Sud-Ouest SO.1220 / SO.1221 Djinn / YOH-1
The experience acquired by Sud-Ouest in building its two prototypes of the Ariel led to the SO.1221 Djinn. The Djinn's began with two single-seat SO.1220 prototypes, F-WGVO and F-WGZX, the first of which made its maiden flight on 2 January 1953. A simple uncovered structure of welded steel tube carrying a two-blade rotor above it, and with a single exposed seat for its pilot. Its powerplant was a Turbomeca Palouste turbo-compressor producing a large volume of compressed air which, using a similar distribution method to that of the Ariel, was discharged at the blade tips. These were both intended primarily to prove the rotor and propulsion systems.
F-WGVO was later fitted experimentally with agricultural spray booms.
On 16 December 1953 the first of five 2-seat SO.1221 prototypes was flown, having a fully enclosed cabin, two side-by-side seats, an open-framework tail boom, and an all-up weight of 600kg. On 29 December this aircraft established a new altitude record in its class of 4789m.
The Djinn was the world's first production helicopter to make use of the 'cold jet' principle of propulsion. This system used a modified Turbomeca Palouste IV engine as a turbo-generator to feed compressed air through the rotor shaft to ejectors built into the tips of each rotor blade. The air itself is in fact warm enough to eliminate the need for other means of de-icing the blades. No tail rotor is fitted, the aircraft having two outrigged fins and a large central rudder that is situated in the line of the residual thrust exhaust from the engine to provide directional control. The craft's small spartan two-seat cockpit was surrounded by a sectioned bubble-type enclosure and transparent side doors, which combined to provide excellent visibility forward and to both sides. Cockpit instrumentation was quite basic in the standard SO.1221, and The Djinn's landing gear was of the skid type, with small retractable wheels to facilitate ground handling.
Twenty-two pre-series SO. 1221's were then built, primarily for evaluation for the French Army, and the first of these was flown on 23 September 1954. Three machines from this batch were evaluated by the U.S. Army, under the designation YOH-1.
In late 1956 the US Army leased three examples for evaluation in the observation role. The Djinn, which had first flown in December 1953, was already in service with the French Army as an observation craft and its success in that role, coupled with its relatively low per-unit cost and fairly basic maintenance requirements, piqued the Army's interest. The machines obtained by the Army (serials 57-6104 through -6106) were the first helicopters acquired under the new HO (helicopter, observation) classification, and were designated YHO-1. the three YOH-1s were consequently fitted with additional U.S. military-standard avionics and communications equipment for their Army evaluation.
The Army's engineering and operational evaluation of the YOH-1 found the aircraft to be well built, relatively easy to maintain under field conditions, and an exceptional observation platform. The Djinn was not adopted for service use, however, primarily because the Army faced continuing budgetary constraints and some domestic political opposition to the procurement of French, rather than American (or Canadian) aircraft. In early 1958 all three YOH-1s were returned to Sud-Ouest for ultimate delivery to the French Army.
Chief customer for the Djinn has been France's Aviation Legere de l'Armee de Terre, which received one hundred of the one hundred and fifty production Djinns completed up to 1961, and still had about half of these in service in mid-1967. The first production aircraft was flown on 5 January 1956, and French and US certification was gained in April 1958. Six were also delivered to the Federal German Heeresfliegerei. The military Djinns operate at a slightly higher gross weight - 800kg - than the civil models. One was used in France for the first experiments in launching Nord SS.10 anti-tank missiles from a helicopter, but the Djinn's main military functions have been those of observation, liaison, training and (with one pilot and two external litters) casualty evacuation.
Between forty and fifty civil Djinns were active in ten countries, most of them in an agricultural role, for which Sud-Aviation offered renewed conversion facilities in 1965. The so-called 'agricopter' version of the Djinn can carry up to 200 litres of liquid chemical in twin tanks, and is fitted with lateral spray bars for the spraying, dusting or 'fogging' of crops with fertilisers or pesticides.
When production ended in the mid-1960s a total of 178 had been built, exported to about 10 countries. Many were used in an agricultural role, equipped with two tanks to contain liquid chemicals and spray bars for its distribution. By the time that production ended Sud-Ouest had twice changed its name, to Ouest-Aviation on 1 September 1956 and Sud-Aviation on 1 March 1957 when it merged with Sud-Est Aviation; this explains why the Djinn is sometimes recorded as the Ouest S.O.1221 or Sud-Aviation S.O.1221.
Sud-Ouest SO-1221 Djinn
Engine: 1 x Turbomeca Palouste IV turbo-compressor, 179kW / 237 shp
Main rotor diameter: 32 ft 10 in / 10.97 m
Fuselage length: 17.388 ft / 5.3m
Height: 8.530 ft / 2.6m
Width of hull: 6.332 ft / 1.93 m
Max take-off weight: 800kg / 1,550 lb
Empty weight: 793.8 lb / 360kg
Max speed: 70 kts / 130km/h / 75 mph
Endurance: 2h 15min
Initial climb rate: 1279.53 ft/min / 6.5 m/s
Service ceiling: 13123 ft / 4000 m
Range: 103 nm / 190 km
Typical range: 100 miles at 44 mph
Sud-Ouest SO.1221 "Djinn"