Sigma
Role	Open class sailplane
National origin	United Kingdom
Manufacturer	Operation Sigma Ltd
Designed by	John Sellars
First flight	12 September 1977
Status	still flying
Number built	1

The Sigma is an experimental glider developed in Britain from 1966 by a team led by Nicholas Goodhart.

Its unusual feature is its ability to vary its wing area using Fowler flaps. It had been tried before by the Hannover Akaflieg in 1938 with their AFH-4, in the South African Beatty-Johl BJ-2 and in the LET L-13 Blaník.

A company was set up which attracted sponsorship from Hawker Siddeley and assistance from eminent aerodynamicists. Despite a fire in 1968 and a relocation, it eventually flew for the first time on 12 September 1971 at Cranfield.

The wings and tail boom are of aluminum alloy construction and the front of the fuselage is glass-fibre composite. It features a retractable main wheel and air brakes. A tail parachute was originally fitted. The hydraulic pressure needed to move the flaps was provided by the pilot pumping on the rudder pedals. This proved to be tiring. Because of bending in the wings, moving the flaps in flight was found to be almost impossible. The glide ratio also proved to be disappointing at 41:1. Consequently the project was wound up in 1977.

The aircraft was moved to Canada in 1979 by David Marsden. Among the modifications, the flap system was replaced and the tail parachute was removed. The glide ratio only increased to 47:1. However its good climb rate made it comparable with other Open Class gliders of the time. It broke the US 300 km triangle record in 1997 at 151 km/h.

[edit] Specifications (before conversion)

Data from Sailplanes 1965-2000

General characteristics

• Crew: One
• Length: 28 ft 10 in (8.8 m)
• Wingspan: 68 ft 11 in (21.00 m)
• Wing area: 131.3 - 177.6 ft² (12.2 - 16.5 m²)
• Aspect ratio: 36.2 - 26.8
• Empty weight: 1,338 lb (607 kg)
• Gross weight: 1,550 lb (703 kg)

Performance

• Maximum glide ratio: 41

[edit] References

• Martin Simons, Sailplanes 1965-2000, Equip, 2004, ISBN 3 9808838 1 7

[edit] External links

• Article in Flight International magazine 27 March 1969

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