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).
Investigation into the cause and potential cures for a resonance 'boom' vibration in Phantom II cars.
| Identifier | ExFiles\Box 182\M19\ img153 | |
| Date | 18th April 1931 | |
| - 2 - sets is 6600/minute. This frequency therefore appears to be a resonance frequency of Phantom II cars. while running at this speed on tran sets we held a microphone against various parts of the car connecting it to headphones. we found the vibration is transmitted to the frame by the shock absorbers, particularly the rear ones, since when the microphone is held against them a note of frequency 6600/min. is heard, but not when the micro- phone is held against the spring shackles. It was also found that any part of the side members, the middle tubular cross member and the dashboard were all vibrating at 6600/minute. In test rigs the vibration at 32 m.p.h. is very apparent but is accompanied by very little boom. Again the 60 m.p.h. engine boom is almost undetectable in test rigs even in the gears. On complete cars the boom is always worse the lower the gear in use. we have noticed that P.II cars boom at 12 mph. when equipped with Dunlop studded tyres. The frequency of inter- ruption of the surface of the tyre at 12 m.p.h. is 6600/minute. By elimination it was found that the rear tyres only cause this boom. In reply to the point raised in R1/M12.4.31. that the Hardy universal has an effect on the boom, we have been runn- ing 25-TX with this replaced by a steel disc, a whitemetal bearing being fitted between the flywheel cover and the shaft of the clutch driven member. Under these conditions no differ- ence in the boom at 60 m.p.h. was observable. As to curing the boom, we have found that removal of the rear engine feet always lessens its magnitude but does not alter the speed; that loosening the scuttle bolts affects the amplitude of the boom (but not always to decrease it); that isolating the steering column from the dashboard generally lessens the boom particularly if the rear engine feet are absent. Hs{Lord Ernest Hives - Chair}/Grylls. | ||