Russian K-7 Heavy Aircraft

Kalinin K-7 (Russian: Калинин К-7) was a heavy experimental aircraft designed and tested in the Soviet Union in the early 1930s. K-7 was of unusual configuration with twin booms and large underwing pods housing fixed landing gear and machine gun turrets. In the passenger version, seats were arranged inside the 2.3 meter (7 ft 7 in) thick wings. The airframe was welded from KhMA chrome-molybdenum steel. The original design called for six engines in the wing leading edge but when the projected loaded weight 2 more engines were added.  The only prototype crashed during a test flight.