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The Aircraft Engines of World War II

The Bf 109C had a 5,062 pound gross weight and weighed 3,522 lbs. empty. With a 1,127 lb. payload and 413 lbs. of fuel, it had a range of 405 miles and a maximum speed of 292 mph. It was powered by one Junkers Jumo 210 engine of 730 horsepower at takeoff. The Bf 109K had the larger DB605 engine of 2,030 horsepower at takeoff and a gross weight of 7,440 lbs. It weighed 4,886 lbs. empty. With a payload of 1,894 lbs., and 660 lbs. of fuel, it had a range of 526 miles and maximum speed of 452 mph.

Both the Boeing B-17B and the Bf 109C were much cleaner than their later variants, which were encumbered with additional armament, bulges for coolers, and so on.

The second supercharger stage for the V-1710, when available, was of questionable reliability and anyway too big a change to make to the P-40, now in mass production. Consequently, the P-39 and P-40’s reputation, and that of the V-1710, declined.

While the Merlin engine is well known because of its successful use of supercharging in the Spitfire, it is not so well known that the P&W R-1830 was the first aircraft engine to be qualified and go into production with a two-stage-supercharger, for the Grumman F4F Wildcat fighter.

VF-3 Wildcats

Lt. Cmdr. John S. Thach (foreground) and Lt. Butch O’Hare in their VF-3 Wildcats. The stubby Wildcat with its Pratt & Whitney Twin Wasp R-1830-76 radial was the first production aircraft to boast two-stage supercharging. National Archives photo

All combatants had engines equipped with one or two stages of supercharging, as required for mission altitude. Early high-altitude aircraft engines used turbochargers, which were more available than a geared second stage. In fighters, the Allison V-1710 was initially turbosupercharged for the P-37, P-38, and P-39; but the turbocharger was dropped for the P-39 for a number of reasons, including a need for further streamlining which deleted space for the bulky turbocharger, and because it did not have the range required for high-altitude escort or intercept anyway. The evolution of the P-37 to the P-40 also deleted the bulky turbocharger and its cooling gear. The second supercharger stage for the V-1710, when available, was of questionable reliability and anyway too big a change to make to the P-40, now in mass production. Consequently, the P-39 and P-40’s reputation, and that of the V-1710, declined.

Japanese and Russian engine development is not well documented.


The Supercharger Story

Supercharging was first used to improve the fuel-air mixture (the charge) to the engine without increasing pressure. It was then used to restore performance at high altitude, and later, to increase low-altitude performance significantly beyond the engine’s naturally aspirated sea-level capability. The timing of these increases in demands from the supercharger was always constrained by fuel octane rating and supercharger aerodynamic capability.

One-stage engine-driven superchargers were first demonstrated during World War I, but were not used in production until the late 1920s. Turbochargers had also been demonstrated during World War I, but the durable materials necessary for the turbine were not available until the late 1930s. By 1939, clutched gearing (two-speed) had been developed to increase supercharger speed at altitude. Early in the war, two-stage engine-driven superchargers were developed, and turbochargers were added to the single-stage engine-driven units to further increase altitude performance. Intercooling between stages and between the supercharger and the engine was also developed to reduce charge temperature. Boost control valves released air at low altitudes so as not to overpressure engines or hit fuel octane limits.

Dr. Stanley Hooker of Rolls-Royce did much to advance supercharger performance. His improved supercharger was qualified in the Merlin engine in November 1941, giving the Spitfire ascendancy over the then-new Focke Wulf Fw 190. Hooker continued to refine his supercharger, bringing the Merlin up to 2,200 rated horsepower (2,780 demonstrated|) by the end of the war. This allowed the Spitfire to reach 47,000 ft altitude. Similar work advanced the Roll-Royce Griffon to 2,540 horsepower.

P-38 Lightnings

The P-38 Lightning became an icon during World War II. The turbosuperchargers for the Allison engines protrude above the booms at the wing trailing edges, their cooling intakes just behind on either side of each boom. Lockheed Martin photo

By 1945, three-speed and three-stage supercharging was in development and/or limited use, constrained by fuel ratings.  Daimler Benz developed its engines to use many variations of supercharging, although few of these variations reached production. German production engines typically used hydraulic clutches to provide variable speed control for a single-stage supercharger, enabling them to avoid use of two-stage superchargers while still obtaining adequate performance.

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