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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.

The early work done by Sanford Moss and General Electric in superchargers was of decisive benefit to the B-17, Consolidated B-24, Lockheed P-38, and Republic P-47. Later models of the North American P-51, using the Packard-built Rolls-Royce engines, benefited from two-stage supercharging.


The Fuel Story

By the early 1920s, users had noticed that fuels from different sources had different properties in the engine. Particularly noticeable were engine knock (pinging) and detonation; and testing was initiated to find the knock limit of various fuel types. It was found that several formulations of fuels could be successfully burned in an engine.

The Fight in the Clouds

Four U.S. Army Air Force North American P-51 Mustang fighters from the 375th Fighter Squadron, 361st Fighter Group, from RAF Bottisham, Cambridgeshire (UK), in flight on July 26, 1944.

First, the natural fuels and blends of several of them were investigated, and then it was found that synthetic branched-chain paraffin-based and aromatic hydrocarbon compounds yielded several useful blends. Fuel development focused on the mass production of natural and synthetic blends to maximize the yield of a barrel of oil. Sam Heron played a major role in coordinating fuel development for the benefit of the U.S. government. Octane ratings were devised to reflect the greater resistance to knock . This allowed engines to have supercharger boost increased, with ignition timing optimized for power rather than knock, allowing much higher power ratings.

Characteristically, turbine production development at established engine manufacturers was done almost entirely by teams of engineers with little experience with piston engines. The experienced development staffs at the major engine builders were committed to wartime production of piston engines.

Engine designs were also modified to withstand higher power and to tolerate different chemical properties of the new fuels.


The Gas Turbine Story

The development of gas turbine engines (jet engines) began outside of the engine industry in Germany, Great Britain, and the United States, with Frank Whittle of Great Britain being recognized for conceiving the first functional jet engine, closely followed by Hans von Ohain of Germany. It was von Ohain’s engine which flew first, however, in a Heinkel He 176 in August 1939.

In the United States, Northrop’s Vladimir Pavlecka and Lockheed’s Nathan Price independently designed turboprop and turbojet engines that never flew. The companies for which these inventors worked were judged by the government to have inadequate resources for development and production.

Me 262

An Me 262 flashes through the frame of an Allied escort fighter’s gun camera. National Archives

Characteristically, turbine production development at established engine manufacturers was done almost entirely by teams of engineers with little experience with piston engines. The experienced development staffs at the major engine builders were committed to wartime production of piston engines. The first operational turbojet engine was the German Junkers Jumo 004, designed by Anselm Franz and flown in the Messerschmitt Me 262 fighter on July 18, 1942. It became operational in April 1944.

Other wartime jet engines and aircraft included the de Havilland H.1 used in the Gloster Meteor 3/5/43. The Whittle engine was produced by Rolls-Royce as the Welland, for the production Meteor. A Welland-powered Meteor flew on June 12, 1943; becoming, on July 27, 1944, the only Allied jet fighter operational in World War II. The GE IA engine, developed from the Whittle engine, flew on America’s first jet flight, Oct. 2, 1942 in the Bell P-59, which was relegated to training. The Lockheed P-80 fighter flew with the de Havilland H-1 on Jan. 8, 1944, and with its production engine, the GE J33, on June 10, 1944. Japan and Russia built and flew jet aircraft before the war ended, with no follow-on production.

P-80 Shooting-Star

An XP-80A, ca. 1944. This historic Lockheed airplane was designed and built from drawing board to takeoff in just 143 days. Flying higher and faster than any airplane in the world, the Shooting Star was assigned to military units in Okinawa, Germany, Alaska, the Panama Canal Zone, Japan, and in the United States. The Shooting Star was the first jet plane produced in quantity. Lockheed Martin photo

As a result of development and production difficulties, only a few thousand turbine engines were produced by all combatants, compared with well over one million aircraft piston engines.


The Engine Designers

Individuals dominated engine design, just as they did airframe design. However, in most cases, development was accomplished by teams generally unrecognized outside of the industry. In the field of engines, one of the first individuals to reach prominence was Sir Henry Royce, of Rolls-Royce (R-R), and attention to detail in liquid-cooled engines was his hallmark. His work was continued by A.J. Rowledge, who had designed the Napier Lion at the end of World War I; and then by Arthur Rubbra and Cyril Lovesey, who grew the Merlin engine throughout World War II.   Roy Fedden of Bristol Engines sponsored sleeve valves in aero engines, putting great effort into bringing them into production for both liquid- and air-cooled engines. Leonard Hobbs joined Pratt & Whitney in time to influence all of their multi-row air-cooled engine programs and kept P&WA to the goal of optimizing that engine type, via the R-1830, R-2800, and the R-4360. Ronald M. Hazen joined Allison in time to complete the development of the V-1710, maturing it from 750 horsepower to its initial production rating of 1,150 horsepower, and then through further uprating up to a demonstrated 3,200 horsepower. Jesse Vincent of Packard was instrumental in all of Packard’s aero engine activities, from their first V-12 in 1915/1916 to leading the Liberty program in World War I, and initiating the licensed manufacture of the Merlin for World War II. Packard made many improvements in Merlin function and ease of production. S.D. (Sam) Heron, a British engineer who began his career with what became the Royal Aircraft Establishment during World War I, emigrated to the United States and finished his career working for the U.S. Army’s Wright Field engine development section. There, he initiated the Hyper engine program, and concurrently worked with the oil companies to raise the octane rating of gasoline, as already discussed. Heron is one of the top contributors in the world to successful high-power piston-engine development, having also helped refine the design of air-cooled cylinders, and inventing the sodium-cooled exhaust valve. Another, working outside of the engine industry, was the influential consultant Harry Ricardo, who conducted independent pioneering research on engine design parameters, supercharging, fuels, and materials.

He 162 and Ju 290

Looking diminutive in comparison with the massive Ju 290, a Heinkel He 162 Salamander is one of the captured German aircraft exhibited at various air shows after World War II. Robert F. Dorr Collection

Jet engine development was accomplished by teams led by Anselm Franz of Junkers , Stanley Hooker of Rolls-Royce and Hermann Oestrich of BMW. At General Electric, Donald F. Warner, Dale Streid, Glen Warren and Alan Howard pioneered, and later Gerhard Neumann would become prominent.

Engine development always took longer than airframe development, and aircraft designers usually received more public acclaim than engine designers. Yet aircraft designers would be the first to recognize the absolute necessity of having good engines to obtain good performance.

This article was first published in Aviation 100: Celebrating a Century of Manned, Powered Flight.

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