The Polikarpov R-5 was a Soviet-originated biplane reconnaissance / light bomber of the interwar period. Design work spanned three years leading up to a first-flight in 1928 (with the German BMW VI engine) and series introduction followed in 1930, between 6,000 and 7,000 examples ultimately being produced. The type served as the standard reconnaissance and light-attack platform for the Soviet Air Force from 1931 into World War 2 (1939-1945). The series was officially given up for good in 1944 though it continued to fly for other operators after that.
As flown, the R-5 was primarily constructed of wood and fabric as was common for the time. It showcased a relatively streamlined fuselage containing the engine at the nose and cockpit over midships. A biplane wing arrangement of single-bay, unequal-span configuration was used, these braced by N-type struts. The twin-wheeled undercarriage was fixed and of the "tail-dragger" sort while the single-finned tail unit was highly conventional. Easy to manufacture on a grand scale, the biplane was noted as even easier to fly.
The main 1930 production form carried a crew of two and had a running length of 34.7 feet, a wingspan of 50.9 feet, and a height of 10.7 feet. Empty weight was 4,340lb against an MTOW of 7,160lb. Power was from the Mikulin M-17B V-12 liquid-cooled inline piston engine developing 680 horsepower and driving a two-bladed propeller unit at the nose. Maximum speed reached 142 miles-per-hour and range was out to 500 miles. Its service ceiling was 21,000 feet and 3,280 feet could be reached in just over two minutes. Typical armament was 1 x 7.62mm PV-1 machine gun in a fixed, forward-firing mounting and 1 x 7.62mm DA (Degtyaryov) machine gun on a trainable mounting in the rear cockpit. Up to 550lb of bombs could be carried.
Some of the R-5's earliest combat exposure occurred during the Spanish Civil War (1936-1939) where the Republican Air Force was the recipient of some thirty-one examples from the Soviet Union. Operations began in 1936 but these gave a poor showing as daylight bombers and were thus relegated to the night time bombing role. Beyond this, the R-5 was used in the Second Sino-Japanese War (1937-1945) by way of the Sino-Soviet Treaty (a non-aggression pact) of 1937 - enhancing Chinese offensive and defensive power against the invading Japanese.
Serving with both the Soviets and Mongolia, the aircraft was, once again, used against the Japanese at the Battle of Khalkhin Gol in 1939 (resulting in a Soviet/Mongolian victory). From there, the type was continually pressed into service during the Soviet Invasion of Poland (September 1939) and throughout the 1939-1940 "Winter War" with neighboring Finland - again with mixed results. Their numbers were such that the series was still in active operations during the Soviet war against Germany from 1941 until 1945 - however, against more modern adversaries, the R-5 had seen its best days behind it.
During the pre-war, wartime, and post-war years, the R-5 also existed in the civilian marketplace and used primarily to ferry cargo loads or passengers or a mix of the two.
Main production models were designated simply as "R-5" and these carried M-17B engines initially before switching to the M-17F from 1933 onward. Total production resulted in 4,914 units. The "R-5Sh" was the dedicated ground-attack light bomber form and carried 4 x 7.62mm PV-1 machine guns at the wing mainplanes. The "R-5a" was a twin-float waterborne variant and 111 were produced from 1934 until 1935. The "R-5D" was a long-range variant that existed as a single example. The R-5 "Jumo" was a prototype utilizing side-by-side seating for two in an enlarged rear cockpit space. The "R-5M-34" was a testbed for the M-34 series engine. The "R-5T" were fifty single-seat torpedo bomber forms first flown in 1934 and built in 1935. A two-seat model allowed for an observer to be carried. The "R5-SSS" was an improved variant with additional performance-enhancing streamlining as well as more machine guns - production exceeding 100 units from 1935 until 1936.
Some 1,031 were built to the "R-Z" standard for the dedicated reconnaissance / light bomber role. First-flying in January 1935, this variant carried as many as seven machine guns into battle. The variant resulted in the "R-ZSh", "P-Z", "PT", and "R-ZR" sub-variants in time.
The Grigorovich design bureau modified one R-5 into a light-class ground-attack form in 1930 as the "LSh". The "TSh-1" was a heavy-class ground attacker carrying 6mm of armor plating but only three prototypes were completed. The "TSh-2" followed with a new lower wing mainplane member design that resulted in ten aircraft being built to the standard. The "ShON" was another light-attack entry but completed for the COunter-INsurgency (COIN) role with folding wings, improving transport and storage of the aircraft. Thirty were ordered and the variant was used against Basmachi Rebels in Central Asia for their time in the air.
The "P-5" became a civilian-minded Aeroflot light transport powered by the M-17B engine and 1,000 were produced into 1940. The limited-production "P.5a" featured twin floats for water landings and take-offs. The "R-5L", appearing in 1931, was another limited production form and this model included seating for two in a passenger cabin section. The "P-5L" was another passenger transport form, this appearing in 1933.
A new semi-monocoque fuselage construction approach was instituted in the "PR-5" and these carried four passengers when operated by Aeroflot. Some 210 were converted from existing airframe stocks to the new, all-modern standard. The "PR-12" was based in the PR-5 but production only totaled a single unit, this arriving in 1938.
The "ARK-5" were two Arctic exploration units that included a heated cockpit. It carried cargo in aerodynamic containers integrated into the lower sides and lower wing mainplane members to maintain lift-versus-drag efficiency.
In all, the R-5 was utilized by a handful of global operators beyond the Soviet Union - though they were largely Soviet-aligned nations of the period. These included Iran, Mongolia, Spain, and Turkey.