3 Jets

It has been said that World War II advanced the airplane by 50 years. Yet it can also be accurately stated that there were really only two revolution­ary technological advances to come out of the war—radar and the jet engine—and America had nothing to do with the discovery of either. Not only were the Americans a bit slow at the beginning, they were even slower at appreciat­ing how great a leap the jet engine represented in the potential for air commerce. This was dem­onstrated by the reluctance of American air­craft manufacturers and air carriers to pursue jet engine potential after the war.

The idea of turbine engines first manifested itself in England in 1884, when Charles Par­sons, who was called the greatest engineer since James Watt, developed a stationary steam tur­bine that he applied to the generation of elec­tric energy. Within his lifetime his patent was applied to all major world power stations, includ­ing in the United States by George Westing – house. Although his original patent claimed the use of the steam turbine for ships, it was not until 1894 that he built a 100-foot vessel, the Turbinia, which he powered by means of a steam turbine to a speed of 34 knots. The British Admiralty adopted the steam turbine in 1905 as the exclu­sive propulsion system in all classes of its war­ships. The steam turbine was soon also applied to new construction for the mercantile fleet and by Cunard for luxury passenger liners.

In the early 20th century, attempts to apply the turbine technology to internal combustion engines, or gas turbines, met with disappoint­ment. The design of the gas turbine called for the induction of air (as in a reciprocating engine) that would be compressed prior to ignition (as in a reciprocating engine). In the reciprocat­ing engine, the compression is accomplished by means of the piston, but in the turbine engine, the compression is delivered by means of a series of rotating vanes (the compressor) located in front of the combustion chamber. Although the idea of the gas turbine proved workable, its fuel consumption was four times that of the inter­nal combustion engine, and the economics of the invention simply prevented its adoption into commercial use.

The use of compressors in aircraft engines, however, did find continued use as the combined technology associated with aircraft engines and aircraft designs matured during the early years of aviation. As early as World War I, a turbocharger was fitted to a French aircraft to enable increased engine performance at higher altitudes. Turbo­chargers use the engine’s exhaust gases to propel the turbocharger’s compressor, thus making use of the free fuel source of the exhaust to compress air for induction into the engine’s cylinders as the aircraft climbs into the thinner air at altitude. This technology was used to good effect in the design of the American fighters and bombers used in World War II. The B-17, for instance, could carry its bomb load to 34,000 feet.

The idea of utilizing the smooth, vibration – free rotation of a turbine, instead of the oscil­lating pistons of the much more cumbersome internal combustion engine, continued to occupy the minds of engineers and inventors. The first serious work on developing the jet engine, or tur­bojet, was commenced almost simultaneously in the 1930s in both England and Germany.

In England, Frank Whittle, an officer in the Royal Air Force (RAF), conceived that the application of the principles of the gas turbine might be applied, not to drive a shaft or propel­ler, but to produce a source of thrust for pro­pulsion. In 1930, he was awarded a patent for his design, which was replete with compressor, combustion chamber, and turbine. Although his ideas and designs appeared to be workable, no assistance was forthcoming directly from the British government. The RAF did allow him to continue his work while on duty, and even approved his securing engineering and advanced degrees at government expense, culminating in a master’s degree from Cambridge. By 1935, Whittle had almost given up on his dream of
producing a prototype jet engine when he was approached by two RAF officers willing to capi­talize a company for this work. A company was formed, Power Jets, Ltd., and a workable proto­type was achieved. At last, government interest was piqued, and direct funding of refinements of his engine was provided. Shortly, in 1939 and in conjunction with the Gloster Aircraft Company, Whittle was given a contract to produce Eng­land’ s first fighter jet airplane, the Meteor. It first flew in 1941.

