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).
Proposal for a variable pitch fan pulley system to address excessive fan noise.
| Identifier | ExFiles\Box 135\4\ scan0030 | |
| Date | 6th June 1939 | |
| 1135 10HH To By/Ald.{F. Allwood - Experimental Design} Rm{William Robotham - Chief Engineer}/Ed.{J. L. Edwards}1/JH.6.6.39. Variable pitch fan pulleys. In view of the excessive fan noise experienced on W.80, we feel that a scheme for a variable pitch fan pulley might be helpful. We should be glad, therefore, if you would look into a scheme on the following lines, and let us know whether this could be incorporated on B.80 engines. (a) Fan pulley. This should be made up from two halves, screwed together by a multistart thread to give an axial movement of 3/8" for say 90° displacement of one flange. The rotating half of the pulley would be bolted to the fan, and the air force on the blades would tend to screw the pulley together as the fan speed rose. This would have the effect of increasing the pitch circle diameter, and control could be effected by a clock spring inside. The return to the original diameter as the speed was reduced would be effected by a combination of the belt tension and the spring. (b) Crankshaft pulley. This pulley will probably present the greatest difficulty as it is limited by the proximity of the crankshaft damper, and it may not be found possible to employ the whole 3/8" displacement suggested. The scheme to be employed on the pulley is simply to spline the two pulley halves together, holding them together by springs. It is anticipated that the air force on the fan will be sufficient to expand this pulley by forcing the belt down the V.{VIENNA} Thus decreasing the pitch circle diameter. The return would be effected by the combined effects of the springs and the centrifugal force of the belt. The above is given merely as a start for some scheme, and there is little doubt that improvements in detail will become apparent as the design progresses. On completion Messrs. Ferodo have promised to try the job out on their rig. Rm{William Robotham - Chief Engineer}/Ed.{J. L. Edwards} | ||