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).
Analysis of crankshaft and crankcase vibrations and proposed experiments.
| Identifier | ExFiles\Box 137\4\ scan0027 | |
| Date | 22th July 1929 | |
| (4) (2) Local vibrations of the shaft in the case, due to the various cranks distorting centrifugally relative to one another, and dragging the bearings with them. (3) "Whirling" of the shaft as a whole, inspite of the bearings. (4) Vibrations of parts of the crankcase. (5) Torsional crankshaft vibrations. Considering these singly : (1) We intended to verify this by putting the shaft out-of-balance, but we are not very satisfied with these experiments. We took the shaft out of the case after all the above experiments were finished, and checked it for static balance with and without the flywheel. In both cases the balance was excellent, and it would stop in any position on the knife edges. This is better than the drawing limits. We propose doing some experiments to find out how much out-of-balance will pass undetectable. (2) We shall shortly try the counterweighted shaft and this should reduce the centrifugal loading on the main bearings and the hogging and sagging moments on the crankcase. We are quite satisfied that the crankcase is distorting, as vibrations can be plainly felt at the outside of the case. We find that the general thickness of the "SS{S. Smith}" crankcase is only .225" as against .250" for the Phantom - 10% less. We consider this will more than make up for the possibly stiffer main-bearing construction adopted on "SS{S. Smith}". We propose to try a crankcase in cast iron, or alternatively a stiffer one in aluminium, obtained by rubbing the cores away. (3) "Whirling" is another solution that presupposes rather flimsy bearings. We should expect to be able to accentuate certain of the periods by only having certain bearings in and allowing certain modes of vibration. We may also get a clue from the result of the test with counterweights. (4) We do not think this probable, but the inside webs may be drumming, or something similar. (5) We think this is already ruled out by our test with slipper wheels; also, we do not see where the disturbing impulses could come from. Contd. | ||