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).
Chassis wobble testing, exploring the effects of engine mounting and frame stiffness.
| Identifier | WestWitteringFiles\T\March1929-December1929\ Scan024 | |
| Date | 12th March 1929 guessed | |
| (2) PERIODIC NATURE OF WOBBLE. A chassis with the original diabolo rubber mounting was exhibited on a bump test with alternate bumps on the drums, and it was clearly shewn that the radiator wobble came on at a critical speed. PROGRESS OF RESULTS. After the shoe scheme with .225 rubbers was found to violently wobble on the test road it was rebuilt with new front feet having maximum area possible and thin rubber linings fore and aft to obtain the maximum possible stiffness. Another chassis was also prepared with the original SS.{S. Smith} mounting having flexible diabolo rubbers so that we had two chassis each with the cross in the frame, but one with the most rigid engine mounting and the other the most flexible. Both of these cars experienced violent and equally unpleasant radiator wobbles on the test road, the former of quick periodicity at the higher road speeds, and the latter of slower periodicity and greater amplitude at somewhat lower road speeds - about 5 to 10 MPH. less. In these two examples we had the engine acting as a rigid cross and also as a flexible cross with a small amount of damping in each case. (1) The first conclusion formed from this test was that it is not possible to alter the flexibility of the frame either up or down enough merely by altering the engine mounting to escape from the wave band in which periodic radiator wobble occurs. (2) The second conclusion formed was that to proceed in any case in the direction of still further increased stiffness was out of the question as the engine would have to be used to the maximum extent as a rigid cross, and the booming and roughness produced thereby would be quite unacceptable. The ideal in this direction would be an infinitely rigid frame with an engine mounted on soft rubbers, unfortunately beyond practical achievement at the moment. (3) The third conclusion was that logically there were two avenues of development - (a) To utilise the engine to the maximum extent to damp the oscillations so that the period would never come up (b) To proceed in the direction of making the frame sufficiently flexible to escape from the lower edge of the periodic wave band. This implied removing the X. member from the frame which for want of a better word was known as "degutting the frame". | ||