yakovlev based his desing on three starting points, The Klimov M-106 Vee engine rated at 1,350 hp (1.007 kW), concentration of light armament in the forward fuselage, and a simple structure to ensure easy maintenance in the field. The use of stressed skin in combination with a light-alloy structure was considered as well, but decided against.
 

Alternatively to the 20 mm ShVAK cannon a 0.50 inch (12,7 mm) Beresin UBS gun, 250 rounds, could be installed. Later prototypes were altered, as can be expected, and featured a separate duct for the oil cooler under the engine, air inlets for the carburetor in the wing leading edges, ejector exhaust stubs, increased chord of the fin, a fixed tailwheel, and a revised cockpit/rear turtledeck combination.