piston engine in its many different forms (rotary and static radial, air-cooled and liquid-cooled inline) was the only type of powerplant available to aircraft designers. This was acceptable as long as only low-performance aircraft were required, and indeed all that were available. Pre World War II In 1928, RAF College Cranwell cadet Frank Whittle formally submitted his ideas for a turbo-jet to his superiors. In October 1929, he developed his ideas further. On 16 January 1930 in England, Whittle submitted his first patent (granted in 1932). The patent showed a two-stage axial compressor feeding a single-sided centrifugal compressor. Practical axial compressors were made possible by ideas from A.A. Griffith in a seminal paper in 1926 ("An Aerodynamic Theory of Turbine Design"). Whittle would later concentrate on the simpler centrifugal compressor only, for a variety of practical reasons. Whittle had his first engine running in April 1937. It was liquid-fuelled, and included a self-contained fuel pump. Whittle's team experienced near-panic when the engine would not stop, accelerating even after the fuel was switched off. It turned out that fuel had leaked into the engine and accumulated in pools. In Spain, pilot and engineer Virgilio Leret Ruiz was granted a patent for a jet engine design in March 1935. Republican president Manuel Azaña arranged for initial construction at the Hispano-Suiza aircraft factory in Madrid in 1936, but Leret was executed months later by Francoist Moroccan troops after unsuccessfully defending his seaplane base on the first days of the Spanish Civil War. His plans, hidden from Francoists, were secretly given to the British embassy in Madrid a few years later by his wife, Carlota O'Neill, upon her release from prison. In 1935, Hans von Ohain started work on a similar design to Whittle's in Germany, and it is often claimed that he was unaware of Whittle's work. Ohain said that he had not read Whittle's patent, and Whittle believed him (Frank Whittle 1907–1996). However, the Whittle patent was in German libraries, and Whittle's son had suspicions that Ohain had read or heard of it. Years later, it was admitted by von Ohain in his biography that this was so. Author Margaret Conner states ″Ohain's patent attorney happened upon a Whittle patent in the years that the von Ohain patents were being formulated". Von Ohain himself is quoted as saying "We felt that it looked like a patent of an idea" "We thought that