It was the first production French helicopter, as well as being one of the first practical European helicopters to be produced. The Djinn was also the first rotorcraft to harness tip-jet propulsion to enter production. The Djinn was developed to function as a practical implementation of the earlier experimental Sud-Ouest Ariel rotorcraft. Atypically, the rotor was driven by compressed-air jets at the end of each blade, which had the benefit of eliminating the need for an anti-torque tail rotor. On 2 January 1953, the proof-of-concept SO.1220 performed its maiden flight; it was followed by the first of the SO.1221 Djinn prototypes on 16 December 1953. During the subsequence test program, one of the prototypes was recorded as having achieved a world altitude record. Having been suitably impressed by the performance of the Djinn during testing, both the French Army and the German Army chose to procure the type, as well as a number of other customers. Operationally, the type was used for various purposes, including liaison, aerial observation, training, and casualty evacuation. The Djinn was phased out of production during the 1960s as a consequence of the greater success of the comparably more conventional Aérospatiale Alouette II and Aérospatiale Alouette III helicopters. The Sud-Ouest Djinn was the first tip-jet propelled rotorcraft to enter production. As such, the propulsion system involved a Turbomeca Palouste gas turbine engine that drove a pump to produce compressed air, which was in turn fed into the aircraft's hollow rotor blades to exit at their tips, causing the blades to rotate. The rotor hub assembly, which freely oscillated around a spherical thrust bearing, was mounted on a steel pylon by means of a ball joint and rubber shock absorbers. Unlike some of the experimental tip-jet designs of the era, a 'cold' tip-jet approach was used: that there was no combustion activity present at the exhaust nozzles installed at the ends of the rotor blades. Consequently, the nozzles produced little noise in operation, and were claimed by Sud-Ouest to be "noiseless". The all-metal rotor blades, through which the compressed air travelled to be ejected at the blade tips, consist of a spar of tapering thickness, a honeycomb-filled trailing edge, and feature faired roots to the increase their lift coefficient. It was claimed that the blades possessed a highly homogenous structure, a highly finished surface and a constant profile, and could be easily dismantled to facilitate inspection of the main spar. The blade had no risk of icing owing to the internal current of warm air. The Djinn used relatively standard flight controls, such as the collective pitch control (upon which the throttle was positioned) and adjustable friction trims. Apart from its method of propulsion, the Djinn was a relatively conventional helicopter, featuring a two-seat side-by-side configuration in an enclosed cabin. The cockpit is provided with an array of plexiglas panels, which provide the occupants with a high level of all-round visibility. Directly to the rear of the cockpit was the rotorcraft's single Palouste engine. The engine lacked any electronics and had to be hand-started via a crank handle located on the starboard side of the fuselage. The Djinn possessed the ability to fly at high overload weights for around 5 sec by correctly harnessing the accumulated kinetic energy of the rotor; this 'jump' technique was successfully used to achieve certification for it to be operated to carry heavy payloads, some of which could represent up to 54% of the rotorcraft's overall gross weight. For more information on development, design and operational history, click here.
