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).
Tests conducted to investigate the cause of a 'boom' or vibration in the Phantom II model.
| Identifier | ExFiles\Box 13\7\ 07-page096 | |
| Date | 11th March 1931 | |
| To R.{Sir Henry Royce} From Hs.{Lord Ernest Hives - Chair} c. to SS.{S. Smith} Mor. c. to E.{Mr Elliott - Chief Engineer} Da.{Bernard Day - Chassis Design} c. to By.{R.W. Bailey - Chief Engineer} P.2. BOOMS AND VIBRATIONS. We consider that we have done enough tests now to be able to say definitely that on Phantom II the flywheel is not the cause of the boom which is complained of by customers. We have made the following tests to prove this point :- (1) We have run with the flywheel and clutch removed except for the back plate. This made no difference to the speed or intensity of the boom. (2) We ran with aluminium flywheel and clutch parts. This made no difference to the speed or intensity of the boom. (3) We ran with a tail bearing to control the flywheel. This made no difference to the speed or intensity of the boom. We have still to run a test with the stiffer flange on the crankshaft and the stiffer flywheel, but we think we have done sufficient to be able to say definitely that it is not the flywheel. It will be realised that the boom which is complained of is there either full load, light load, or with the throttle shut. It can easily be picked out by running the engine up light with the car stationary. We made one test in order to prove whether it was the unit construction of the gearbox which made Phantom II differ from Phantom I. With the engine run light on one car we could pick out a very definite boom at 2100 A.P.M. We confirmed by road tests that this was the boom complained of. We then removed the gearbox entirely. This made not the slightest alteration to the speed or intensity of the boom. On one car we found that disconnecting the steering from the dashboard we reduced the boom considerably and we could bring it on and off by either pressing the steering tight against the dash or holding it away. However, on the next car we tried this on it made no difference. In the case of another car we improved it definitely by slacking off the dashboard. This is still being explored. We have also towed the car on the road with pistons and rods. Under this condition the booms were bad. We then removed the pistons and rods and towed the car. The booms were then reduced by 85%. The boom that was left, however, was at the same speed. We added balance weights | ||