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"Stal-8" / I-240

The design bureau of Polikarpov, Sukhoi, and D.P.Grigorovicha released a new fighter, which corresponded to a fresh tactical and technical requirements for the year. At the end of November 1933, Bartini got himself the task to create a fighter, personally by the People's Commissar of Heavy Industry. The fighter, called "Steel-8" (VVS cipher - I-240), to build private building in the fenced off workshop of the plant 240.

In aerodynamic configuration was almost identical to the "Steel-6", differing in larger sizes due to the use of the new French engine "Hispano-Suiza" with a power of 860 horsepower and all-metal construction. The production technology was tested at the previous type. Of course, at the request of the military to "Steel-8" came to a head lamp pilot acting on the fuselage. When fixed dihedral visor lamp cover can be moved forward by a through flow of air beneath it had no tendency to spontaneous collapse in flight. Only the pilot can push the transparent cap back when the cabin is closed. The canopy worked on a full-size layout, and a scale model (1: 5) passed wind tunnel Air Force Academy imeni N.B.Zhukovskogo.

The fighter was armed with two synchronized machine guns ShKAS mounted on the motor with the cartouche on the wheel niche. Water radiator located in the wing, like a prototype, and the oil cooler was arranged in the wing root area under the right fairing junction with the fuselage. External forms Bartini fighter gave the impression that it was designed not in 1934, but five or ten years later, so perfect was the aerodynamics. "Steel-8" was estimated to be broadly consistent with the period of the Second World War. At an altitude of 3000 meters of its maximum speed would be 630 km / h, service ceiling - 9000 m at take-off weight in one and a half tons. These figures are quite justified, given that the aircraft had very clean lines, with minimal deviations from the theoretical contours, much lower than in production.

"Steel-8" was the USSR's first all-metal aircraft to use spot welding. Its monocoque fuselage represented a hollow sheet profiles U-shaped cross-section. The wing spars and ribs were welded tubular truss. The sheathing wing was internal - 0.8 mm thick outer - 0.5 mm. Across the span of the condenser to the rear wing ailerons were hung four sections, which on takeoff, landing and turns performed the function of flaps. Aileron and rudder rotation was cable operated. The elevator was deflected in response to the movement of the pilot's handle through rigid tubular rods. The longitudinal control channel circuit was set up mechanism to change the elevator deflection angle, depending on the flight speed. Two gas tank capacity of 175 liters were placed in the root zones of the wing consoles. Lenticular oil tank, also welded construction, its upper side fit into the outer contour of the fuselage before the cabin. In flight, especially at high speeds, the oil tank is also cooled by the flow.

The creation of a talented designer can not be ordinary. Bartini did not use common profiles for the wings and tail. His profiles were one and a half to two times more efficient aerodynamic quality and considerably more stable stall characteristics at large angles of attack. Perfectly owning mathematics, Bartini applied it for the analytical determination of arc profiles. Bartini found lines corresponding dependencies so that at the junction of two conjugate curves of their function would not tolerate the gap up to the second order. And the air flow felt filigree contours and smooth parted with the least resistance.

Unfortunately, I-240 was not completed, and construction ceased in the end of 1934 approximately 60% completion stage. Chief of CAF management was not needed, but SUAE also had its prototype in terms of construction and did not want to have. In addition, they were strong competitors made the I-16, I-14, SP-1. The vulnerability of cooling systems in air combat or by anti-aircraft fire actually reduced the combat capability of "Steel-8." Measures to increase the survivability of the system were outlined, with the capacitor division into compartments under the autonomous circulation of antifreeze, but GU GVF, while on an outstanding occasion, stopped funding the work.