During the 1920s, the Polikarpov 2I-N1 / DI-1 emerged as a prototype Soviet two-seat fighter.
Unfortunately, the sole prototype encountered a tragic fate on its ninth flight as it succumbed to manufacturing defects.
Consequently, the program was abruptly terminated, halting any further development or production of this aircraft.
In October 1924, Nikolai Nikolaevich Polikarpov initiated the design of a two-seat fighter known as the 2I-N1 at Zavod (Factory) Nr. 1 located in Khodynka Aerodrome, Moscow.
This particular aircraft held significance as it was the first indigenous two-seat fighter developed in the Soviet Union.
Structurally, it featured a single-bay biplane design with a sesquiplane configuration for its wings.
The fuselage, which took on an oval shape, was constructed using moulded birch plywood known as ‘shpon’.
Similarly, the wings were also covered with this material.
While the upper wing possessed two spars, the lower wing only had one.
Interestingly, the wings did not incorporate internal bracing wires; instead, they were built using plywood ribs with lightening holes and stringers.
V-struts made from Duralumin were employed to separate and connect the wings to the fuselage.
External steel bracing wires were utilised as well.
The undercarriage axle was enclosed by an airfoil, and a small ski functioned as the tailskid.
The aircraft was equipped with an imported Napier Lion engine, which had a power output of 336 kilowatts (451 horsepower).
This engine was housed within a metal cowling.
In terms of fuel and oil capacity, it could carry up to 547 kilograms (1,206 pounds).
As for armament, the fighter was armed with a single fixed 7.62 mm (0.300 in) synchronized PV-1 machine gun, along with a 7.62 mm DA machine gun mounted on a ring in the observer’s cockpit.
The prototype’s inaugural flight occurred on 12 January 1926, and it was now referred to as the DI-1.
During subsequent test flights, the DI-1 showcased exceptional performance, with Polikarpov himself serving as the observer on the fourth and eighth flights.
However, tragedy struck during the ninth flight on 31 March 1926.
While conducting speed runs at a height of 100 metres (328 ft) over Khodynka Airfield, the upper surface of the right upper wing suddenly tore off, followed by the lower skin.
This catastrophic event led to the collapse of both right wings, resulting in the DI-1 crashing and claiming the lives of both the pilot, V. N. Filippov, and the observer, V. V. Mikhailov.
Upon examining the wreckage, it was discovered that significant portions of the wings’ skin were poorly glued, and several rib caps and stringers were not glued at all.
Additionally, numerous panel pins were not properly connected to the structure, and several bradawl holes, crucial for equalising pressure within the wing, were completely absent.
This devastating incident sent shockwaves throughout the aviation industry, leading to a six-month halt in design work.
In response to the loss, Polikarpov erred on the side of caution and constructed subsequent aircraft with a stronger, albeit heavier, structure than necessary.
Regrettably, all further progress on the project was abandoned following the crash, ostensibly due to the unavailability of a suitable engine. Specifications Crew 2 Length 9.75 m (32 ft 0 in) Wingspan 12 m (39 ft 4 in) Wing area 27.15 m2 (292.2 sq ft) Empty weight 1,153 kg (2,542 lb) Gross weight 1,700 kg (3,748 lb) Powerplant 1 × Napier Lion W-12 water-cooled piston engine, 336 kW (451 hp) Propellers 2-bladed fixed-pitch propeller Performance Maximum speed 268 km/h (167 mph, 145 kn) Range 800 km (500 mi, 430 nmi) Service ceiling 7,100 m (23,300 ft) Time to altitude 5,000 m (16,404 ft) in 13 minutes Wing loading 63 kg/m2 (13 lb/sq ft) Power/mass 0.197 kW/kg (0.120 hp/lb) Horizontal turn time 12 sec Armament Guns 2 × 7.62 mm (0.30 in) machine guns Sources King of Fighters – Nikolay Polikarpov and his Aircraft Designs – Vol 1 & 2. The History of Soviet Aircraft from 1918-Vaclav Nemecek. The Osprey Encyclopedia of Russian Aircraft 1875–1995-B Gunston. Polikarpovs Biplane Fighters-Yefim Gordon & Keith Dexter.
