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).
Supercharger performance, comparing different engine models, gear ratios, and rotor diameters.
| Identifier | WestWitteringFiles\V\December1930-February1931\ Scan026 | |
| Date | 15th December 1930 guessed | |
| -3- Reviewing these figures we are of the opinion that the best full supercharger "H" performance is obtained with the 8.8/1 gear ratio and 10.25" diameter rotor (Col.1.) the corresponding M.S. engine has a better performance than the existing "H" MS. The corresponding "H" MS. being the one which requires a change of supercharger gears only - all existing rotors will be serviceable as present standard is 10.25" diameter. We should, however, like to point out that in order to change supercharger gears on our engines it is necessary to remove the wheelcase for lining up purposes, if this could be avoided on later engines it would considerably improve the interchangeability from full to moderate superchargers. Fuel consumptions on the modified M.S. "H" are approximately the same as those for the standard M.S. "H", the full supercharged "H" consumptions compare favourably with the full supercharged "F" engine. SUMMARY. The first attempt at fully supercharging the "H" engine gave us a rated altitude of 12,000 ft. - we now get 10,000 ft. Detonation at rated altitude was Z" 20' we do not get any with present engine. Detonation at 'take off' always being approximately Z" 20 ft. our first engine gave 500 BHP. our present engine 675. Our first engine detonated at Z" 30 ft. at rated boost of plus .5" Hg. our present engine does not detonate at plus .60" Hg. rated boost. This comparison shows briefly the reduction in detonation and increase in performance obtained by the development work on the full supercharged "H" engine. It will be noticed that in the case of the 10.25" rotor and 8.8/1 gears and the 9.5" rotor and 9.5/1 gears that although rotor tip speeds are the same in both cases the rated altitude with the 10.25" rotor is 1,000 ft higher than with the 9.5" rotor. This is due to the full rotor giving more boost at the same tip speed than the reduced rotor. We suggest the reason for this is that with the smaller diameter rotor a certain amount of air slip occurs between the rotor tip and diffuser ring. It is suggested that we type test a full supercharged "H" engine with the following modifications to the existing moderate supercharged "H" engine. contd. | ||