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 for 40/50 balance weights on a stiffened Phantom crankshaft.
| Identifier | ExFiles\Box 14\2\ Scan127 | |
| Date | 2nd August 1931 | |
| 87010. To R.{Sir Henry Royce} from Hs{Lord Ernest Hives - Chair}/Cry. c. Dg. Wor.{Arthur Wormald - General Works Manager} c. E.{Mr Elliott - Chief Engineer} De. Ry. Hs{Lord Ernest Hives - Chair}/Cry/2/AML.8.31. 8634. 40/50 BALANCE WEIGHTS. We have carried out some calculations as to the amount of balance possible with the stiffened Phantom crankshaft Lec.2925. The stiffness of this shaft is 115000 lbs.ft. per radian, giving a top period of 4350 R.P.M. Balance weights must not reduce this below 3900 R.P.M. (100 M.P.H.) The inertia of all the weights must therefore not exceed 217 lbs-in². The out of balance per crank and big end is 22 lbs-in. Therefore each of the 12 weights must have a moment of 11 lbs-in, and a polar inertia not exceeding 18 lbs-in². The thickness of each weight cannot greatly exceed 1.25". The balance weight shown of approximately the correct moment, has more than twice too much inertia. To reduce the inertia to 18 lbs-in² the value of k² would have to be not greater than 4.4 which is impossible. We cannot therefore fully balance this crankshaft. If the shaft was fully balanced, the critical speed would be at 3400 R.P.M. Hs{Lord Ernest Hives - Chair}/Cry. | ||