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, critical speed calculations, and crankshaft performance for the Phantom and 20 HP models.
| Identifier | ExFiles\Box 25\3\ Scan149 | |
| Date | 9th September 1926 guessed | |
| contd :- -3- Working this out on the lines given in our first report we find that the free period would be 158 oscillations per second or 9480 oscillations per minutes. We know from the 20 HP. results that the disturbing force has three impulses per revolution and should therefore expect the critical speed to be 9480/3 = 3160 r.p.m. This agrees with the actual vibration we experienced at 3150 r.p.m. and tends to confirm that this is the critical speed of the Phantom crankshaft. In practice we should seldom expect to run to the critical speed because this represents a top gear speed of 88 m.p.h. and again the valves start bouncing about this speed. The results of these tests and the conclusions drawn therefrom shew that although the crankshaft is consider-ably heavier than the 20 HP. the increase of stiffness counter-acts the greater inertia and keeps the critical speed approx. the same as the 20 HP. At the first opportunity we shall make a torsional deflection test on a Silver Ghost. Hs{Lord Ernest Hives - Chair}/A.{Mr Adams} C. Lovesey. | ||