Ye 151/1 / Ye-151/2
Following close on the heels of the Ye-150, the OKB started work on the full-scale mock-up of a new prototype—the Ye-151— armed with a rotating twin-barrel cannon that was set on the forward fuselage structure and that revolved around the air intake case axis. With the cannon (a 23-mm TKB-495 whose axis of rotation was perpendicular to its annular support axis) at its widest angle, a noticeable torque occurred that disrupted the aircraft’s three-axis stability and made it impossible to shoot accurately. For the Ye-151/2 the cannon and its support were moved behind the cockpit and thus closer to the aircraft’s center of gravity.
The Ye-151’s forward fuselage was longer than that of the Ye-150, but the dimensions of the air inlet duct did not need to be modified because the ammunition boxes and belts were transferred to behind the cockpit. Wind tunnel experiments proved that the internal aerodynamics of the extended duct improved the engine’s operation. This arrangement was retained for future aircraft of this family, starting with the Ye-152A.