| C.11 | |
|---|---|
| Role | Experimental autogyro |
| National origin | UK |
| Manufacturer | Parnall |
| Designer | Harold Bolas, Juan de la Cierva |
| Status | Abandoned project |
| Number built | 1 |
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]
The 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]
The 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]
Juan 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]
Data from Brooks 1988, p.96
General characteristics