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Hoffman monoplane built for J Leslie Youngblood of Chicago in 1934. It was similar in many respects to the Arup S-2. via Bill Rose Crook’s Design Studies Dr Louis Henry Crook (1887-1952) was a highly respected aerodynamicist who worked for the Naval Aerodynamical Labora- tory, taught theoretical and applied mechan- ics at the Catholic University of America, and undertook research as an aviation consultant. His area of expertise was wind tunnel testing and he wrote many papers on aviation sub- jects ranging from pure aerodynamics to ideas about supersonic flight and guided mis- siles. During the 1930s Dr Crook became inter- ested in Arup-type aircraft and he started to develop improvements to the basic design. Crook noted that, although the low aspect ratio configuration produced a low lift coeffi- cient at small angles of attack, it also provided a number of interesting advantages that included increased stability. However, Crook went on to suggest that low aspect ratio air- foils were particularly suitable to what he described as thrust augmentation (which would now be called an internal ducted fan arrangement) and he went on to consider the future use of a gas turbine. RAOUL J HOFFMAN 1934 Arup S-2 and Arup S4 outside the company’s hangar at South Bend in Northern Indiana. Circa 1936. via Bill Rose RAOUL J HOFFMAN 1934 18 S-2. It was fitted with an 85hp (63kW) Cirrus Mk 111 engine and Hoffman planned to fit a fully retractable undercarriage, although this was never installed. During a flight in 1936 this aircraft caught fire and crashed. Snyder and Hoffman now turned their attention to the next design called Arup S-4, which was essentially a second S-3 but with further minor modifications to the control sur- faces. The aircraft first flew in 1935 and con- tinued to fly until the outbreak of World War Two. One of the last designs Snyder produced was a low aspect ratio twin-engined mono- plane, but it never progressed much further than the drawing board. At the beginning of World War Two the Arup aircraft were donated to scrap metal drives and that was the end of this story, although a scale replica of Arup S-2 was built and flown in 1985. There can be little doubt that these aircraft had a considerable influence on Charles Zimmer- man who worked for NACA and was respon- sible for designing the better-known Chance Vought ‘Flying Pancake’. Arup S-2 and Arup S4 outside the company’s hangar at South Bend in Northern Indiana. Circa 1936. via Bill Rose Secret Projects: Flying Saucer Aircraft