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Soko S-55-5
History and Description
In 1954, ten Westland WS-51 Mk. 1B were the first helicopters introduced to the Yugoslav Air Force (JRV). They served as the basis for the development of the 27th helicopter squadron, the first unit with this new type of aircraft. The plan eventually called for the acquisition of more helicopters. In 1957, one Westland WS-55 Series 1 with the PW-1340-57 550 hp engine was obtained for testing. This unique S-55 (in JRV official documents, the British prefix W is not used) was first tested at the Aviation Test Center (VOC). At the end of the 1950s, a decision was made to acquire the first batch of finished S-55 (WS-55) in two variants (the basic S-55-5 and the anti-submarine S-55-7). After that, a license was acquired for production at the “Soko” factory in Mostar. The engine was imported, while the transmission was made in factory “21. May” from Rakovica. November and December of 1960 saw the arrival of the first examples. They were S-55-5 with registration numbers between 11700 and 11703 and S-55-7 with numbers 11900 and 11901. When they were introduced into the armament, the Mi-4 had already arrived from the USSR with twice the payload capacity and at a 20 percent lower price. Although the Mi-4 had the advantage, due to the ambition to develop domestic industry, work continued on the S-55. By 1976, 34 S-55-5 (model numbers from 11704 to 11737) and four S-55-7 (model numbers from 11902 to 11905) had been built. Initially, 90 aircraft were to be produced, but production was discontinued due to the complete obsolescence of the aircraft. Subsequently, it turned out that the S-55 had serious structural defects and limited performance.
The first JRV experiences with rocket weapons on helicopters were gained on the S-55. In 1966, two side mounts for two FFAR 2.75-inch (VVRS 69.8 mm) unguided rockets were attached to S-55 No. 11700. In JRV’s inventory, there were large quantities of these missiles intended for arming F-86D fighter planes. At first, pilots found it difficult to keep crosshairs on target for more than 3 seconds, but after special training, they were able to do so. In 1970, an S-55 with serial number 11701 was equipped with four launch rails for 9M14 Malyutka missiles. These missiles were extensively introduced into the JNA’s armament at that time. After several tests, it was discovered that the S-55 could not be used as an armed helicopter due to strong vibrations. Therefore, both S-55 helicopters were later disarmed and returned to the squadron
Specifications
Crew: 2
Length: 19.1 m
Diameter of the rotor blades: 16.16 m
Height: 4.07 m
Empty weight: 2710 kg
Normal takeoff weight: 3270 kg
Maximum takeoff weight: 3630 kg
Fuel capacity: 470 kg
Maximum speed: 176 km/h
Cruise Speed: 139 km/h
Range: 485 km
Engine: Pratt & Whitney Wasp R-1340-40, 410 kW (600 hp)
Armament:
- 2x FFAR 2.75-inch (VVRS 69.8 mm) unguided rocket launchers
or - 4x 9M14 Malyutka missiles
Gallery
Launch rails for 9M14 “Maljutka” missiles on S-55-5, serial no. 11701
