Frank Whittle developed one of the earliest turbojet engines, critical for the future of the Allied war effort during World War II.
On the morning of May 15, 1941, some eleven months after the fall of France to Adolf Hitler’s advancing German army, the experimental jet-propelled aircraft bearing the official name Gloster/Whittle E.28/39 was successfully tested in the air by test pilot Gerry Sayer. The airplane had been developed in a little more than two years by Gloster Aircraft Company
The plane that was tested in May, 1941, like the jet engine that powered it, had a number of predecessors. In fact, the May, 1941, flight was not the first jet-powered test flight: That event occurred on August 27, 1939, when a Heinkel aircraft powered by a jet engine developed by Hans Pabst von Ohain accomplished a successful test flight in Germany. During this period, Italian airplane builders were also engaged in jet aircraft testing, with lesser degrees of success.
Without the knowledge that had been gained from Whittle’s experience in experimental aviation, the test flight at the Royal Air Force’s Cranwell airfield might never have been possible. It was Whittle’s repeated efforts to develop turbojet propulsion engines that guaranteed the success of the flight.
Whittle’s contribution to the development of turbojet engines began in 1928, when, as a twenty-one-year-old Royal Air Force (RAF) flight cadet at Cranwell Academy, he wrote a thesis entitled “Future Developments in Aircraft Design.”
Although Whittle later stated that the speeds he had in mind at that time were about 805 kilometers (500 miles) per hour—close to those of the first jet-powered aircraft—his earliest idea of the engines that would be necessary for such planes focused on rocket propulsion. (That is, “jets” in which the fuel and oxygen required to produce the explosion needed to propel an air vehicle forward are entirely self-contained in the engine, or, alternatively, gas turbines driving propellers at very high speeds.) Later, it occurred to him that gas turbines could be used to provide forward thrust by what would become “ordinary” jet propulsion (that is, “thermal air” engines that take the oxygen they need to ignite their fuel from the surrounding atmosphere). Eventually, such ordinary jet engines would function following one of four possible systems: the so-called athodyd, or continuous-firing duct; the pulsejet, or intermittent-firing duct; the turbojet, or gas-turbine jet; or the propjet, which uses a gas-turbine jet to rotate a conventional propeller at very high speeds.
The principle of jet propulsion, the turbojet, was tested successfully in flight in May, 1941. Turbojets involve a straightforward technical improvement over the simplest form of jet propulsion, the continuous-firing duct jet. The latter consists of an open-ended tube that receives an inflow of air that is heated by burning fuel passing through holes located midway along the duct. The heated air expands, instantly creating increased pressure inside the tube. The resulting phenomenon, forward thrust, comes as the heated air passes out of the back of the duct under pressure, at the same time sucking more air in through the front, thus reinforcing thrust process continuously.
In the next stage, the turbojet, increased levels of pressure, and therefore increased thrust, are obtained by placing an air compressor near the front of the engine duct ahead of the combustion chamber. This compressor gains its energy by tapping, out of the rear section of the jet duct into a gas turbine mounted around its outer circumference, only a carefully calculated amount of pressure from the thrust force leaving the combustion chamber. Turbojet turbines do not contribute in any direct way to the thrust of the overall engine. Their sole purpose is to drive the compressors that—as a result of their key function—literally push a greater mass of heat-expandable air into the combustion chamber, creating the increased force of jet propulsion characteristic of this engine design.
When Whittle demonstrated his interest in designing a workable combination of turbojet-propulsive engines and an airplane most aerodynamically capable of utilizing the power produced by such jets, he did not receive enthusiastic support. In fact, many aspects of technical progress that were incorporated eventually into the airplane tested in 1941 were finished and patented in the early 1930’s, well before a viable economic market existed for their practical use. One example is that of Bristol Aircraft Manufacturing
The first sign of developments that would appear increasingly logical only in 1938 and 1939, when clouds of war were forming, occurred in January, 1936, when the founders of Jet Power Limited,
As the project proceeded between 1936 and 1941, several essential liaisons would develop. By the time of the May, 1941, flight, this meant that Rover and Gloster Aircraft would share in the complicated construction and testing phases that preceded plans for the flight. Because the two big manufacturing concerns, BTH and Rover, needed exact specifications, particularly concerning power thrust, of the engines that would be mounted on the aircraft, “wholesale” communication of Power Jets’ detailed plans created some difficulties. These problems concerned not so much security of information as the aircraft manufacturers’ disagreements with what Power Jets insisted should be incorporated into the test aircraft’s design. Such disagreements delayed progress on the plane. The Air Ministry’s insistence that work not be suspended, however, prevented any actual stop. In fact, once it became apparent that England’s declaration of war would lead to an extension of hostilities from eastern to western Europe, completion of the first jet aircraft’s testing process immediately became urgent.
By the time of the 1941 flight, several different engine and aircraft models had been developed as candidates for the first test experience. Such diversity of prospective engine models stemmed in part from an interchanging process. This meant incorporating either technical principles or actual parts (such as engine mounts) that had been tested in earlier design models, both of engines and aircraft, into a chain of later versions.
The aircraft that was to be used to test the flight performance was completed by April. On April 7, tests were conducted on the ground at Gloster Aircraft’s landing strip at Brockworth by Gloster’s chief test pilot, Sayer. At this point, all parties concerned tried to estimate if the jet engine’s revolution-per-minute capacity would be sufficient to push the aircraft forward with enough speed to make it airborne. Sayer dared to take the plane off the ground for a limited distance of between 183 meters (600 feet) and 273 meters (895 feet), despite the technical staff’s warnings against trying to fly in the first tests. On May 15, the real first flight test was conducted at Cranwell. During that test, Sayer flew the plane, now called the Pioneer, for seventeen minutes at altitudes exceeding 305 meters (1000 feet) and at a conservative test speed exceeding 595 kilometers (370 miles) per hour, which was equivalent to the top speed then possible in the RAF’s most versatile fighter plane, the Spitfire.
