May 2016

2016 May photoSud-Ouest SO.1310 “Farfadet” [Elf] Compound Gyrodyne
First flight: May 8, 1953

Interest in the Unloaded Rotor-type Convertiplane VTOL was growing in France during the 1950s, and resulted in the construction and testing of the SO.1310 model.

The SO.1310 was a gyrodyne-type aircraft, featuring a tip-jet driven, three-bladed, 11.2 m (36.7 ft) diameter rotor; a pair of low-mounted, stubby wings with a 6.4 m (21 ft) span; and a turboprop engine driving a nose-mounted, variable-pitch propeller. It had a conventional-appearing tail assembly — the plane sat on a tricycle landing gear with the aircraft nose tilted upward.

The power plant for the craft’s variable pitch, forward-pulling propeller was a 360 shp Turbomeca Artouste II turbo-prop engine. For the overhead three-bladed rotor a 360 horsepower Turbomeca Arrius II gas generator was used, which fed compressed air to the small combustion chambers at the tips of the rotor. This provided the propulsive force for the rotor.

During forward flight, the rotor used for take-off continues to auto-rotate, but with reduced lift with the greater part of the lift generated by the fixed wing. Cruise speeds as a helicopter and autogyro were 97 mph (160 kph) and 156 mph (251 kph) respectively. Range approximately 250 mi (402 km).

Mounted over the fixed wing is the pilot's cabin, fitted with dual controls. While in the cabin there was room for either three passengers, a freight load or two stretchers, vertically stacked.

Note that the overhead rotor was sized/optimized such that it tips passed very near the vertical stabilizer of the tail assembly.

First flown as a pure helicopter on May 8, 1953, for 20 minutes, the aircraft achieved transition to forward flight on July 1, 1953.

A number of additional flights would follow, but that would be the end for the promising program with the exact reason being unknown.

(Photos via Nico Braas and Ray Watkins, 1000aircraftphotos.com; text by Peter Noell)

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