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).
Reduced performance of an autovac fuel system at an altitude of 15,000 feet.
| Identifier | ExFiles\Box 40\4\ Scan059 | |
| Date | 3rd May 1923 | |
| To Hs.{Lord Ernest Hives - Chair} from EFC. X. 3579. EFC3/T3.5.23. X. 3579 - RE AUTOVAC. AT 15,000 FEET. Assuming a low altitude air temperature of 15°C and pressure of 100%, then at an altitude of 15,000 feet the air density is reduced to 63%, the air pressure to 56.5%, the engine I.H.P. to 59% and the engine B.H.P. approximately to 55%. It can be shown that the reduction of pressure at a throat and beyond, (at any rate for small reductions such as those with which we are dealing), due to stream line motion from the ambient air into and through the throat, and to frictional resistances in intake tubes expressed as a percentage of the pressure of the ambient air, is independent of variations of the ambient pressure, so that the actual reduction for lifting the petrol in an autovac system is proportional to the outside pressure. Hence at 15,000 feet the autovac would only be capable of lifting the petrol to 56.5% of the height to which it could lift it at the low altitude. At the high altitude the weight of air and petrol taken in by the engine ( to which the I.H.P. is assumed to be proportional), it being supposed that the proportional mass of petrol is adjusted by mixture control to give the same mixture strength, will be only 59%, so that for the same throat opening a full autovac supply would last correspondingly longer, and the ratio of potential supply to the demand would Contd. | ||