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).
Engine cooling performance in relation to gear selection and fan speed.
| Identifier | ExFiles\Box 24\4\ Scan252 | |
| Date | 18th September 1924 | |
| R.R. 493A (40 H) (SL 42 12-7-23). J.H., D.{John DeLooze - Company Secretary} -2- EXPERIMENTAL REPORT. Expl. No. REF: HS{Lord Ernest Hives - Chair}/Rm{William Robotham - Chief Engineer}/LG18.9.24. Second gear creates an apparent paradox, however, for the finishing temperature in this case rises above that on the third speed. This illustrates an important point. 25 m.p.h. was the lowest average speed at which the hill could be climbed on top so this speed was selected for the test. On second gear at this speed, however, the fan r.p.m. should be 2,320, a speed which we know from tests it seldom attains. The belt therefore slipped and the means upon which we were relying for our increased cooling having failed - the radiator temperature rose. This demonstrates that if the engine speed climbing a hill on an indirect gear exceeds 1700 r.p.m., no additional cooling will be gained, but the position will rather become worse, even with the fan belt dead-tight. Graph B. illustrates that provided the critical engine speed is not passed, the lower the gear, the less the possibility for boiling. In this case, at 20 m.p.h. on 2nd. gear, the fan was turning over at 1860 r.p.m. which we know is feasible, and in consequence, a distinct gain instead of loss is manifested over 3rd. speed. In the last series of tests illustrated in Graph C. the fan speed was kept constant, the road speed being varied. Under these conditions the capacity of the radiator to deal with heat units is definitely reduced on the lower gears, for while the fan speed is kept constant, the air velocity through the radiator is diminished due to the reduced road speed. centd :- | ||