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.
FACTS AND FIGURES
© 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.
