Polikarpov I-15
The Polikarpov I-15 was a Soviet single-seat biplane fighter aircraft designed in the early 1930s, notable for its distinctive gull-shaped upper wing that earned it the nickname Chaika (Russian for "seagull") and provided enhanced pilot visibility.[1][2] Developed by Nikolai Polikarpov, it first flew in October 1933 with test pilot Valery Chkalov at the controls and entered production and service with the Soviet Air Force (VVS) in late 1934.[3] Featuring a mixed construction of steel-tube fuselage, wooden wings covered in fabric, and fixed undercarriage, the I-15 was powered by an air-cooled radial M-22 engine (a licensed Bristol Jupiter) producing 480 horsepower, achieving a maximum speed of approximately 350 km/h (217 mph) at 3,000 meters, a service ceiling of 7,250 meters (23,786 feet), and a range of about 500 km (310 miles).[3][1] Its armament consisted of two synchronized 7.62 mm PV-1 machine guns in the upper fuselage, with provisions for up to four in later modifications, and it could carry light bombs or rockets for ground-attack roles.[4] Around 384 to 600 examples were produced in the Soviet Union between 1934 and 1937, with additional license production in Spain totaling about 237 units.[1][4] The I-15 quickly became a cornerstone of Soviet aviation during the interwar period, marking a significant advancement in biplane design with superior maneuverability that allowed it to outperform many contemporaries in dogfights despite the era's shift toward monoplanes.[2] It saw its first combat during the Spanish Civil War (1936–1939), where over 150 were supplied to Republican forces and achieved notable successes against Italian Fiat CR.32 biplanes and German Heinkel He 51s, claiming hundreds of victories while suffering losses to anti-aircraft fire and superior numbers.[4] Exports and volunteer operations extended its reach to the Second Sino-Japanese War (1937–1945), with 255 delivered to China in 1937 alone and Soviet pilots flying them in defense of Shanghai and Nanking against Japanese forces; by 1939, totals reached 347 aircraft.[2] Further engagements included the Battles of Khalkhin Gol (1939) against Japan, where I-15s supported Soviet-Mongolian troops, and the Winter War (1939–1940) against Finland, though harsh conditions limited their effectiveness.[3][4] By the onset of World War II, the I-15 was obsolescent but remained in frontline VVS service during Operation Barbarossa in June 1941, with over 1,000 operational (including variants) initially used for air superiority and close air support before transitioning to training and rear-area duties by 1942–1943.[2] Its legacy influenced subsequent designs, leading to the improved I-15bis (or I-152) variant introduced in 1937, which featured a more powerful M-25V engine (750 hp), straight upper wings for better aerodynamics, four 7.62 mm ShKAS machine guns, and increased bomb load capacity up to 200 kg, with production exceeding 2,400 units and a top speed of 379 km/h (235 mph).[3][4] The ultimate evolution, the I-153 Chaika of 1939, incorporated retractable landing gear and an M-62 engine (1,000 hp) for a maximum speed of 445 km/h (276 mph), seeing over 3,400 built and continued combat use into 1942, including ramming tactics against German aircraft.[3] Despite their biplane configuration, these Polikarpov fighters exemplified Soviet engineering resilience, bridging the gap to modern monoplanes like the I-16 and contributing to the VVS's early-war experience.[1]Design and Development
Design Features
The Polikarpov I-15 originated as an evolution of the earlier Polikarpov I-5 fighter, with design work beginning in 1933 under the designation TsKB-3 before being redesignated I-15.[4][3] It adopted a sesquiplane configuration, featuring a larger upper wing and a smaller lower wing to enhance structural efficiency and pilot visibility.[5][6] The distinctive gull-shaped upper wings, which connected directly to the fuselage without a center section, earned the aircraft its Russian nickname "Chaika" (seagull) due to their curved, bird-like profile.[4][7] The I-15 employed mixed construction typical of Soviet biplanes of the era, with a welded steel-tube fuselage frame covered in duralumin forward and fabric aft, while the wings used wooden spars reinforced by steel members and fabric skinning.[6][8] It featured fixed tailskid landing gear with faired wheels, providing simplicity and robustness for operations on rough fields, though later modifications removed the fairings for weight savings.[5][8] Initial production models integrated the nine-cylinder M-22 radial engine, a licensed Bristol Jupiter producing 480 horsepower, housed in a Townend ring cowling to improve cooling airflow and reduce drag around the cylinders.