From
1956, the Soviet light three-seat or 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 many as 1594 were manufactured. In
1957, works started in WSK PZL-Świdnik to modernize the helicopter and fit it with an enlarged, five-seat cabin. One of the design goals was to make training easier, by placing the two pilots side by side. In the air ambulance role, treating a patient inside the fuselage was easier than in side capsules. The most obvious difference was a larger cabin, extended towards the front, but in fact most fuselage parts were reconstructed. The cabin had two wide side doors, sliding rearwards, being an improvement over the Mi-1, in which its automobile door could not be opened in flight and had to be removed for some purposes. Only 86 helicopters were produced in four series, differing in details, plus three prototypes (some sources say 91 or 85). They were produced almost exclusively for Poland, while the SM-1 remained the main export product of Świdnik at that time. The helicopter was manufactured only in one variant, and could change its role to passenger, transport, air ambulance or flying crane. in
Kraków ,
Weston-super-Mare. Visible is a hatch in a nose. Basic variant had seats for three passengers on a rear bench and one seat next to a pilot. There were no double controls. In the air ambulance configuration, single
stretchers were carried in the fuselage: loaded through a special hatch in a fuselage front, on the right side. A physician could sit behind the pilot, while other seats were removed. An additional two patients could be carried in detachable external closed capsules on either side of the fuselage, typical for Mi-1. All variants could carry additional 140 L external fuel tank on the left side, extending range to 500 km (it could not be used with side capsules). The crane variant (sometimes known as SM-2D) was used in limited numbers for
search and rescue missions; it had a hydraulic winch that could lift 120 kg, in a place of a right front seat. After removal of all passenger seats, 320 kg of load could be carried. They had a durability of 600 flight hours, like contemporary SM-1 helicopters. ==Operational history==