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).
Flywheel and torsional vibration experiments, including analysis of the Phantom model.
| Identifier | ExFiles\Box 25\3\ Scan176 | |
| Date | 9th November 1926 guessed | |
| contd :- -2- amplitude of the high speed vibration decreased, while that at the lower speed increased until the damping became virtually infinite - or the slipper wheels became solid - when the entire vibration was transferred to the lower speed due to the added polar inertia to the crankshaft. Considering this as applied to the case of the non-rigid flywheel we could imagine that this also possessed two modes of vibration - one at the observed critical speed with the flywheel rigidly connected, and another outside our speed range which would reach its maximum value when the flywheel became 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 that 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 maximum amplitude at approximately 3300 RPM. The appended polar diagram of this vibration taken with a similar instrument to what was used for the 20 HP. experiments, shews that at this speed exists the condition of resonance as indicated by the three crests on the diagram. The same diagram reduced to a flat base is given as a comparison with the 20 HP. and we see that the amplitude is less than with the latter engine. All these investigations where we have used the vibration recording apparatus we have been unable to employ our usual slipper damper and therefore, as no external damping has been used, contd :- | ||