Superchargers and Supercharging - 19th National Aeronautical Meeting Paper 310041
CLASSIFYING the superchargers used for present aircraft and automobile service as Roots, centrifugal and vane types, the author states that the vane type for this service is a more recent development than the other two and describes each type. He states further that the ideal type should satisfy many requirements closely related with those of a well-designed engine-such as being light, compact and reliable-and that the practice of supercharging has increased considerably during the last few years.
The comparative performance of superchargers is treated at some length, and engine-performance data are presented. The power developed by an engine equipped with geared-centrifugal, turbo-centrifugal and Roots superchargers is illustrated by curves, control methods are compared, net engine-power is computed, and flight-test data on comparative performance are analyzed.
After discussing the effect of supercharger capacity on performance, the author states that, in the selection of a supercharger for use on an airplane designed to meet definite performance requirements, the question arises whether it is advisable to choose a supercharger of sufficient capacity to maintain sea-level pressure to the maximum useful altitude or to choose one of smaller capacity that requires less power. Selection of the best supercharger-capacity depends largely upon the way in which the type of supercharger in question affects the engine power, the percentage of engine power required by the supercharger and the kind of service for which the supercharged engine will be used.
Following a statement of the influence that supercharger capacity has on performance and an analysis of the effect of “boosting,” the author concludes that the supercharging of engines of low compression-ratio is impracticable and that it is desirable that an engine have a compression ratio of at least 4.5:1.