The principle of ducted fans is well understood now. They require a duct with correct tapering at each end and a low drag but powerful engine at its core. Multiple-bladed propellers, or a fan as on a modern high-bypass turbofan are needed for efficiency. Placing a Tiger Moth engine inside a fat tube doesn't cut it. An Italian government engineer, Luigi Stipa, convinced the Caproni Company to build an aircraft to test his theory that a tubular fuselage gave significant extra thrust to a conventional engine and propeller. The resulting Caproni-Stipa aircraft had a corpulent annular fuselage, which concealed a Gipsy engine and two-bladed propeller. All this achieved was high drag and low noise, although the landing speed was reduced to 68km/h. Performance was otherwise lower than a conventional airframe with the same powerplant.
Stipa claimed that the outer fuselage was profiled to generate lift. It was said that this contributed 37% of the total. The Stipa's pilot and passenger had to sit in cockpits perched atop the fuselage. An inherent flaw in the design is that there is little room for any payload. Humped surfaces around the cockpits would have seriously impeded the view of pilot and passenger unless they leaned to one side, which would have been essential during take-off and landing.
Specification CREW 2
ENGINE 1 x 120hp de Havilland Gipsy III inline piston engine
WEIGHTS Take-off weight 800 kg 1764 lb
DIMENSIONS Wingspan 14.28 m 46 ft 10 in Length 5.88 m 19 ft 3 in Height 3.00 m 9 ft 10 in
PERFORMANCE Max. speed 131 km/h 81 mph
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