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).
Calculations on crankshaft stiffness and frequency for straight-eight and twin-six engines.
Identifier | ExFiles\Box 23\5\ Scan077 | |
Date | 2nd March 1928 guessed | |
contd :- -5- per rev. In a straight-eight there would be four per rev., owing to the four torque variations instead of three. This means that to retain the period at 3300 r.p.m. where the 20 HP. crankshaft has a frequency of 9900 per min., the eight cyl. shaft must have a frequency of 13,200 per minute. Taking into account the increase in inertia with the increase in the number of cyls., the stiffness would have to be 32,800 lbs.ft/radian (i.e. 100% greater than standard). This stiffness would also have to be attained in a shaft 33% longer. It is of interest to note that the Stutz eight cyl. crankshaft has a stiffness of 54,400 lbs.ft/radian. Its period is at 3800 r.p.m. The period rises as the square root of the stiffness of the crankshaft. (2) Twin-six engines. Allowing for twice the inertia due to connecting rods and pistons, and also 20% increase in the inertia of the crankshaft itself, this engine would only require a shaft of stiffness 19,800 lbs.ft/radian, or 18% stiffer than standard. This could be easily attained. Hs{Lord Ernest Hives - Chair}/S.S.Tresilian. | ||