Letter to the Engineering Laboratory in Cambridge regarding crankshaft dimensions, test results, and a formula for estimating torsional periods.
| Identifier | ExFiles\Box 25\3\ Scan344 | |
| Date | 3rd May 1928 | |
| X634 Expt: Dept: Hs {Lord Ernest Hives - Chair} /Ten2/LG. 3rd. May 1928. H. {Arthur M. Hanbury - Head Complaints} Constant Esq., Engineering Laboratory, Cambridge. X8010 X5010 -> for prints Dear Constant, CRANKSHAFTS. I attach a table which gives the dimensions and results of tests on practically all the shafts that we have had experience with. The crankshaft named 'India(Production 20 HP. with 4-speed box and Front Wheel Brakes) 111' is a stiffer version of the standard 20 HP., with 1/8" on the journals, and .550" on the width of the webs. The figure given in this table for the web width is the one I use in Carter's formula, i.e. the mean value if it is varying. When a web is described as 'oval', it has an elliptical section transverse to the crankshaft axis. When described as 'bevelled' it has a flat on the outer edge at the crank pin end only. I also send you a table shewing the results of our simple method of estimating torsional periods in car engines. The formula used is: Critical r.p.m. = 60/n x 1/2π x √Cs(1/Tc + 1/Tf {T. Fisher} ) n = No. of vibrations per rev. which is 3 in a 6-cyl. 4 in a straight-8. 6 in a twin-6. Cs = stiffness of whole shaft (including nose etc.) in lbs.ft/radian as measured. Tc = effective inertia of crankshaft system in 'slugs-ft²' Tf {T. Fisher} = Flywheel inertia. contd :- | ||
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).