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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.

FUEL injection offers two main advantages over the carburetor: Low volatile fuels (safety fuel), which reduce the fire hazard, can be used; and the combustion chamber can be scavenged without the loss of fuel by the use of large valve overlap. Other advantages are improved starting, acceleration, maneuverability, and distribution of fuel, as well as freedom from icing. The National Advisory Committee for Aeronautics has investigated the factors influencing the injection of fuel into the engine cylinder. This investigation included the time of start of injection, the length of the injection period, the location of the fuel-injection valve in the cylinder, the rate of fuel injection, the type of fuel spray, and the maximum injection pressure. Tests were conducted on cylinders with two and four valves having pent-roof, disc, and spherical combustion-chamber forms.