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).
Comparison of resonating harmonics and torsional periods for 6-cylinder, straight-eight, and twin-six engines.
| Identifier | WestWitteringFiles\R\2December1927-February1928\ Scan146 | |
| Date | 8th February 1928 guessed | |
| contd :- -3- are resonating at the various torsional periods. RESONATING HARMONICS. 6-cylinder. Period. Inertia torque. Gas torque. Cycles per rev. 3300 3rd + 246 lbs.ft. 6th. 37 lbs.ft. 3 2200 9th. 37 " 4 1/2 1650 6th. - .1835 " 12th. 16.7 " 6 1320 15th. 5.7 " 7 1/2 1100 9th. .000 " 18th. 3.3 " 9 Straight-eight. 3300 4th. + 33.1 " 8th. 64 " 4 2200 12th. 22 " 6 1650 8th. + .0039 " 16th. 5.4 " 8 1100 20th. 2.7 " 10 Twin-six. 3300 6th. 174 " 3 1650 6th. - .385 " 12th. 33 " 6 1100 18th. 6 " 9 While the figures given for the gas torques in the above table may not be strictly accurate, they are at least comparative, and enable a few conclusions to be drawn. It will be seen that on the overrun the twin-six will be dead smooth, and without a critical period at all. The straight-eight will have a less serious critical period under power than either of the others. Its critical period moreover will be incomparably better on the overrun than when under power. The six-cyl. is seen to be exceptionally bad on the overrun; the gas torque effects on the critical period are almost negligible. One factor to be borne in mind in connection with the above table is that these three engines, having different numbers of the same cylinders, will not be of the same size or H.P. contd :- | ||