The Polikarpov I-180 () was a 1938 Soviet fighter prototype. It was the last attempt to extract performance from the basic Polikarpov I-16 design. The development cycle was plagued with problems, especially with the death of the star Soviet test pilot Valery Chkalov in one of the prototypes.
Design and development
The I-180 represented a further development of the basic I-16 design in order to take advantage of the new radial engines coming into service. It was designed to meet a requirement of the Soviet Air Force of January 1938 for a new interceptor aircraft with a radial engine. It was preceded by a series of projected I-16 variants with a more powerful Tumansky M-88 two-row radial engine: I-161, I-162, I-163, I-164, I-165, I-166 and I-167.
The I-180 was a single-engine, low-wing monoplane aircraft of mixed construction with a duraluminum frame covered in plywood and fabric. The pilot sat near the tailfin in an open cockpit with a windshield similar to the I-16. The landing gear was retracted pneumatically, including the tail wheel. The main visual difference between the I-180 and I-16 was a new wing with a perpendicular straight leading edge, and an aerodynamically refined fuselage with a longer slim engine cowling. The new fighter was to be powered by an 820 kW (1,100 hp) M-88 engine, a development of the license-built Gnome-Rhône Mistral Major (known as M-85 in the USSR), and represented the next step in evolution from the 1937 I-165-11 prototype. The proposed armament consisted of four 7.62 mm (0.3 in) ShKAS machine guns and 200 kg (440 lb) of bombs. Dmitriy Tomashevich was assigned as the lead designer.
The ill-fated development of the I-180 started early on. The only version of the M-88 available at the time used reduction gear requiring a very large propeller, at least in diameter – massive for an aircraft that in layout and dimensions resembled an I-16 with an elongated nose. Even before leaving the drawing board, the fighter had to be redesigned for an M-88R engine with reduction gear and a constant-speed propeller. The projected top speed fell from 572 km/h (355 mph) to 557 km/h (345 mph). The first prototype, however, was eventually fitted with a similar M-87 950 hp engine, because the M-88R was not ready. The prototype was built at Number 156 Factory in Moscow.
Testing and evaluation
The VISh-23Ye propeller was delayed, and early test runs were conducted using a different propeller with manual pitch control (VISh-3Ye). Consequently, the engine was prone to overheating, and to compensate for this the cowling flaps restricting airflow around the engine were removed. Despite these problems, and the fact that the prototype had not completed all ground tests, the authorities were demanding a test flight as soon as possible. Polikarpov himself objected to flying the prototype before it would be ready, around February 1939, but he could not stop it. The series of events which took place on 15 December 1938, while not entirely clear, are tragic. Neither Polikarpov nor Tomashevich approved the initial flight, and no one had signed the form releasing the prototype from the factory. The famous Soviet test pilot Valery Chkalov took off and made a low-altitude circuit around the airfield. For the second circuit, Chkalov flew farther away, climbing to over 2,000 m (6,560 ft), even though the flight plan specifically forbade exceeding 600 m (1,970 ft). Chkalov apparently miscalculated his landing approach and came in short of the airfield but, when he attempted to correct, the engine stalled. The pilot was able to avoid several buildings but crashed into a power line. Chkalov was thrown from the cockpit, badly injured, and died two hours later.
The official government investigation concluded that the engine stalled because it became too cold in the absence of the cowl flaps. Others hypothesized that Chkalov rapidly advanced the throttle and flooded the engine. As the result of the crash, Tomashevich and several other officials, including Arms Industry Department director S. Belyakin, who urged the first flight, were immediately arrested. Years later, fellow test pilot M.M. Gromov blamed the designers for flawed engine cooling and Chkalov himself for deviating from the flight plan. Chkalov's son also claimed that a plot to assassinate his father had been brewing in the months preceding his death, but the circumstances of the crash make foul play unlikely. Regardless, with Chkalov's death Polikarpov's reputation with Joseph Stalin suffered a blow from which he would never recover.