The Polikarpov U-2 or Po-2 served as a general-purpose Soviet biplane, nicknamed Kukuruznik (Russian: Кукурузник, from Russian "kukuruza" (кукуруза) for maize), NATO reporting name of "Mule".[2] The reliable, uncomplicated and forgiving aircraft served as a trainer and crop-duster. It is the second most produced aircraft, and the most produced biplane, in the history of aviation.
Design and development
Aircraft was designed by Nikolai Polikarpov to replace the U-1 trainer (Avro 504). Its name was changed to Po-2 in 1944, after Polikarpov's death, according to the new Soviet naming system using designer's initials.
The prototype of the U-2, powered by a 74 kW (99 hp) Shvetsov M-11 air-cooled five cylinder radial engine, first flew on 24 June 1927 piloted by M.M. Gromov. After some modifications next flight took place on 7 January 1928. Aircraft from pre-production series were tested at the end of 1928 and serial production started in 1929 in Factory Nr 23 in Leningrad. Production in Soviet Union was ended in 1953, license-built CSS-13 in Poland were produced until 1959.
[edit] Operational history
A damaged and abandoned Po-2 forced to land in Ukraine, 1941.From the beginning, the U-2 became the basic Soviet civil and military trainer aircraft, mass produced in a factory "Red Flyer" near Moscow. It was also used for transport, and as a military liaison aircraft, due to its STOL capabilities. Also from the beginning it was produced in an agricultural aircraft variant, what earned it its nickname Kukuruznik. Although entirely outclassed by contemporary aircraft, the Kukuruznik served extensively on the Eastern Front in World War II, primarily as a liaison, medevac and general supply aircraft. It was especially useful for supplying Soviet partisans behind the front line. Its low cost and easy maintenance led to a production run of over 40,000. Manufacturing of the Po-2 in the USSR ceased in 1949, but until 1959 a number were assembled in Aeroflot repair workshops.
After first trials of arming the machine with bombs in 1941, from 1942 it was adapted as a light night ground attack plane. Wehrmacht troops nicknamed it Nähmaschine (sewing machine) for its rattling sound. The material effects of these missions was mostly insignificant, but the psychological effect on German troops was much more noticeable. They typically attacked by complete surprise in the dead of night, denying German troops sleep and keeping them constantly on their guard, contributing yet further to the already exceptionally high stress of combat on the Eastern front. Their usual tactics involved flying only a few meters above the ground, rising for the final approach, cutting off the engine and making a gliding bombing run, leaving the targeted troops with only the eerie whistling of the wind in the wings' bracing-wires as an indication of the impending attack. Luftwaffe fighters found it extremely hard to shoot down the Kukuruznik because of three main factors: the rudimentary aircraft could take an enormous amount of damage and stay in the air, the pilots used the defensive tactic of flying at treetop level, and the stall speed of both the Messerschmitt Bf 109 and the Focke-Wulf Fw 190 was similar to the Soviet craft's maximum cruise speed, making it difficult for the newer aircraft to keep a Po-2 in weapons range for an adequate period of time.[3] The U-2 was known as the plane used by the 588th Night Bomber Regiment, composed of all-women pilots and ground crew. The unit became notorious for its daring low-altitude night raids on German rear-area positions, with veteran pilots Katya Ryabova and Nadya Popova on one occasion flying 18 such missions in a single night. The women pilots observed that the enemy suffered a further degree of demoralization simply due to their antagonists being female. As such, the pilots earned the nickname "Night Witches" (German Nachthexen, Russian Ночные Ведьмы/Nočnye Ved’my). The unit earned numerous Hero of the Soviet Union citations and dozens of Order of the Red Banner medals; most surviving pilots had flown nearly 1,000 combat missions at the end of the war and had taken part in the Battle of Berlin.
