The story of Frank Whittle and the invention of the jet engine would make a great B movie, and probably has. I can just see all the mustachioed boffins of the Air Ministry conferring in their offices about how to rid themselves of this pestilential fellow obsessively slaving away in a brick basement in the countryside, while we in the audience, knowing that the jet age is just around the corner, cluck over their folly. The obtuseness of military bureaucrats harassed poor Whittle for a time into a diet of amphetamines and barbiturates, but he still managed to die at 89 - good news for worried substance-abusers.
His German counterpart, Hans Joachim Pabst von Ohain, seemingly had quite a different experience. Von Ohain, who worked for bomber manufacturer Ernst Heinkel, seems to have sailed from paper sketches to an airworthy jet engine in the space of three or four years, while poor Whittle, who had a head start, took a dozen.
Whittle had begun thinking about jet engines in 1928, when he wrote a college thesis on future developments in aviation. He was prescient, considering that this was the heyday of the biplane and Lindbergh had only recently crossed the Atlantic. "It seems," he wrote, "that, as the turbine is the most efficient prime mover known, it is possible that it will be developed for aircraft, especially if some means of driving a turbine by petrol could be devised." At first he was thinking of a turboprop, but by 1930 he had realized that an airplane could be propelled by the fast-moving gases of the turbine exhaust alone, and that thrust obtained in that way had advantages, for high speed flight, over thrust obtained by means of a propeller. In that year Whittle took out a patent on an engine design consisting of an air compressor driven by a gas turbine, with a gas-generating burner between them. This was, in general outline, a complete jet engine. Mechanically, it had much in common with the turbosupercharger, which had been developed for aircraft use during World War I, a principal difference being that the heat source for the turbosupercharger - what we now call a turbocharger - is external.
Whittle's first operable engine was a crude lash-up that resembled a large model of the cochlea. It was intended only to test the feasibility of the idea - of which I'm sure he had, in his heart, no doubt - and Whittle experimented with alternative designs before arriving at the one that actually propelled an airplane on May 15, 1941. The physical arrangements of Whittle's first flight engine and Ohain's, which had already flown, unbeknownst to the British, on August 27, 1939, were not greatly different. What strikes the modern eye about both engines is that they were so short and fat, as though the designers had wished to imitate as closely as possible the proportions of a conventional radial engine.
The large diameter of these primitive jet engines was due to their use of centrifugal compressors, which take in air at a central point and sling it outward through a narrowing passage. (If you've seen a turbocharger dismantled, you've seen a centrifugal compressor.) Though mechanically robust, aerodynamically undemanding, and able to produce compression ratios of 3:1 or better in a single stage, the centrifugal compressor has the disadvantage of a large diameter and a tortuous airflow path if two of them are used in series to achieve higher compression.
The extreme stubbiness of Whittle's and Ohain's early engines was probably due to a desire to control structural weight and to keep the main shaft, which carried thousands of horsepower from the turbine to the compressor, as short as possible. The 10 burner "cans" in Whittle's engine, which were longer than the whole rest of the engine together, were disposed around its perimeter, with airflow reversing direction to enter them and reversing yet again on the way out into a turbine located just a few inches behind the compressor. The large size of the burner cans was due to the difficulty of getting the fuel to burn completely before reaching the turbine. In a modern engine, the burners, which are highly efficient, occupy relatively little space, while the compressor, which develops pressures 10 times higher than Whittle's did, is proportionately much larger.
