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).
Technical discussion on crankshaft vibration, torsional periods, and balance.
| Identifier | ExFiles\Box 14\2\ Scan062 | |
| Date | 1st November 1929 | |
| He/Tan5/AD.11.29 CONTD. -11- on existing crankshafts, owing to the possibility of being misled. (4) Crankshafts. We cannot yet say that the large pin crankshaft is an improvement in high speed vibration. The shaft is 17% stiffer and should raise the period from 3600 to 3900 r.p.m. Actually we believe that since nearly all the added weight is in the pins, the period is hardly any higher. We are investigating this further. We believe that the torsional periods of our shafts are high enough as they are at present. Modifications merely directed to raising their top periods are not likely to produce a reduction in high speed vibration, as our experience is that the top periods are now so high that pushing them higher does not affect the vibrations we are now experiencing in the engines at max. R.P.M. The torsional period need not be more than 10 - 15% above the max. obtainable R.P.M. The top period of the standard Phantom II is at 70 M.P.H. in 3rd gear and 95 m.p.h. in top. Much attention is paid by some firms to dynamic and static balance in crankshafts, but our tests show that the most important feature, which is also the most difficult to obtain, is good distortion balance, i.e. a tendency to maintain static or low speed dynamic balance up to high R.P.M This can only be obtained by proper mass distribution in | ||