Design and Development
From 1956, the Soviet light four-seat helicopter Mi-1 was produced under license in the Polish WSK PZL-Świdnik works in Świdnik, under a designation SM-1 - and as much, as 1594 were manufactured. In 1957, works started in WSK PZL-Świdnik to modernize the helicopter and fit it with enlarged, five-seat cabin. One of goals was to make training easier, placing two pilots side by side. Main designer was Jerzy Tyrcha.
Most evident difference was larger cabin, extended towards front, but in fact most fuselage parts were reconstructed. The cabin had two wide side doors, sliding rearwards. Unchanged were: engine with transmission and rotor, fuselage boom and landing gear. The prototype flew first on 18 November 1959. It appeared successful and a limited production started in 1960. Its take-off characteristics and performance were slightly worse, than of Mi-1/SM-1 - one of reasons was found an unsuitable carburetor intake, but it was improved only on some helicopters.
Only 91 helicopters were produced (some sources say 85). They were produced only for Poland, while the SM-1 remained main export product of Świdnik at that time. Three similar variants were produced: military liaison aircraft, air ambulance and flying crane; their equipment could be exchanged.
Basic liaison and transport variant had seats for three passengers on a rear bench and one seat next to a pilot. In the air ambulance variant, single stretchers were carried in the fuselage - loaded through a special hatch in a fuselage front, on the right side. Additional two injured could be carried in detachable external closed capsules on either side of the fuselage. All variants could carry additional external fuel tank 140 l on the left side, extending range to 500 km (it could not be used with side capsules). The crane variant (known as SM-2D) was used in limited numbers for search and rescue missions, and it had a hydraulic winch, that could lift 120 kg, in a place of a right front seat.
Read more about this topic: PZL SM-2
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