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 speed ratios, belt drive optimization, and proposals for road experiments.
| Identifier | ExFiles\Box 66a\4\ scan0038 | |
| Date | 20th March 1925 | |
| EFC3/T20.3.25. -5- Contd. is found to be .85 only for fan 18, as compared with (1). Seeing that the 40/50 engine fan ratio is 1.20, this puts the lower limit of fan speed for the 18 fan as nearly down to engine speed. The pulley on the fan would be imagined increased in size; a great reduction in power required to drive would be effected; the cooling effect at moderate speeds would remain practically the same; a definite advantage in cooling should accrue at high speeds; and a much more infrequent adjustment of belt and a very much greater length of belt life might be expected. Probably the higher limit would be considered to be driving the fan with the same engine fan speed ratio as at present, in which case the power would be less at all speeds and especially so at higher speeds, and the wear and frequenty of adjustment of belt less than at present, in spite of the thrust being considerably greater at moderate speeds and still more considerably greater at high speeds, so much so in fact that it might be worth while selecting an intermediate belt drive ratio of, say, 1.1 to 1. Might we suggest that comparative experiments on these fans be made on the road with these three (or at any rate the two higher) alternative ratios ? For the time being, fan No. 15, which we have handed to the D.O. so that they can proceed with production instructions, is no doubt quite a reasonable proposition, and being a rather higher speed fan than 18 | ||