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).
The investigation of torsional oscillations, piston weights, and the effects of a stiffer crankshaft.
| Identifier | WestWitteringFiles\P\2July1926-September1926\ Scan181 | |
| Date | 20th September 1926 guessed | |
| contd :- -6- 8 3/4° while the three rear pistons gave 2 3/4°. This is proof that the pistons farthest from the flywheel are the most effective in the promotion of torsional oscillations. The effect of piston weights on the amplitude was next investigated. For this purpose the tops of the pistons carrying the rings were removed which reduced the reciprocating weight from 1.75 lbs. to 1.187 lbs. Vibration diagrams showed that this only reduced the amplitude from 8 3/4° to 7°. We expected a larger reduction than this and think that perhaps removing the tops of the pistons does not give an accurate comparison with respect to the weight effect because of the absence of the ring friction and probable air cushioning, all of which would tend to reduce the inertia impulses on the crankshaft. We shall check this effect of weight more accurately another time. STIFFER CRANKSHAFT. One feature of the stiffer crankshaft we have demon-strated is that not only is the critical speed raised approx: 270 r.p.m. for an increase in stiffness of 12% but the amplitude of the vibration is reduced at the critical speed and the lower full load vibratory speed. The amplitude measured from the diagram is now 6° at the critical speed instead of 8 3/4°. Diagrams are shown on the attached print of the full load vibration with the standard and stiffer crankshaft for comparison. It will be noticed that the speeds at which these dia-grams are taken are slightly lower than given in the previous report. These speeds are those which gave the contd :- | ||