Parnall C.11
The Parnall C.11, sometimes known as the Cierva C.11 or Parnall Gyroplane[1][2][3] was a two-seat experimental autogyro built in the UK in 1928.[4] The aircraft was badly damaged on its first attempted take-off and although repaired, today it is uncertain whether it ever actually flew.[5] DesignThe layout of the C.11 was typical of the tractor-powered autogyros of the era: an aeroplane-like fuselage with a rotor mounted on a mast above it.[1][2][6] In this case, the aircraft was also equipped with small, stub wings,[1][2][6] which carried large, full-span ailerons.[7] The pilot and a single passenger sat in tandem, open cockpits.[1][2][6] It had fixed, tailskid undercarriage, and a conventional tail.[1][2][6] Power was provided by a piston engine in the nose powering a tractor-mounted propeller.[1][2][6] The rotor blades were braced by telescopic struts and were equipped with drag hinges.[7] Pre-rotation was originally achieved by a rope and pulley.[7] Like the C.10 built around the same time, the C.11's rotor mast was carried by an unusually complicated six-strut pylon, and two control rods ran between the fuselage and the rotor head.[1] The purpose of these features is unknown today,[1] although the intention might have been to vary the position of the rotor fore-and-aft to test it in different positions, and the control rods might have been part of a mechanism to adjust the tilt of the rotor.[8] The complex rotor support was eventually replaced by a simpler, pyramidal design.[8] DevelopmentThe C.11 was built by Parnall's to an order by the Cierva company.[1] The airframe design was largely the work of Parnall designer Harold Bolas and the rotor components the work of Juan de la Cierva.[1][2][3] Construction was completed in November 1927 and it was issued UK civil registration G-EBQG.[1][2][9][7] Operational historyJuan de la Cierva attempted the first test flight of the aircraft at Yate Aerodrome in February 1928.[1][2] The C.11 rolled over during taxiing and was severely damaged.[4][1][2][10] The accident investigation concluded that Cierva had attempted take-off before the rotor was sufficiently spun up.[4][8][5] Many years later, designer Bolas speculated that the rollover (like the rollovers of the C.10) were caused by ground resonance, an unknown phenomenon at the time.[8][7] The C.11 was reconstructed in October, and substantially modified.[1] In this form, it has a smaller main rotor, and the stub wings were moved forward, given more dihedral, and a different bracing strut arrangement.[1][6] The main undercarriage was also redesigned.[1][6] The bracing struts on the rotor were replaced by wires.[6][a] It is possible that the aircraft flew in this configuration.[8] Another major rebuild took place over a year later.[8] This time, the framework of struts supporting the rotor was replaced with a simpler one,[4][8][5][6] and a rotor pre-rotation mechanism was added, taking power from the engine.[8][5][6] This mechanism was reportedly designed by Frank B. Halford and although at 75 pounds (34 kg), too heavy to be practical, similar pre-rotation devices would soon be installed on other autogyros.[8] On 8 January 1930, the pre-rotation mechanism was demonstrated to representatives of the Royal Aircraft Establishment.[8] It is unknown whether the C.11 flew in this final configuration (or indeed, at all).[8][5] In 1931, Cierva gave it to Air Service Training at Hamble, where it was used as an instructional airframe.[4][8][6] It was struck from the civil register the same year.[8][6] The last known sighting of the aircraft was at ATS in late July 1934.[6]
Specifications (approximate)Data from Brooks 1988, p.96 General characteristics
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