[7][3] Later variants transitioned to the more powerful M-25 engine for enhanced performance.[4] Aerodynamically, the I-15 prioritized exceptional maneuverability over outright speed, with its two-bay staggered biplane arrangement allowing tight turns and superior handling in dogfights, achieving a top speed of approximately 350 km/h.[5][4] The gull-wing design not only aided lift distribution but also improved the pilot's forward view by angling the upper wing roots downward toward the cockpit.[6][8] This configuration, combined with the Townend cowling, addressed early stability issues at higher speeds while maintaining the biplane's inherent agility.[3][8] Armament consisted of four synchronized 7.62 mm PV-1 machine guns mounted in the upper fuselage ahead of the cockpit, positioned between the engine cylinders for effective fire synchronization with the two-bladed propeller.[6][8] The design included provisions for light ground-attack roles, such as underwing racks for up to two 50 kg bombs or six RS-82 rockets, allowing versatility beyond pure interception.[4][5][9] The single-seat open cockpit was positioned just aft of the upper wing, offering the pilot basic instrumentation and a raised fuselage spine for partial rearward protection, though visibility was somewhat obstructed by the engine and gull wings.[5][8] This layout emphasized quick responsiveness in close-quarters combat, aligning with the aircraft's role as an agile biplane fighter.[6]Prototyping and Testing
The initial prototype of the Polikarpov I-15, designated TsKB-3, completed construction in October 1933 and conducted its maiden flight later that month under the control of test pilot Valery P. Chkalov. Design work occurred under difficult conditions, as Polikarpov developed the aircraft while imprisoned in the "Sharpener" labor camp.[3] Early flight tests from November 18, 1933, revealed longitudinal instability attributed to the gull-wing upper biplane configuration, which was partially mitigated through wing incidence adjustments and improved at higher speeds, though pilots noted sensitivity to control inputs.[3] A minor accident occurred on November 23 during these factory trials, but testing resumed and concluded within 26 days, demonstrating the aircraft's exceptional maneuverability, including a record 360-degree turn in 8 seconds.[4] The prototype was initially powered by an imported Wright Cyclone SGR-1820-F3 radial engine producing 630 hp at sea level and up to 715 hp at 6,500 ft, but subsequent development shifted to Soviet-licensed variants for production readiness.[6] By 1934, the second prototype incorporated the less powerful M-22 (a licensed Bristol Jupiter, 480 hp), while 1934-1935 airframes transitioned to the more capable M-25 (licensed Wright Cyclone, 750 hp), which enhanced performance to a climb rate of approximately 13 m/s and a service ceiling of 8,000 m.[5] State acceptance trials in December 1933 and April 1934 validated these improvements, including wind tunnel evaluations at the Central Aero-Hydrodynamic Institute (TsAGI) for aerodynamic refinement, armament synchronization with four 7.62 mm PV-1 machine guns, and spin recovery assessments that confirmed the biplane's inherent stability in autorotation.[6] Development faced challenges typical of radial-engine biplanes, including engine overheating and vibrations from the M-25, as well as fuel and oil leaks, which were addressed through iterative cowling redesigns to improve airflow and cooling efficiency.[4] Modifications such as an enlarged vertical stabilizer were implemented based on spin evaluations to enhance directional stability during high-angle-of-attack maneuvers. Approximately five to seven prototypes and pre-production airframes were constructed to iterate these solutions before full-scale manufacturing.[3] Following successful state trials, the I-15 was certified and adopted by the Soviet Air Forces (VVS) in early 1934 as the primary interceptor, with initial production orders placed for 476 aircraft at Factories No. 1 and No. 39 in Moscow, marking the transition to series production later that year.[6]Operational History
Spanish Civil War
