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).
Test bed and torsion test results comparing a four-bearing and a seven-bearing Bentley crankshaft.
| Identifier | ExFiles\Box 85\5\ scan0084 | |
| Date | 19th January 1935 | |
| To Sg.{Arthur F. Sidgreaves - MD} & Wor.{Arthur Wormald - General Works Manager} c. to E.{Mr Elliott - Chief Engineer} c. to By.{R.W. Bailey - Chief Engineer} c. to By.{R.W. Bailey - Chief Engineer} Four Bearing Crankshaft - Bentley. Test bed running of the engine fitted with a narrow pin 4 bearing crankshaft to EX.14348 showed the half period to be at 2700 r.p.m. This crankshaft has the same amount of balance as the standard 7 bearing shaft's centre and end bearings on each of the three two-throw units. The balance weights are slightly extravagant in inertia, as those next to the two centre bearings are not split up Chrysler fashion. The critical speed of the engine is disappointingly low, being very little higher than the narrow pin 7 bearing crankshaft. Torsion tests were carried out on this crankshaft and a production one, the results obtained being - 4 Bearing Stiffeners (S) 50,000 lbs.ft/radius Inertia of crankshaft 224 lbs.in.² Of big ends + pistons 61.1 Effective inertia I - (285.1 / 3) + 10 = 103.4 sqrt(S/I) = 21.8 7 Bearing 42,500 lbs.ft/radius. 187 lbs.in.² 69.3 (256.3 / 3) + 10 = 95.4 sqrt(S/I) = 21.1 Knowing the critical speed of the standard engine to be 5000 r.p.m. we should expect that for the 4 bearing engine to be (5000 * 21.8 / 21.1) = 5175. The fact that we were running with a disc flywheel would further raise the period about 100 to 150 r.p.m. judging by previous results. | ||