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).
Analysis and specifications for an 18-inch single disc clutch, including spring calculations and torque data.
| Identifier | ExFiles\Box 130\3\ scan0140 | |
| Date | 2nd December 1940 | |
| Ra/GB.6/GT.2.12.40. - 4 - On the 18" single disc clutch there are 16 springs, so that each must carry a load of 299 lbs. The Borg & Beck drawing shows a spring length of 2.57" when the clutch is released. The spring length when the spring is fully worn and engaged is 2.96". The pocket diameter is 1.375". It is not possible to get a spring in this space without it being seriously overstressed. It is possible to increase the pocket length by 1". The spring lengths would then be as follows:- Clutch release 3.75" " fully worn 3.96" The pressure plate springs will have the following particulars:- Mean coil dia. = 1.10" Wire dia. = .232" dia. (No.4 S.W.G.) Number of working coils. = 13.4 Stress (uncorrected at 299 lb. load). = 67,100 Rate. = 244 lb./inch. Load in clutch release position. = 299 + .19 x 244 = 394 lb. Uncorrected stress at 394 lb. load. = 88,500 Corrected stress. = 116,650 p.s.i. Ra/GTS. has shown that a torque of 1192 lb.ft. is obtainable from a Kestrel engine with a compression ratio of 6 to 1. If the m.e.p. on the Merlin engine is only 5% lower as a result of using a 5.5 to 1 compression ratio, the torque from this engine would be 1437 lb.ft. This would make the use of an 18" twin disc clutch highly desirable to ease the pressure spring situation, unless we can rely on a coefficient of friction of at least .25. Messrs. Borg & Beck have evolved a dumbell construction for the clutch disc hub, which is in effect a universal joint to look after mis-alignment between engine and gearbox. Details of this are shown in the drawings which have been passed to Rv. Ra/GB. | ||