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).
Technical analysis comparing fan speed ratios, cooling effects, and power requirements between a standard and an experimental fan.
| Identifier | ExFiles\Box 75\3\ scan0044 | |
| Date | 9th February 1925 guessed | |
| EFC1/T9.2.25. -5- Contd. It would, however, appear that we do not want to lower the fan speed ratio to such an extent that at moder- ate speeds we get less thrust (assumed to represent the cooling effect) for a given road speed than at present. The average ratio between corresponding speeds for similar thrusts on these two fans (present standard and best experimental) we find to be .965, i.e. we can presumably produce the same cooling effect by driving this new fan with only .965 of the present ratio, this corresponding to a new fan driving ratio of 1.27. This would make the 50 m.p.h. ideal fan speed .965 x 3200 = 3080 r.p.m., which is not far removed from the speed at which, with this fan, the belt begins to slip. Then considerable saving of the belt might accrue. If we do, however, keep the fan pulley and there- fore the ratio as at present standard, we should get at the same time :- (1) Improved cooling effect at all engine speeds - particularly at the higher speeds. and (2) Some degrease as compared with standard conditions (though smaller than in the 1.27 ratio case) in the wear of belt. because in spite of the increased thrust produced by the new fan, the power required is still considerably less for the same speed than that for the standard fan. The curves on sheet I, as given, are more suitable for a comparison of fans run at corresponding speeds (same thrusts). | ||