Once it was clear that the tests undertaken at Cranwell were not only successful but also highly promising in terms of even better performance, a second, more extensive test date was set for May 21. It was this latter demonstration that induced the Ministry for Air Production (MAP) to initiate the first steps to produce what would be called the Meteor jet fighter aircraft on a full industrial scale in barely more than a year after the Cranwell test flight.
At the time activities that would lead to the flight were taking form in England (specifically, in July, 1936), the Junkers engine and aircraft companies in Hitler’s Germany created a new secret branch dedicated to the development, under the highly qualified engineer Herbert Wagner, of a turbojet-driven aircraft. In the same period, Junkers’ rival in the German aircraft industry, Heinkel, Inc., engaged von Ohain, who was far enough along in his work on the turbojet principle to have patented a device very similar to Whittle’s in 1935. A later model of this jet engine would power a test flight aircraft in August, 1939, shortly before the outbreak of World War II.
Frank Whittle (left) stands by the turbojet engine he designed.
To measure the potential impact of what Whittle’s project accomplished by 1941, however, it is essential to realize that as each year went by between 1936 and 1941, the critical nature of competition obviously would be magnified. In the last stages before testing the Gloster/Whittle jet—specifically during November and December, 1940—the staff of Power Jets was increased by fifty-three skilled personnel. This was a major expansion when one compares the modest number of jet propulsion experts available only four years earlier. Ironically, what Whittle’s effort to develop the turbojet accomplished by the first successful test flight in 1941 was far from adequate to assure the Allied cause that if jet propulsion technology was to assume a key role in running the war, a balance could be held between England and Germany.
On one hand, the British Ministry for Aircraft Production reacted immediately to the prospect of using jet-propulsed aircraft against the German air raid threat in the so-called Battle for Britain. This was done despite signals in the second half of 1941 from Whittle and others that a number of technical complications still needed to be worked out before considering the original jet engine used for testing to be fully operational in the air.
On the other hand, the English defense establishment had to consider what had to be done immediately to carry on an air war over Europe against Hitler’s Luftwaffe. The course of aircraft production over the next few years after the Meteor’s May, 1941, test flight indicates that because of the high number of aircraft losses inflicted on the RAF during 1940 and the first half of 1941, the most immediate practical need was a life-or-death issue: replacement of English Spitfire propeller-driven fighters. This meant that the RAF’s demand for conventional aircraft remained a priority over the next few years.
In the meantime, the wider impact of the flight was the result of decisions made by General H. H. Arnold, chief of staff of the U.S. Army Air Corps. Arnold had visited the Power Jets testing site in March of 1941. Even before learning of the successful flight in May, he made arrangements to have one of Whittle’s engines shipped to the United States to be used by General Electric Corporation as a model for separate U.S. production. The engine arrived in October, and within one year, a General Electric-built engine powered a Bell Aircraft plane, the XP-59 A Airacomet, in its maiden flight. This was six months prior to the formal inauguration of the first English Meteor aircraft. The October, 1942, inauguration of the XP-59 A was not witnessed by Whittle, but he visited the United States in May, 1942, to confer with American engineers working on the project.
Meanwhile, German engineers had scored even more impressive advances, as their research and development projects did not depend (as General Electric’s did) on borrowed technology. One result of German technology, the V-1 unpiloted jet-propelled bomb, would become notorious when it began flying against English targets at a fairly early stage in the war. Less effective than the V-l or its successor, the (rocket-propelled) V-2, was the only jet aircraft that was actually used in the war: the Messerschmidt Model 262
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Constant, Edward W., II. The Origins of the Turbojet Revolution. Baltimore: Johns Hopkins University Press, 1980. This book covers a wide variety of technical questions of turbojet functioning, but it devotes more space than any other technically oriented publication to the evolution of what became the Gloster/Whittle experimental jet plane tested in 1941. -
Cumpsty, Nicholas. Jet Propulsion: A Simple Guide to the Aerodynamics and Thermodynamic Design and Performance of Jet Engines. 2d ed. New York: Cambridge University Press, 2003. Comprehensive overview of the history, function, and design of turbojet engines. Bibliographic references and index. -
Golley, John, and William Gunston. Whittle: The True Story. Washington, D.C.: Smithsonian Institution Press, 1987. Aside from Whittle’s autobiography (1953), this is the most complete account of his experiences developing the plane. -
Griffith, A. A. “Report on the Whittle Jet Propulsion System.” Report No. E 3545 (ARC 2897). Farnborough, England: Royal Aircraft Establishment, February, 1937. Although compiled before World War II, this official report on the development of the Whittle engine was kept closed until several years after the war. -
Whittle, Frank. “The Early History of the Whittle Jet-Propulsion Gas Turbine-1.” In The Aeroplane. London, 1945. Written for the layperson, this account of how the Whittle turbojet worked is one of the earliest descriptions made available to the general public. -
_______. Gas Turbine Aero-Thermodynamics: With Special Reference to Aircraft Propulsion. New York: Pergamon Press, 1981. This textbook contains technical material on subjects such as dealing with shock waves in the air, effect of height and speed on performance, and Whittle’s ideas on designing a “Super-Thrust Engine” in the 1980’s, “regardless of fuel consumption.” -
_______. Jet: The Story of a Pioneer. London: Frederick Müller, 1953. Whittle’s autobiographical account of his pre-World War II experiences in the Royal Air Force and Power Jets, as well as his immediate postwar career as a paramount representative of a struggling new area of aviation technology.
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