A BRIEF HISTORY OF THE TURBOJET

One might argue that the turbojet engine had its beginnings with the turbosupercharger, since the latter has an exhaust-driven turbine that drives a compressor to supply air to the engine. These are the essential ingredients of a turbojet engine. Dr. Sanford A. Moss is generally credited with developing the turbosupercharger, at least in this country. In 1918, Moss successfully tested his turbosupercharger atop Pikes Peak. Two years later, a La Pere biplane equipped with a turbosupercharger set a world altitude record of over 10,000 m.

In 1930, Frank Whittle (later to become Sir Frank Whittle) received a patent for a turbojet engine. Unfortunately, he was unable to gain support for the development of his design. It was not until 1935, when a young German aeronautical engineering student, Hans von Ohain, received a German patent on a jet engine, that development work began in earnest on the turbojet engine. On August 27, 1939 (some references say June 1939), the first turbojet engine was flown in a Heinkel He 178. This engine designed by von Ohain delivered 4900 N (11001b) of thrust. It was not until May 1941 that Whittle’s engine was flown in England.

German jet engine development progressed rapidly. By 1944, both BMW and Junkers turbojet engines were introduced into the Luftwaffe. One can imagine the astonishment of the allied aircrews upon first seeing propellerless airplanes zip by them at incredible speeds of over 500 mph.

On October 1, 1942, the first American jet-propelled airplane, the Bell Airacomet, was flown. This twin-engine airplane was powered by an Ameri­can copy of Whittle’s engine built by the General Electric Co. Designated the “1-А,” the engine weighed approximately 4450 N (10001b) with a thrust-to – weight ratio of 1.25. The first production American jet aircraft, the Lockheed F-80, first flew in January 1944. In production form, it was powered by the J33 engine, which delivered a thrust of approximately 17,800 N (4000 lb) at a weight of 8900 N (2000 lb).

General Electric’s J47 was the first turbojet power plant certified in the United States for commercial aviation in 1949. The world’s first commercial jet transport to fly, however, on July 27, 1949, was the British built de Havilland Comet powered by four de Havilland Ghost 50 Mkl turbojets. This eiigine, incorporating a centrifugal compressor, developed 19,800 N (44501b) of thrust. The Comet must be recognized as one of the most famous airplanes in history, because it truly ushered in the age of jet transportation. Un­fortunately, its career was short-lived after three of the nine that had been built broke up in the air. An exhaustive investigation showed the cause to be fuselage structural fatigue because of repeated pressurizations. Despite its tragic demise, the Comet proved the feasibility of commercial jet trans­portation and paved the way for Boeing’s successful 707. This airplane first

took to the air on July 15, 1954, powered by four Pratt & Whitney JT3 (military designation J57) turbojet engines. Each engine developed a static thrust of approximately 57,800 N (13,0001b) with a dry weight of 18,200 N (41001b).

A historical note of interest is the following quotation taken from a report by the Gas Turbine Committee of the U. S. National Academy of Sciences in 1940.

“… Even considering the improvements possible… the gas turbine could hardly be considered a feasible application to airplanes mainly because of the difficulty with the stringent weight requirements ”

This conclusion, made by a panel of eminent persons, including Dr. Theodore von Karman, is a sobering reminder to any engineer not to be too absolute.