North Korean forces used the Po-2 in a similar role in the Korean War. A significant number of Po-2s were fielded by the Korean People's Air Force, inflicting serious damage during night raids on Allied bases.[4] UN forces named the Po-2's nighttime appearance Bedcheck Charlie and had great difficulty in shooting it down — even though night fighters had radar as standard equipment in the 1950s, the wood-and-fabric-construction of the Po-2 gave only a minimal radar echo, making it hard for an opposing fighter pilot to acquire his target. On 16 June 1953, a USMC AD-4 from VMC-1 piloted by Major George H. Linnemeier and CWO Vernon S. Kramer shot down a Soviet-built Polikarpov Po-2 biplane, the only documented Skyraider air victory of the war.
[edit] Variants and design stages
U-2: Basic model, built in large numbers as a two-seat primary trainer. It was also built in many different versions, both as civil and military aircraft. The U-2 variants also included a light transport, utility, reconnaissance and training aircraft. Power plant was the M-11 radial piston engine of 75 kW (100 hp). Later models were also equipped with uprated M-11 engines of 111 kW (150 hp). Some aircraft were fitted with a rear closed cabin, other were fitted with sledges or floats.
U-2A: Two-seat agricultural crop dusting aircraft, powered by a 86 kW (115 hp) M-11K radial piston engine. Later redesignated Po-2A after 1944.
U-2AO: Two-seat agricultural aircraft.
U-2AP: Agricultural aircraft, with a rear cab replaced with a container for 200-250 kg (441-551 lb) of chemicals. 1,235 were built in 1930-1940.
U-2G: This experimental aircraft had all the controls linked to the control column. One aircraft only.
U-2KL: Two aircraft fitted with a bulged canopy over the rear cabin.
U-2LSh: Two-seat ground-attack, close-support aircraft. The aircraft were armed with one 7.62 mm (0.30 in) ShKAS machine-gun in the rear cockpit. It could also carry up to 120 kg (265 lb) of bombs and four RS-82 rockets. Also known as the U-2VOM-1.
U-2LPL: Experimental prone-pilot research aircraft.
U-2M: This floatplane version was fitted with a large central float and two small stabilishing floats. Not built in large numbers. Also known as the MU-2.
U-2P: Floatplane version, built only in limited numbers, in several variants with different designations.
U-2S: Air ambulance version, built from 1934. It could take a physician and an injured on a stretcher on a rear fuselage, under a cover. Variant U-2S-1 from 1939 had a raised fuselage top upon the stretcher. From 1941 there were also used two containers for stretechers, that could be fitted over lower wings or two containers for two seating injured each, fitted under lower wings.
U-2SS: Air ambulance aircraft.
U-2ShS: Staff liaison version, built from 1943. It had a wider fuselage and a closed 4-place rear cab.
U-2SP: Civil transport version, could carry two passengers in open individual cabs, built from 1933. Other roles included aerial survey, and aerial photography. 861 were built between 1934 and 1939.
U-2SPL: This limousune version was fitted with rear cabin for two passengers.
U-2UT: Two-seat training aircraft, powered by a 86 kW (115 hp) M-11D radial piston engine. Built in limited numbers.
U-2LNB: Soviet Air Force night attack version, built from 1942. Armed with one 7.62 mm (0.30 in) ShKAS, plus up to 250 kg of bombs under the wings for land support. Earlier aircraft were converted to improvised bombers from 1941.
'U-2VS : Two-seat training and utility aircraft. Later redesignated Po-2VS after 1944.
U-2NAK: Two-seat night artillery observation, reconnaissance aircraft. Built from 1943.
U-3: Improved flying training model, fitted a 149 kW (200 hp) M-48 engine.
U-4: Cleaned-up version with slimmer fuselage. Not built in large numbers.
-(Total U-2 manufacture: 33,000)
Po-2: Basic post-war trainer variant.
Po-2A: Post-war agricultural variant.
Po-2GN: "Voice from the sky" propaganda aircraft, fitted with a loud speaker.
Po-2L : Limousone version with an enclosed passenger cabin.
