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 from Mechanics Universal Joint Company discussing the critical speeds of drive shaft tubes and providing a formula.
| Identifier | ExFiles\Box 181\M9\ img075 | |
| Date | 19th October 1931 | |
| COPY. MECHANICS UNIVERSAL JOINT COMPANY. Division of Borg-Warner Corporation ROCKFORD, ILLINOIS October 19, 1931. C.A.S. Engineering Company, 3-132-140 General Motors Bldg. Detroit, Michigan. Attention Mr. R.{Sir Henry Royce} Rolph. My dear Bud: We are in receipt of your letter of October 16 regarding discussion that you had with Mr. Olley of the Cadillac Company in regard to critical speeds of tubes. We note that Rolls Royce are using a 2-1/4" tube with 1/8" wall for drive shaft assembly that is 59" long between centers of joints. This is a rather small diameter tube for so long a shaft and the fact that they could operate it at as high a speed as 4100 rpm. proves that their work is exceptionally fine. For a shaft of this length to operate at 4100 we would probably recommend a 3" x 14 Ga. tube or if it would be necessary to use a minimum tube diameter, a 2-3/4" x 14 Ga. would no doubt work out. Our formula is as follows. RPM = (4705000 / Span²) * √(D² + d²) "D" is the O.D. of the tube and "d" is the I.D. of the tube. The RPM as obtained from this formula should be reduced 20 or 30% as a factor of safety. The longer the shaft and the higher the speed, the greater should be the reduction. We do not understand the formula that you say Mr. Olley thought was used by the Rolls Royce Company. Yours very truly, MECHANICS UNIVERSAL JOINT COMPANY CES/IS C.E.Swenson Chief Engineer. | ||