The Soviet Union supplied approximately 150 Polikarpov I-15 fighters to Republican Spain between late 1936 and 1938 as part of its military aid program, with the aircraft arriving in batches at ports like Cartagena and forming the backbone of the Republican fighter force. These planes were nicknamed "Chatos" (snub-nosed) by Spanish pilots due to their distinctive flat-nosed appearance and were organized into dedicated escuadrillas, initially flown by Soviet volunteer pilots before transitioning to Spanish crews. The I-15's agility, stemming from its gull-wing biplane design, proved particularly effective in close-range dogfights during this European theater debut.[4] The I-15 saw its first combat missions in November 1936, intercepting Nationalist bombers over Madrid and claiming several early victories against slower opponents. In 1937, during key engagements like the Battle of Guadalajara, the Chatos achieved notable successes against Italian Fiat CR.32 biplanes, exploiting superior climb rates (up to 15 m/s) and tight turning radii to secure initial kill ratios around 5:1 in favorable conditions. Republican pilots reported the I-15's maneuverability allowed it to dominate turning fights at low to medium altitudes, where the CR.32's similar top speed of about 360 km/h could not compensate for the Polikarpov's energy retention in vertical maneuvers. These early triumphs temporarily disrupted Nationalist air superiority and boosted Republican morale.[10][11] Tactically, the I-15 evolved from pure air superiority roles to escorting SB-2 bombers and conducting ground-attack missions with light bombs and machine-gun strafing, adapting to the fluid front lines of the war. However, the arrival of German Messerschmitt Bf 109 monoplanes in late 1937 shifted the balance, as the I-15's level speed of approximately 370 km/h proved inadequate against the Bf 109's 470+ km/h, leading to ambush tactics favoring hit-and-run dives over prolonged engagements. By the war's end in 1939, high attrition occurred, with the majority of the approximately 390 total I-15s (Soviet-supplied and Spanish-licensed) lost in combat, accidents, or ground attacks; Nationalists captured 53 flyable examples.[4][9] Combat experience in Spain provided critical operational insights for Soviet aviation doctrine, with Republican and Soviet pilots' reports emphasizing the need for improved horizontal speed and retractable undercarriage to counter emerging monoplane threats—issues later addressed in designs like the I-16. Feedback from over 3,000 estimated combat sorties underscored the I-15's strengths in agility but exposed its limitations in sustained pursuits. After the Republican defeat, surviving Chatos (including captured examples) were incorporated into the Nationalist Spanish Air Force, serving in training and secondary roles until around 1950.[12][4]Second Sino-Japanese War
The Republic of China Air Force (ROCAF) received 255 Polikarpov I-15 fighters from the Soviet Union in the autumn of 1937 as part of Operation Zet, a covert aid program to bolster Chinese defenses against the Japanese invasion.[9] These deliveries continued through 1941, with additional I-15bis variants bringing the total number of Polikarpov biplane fighters to approximately 477 by 1939, operated by Soviet volunteer groups, such as the 1st Air Brigade under commanders like F.P. Polynin, and Chinese squadrons including the 21st and 22nd Pursuit Squadrons.[13] The Soviet volunteers, numbering around 250 initially and expanding to over 3,600 personnel by 1941, flew alongside ROCAF pilots to form a mixed force capable of challenging Japanese air superiority in defensive operations.[2] I-15s conducted intercepts, for example on November 21, 1937, near Nanjing, claiming one Japanese bomber and two Mitsubishi A5M fighters with no losses reported. In early 1938, Soviet and Chinese pilots claimed around 30 Japanese aircraft in the first two months, primarily Kawasaki Ki-10 biplane bombers and Nakajima Ki-27 fighters, often employing hit-and-run tactics that exploited the I-15's superior maneuverability in dogfights at low altitudes.[14][15] However, as Japanese tactics evolved, the biplanes suffered high attrition, particularly from the faster Nakajima Ki-43 Hayabusa starting in 1941, leading to lopsided exchanges where I-15 formations claimed victories but lost multiple aircraft per engagement; Japanese records indicate over 200 I-15 family aircraft destroyed in combat by mid-1941.[15] To adapt to China's dusty and tropical environments, I-15s underwent field modifications including sand and dust filters for the radial engines and underwing bomb racks enabling light ground attack roles with up to 100 kg of ordnance, enhancing their utility in supporting retreating ground forces during the Battle of Wuhan.[4] Chinese pilot Liu Chi-Sheng, flying I-15bis variants, achieved ace status with at least 10 confirmed victories, including several Ki-27s, contributing to the type's reputation among ROCAF squadrons despite the overall pilot training challenges.[16] Strategically, the I-15 provided critical air cover for Chinese ground operations from 1937 to 1941, delaying Japanese advances and forcing tactical shifts in Imperial Japanese Navy Air Service doctrine, which accelerated development of more agile monoplanes like the A6M Zero to counter the biplane's turning radius.[17] By late 1941, attrition and obsolescence led to their replacement by Curtiss P-40 Warhawks flown by the American Volunteer Group, though surviving airframes continued in secondary roles. Over 200 Soviet pilots were killed in action during these operations, underscoring the intense attritional nature of the air campaign.[18] Remnants of the I-15 fleet were repurposed for training ROCAF recruits until 1945, preserving operational experience amid ongoing Japanese occupation.[13]Battles of Khalkhin Gol
