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 impeller design, materials, and performance in American aircraft engines.
| Identifier | WestWitteringFiles\V\December1930-February1931\ Scan068 | |
| Date | 23th December 1930 guessed | |
| - 2 - (8) The material of the vanes is not only stressed radically but tangentially as well making for unusual strength. The "composite design" (patent applied for) in which the centrifugal load developed by the aluminium discharge portion of the impeller is partly carried by the interlocking steel hub, can be operated at a speed considerably higher than the bursting speed of the present design and is suitable for creating 20 in.HG and more pressure at a corresponding R.P.M. (9) The impeller can be manufactured cheaply because it can be generated fully automatically on a machine tool. There is no subsequent bending or warping of the vanes, not even a hand trimming of the inlet edges. ----------------- The present Supercharger Impeller design used in American Aircraft Engines. GENERAL. When radial engines were first equipped with centrifugal impellers it was more or less the latter's exclusive function to improve the mixture and its distribution. Today however, the impeller has the function of a real supercharger creating an appreciable manifold pressure which results in a considerably increased M.E.P. It is the belief of many authorities that much higher supercharger pressures than those already used will soon be common. Even with the manifold pressure used today and to a larger extent yet with still higher supercharging pressures, it is most important to obtain as high an adiabatic efficiency of compression in the supercharger as possible. Poor supercharger efficiency means not only that a considerable part of the engine H.P. output is required to drive the impeller but also a serious decrease in M.E.P. offsetting to a large extent the gain in M.E.P. brought about by the higher manifold pressure. To illustrate these conditions I have plotted the attached curves LS-131 & LS-132. The curves are self explanatory. THE HYDRAULIC DESIGN OF THE PRESENT IMPELLER. The impeller at present used in American aircraft engines is of exactly the same type and design as the one used for large commercial blower installations. The only difference between the two being that the former is much smaller in size than the latter and operates at a much higher speed. Specialised work contd. | ||