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).
Page of a report discussing crankshaft resonance, flywheel friction effects, and torsional vibrations related to the Phantom model engine.
| Identifier | ExFiles\Box 25\3\ Scan163 | |
| Date | 9th November 1926 guessed | |
| contd :- -3- free on the crankshaft. We have calculated that this assumed higher resonant speed would be at 6580 r.p.m. The system considered being the crankshaft unit without the flywheel and the basis for calculation being the rigidity of the shaft, its own inertia and an allowance for the piston masses. Running the engine with a flywheel clamping friction of 400 lbs.ins. - which value considerably reduced the vibration amplitude at the critical speed - we found at lower speeds the crankshaft tended to 'thrash' against the stops of its limited travel, apparently due to the friction being insufficient to enable the flywheel to 'smooth out' the explosion impulses and not due to any crankshaft torsional vibration. Therefore from these experiments we find that although the vibration amplitude can be considerably reduced by employing a flexible mounting for the flywheel, the cyclic irregularities become very evident at low speeds due to the explosion impulses. Of course, this latter trouble is reduced as the friction is increased but at the expense of increasing the amplitude of the torsional vibration. PHANTOM TORSIONAL VIBRATIONS. We have now graphically recorded a torsional oscillation on the Phantom at a speed of 3300 r.p.m. This vibration is evident over a fairly wide range starting below 3000 r.p.m. but seems to reach a max. amplitude at approx. 3300 r.p.m. The appended polar diagram of this vibration taken with a similar instrument to what we used for the 20 HP. experiments shews that at this speed exists the condition of contd :- | ||