running at a torsional critical speed. The noise produced must depend, inter alia, on the manner in which driven auxiliaries are disturbed by torsional oscillation of the crankshaft. I have no experience of motoring crankshafts bare. Lateral vibrations do occur under ruming conditions and at definite speeds as the base circles of torsiograms show. How far the vibration recorded is due to crankshaft flexing, and how far it is general, has not yet been investigated. In one case, torsiograms taken at different places on different engines of the same type show the same outer circle movement, which indicates that it is not a question of mounting. Sometimes the outer circle changes to an ellipse, and sometimes it / | ||