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 comparison of crankshaft inertia and stiffness between a 20 HP engine, a Lorraine-Dietrich engine, and a Goshawk engine.
| Identifier | WestWitteringFiles\Q\2April1927-June1927\ 40 | |
| Date | 22th April 1927 guessed | |
| contd :- -7- of benefit in raising the periodicity. As an example of this the stiffer shaft made for the std. 20 HP. which was 18% stiffer than std. raised the master period to 3500 r.p.m. We have not however determined the inertia of this shaft. Consider for the moment the Lorraine crankshaft assembly. The following figures will be of interest for comparison with the 20 HP. RR. LORRAINE DIETRICH. ----------------------------------------------------- PART. | INERTIA ETC: ----------------------------------------------------- Flywheel inertia. | .3767 Fan pulley " | .001437 Big ends total inertia. | .01058 Half pistons.(Assumed con- | .00587 centrated at big ends). Crankshaft inertia. | .04322 Crankshaft stiffness. | 28350 lbs.ft/rad. Master period. | 3900 r.p.m. The stiffness of this shaft is approx. 75% greater than the Goshawk but it will be noticed that the inertia of the parts has also increased, being now equivalent to .02130 lbs.ft2 at the front end or an increase of 33% over the Goshawk. The crankshaft has four bearings and is the same length within .35" as our 20 HP. The sum of the lengths of the journals and crank pins is respectively very nearly alike in each engine. It is noticeable however that the Lorraine crankshaft has proportionately greater inertia for its stiffness than our std. 20 HP. crankshaft. The ratio inertia to stiffness is contd :- | ||