2018 Year at a Glance

2018 Year at a Glance

1946 Dorand G.II “Gyroplane”

In 1938, René Dorand established the Société Française du Gyroplane (French Gyroplane Company), as a follow-on to the joint company with Louis Breguet, the Syndicat d'Etudes de Gyroplane ("Syndicate for Gyroplane Studies"), that led to the first truly successful experimental helicopter, the coaxial Gyroplane Laboratoire.

The French Navy commissioned Gyroplane to design a combat helicopter for costal defense and anti-submarine warfare. Dorand designed the new machine, using the coaxial rotor layout previously used on the Gyroplane Laboratoire. The new helicopter was designated the Gyroplane G.20, but it is also known as the Dorand G.20 or the Dorand G.II.

The G.20 had a cigar-shaped metal fuselage with a V-tail having fabric covered control surfaces. The pilot sat in the streamlined, Plexiglas paneled nose with either one or two crewmen positioned behind him.

The G.20 helicopter utilized two three-blade, coaxial rotors. The lower rotor by design had a smaller diameter than the top rotor to ensure the blades tips would not collide. The upper rotor had a diameter of 50.5 ft (15.4 m), and the lower rotor diameter was 42.7 ft (13 m).

The G.20 magnesium blades were made of two parts with a box forming the leading edge and a separate attached trailing edge. The rotor hub allowed for both cyclic and collective pitch control, and no tail rotor was used since the coaxial rotors were counter rotating.

The G.20 was powered by two air-cooled, inverted, inline, six-cylinder engine Renault 6Q-04 engines with a total displacement of 580 cu in (9.5 l). The 6Q-04 was supercharged and produced 240 hp (189 kW) at 2,500 rpm.

Power from the engines was transferred to the rotors via a gearbox/clutch such if one of the engines failed, that failed engine would be automatically disconnected, with the remaining engine powering both sets of rotors. The G.20 was supported by two rearward-retractable main wheels and a fixed tailwheel. The space in the fuselage between the main gear and below the rotors could be used for either bombs or a single depth charge.

The original G.20 design included a machine gun mounted on the helicopter’s side and a turret mounted on top of the rotor mast, with both gunner positions operated by separate crewmen. The mast turret was unique in that it was essentially a hollow shaft to which the rotors were attached. A gunner was to occupy the center of the rotor shaft giving the crewman an unobstructed 360 degree field of fire.

However, all armament and the rotor turret were omitted from the G.20 aircraft as built. The helicopter’s final role was defined only as observation, liaison and mail-carrying.

The G.20’s fuselage had a length of 36.3 ft (11 m), height of 10.3 ft (3.1 m). The helicopter’s empty weight was 3,100 lb (1,400 kg); normal operating weight was 5,500 lb (2,500 kg), and maximum weight was 6,600 lb (3,000 kg).

Construction of the G.20 started in Guethary, France in 1938. When the German Army invaded France in 1940, the helicopter was moved to Chambéry in south-eastern France, near Italy, and construction resumed. The completed Dorand G.20 is shown in the photo after World War II.

The G.20 was completed in 1947 and underwent ground tests. However the French military showed little interest in the project and provided no additional funding. Consequently, further development and testing of the G.20 was abandoned, and the helicopter never flew.

Gyroplane did construct a four-passenger helicopter, the G.11E, which first flew in 1949. The G.111 was a follow-on project that first flew in 1951, but without sales orders, Gyroplane went out of business in 1952.

Photo: oldmachinepress.com
Text: Pete Noell

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