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).
Letter containing crankshaft inertia and critical frequency calculations.
| Identifier | ExFiles\Box 173\2\ img059 | |
| Date | 20th February 1934 | |
| USA To Rm.{William Robotham - Chief Engineer} from Hs{Lord Ernest Hives - Chair}/Gry.{Shadwell Grylls} c/o.{Mr Oldham} M.{Mr Moon / Mr Moore} Olley, Esq., The Cadillac Motor Co., Detroit, Michigan, U.S.A. Hs{Lord Ernest Hives - Chair}/Gry.{Shadwell Grylls}8/KW.20.2.34; Many thanks for yours of the 6th Feb. The Packard I ran was an aged 3 1/2 + 5 and had a top period at about 2800, not noticeable with the damper fitted. Calculations of our crankshafts - 40/50. Inertia of shaft 480 lbs. in.2 of big ends and 3 pistons 210 ------------------------- 690 1/3 of this 230 Inertia on nose 20 ------------------------- Total 250 lbs. in.2 = .054 Slugs ft.2 Stiffness of Crankshaft 90,000 lbs.ft./radian. Critical frequency 1/211 90,000 ------ .054 = 200 /sec. = 12000 /minute. i.e. 3 per rev. at 4,000 r.p.m. | ||