The Polikarpov I-15 and its improved variant, the I-15bis, were deployed by Soviet fighter aviation regiments during the Battles of Khalkhin Gol from May to September 1939, where they supported joint Soviet-Mongolian operations against Japanese forces along the Mongolia-Manchuria border. Approximately 49 I-15bis were initially available to the 22nd Independent Air Regiment (IAP) with 35 aircraft and the 70th IAP with 14, operating under the Soviet 1st Air Army Group attached to the 57th Special Corps.[19] Mongolian pilots, trained on Soviet types, participated alongside their Soviet counterparts in these units, contributing to the overall air effort in the theater.[20] The I-15 family engaged primarily in dogfights against the Japanese Nakajima Ki-27 fighters, leveraging the biplane's tight turning radius for close-range combat despite the Ki-27's speed advantage. Soviet records indicate the biplane units flew over 200 sorties between May and August, claiming numerous victories while suffering losses in intense engagements, such as the eight I-15bis downed on 28 May during a battle against 18 Ki-27s.[19] These actions helped secure local air superiority, allowing the I-15s to conduct effective ground support for General Georgy Zhukov's August counteroffensive by strafing and bombing Japanese positions.[21] Tactics emphasized the I-15's strengths, including low-level attacks with rockets, bombs, and machine guns against troop concentrations and high-altitude intercepts up to 5,000 meters, where its climb rate provided an edge in initial engagements.[19] By mid-battle, the type's limitations became apparent, leading to its partial replacement by newer designs, but it remained vital for reconnaissance and night operations. The No. 3 Air Corps, incorporating I-15-equipped squadrons, played a decisive role in establishing overall Soviet air dominance, which facilitated the encirclement and defeat of Japanese forces, culminating in their withdrawal following the 15 September armistice.[9] Notable pilots, including ace Sergei Gritsevets—who achieved multiple victories primarily in I-16s but advised on biplane tactics—highlighted the I-15's contributions, with some biplane pilots credited for shared kills in mixed formations.[22] Operations across the arid steppe terrain exposed the aircraft to severe dust conditions, yet the I-15 demonstrated robust engine filtration and airframe durability, providing valuable lessons for enhancing dust resistance in subsequent Soviet fighter designs.[19]World War II
During the Winter War against Finland from November 1939 to March 1940, the Polikarpov I-15 and its variants, including the I-15bis, formed approximately 30% of the Soviet fighter inventory deployed to the theater, though they were primarily assigned to reconnaissance and ground attack missions rather than air superiority roles. Around 50 I-15s participated in operations over Lake Ladoga, providing close air support and escort for bombers amid harsh winter conditions; Soviet pilots claimed over 20 enemy aircraft destroyed, including Finnish fighters, but suffered significant losses to superior Finnish Brewsters and ground fire.[4][2] With the German invasion under Operation Barbarossa in June 1941, roughly 1,000 I-15s remained in Soviet frontline service across Ukraine and Belarus, where they were rushed into close air support and interception duties against the Luftwaffe. Despite initial agility advantages in dogfights at low altitudes, the biplanes proved obsolete against the faster and better-armed Messerschmitt Bf 109s, resulting in heavy attrition—hundreds lost in the opening weeks, many on the ground during surprise attacks. By mid-1941, as Yak-1 and LaGG-3 monoplanes entered production, I-15 units were withdrawn from primary combat, with total wartime combat losses estimated at around 300 aircraft.[3][4][21] In subsequent years, surviving I-15s shifted to secondary roles, including advanced training for transitioning pilots and limited night fighting experiments, such as conversions equipped with searchlights for anti-bomber patrols (e.g., the I-15SP variant). A small number saw indirect Pacific involvement through returned Lend-Lease aircraft via Soviet allies, though frontline use there was negligible. Overall, the type flew over 1,000 sorties in 1941–1942 defensive operations, contributing to early war stabilization but highlighting biplane vulnerabilities that spurred Soviet emphasis on modern monoplanes and, eventually, jet development; most were demobilized by 1943 and scrapped post-war.[3][5][4]Production and Variants
