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).
Report page comparing inertia and stiffness figures for two different engine models.
| Identifier | WestWitteringFiles\Q\2April1927-June1927\ 38 | |
| Date | 22th April 1927 guessed | |
| contd :- -5- and replaced by a mass at the front end having one-third the inertia of these parts. A better approximation would be to treat each crank throw as an equivalent flywheel and from a knowledge of the stiffness of the shaft between adjacent crankpin centres deduce the natural frequency. The first and rougher approximation however serves to illustrate the point. The following figures for the std. 20 HP. and 1-G-1 are of interest :- PART. | STD. 20 HP. | 1-G-1 ---|---|--- Flywheel inertia. | .6911 lbs/ft2 | .43705 lbs/ft2 Spring drive hub inertia. | .00582 " | .00025 " Big ends - total - | .00799 " | .00525 " Half pistons (assumed concentrated at rad. of throw) | .00563 " | .00502 " Crankshaft inertia. | .016823 " | .01403 " Crankshaft stiffness. | 1622 lbs/ft/rad. | 14750 lbs/ft/rad. Master period. | 3300 r.p.m. | 3800 r.p.m. The equivalent inertia of the crankshaft considered acting at the end, and assuming the mode of the vibration very near the flywheel, would be .0168/3 = .0056 or approx. the same value as the spring drive hub. Therefore if we consider an imaginary case in which the whole inertia of the crankshaft could be removed and the shaft still retain the same stiffness, we should expect to raise the 'master period' only by the same amount as removing the spring drive hub. Again the equivalent inertia acting at the front end is - contd :- | ||