In Germany, Hans von Ohain, a doctorial student in physics at the University of Gottingen, was similarly motivated to develop an efficient compressor for the gas turbine. His efforts led to early disappointments, but tests revealed enough success that his university mentors used their influence to introduce Ohain to Ernst Heinkel, the noted aircraft builder. Ohain found kindred spirits at Heinkel’s company, and with that sup­port a workable jet engine, of much simpler design than Whittle’s, was incorporated into a newly designed airplane, the He 178, for its test flight in August 1939. The test was completely successful and ultimately produced the Jumo – 004 (see Figure 19-3), later incorporated into the Messerschmidt 262 and Heinkel 280. These air­planes made limited but impressive appearances over the skies of Europe during World War II.

Although the United States did not have a jet research program, in 1938 General Hap Arnold (see Chapter 17), having taken command
of the Army Air Corps was a member of the NACA Main Committee. One of the R&D proj­ects underway at that time was called jet assisted takeoff (JATO), the purpose of which was to accelerate aircraft for takeoff using rockets. As a result of letters received from Charles Lindbergh while on a tour of Nazi facilities and equip­ment that same year at the invitation of Hermann Goering, in which Lindbergh related the speeds of German pursuit aircraft exceeding 400 mph, Arnold stepped-up propulsion research by bring­ing in scientists and engineers from Caltech and the Massachusetts Institute of Technology (MIT). But it was not until April 1941 that Whittle’s jet engine research was made known to General Arnold by the British.

Upon receipt of those plans and specifica­tions, in September of that year Arnold created a super secret production team composed of Bell Aircraft engineers and General Electric personnel. General Electric was chosen as the most experi­enced turbine producer in the country, and it was given the assignment of developing an American model along the lines of Whittle’s design. Only 15 people composed the Bell/GE project, known as “Super-charger Type #1.” It was assigned an old project number to avoid suspicion and the work teams were divided up in a manner that prevented any one person from realizing exactly what they were building. The resulting jet air­craft, the Bell XP-59A “Airacomet” first flew officially on October 2, 1942. But this airplane

was experimental, not a production model, and its limited range and further development precluded its application to the American effort in World War П. This initial American jet R&D, however, expanded to jet bomber adaptation that resulted in the North American B-45 Tornado and the vastly superior Boeing B-47 Stratojet, and to the first operational American fighter, the Lockheed P-80 Shooting Star.

Boeing had engineered and put in service in

1944 a very large wind tunnel capable of design testing shapes at speeds close to the speed of sound. Engineers had been dealing with drag at lower speeds for decades, but compressibility was a phenomenon that had only manifested itself as aircraft gained speeds approaching the speed of sound. Drag also appeared to increase exponentially as the speed of sound was approached. The Boeing tests concentrated on these phenomena and, unlike the B-45, were to result in a sweepback wing design never before incorporated in production aircraft. This design had the effect of delaying the onset of com­pressibility and of raising the speed at which the exponential increase in drag occurred. In short, it facilitated faster flight. Interest in production jet aircraft in the United States was in military air­craft, as evidenced by the B-47 medium bomber program, followed by the B-52 heavy bomber program. The first fully operational jet fighter, the Lockheed P-80, appeared in production in

1945 with its straight wings. The swept-wing North American P-86 (designation changed to F-86) appeared in production in 1948 and set the world speed record that year at 671 miles per hour. These and the other jet aircraft of the time incorporated the conventional turbojet engine with all of its drawbacks and shortcomings. Chief among these drawbacks was fuel consump­tion, followed by high initial cost, and frequent maintenance requirements. Airline chieftains were wary of the new, noisy technology. While there was little long-term operational data on jet engines available at the time, what was known was daunting. The consensus among American airline executives was that the jet was too risky, too unproven, and too expensive to be seriously considered as an addition to the fleet.

In the late 1940s, a secret design concept for an improved jet engine, known as a “twin-spool turbojet” was in the works in military circles. The prototype of this engine would be known as the “J-57,” and it was first tested aloft in 1951. After successful tests, it would be incorporated in a new generation of military airplanes, and it ultimately would make the difference the airline industry needed to consider turbojet propulsion in American commercial aviation. But in the early 1950s, the J-57 was still a military secret.