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).
The benefits of a two-speed supercharger and the operation of an automatic variable pitch propellor.
| Identifier | ExFiles\Box 173\3\ img002 | |
| Date | 22th March 1934 | |
| -2- The claim of the two-speed supercharger is that, by using a low speed drive up to 5000 ft. about 50 more H.P. are available than if a high speed drive were used and the blower throttled to give the same maximum permissible boost as with the low speed blower. It has been demanded by the high speed commercial transport machines to enable them to get above storms, icing conditions and contrary winds without sacrificing take-off. Also they can get a higher cruising speed for the same B.H.P. and petrol consumption at 15,000 ft. with the V.P. propellor than they can at 5000 ft. The two-speed supercharger is used in conjunction with boost control. VARIABLE PITCH PROPELLOR. This is entirely automatic. The whole propellor hub is free to float one or two inches endwise except for the restraint imposed by a number of helical springs which keep it in the rearmost position when at rest; i.e., no thrust. This is the position of minimum pitch. As the thrust increases the hub moves bodily forward against the springs so altering the blade angle by means of a toggle action. We had a flight behind this propellor on a 250 HP. engine. It allowed maximum revolutions for take-off and appeared to work satisfactorily in flight. Its big advantage is that it is a complete unit that can be fitted in the place of any propellor and requires no manual control at all. It is alleged to out-perform the two position Hamilton. It has a big advantage over the "Smith" propellor in that it will take the standard duralumin blade. It does not appear that it will be any lighter than the "Hamilton". It can be fitted with a device to limit the maximum engine revolutions in a dive. This would appear to be a very considerable asset. It is possible that it will be demonstrated in Europe later on in the year. | ||