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 fan efficiency, power consumption, and fan belt limitations at high speeds.
| Identifier | ExFiles\Box 24\4\ Scan237 | |
| Date | 21th September 1924 | |
| R.R. 403A (40 H) (SL 42 12-7-23). J.H., D.{John DeLooze - Company Secretary} -2- EXPERIMENTAL REPORT. Expl. No. 3456 REF: Hml/L/211.9.24 dependent on our fan to maintain our radiator efficiency. In a test on a certain hill comparing the R-H with the Hispano, the difference with and without the fan on the Hispano made only 3°C - the difference with and without the fan on the R-R made 17°C. If therefore the fan is not working at its maximum efficiency, we are at once very badly off as regards keeping the water temperature down. We have recently found by experiment that it takes approximately 3.15 H.P. to drive the fan at 2,000 r.p.m. The cars running in France frequently maintain speeds of 65 to 70 m.p.h. With the 15-tooth axle, 68 m.p.h. is equivalent to an engine speed of 2360 r.p.m., at this engine speed the fan should be running at 2840 r.p.m. The H.P. required to drive it thus would be 8.5 H.P., it being proportional to rather less than the cube of the speed. The horse powers taken for the fan were taken in free air, it may be less in the bonnet but owing to the fact that we know that there is a pressure created under the bonnet by the fan, it should be approximately the figures we give. Tests taken on the dynamometer and on the road show that the present fan belt will give reasonable satisfaction as long as the engine is not run about 1500 to 1750 r.p.m. Once this speed is exceeded, the slip and stretch of the belt is excessive. Apart from the load of driving the fan, the centrifugal tension causes the fan belt to have less embrace on the pulleys. It is conceivable that even though the contd :- | ||