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).
Experimental results for reducing engine booming in Phantom II & 25 HP cars, focusing on engine and mounting modifications.
| Identifier | Morton\M19\ img044 | |
| Date | 21th March 1931 | |
| To R.{Sir Henry Royce} From Hs{Lord Ernest Hives - Chair}/Rm.{William Robotham - Chief Engineer} c. to SG.{Arthur F. Sidgreaves - MD} wor.{Arthur Wormald - General Works Manager} c. to K.{Mr Kilner} Da.{Bernard Day - Chassis Design} c. to Ey. BOOMING CARS P.II & 25 HP. Before answering the questions in R.2/M.13.3.31. we should like to tabulate some of the results we have so far obtained experimentally. Chassis. Engine. We can say quite definitely that so far we have been unable to reduce the booming at its source (which everyone is agreed is in the power unit) to any appreciable extent. By this we mean that if we were handed a booming car we know nothing we could do to the internal parts of the power unit which would enable us to alter the boom at all. The experiments we have done cover various tests with and without the slipper wheel, the flywheel, with ball bearings, with aluminium backs to the flywheel, with stiffer crankshafts and balance weights. They also cover the elimination of the exhaust system by towing the car with the push rods removed. They do not include tests with the stiffer crankshaft hub and stiffer flywheel diaphragm. These tests have been carried out both on the 40/50 and 25 HP. Engine Mounting. Diamond Mounting. What is now known as the "Diamond" engine mounting is the nearest approach to a complete cure that we know of, irrespective of the type of body. Until, however, it has been tried on every type of body fitted to a R.R. car it is impossible to be dogmatic as to its attributes. 25 HP. The diamond mounting was fitted to 18.G.IV, the last 10,000 miles test car. This body boomed badly, and, as we shall show later is the type of body we believe to be worst for booming. When the best use had been made of the diamond engine mounting i.e. the rubbers taking the torque had been made sufficiently flexible, booms were practically non-existent. They can be brought back at any time by - (1) Putting hard rubbers in the engine feet. (2) Tightening up the torque reaction dampers solid. This indicates that the boom gets to the frame by a torsional movement of the engine. The car was passed for steering and jellying, being | ||