Production History
Serial production of the Polikarpov I-15 commenced in early 1934 at Factory No. 1 in Moscow, initially equipped with the M-22 engine, a licensed version of the Bristol Jupiter radial. By the end of 1935, a total of 404 such units had been completed across Factory No. 1 and Factory No. 39, also in Moscow, though early batches suffered from quality issues including substandard materials, engine vibrations leading to deformations and fires, and frequent mechanical breakdowns. These problems were largely addressed through design refinements and improved manufacturing processes by 1936. Of the original I-15 production, 404 were equipped with the M-22 engine and 329 with the M-25 engine.[7][8][3] Production expanded significantly in 1937 with the introduction of the I-15bis variant, powered by the more reliable M-25 engine, and the involvement of additional facilities including Factory No. 21 in Gorky. This scaling enabled an annual output exceeding 1,000 units by late 1937, incorporating export orders for Spain and China. Peak production occurred between 1938 and 1940, with over 2,000 aircraft manufactured annually across multiple plants, including batches for foreign operators; the I-15 series totaled approximately 1,020 units excluding the bis variant.[23][4] Licensed production occurred abroad, with Spain's CASA factories assembling 287 I-15s under agreement, supplementing 284 delivered directly from the Soviet Union. Efforts to license production in China were attempted but yielded limited results, with no significant domestic output recorded until the later Chung 28B, though the country received around 186 I-15bis units by 1939.[24][4] As the German invasion began in 1941, remaining Soviet aviation facilities, including those involved in Polikarpov projects, underwent relocation eastward to the Urals region—such as Factory No. 94 in Novosibirsk—to evade capture, part of a broader evacuation of over 1,500 industrial plants. This disruption, combined with resource shortages and bombing threats, reduced overall aircraft output by approximately 30% in 1941-1942 compared to prewar peaks.[25] The I-15 line was phased out by 1940 in favor of more advanced monoplanes like the I-16 and I-153, with cumulative production across the series reaching approximately 3,000 units, including licensed builds.[24][9]Variants
The Polikarpov I-15 M-22 was the initial production version introduced in late 1934, powered by a 480 hp M-22 radial engine, a Soviet copy of the Bristol Jupiter, and over 400 units were built primarily for early Soviet service and limited exports.[7][6] This variant featured two 7.62 mm machine guns and served as the baseline fighter model before engine upgrades became available.[7] The I-15 M-25, introduced in 1935, represented an upgrade with the more powerful 700 hp M-25 radial engine, a licensed Wright Cyclone, which improved climb rate and overall performance, and approximately 270 units were produced as the standard version for most early operations.[7][6] Later batches of this variant incorporated enhanced armament, including four 7.62 mm PV-1 machine guns and an armored pilot's seat for better protection.[7] A sub-variant with twin 12.7 mm machine guns was also built in limited numbers of about 40 aircraft.[7] The I-15bis, developed in 1937 as the primary evolution of the original design, replaced the gull-shaped upper wing with a straight one for improved stability and visibility, and was equipped with the 775 hp M-25V engine featuring an enclosed NACA cowling for enhanced cooling efficiency.[21] A total of 2,408 units were manufactured between 1937 and 1939 at Factory No. 1 in Moscow, making it the most numerous variant and the backbone of Soviet fighter squadrons during the late 1930s.[21] It retained four 7.62 mm PV-1 machine guns but could be adapted for ground attack with bomb racks or RS-82 rockets.[21] Specialized developments included the I-15bis DM (also known as I-152DM), a 1939 experimental long-range reconnaissance version fitted with ramjet engines for high-altitude performance, of which around 20 prototypes were tested between 1939 and 1940.