In the mid 1930’s Leningrad Factory No.23 was producing versions of the Polikarpov U-2 trainer. In parallel with the development of the serial versions U-2, AP and others, NG Mijelson and AI Morschijin proposed in 1934 the development of a version with a similar layout, but with larger dimensions and a more powerful M-48 engine of 200hp. The objective of this model was to obtain a medium training aircraft in which the students could continue after finishing the initial classes with the U-2.
Construction of the U-3 (Russian: Михельсон/Морщихин У-3) included a number of bolted duralumin aggregates. These aggregates were generally lighter. This, together with some decrease in the reserves of structural resistance, lightened the model. Other minor modifications were introduced with a view to improving performance.
The M-48 engine was protected by a hexagonal-shaped Townend cowling constructed of “Enerzh-6” stainless steel.
The U-3 was tested in 1935 but the results obtained were not much higher than those of the U-2, and the M-48 engine was not produced in series.
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