Turbo-Supercharger Development; Evolution to First Operational Use

     The turbo-supercharger is a small relatively simple and unimposing device used in conjunction with piston-type aircraft engines to boost their power output and/or maintain their power output to high altitudes. Weighing only a couple of hundred pounds, it is essentially nothing more than a pump supplying air under pressure to the engine induction
system.
     During the war years almost everyone was familiar with the B-17, B-24, B-29, P-47, P-38 and P-51. These were the mainstay of the USAAF war effort, yet all except one were completely dependent upon the turbo-supercharger for their superior high altitude performance and would almost certainly have been dismal failures without this equipment. Alone of this elite group, the P-51 had no turbo, depending on the superb internally supercharged Rolls Royce/Packard Merlin for its outstanding speed and high altitude
abilities.
     This article proposes to tell the early development history of the turbine-driven supercharger; it is not meant to be a technical discussion of the turbo. However, for the benefit of those with only a vague idea of the subject and as a background for the history to follow, it is desirable to briefly discuss the types and operation of aircraft engine
superchargers.
     A piston engine, much like the human body, requires large amounts of air to operate. An unsupercharged engine, such as the familiar auto engine, draws air into its cylinders by the low pressure area created by the downward movement of the piston on its intake stroke. If the mass airflow into the engine can be increased, an increase in power is achieved. By installing an air pump to raise the pressure at the engine inlet, and increase the mass airflow, the engine develops more
power.
     The piston engine, again like the human body, loses efficiency (power) as altitude increases and air density decreases. If sea level air density can be maintained at the engine inlet as the airplane climbs, then power output will remain essentially the same as it was at sea level. This again is done by an air pump, that magical thing called a
supercharger.
     Throughout aviation history, only one type of supercharger has seen wide usage, and this is the one with the centrifugal impeller, or compressor. (In Europe, superchargers are often called "compressors." Another common semi-slang term for them in the United States is "blower.") An excellent example of a centrifugal impeller, although on a small scale, is the water pump used on many automobile
engines.
     Branching out from this basic type, there are two major ways of driving the compressor. One method is a gear driven compressor where the unit is driven by power from the engine crankshaft and is usually an internal part of the engine. The other, the turbo-supercharger, utilizes. . . . .