[21] The I-15TP, a two-seat trainer adaptation designated I-152 DIT-2, was prototyped in 1939 for advanced pilot conversion; only two units were built and the project was abandoned due to its complexity.[21][26] The I-15R was a limited ground-attack modification equipped with rocket armament for close support roles, though only a small number were built.[24] Export adaptations totaled approximately 600 non-Soviet aircraft, including versions for Spain known as the "Chato" with integrated local radio equipment and built under license by CASA (287 units plus 284 delivered directly).[7][6][27] Chinese variants, designated Chung 28, incorporated tropical air filters and the original Wright R-1820-F3 engine, with 30 assembled locally for operations in humid conditions.[24]Operators
Soviet Union
The Polikarpov I-15 entered service with the Soviet Air Forces (VVS) in late 1934, rapidly becoming a cornerstone of the fighter aviation fleet during the 1930s and forming the backbone of the VVS's interceptor capabilities.[4] By 1941, over 1,000 Polikarpov I-15 family aircraft (including variants) remained in the VVS inventory, equipping numerous fighter aviation regiments (IAPs) deployed across the Western and Far Eastern fronts to defend key strategic areas.[5] These units operated the I-15 in accordance with Soviet doctrine emphasizing close air support and air superiority, with pilots like future ace Alexander Pokryshkin conducting early wartime missions in the type as part of regiments initially outfitted with I-15s and I-153s before transitioning to more modern aircraft.[28] During the initial phases of World War II, the I-15 saw intensive combat employment but incurred heavy losses against superior German fighters in 1941, prompting its gradual withdrawal from frontline roles by the end of 1942 as newer monoplanes took precedence.[4] In response, surviving airframes were reallocated to training duties within the VVS, serving in flight schools such as the Kachin Military Aviation School from 1942 onward to build pilot proficiency in biplane handling and basic aerobatics until the war's conclusion in 1945.[4][29] Postwar, the I-15 was fully phased out of VVS combat service by 1947 in favor of advanced fighters like the Yakovlev Yak-9 and Lavochkin La-7, though a limited number lingered in reserve storage for potential auxiliary roles into the early 1950s.[4] The I-15's design legacy directly influenced the development of the enhanced Polikarpov I-153 Chaika biplane, which addressed key aerodynamic and armament shortcomings for continued VVS use into the early war years.[4]Foreign Operators
The Polikarpov I-15 saw significant adoption by foreign air forces, primarily through Soviet aid during the 1930s. These exports supported Republican forces in the Spanish Civil War and Chinese resistance against Japan, though operational longevity was often limited by maintenance challenges. In Republican Spain, approximately 116 I-15s were supplied by the Soviet Union between 1936 and 1938, with an additional 287 license-built by CASA, forming a core component of the Spanish Republican Air Force (Fuerzas Aéreas de la República Española) for fighter and ground-attack roles.[9][24] The aircraft, nicknamed "Chato" for its snub-nosed appearance, arrived in batches starting with 15 units at Cartagena in October 1936, enabling rapid deployment against Nationalist forces.[24] Following the Republican defeat in 1939, some surviving I-15s entered limited service with the Nationalist Spanish Air Force (Ejército del Aire), primarily for training, until their retirement in 1953.[30] The Republic of China acquired I-15s and I-15bis variants via the Sino-Soviet Non-Aggression Pact, with 255 I-15s delivered in autumn 1937 accompanied by over 250 Soviet volunteer pilots, who flew the biplanes in early engagements over Nanking and other fronts; by 1939, totals reached 477 aircraft.[9] The I-15s remained active until 1945, with some captured examples transferred to Chinese Communist forces toward the end of World War II.[3] The Mongolian People's Republic received more than 30 I-15s through Soviet assistance starting in July 1939, bolstering the Mongolian People's Army Air Force (MPAAF) during the Battles of Khalkhin Gol.[24] These aircraft supported ground operations alongside Soviet units, with deliveries continuing to at least 40 by 1942.[24] The MPAAF retired its I-15 fleet in 1945 as more advanced types became available.[31] Captured examples were operated by Finland (Finnish Air Force) and Nazi Germany (Luftwaffe).[27] Other nations conducted limited evaluations of the I-15, including trials in Turkey and Iran during the late 1930s, but neither adopted the type for service.[3]Specifications
