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).
Additional notes comparing the performance and efficiency of six-bladed and three-bladed 40/50 fans.
| Identifier | ExFiles\Box 75\3\ scan0147 | |
| Date | 20th November 1924 | |
| 20.11.24. 46- Contd. ADDITIONAL NOTES. In the second paragraph on p.4 of the report, it was stated that the result of the comparison (of the six-bladed and three-bladed 40/50 fan) showed that the six-bladed fan was decidedly more efficient at all thrusts (and consequently at all corresponding speeds) than the three-bladed fan. Taking as we do the thrust of the fan as the basic quantity, the two fans are then only properly comparable on their performance on the chassis when their driving pulleys are proportioned so as to drive them at what we call the corresponding speeds, i.e. at fan speeds which will produce the same thrusts for the same engine speed in each case. Knowing the speeds required to produce various thrusts on these two fans, the ratio of the three-blader speed and six-blader speed can be taken, and this ratio is found to be very decently consistent at an average value of 1.303, implying that the three-blader fan should have a pulley of smaller effective diameter than that of the larger one, in the ratio of 1 to 1.3. Then similar thrusts will be produced at similar engine speeds, but the three-blader fan will take more power to drive and be consequently less efficient. Contd. | ||