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Chapter Eight Fans and Ducts In 1935 Abraham S Fink of Aero Improve- flight. It was hoped this technique would ments Inc produced one of the earliest require little training and Zimmerman sug- designs for a ducted fan VTOL aircraft. His gested it would be similar to riding a bicycle. concept fora flat-riser was expected tomatch _ Hiller, De Lackner and Bensen developed the the performance of a modern helicopter and _ idea further, producing ducted fan and pro- it was propelled by two rotors in separate _ peller lifted platforms, but many safety and ducts driven by one or two internal combus- engineering concerns became apparent and tion engines. Each rotor would turn in a dif- _ these projects were finally abandoned. How- ferent direction to counteract torque and _ ever, Aero Design & Development in Israel movable vanes within the ducts provided _ revived the concept many years later. control of the airflow and allowed transition Throughout the 1950s a major European from lift-off/hover to level flight. Supported by programme was undertaken to develop an four landing legs (possibly retractable) the annular-wing VTOL supersonic fighter, which aircraft had a forward cabin to accommodate _ was finally cancelled after a disastrous acci- the pilot and a small number of passengers. dent with the most advanced prototype. Fink envisaged his aircraft as alight VTOL util- Development of the ducted-fan annular- ity transport, but it never progressed beyonda_ _ winged aircraft then surfaced in America dur- paperwork study. ing the 1960s, when Convair produced During World War Two German engineers _ detailed studies for a heavily armoured com- combined the annular (ring) wing with _ bat vehicle with visual similarities to some of ducted fan propulsion for advanced VTOL _ the earlier French designs. This project was fighter concepts. In post-war America, some __ finally abandoned in favour of a more con- research conducted by Charles H Zimmer- ventional attack helicopter, but ducted fan man at NACA Langley generated consider- aircraft would return several decades later in able interest in the possibility of building — the form of small vehicles like the unmanned small personal flying devices that were capa- Sikorsky Cypher drone and various advanced ble of transporting military personnel on UAV designs. specialised short-distance missions. Zimmer- man envisaged a compact machine, pro- Zimmerman’s Shoes pelled by two rotors, that was steered by what Having left Vought when the company relo- Zimmerman called kinaesthetic control. This cated to Texas in 1947, Charles Zimmerman simply amounted to the vehicle’s pilot shifting — returned to NACA Langley where he started his body weight to change the direction of | work on one of his own ideas that dated back to the early 1940s. Zimmerman wanted to A.1935 ducted fan VTOL aircraft design by produce a small VTOL flying machine that an Abraham Fink. US Patent Office average person could control with relative flight. It was hoped this technique would require little training and Zimmerman sug- gested it would be similar to riding a bicycle. Hiller, De Lackner and Bensen developed the idea further, producing ducted fan and pro- peller lifted platforms, but many safety and engineering concerns became apparent and these projects were finally abandoned. How- ever, Aero Design & Development in Israel revived the concept many years later. Throughout the 1950s a major European programme was undertaken to develop an annular-wing VTOL supersonic fighter, which was finally cancelled after a disastrous acci- dent with the most advanced prototype. Development of the ducted-fan annular- winged aircraft then surfaced in America dur- ing the 1960s, when Convair produced detailed studies for a heavily armoured com- bat vehicle with visual similarities to some of the earlier French designs. This project was finally abandoned in favour of a more con- ventional attack helicopter, but ducted fan aircraft would return several decades later in the form of small vehicles like the unmanned Sikorsky Cypher drone and various advanced UAV designs. Side view of an early Zimmerman proposal for a one-man flying platform produced in 1947. via Bill Rose ease. This would be achieved by shifting body balance to direct pitch and roll: Zimmer- man’s kinaesthetic response technique. Ini- tially it appeared that a high centre of gravity would make such a device unstable, but Zim- merman realised that placing the centre of gravity directly above the thrust axis would 133 A 1935 ducted fan VTOL aircraft design by Abraham Fink. US Patent Office Secret Projects: Flying Saucer Aircraft