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).
Torsional oscillation tests conducted on a B.80 No.3 engine with an increased diameter crankshaft.
| Identifier | ExFiles\Box 132\1\ scan0131 | |
| Date | 22th April 1939 | |
| Rm{William Robotham - Chief Engineer}/JRS.1/JH.22.4.39. TORSIONAL OSCILLATION TESTS ON B.80 No.3. (Increased diameter Crankshaft). Two tests were carried out on this engine, both at full throttle and minimum advance for maximum power conditions. The first test was with the standard B.80 damper set at 222 lbs.ft. per degree relative deflection. The amplitude speed curve for this is shown in Fig.1. together with the curve of the standard B.80 with the same damper at its best setting. The two peaks at 3050 and 3450 r.p.m. formed by the vibration absorbing properties of the damper from the 4th. harmonic peak have approximately the same magnitude showing that the damper is correctly tuned. Comparing it with the best setting of the standard B.80, the amplitudes are smaller throughout, and the critical speeds are a little higher, as would be expected with a stiffer crankshaft. The second test is shown in Fig.2. and this again shows the amplitudes slightly smaller and the critical speeds slightly higher as before. When calculating the amplitude from the 1200 r.p.m. torsiograph record it was noticed that the major components of amplitude at this speed was due to a vibration occurring 3 times in two revolution i.e. a 1 1/2 harmonic, Fig.3. The mode of vibration having a node within the crankshaft is really a two node mode of vibration with the second node between the engine and the brake. The frequency of this system is practically independent of the inertia and shaft stiffness of the parts to the rear of the engine and is to all intents and purposes the same as the fundamental frequency of the engine alone. The Mode of vibration having a 1 1/2 harmonic is the real fundamental vibration of the system and has a frequency of 1800 vibrations per minute. This is further shown by the record taken at 3600 r.p.m. which is a combination of the 4th. harmonic of the more important two node vibration and a 1/2 harmonic of the 1800 r.p.m. frequency. | ||