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shaped aircraft during 1944 with primary propulsion being provided by two fully enclosed contra-rotating rotors (that elimi- nated torque problems), mounted in a cen- trally positioned duct. The rotors would be driven by a single gas turbine located behind the duct and air would be forced downwards through a series of lou- vres in the aircraft's underside, allowing pos- itive control in hover and low-speed flight. In level flight the louvres would be angled rear- wards, supplemented by exhaust from the jet engine emerging through nozzles positioned on the trailing surface of each wing, which were adjustable for yaw and roll. To boost level flight performance further, there were proposals to use the jet engine exhaust ports as afterburners. In the event of an engine fail- ure, it was felt that the aircraft would be capa- ble of making an unpowered landing with the louvres closed. The convertiplane designed by Homer Streib in the 1950s. This sophisticated VTOL design used jet engines in swivelling pods to assist with VTOL operation and boost performance in level flight. The US Patent Office and the anticipated performance remain unclear and there are no real indications of the aircraft’s anticipated role, although it was probably conceived as a strike fighter. In 1955, the revived Focke-Wulf Aircraft Company at Bremen took a fresh look at the Professor's VTOL design and undertook some wind tunnel tests with a scale model mostly constructed from wood. The aircraft was now called Rochen (Aquatic Ray or Skate) but this programme didn’t lead to the construction of a manned prototype and by 1958 interest in Focke’s concept had started to fade. F4U-1 Corsair naval fighter. The Convertible Aircraft design is visually similar to the wartime Focke Achgelis VTOL, but there are obvious differences that include the tailplane assembly and a tricycle undercarriage. The concept was credited to Robert Ross and, like the Focke Achgelis VTOL design, this aircraft utilised a set of large internal contra-rotating rotors for lift and level flight, with air ducted through louvres that would be almost closed during level flight. However, the Convertible Aircraft’s powerplant was located directly below the rotor assembly, presumably with exhaust gas channelled into the airflow. The Goodyear concept was closely fol- lowed by a series of studies undertaken by Homer Streib, a designer based in the San Diego area of California. Streib proposed sev- eral different circular-winged aircraft, all using a centrally mounted ducted fan to pro- vide lift. The propulsion unit was to be gim- balled for directional control and it contained two contra-rotating impellers designed to counteract torque. This arrangement would provide a full VTOL capability, with one early idea to tilt the entire assembly through 90° for horizontal flight. This seems to have been abandoned in favour of two additional turbo- Earlier, in April 1945, American designers Charles Neumann and Hugo Baca produced an intriguing VTOL concept that shared a number of similarities with Professor Focke’s design, although this appears to be nothing more than an unusual coincidence. Their two-seat arrowhead-shaped craft used an enclosed contra-rotating rotor assembly, with ducted airflow through louvres to allow VTOL operation and ducts to rearward-positioned louvres for level flight. The Neumann-Baca design was followed in 1953 by a proposal submitted to the US Patent Office by the Goodyear Aircraft Com- pany of Ohio, which was simply called a Con- vertible Aircraft. Although the company is not automatically associated with the construc- tion of fixed-wing aircraft, during World War Two Goodyear became a sub-contractor for Vought and produced many copies of the The pilot was located in a protruding cock- pit nacelle, sitting in a conventional upright position, with two retractable forward wheels and a single retractable tailwheel supporting the aircraft. On the ground this VTOL disc would be raised by about 18° at the front, while the rotors would be level with the ground. Four control surfaces were posi- tioned along the trailing edge of the wing and the design used a single tailfin and rudder. At some stage wind tunnel tests with small mod- els were undertaken at Bremen, but nothing is presently known about this. Specifications 45 German Wartime Flying Discs