The Mi-2 was produced exclusively in Poland, in the WSK "PZL-Świdnik" factory in Świdnik. The first production helicopter in the Soviet Union was the Mil Mi-1, modelled along the lines of the S-51 and Bristol Sycamore and flown by Mikhail Mil's bureau in September 1948. During the 1950s it became evident, and confirmed by American and French development, that helicopters could be greatly improved with turbine engines. S. P. Isotov developed the GTD-350 engine and Mil used two of these in the far superior Mi-2. The twin shaft-turbine engines used in the Mi-2 develop 40% more power than the Mi-1's piston engines, for barely half the engine weight, with the result that the payload was more than doubled. The Mi-2 fuselage was extensively altered from its predecessor, with the engines mounted overhead. However, the external dimensions remained similar. For more details, including the 27 variants and versions, click here.