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).
The influence of a stiffer crankshaft on engine vibration and critical speed.
| Identifier | WestWitteringFiles\P\2July1926-September1926\ Scan141 | |
| Date | 4th September 1926 guessed | |
| contd :- -14- INFLUENCE OF STIFFER CRANKSHAFT. We found that the stiffer crankshaft raised the critical speed from 3350 r.p.m. to 3500 - 3600 r.p.m. The vibration at this speed was probably not quite so internal as with the std. shaft although it was difficult to estimate, both being very severe. Another vibration was also evident at approx. half the critical speed although with the slipper damper it was difficult to detect. We did not use the indicating apparatus with this crankshaft. The torsional rigidity of this shaft worked out at 19100 lbs.ft. whereas the standard shaft had a value of 16220 lbs.ft. thereby shewing an increase of nearly 12%. The raising of the critical speed is what would be expected from the increase of stiffness because the frequency varies inversely as the square root of the stiffness. This crankshaft behaved in just the same way as the standard when driven by a belt and the cylinder head removed. We continued the belt drive tests with pistons lightened by 9 ozs. each and thought the vibrations at the critical speed seemed less severe. We intend to measure the effect of piston weight by means of the indicator. GENERAL CONSIDERATIONS. From the tests we have carried out we have evidence to shew that the inertia torque is the disturbing force responsible for the high speed vibration. contd :- | ||