I-15 (M-25)
The Polikarpov I-15 equipped with the Shvetsov M-25 radial engine represented a later production model of the fighter, featuring compact dimensions suited to its biplane configuration for superior maneuverability in dogfights. Its length measured 6.10 m, wingspan 9.75 m, height 2.20 m, and wing area 21.9 m², contributing to an empty weight of 1,630 kg and a maximum takeoff weight of 2,180 kg.[32][3] The aircraft's powerplant consisted of a single Shvetsov M-25 nine-cylinder air-cooled radial engine, rated at 750 hp for takeoff, which provided reliable performance for the era's biplane fighters despite its open cowling design.[33] Performance metrics included a maximum speed of 367 km/h achieved at 3,000 m altitude, a practical range of 500 km, an endurance of 2.5 hours, a climb rate of 13 m/s, and a service ceiling of 7,500 m, enabling effective operations in low- to medium-altitude engagements.[34] Armament comprised four synchronized 7.62 mm PV-1 machine guns mounted in the upper fuselage, each supplied with 500 rounds of ammunition, offering a balanced firepower for air-to-air combat.[1] For ground attack roles, the I-15 (M-25) could carry optional external loads such as two 50 kg bombs under the wings or eight RS-75 unguided rockets, enhancing its versatility in close support missions.[1] Fuel capacity was limited to 140 liters in internal tanks, with provisions for auxiliary drop tanks to extend operational radius when required.[3]| Category | Specification |
|---|---|
| Dimensions | Length: 6.10 m; Wingspan: 9.75 m; Height: 2.20 m; Wing area: 21.9 m² |
| Weights | Empty: 1,630 kg; Max takeoff: 2,180 kg |
| Powerplant | 1 × Shvetsov M-25 radial, 750 hp at takeoff |
| Performance | Max speed: 367 km/h at 3,000 m; Range: 500 km; Endurance: 2.5 hours; Climb rate: 13 m/s; Ceiling: 7,500 m |
| Armament | 4 × 7.62 mm PV-1 MGs (500 rpg); Optional: 2 × 50 kg bombs or 8 × RS-75 rockets |
| Fuel | Internal: 140 liters; Drop tanks: Provisions available |
I-15bis
The Polikarpov I-15bis represented an evolution of the original I-15 fighter, incorporating design refinements such as a straight upper wing for improved visibility and structural strength, an upgraded engine installation, and enhanced armament options to address limitations in speed and firepower observed in the base model.[4] These modifications, detailed further in the Variants section, enabled better overall performance while maintaining the biplane configuration's maneuverability advantages.[35] Key dimensions of the I-15bis included a length of 6.27 meters, a wingspan of 10.2 meters, a height of 2.19 meters, and a wing area of 22.5 square meters.[35] The aircraft's empty weight was 1,320 kilograms, with a maximum takeoff weight of 1,900 kilograms, reflecting reinforcements to the airframe for increased loads.[5] Performance characteristics were notably improved, with a maximum speed of 370 kilometers per hour.[5] The range extended to 530 kilometers, supported by an endurance of approximately 2.5 hours, while the climb rate reached 12.7 meters per second and the service ceiling was 9,500 meters.[5] These figures underscored the variant's suitability for extended patrols and intercept missions compared to its predecessor.[36] The powerplant consisted of a single Shvetsov M-25V nine-cylinder radial engine delivering 775 horsepower at takeoff, enclosed in a full-length NACA cowling that reduced drag and improved cooling efficiency.[5] This upgrade from the base model's M-25 engine provided greater power output and reliability.[4] Armament configurations emphasized versatility, typically featuring four 7.62-millimeter machine guns for a balanced mix of firepower and ammunition capacity.[5] Alternative setups included two 12.7-millimeter UBS heavy machine guns and two 7.62-millimeter machine guns, while underwing hardpoints allowed for up to four 50-kilogram bombs or six RS-82 rockets, enhancing ground-attack capabilities.[5][4] Fuel capacity was increased to 225 kilograms of internal fuel (approximately 290 liters at standard density), an improvement over the original I-15 that supported longer mission durations without external tanks.[36]| Specification Category | Details |
|---|---|
| Dimensions | Length: 6.27 m Wingspan: 10.2 m Height: 2.19 m Wing area: 22.5 m² |
| Weights | Empty: 1,320 kg Max takeoff: 1,900 kg |
| Performance | Max speed: 370 km/h Range: 530 km Endurance: ~2.5 hours Climb rate: 12.7 m/s Ceiling: 9,500 m |
| Powerplant | 1 × Shvetsov M-25V radial (775 hp) Full NACA cowling |
| Armament | 4 × 7.62 mm MGs (standard) Or 2 × 12.7 mm UBS + 2 × 7.62 mm Optional: 4 × 50 kg bombs or 6 × RS-82 rockets |
| Fuel Capacity | 225 kg internal (improved for extended range) |