Long before the Russian concern of Tupolev OKB was developing famous Soviet Cold War bombers, it tried its hand at fighter design in the I-4 (ANT-5) biplane fighter of 1928. The type became the first Soviet all-metal fighter and was produced in the hundreds during the inter-war period. A handful of variants greeted the service career of this oft-forgotten warplane. Design of the fighter is attributed to Pavel Sukhoi.
Apart from its all-metal design, the I-4 exhibited traditional physical qualities consistent with the inter-period. The single pilot sat in an open-air cockpit behind the upper wing assembly. The upper and lower components were joined to one another by V-type struts. The lower assembly was also shorter in span making the biplane wing arrangement "sesquiplane". The undercarriage, wheeled at the two main legs under center mass, with a skid added under the tail for ground running. The tail unit was conventional with a single fin and low-set horizontal planes.
Engineers elected for the French Gnome-Rhone "Jupiter" 9-cylinder air-cooled radial piston engine of 420 horsepower and this was installed in the nose section. The engine drove a two-bladed propeller which held a large-diameter spinner at its center for aerodynamic efficiency.
Proposed armament had become 2 x 7.62mm machine guns synchronized to fire through the spinning propeller blades. Provision was added later during testing for rockets to be carried along the upper wing - increasing the fighter's attack value.
A first-flight (in prototype form as the "ANT-5") was recorded during August of 1927. This led to some revisions in the design including a new cowling and reworked tail unit. The ANT-5 then entered service as the "I-4".
Performance-wise, the I-4 netted a maximum speed of 160 miles per hour, a range out to 525 miles and a service ceiling up to 25,100 feet. Rate-of-climb was 1,820 feet-per-minute. Empty weight was 2,155lb with a Maximum Take-Off Weight (MTOW) of 3,155lb.
A revised first-series model appeared with the Mikulin M-22 engine (a license-built copy of the Gnome-Rhone "Jupiter" 9ASB) of 460-480 horsepower. The "I-4Z" then followed and this version introduced smaller lower wings. Having the lower wings completely removed - therefore becoming a true monoplane - the aircraft was revised in the "I-4bis" developmental form. The "I-4P" became a converted floatplane derivative.
A total of 369 I-4 fighters were completed into 1934 and the last of the lot was retired from frontline commitments back in 1933 - though the I-4 went on to serve for a time longer as an instructional vehicle. The I-4 series was also briefly trialed as a "parasite fighter" in experiments of the 1930s (that also included the firing of the 76mm Kurchevski recoilless gun from the aircraft), coupled to the new Tupolev TB-1/TB-3 bomber series mothership (detailed elsewhere on this site).
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