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).
Fan power speed curves and issues with driving belt slippage at high speeds.
| Identifier | ExFiles\Box 75\3\ scan0132 | |
| Date | 18th September 1934 | |
| Contd. -2- EFCl/T18.9.34. and the result for ordinary loadings of the motor is reasonably accurate). In determining the fan power speed curves, a copy of which is attached, motor speeds rising by increments of 100 r.p.m. were taken in succession and the corresponding fan speed observed. The driving belt was a Whittle belt running horizontally, the effective diameter of the motor wheel being roughly 12.20", and that of the fan pulley (standard) roughly 5.10". Except at the highest speeds, i.e. above 900 r.p.m. for the motor or above about 2100 r.p.m. of the fan, the drive ratio can, by reasonable attention to the tautness of the driving belt, be kept fairly constant at slightly under 2.40. Above these speeds, however, whether in the case of the six-bladed or three-bladed fan, it was difficult to prevent the belt slipping with any initial degree of tautness, the centrifugal tension of the belt at this speed apparently being such as to cause it to slip in either case, in spite of the fact that the power required in the three-bladed case was definitely less. The speed ratio would fall to the neighbourhood of 2.10. It was for this reason practically impossible to drive the fan at a higher speed than 2110 r.p.m. in the six-blade case, and 2500 r.p.m. in the three-blade case, though motor speeds of 1000 r.p.m. in the former case and 1200 in the latter, could be attained. Contd. | ||