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).
Phantom III flywheel's inertia and stalling issues, proposing a design change.
| Identifier | ExFiles\Box 93\3\ scan0388 | |
| Date | 28th September 1937 | |
| To Da.{Bernard Day - Chassis Design} from Rm{William Robotham - Chief Engineer}/NRC.{N. R. Chandler} c. By.{R.W. Bailey - Chief Engineer} 312 Rm{William Robotham - Chief Engineer}/NRC.{N. R. Chandler}1/MH.{M. Huckerby}28.9.37. PHANTOM III FLYWHEEL. The total energy in the P.III Flywheel complete, is very much less than that in the 25/30 in relation to the weight of the car and the gear ratio, and we think this accounts, to some extent, for the greater tendency of the P.III engine to stall when starting the car from rest at low revs, If we consider the flywheels of both cars to be spinning at 2000 R.P.M. and both brought to rest in one second, we estimate that the energy so given out would produce an acceleration of 3.4 ft/sec.² in the P.III, and 4.36 ft/sec.² in the 25/30, taking cars of average weight, and both started on 2nd. speed. (These figures are relative rather than actual). The inertia of the P.III flywheel complete is 2200lbs/ins² and 2005 forthe 20/25, and while it appears quite logical for the 12 cyl. to have a lighter flywheel per CC than the 6 so far as a smooth turning effort is concerned, this does not apply in assisting a start from rest at low R.P.M. since both engines would fall off in power on loss of revs during clutch engagement. We have made an experimental flywheel ring for the standard 6 finger clutch, which increases the total inertia from 2200 to 3150 lb/ins², or approximatley 43%, but in the case of the new 4 finger Clutch N.S.4998, there is not room in the casing to fit such a ring. Will you please let us have a design for a new clutch cover to provide such extra inertia as can be accommodated in the existing clutch casing? An inertia increase of about 600 to 700 lb/ins² would bring the P.III in line with the 25/30 as regards energy for starting from rest. We have had some experience with increased flywheel inertia with the spring flywheel tried on 39-EX, and results appeared beneficial both as regards stalling and general smoothness. Rm{William Robotham - Chief Engineer}/NRC.{N. R. Chandler} | ||