The Polikarpov Po-2 (also U-2) served as a
general-purpose Soviet biplane, nicknamed Kukuruznik (Russian: from
Russian "kukuruza" for maize; thus, "maize duster" or "crop
duster"), NATO reporting name "Mule".The reliable, uncomplicated
concept of the Po-2's design made it an ideal training aircraft, as
well as doubling as a low-cost ground attack, aerial
reconnaissance, psychological warfare and liaison aircraft during
war, proved to be one of the most versatile light combat types to
be built in the Soviet Union. As of 1978 it remained in production
for a longer period of time than any other Soviet-era aircraft.
It is one of the most produced aircraft, and may
be the most produced biplane with production possibly as high as
30,000 Po-2s built between 1928 and 1959. However, production
figures for Polikarpov U-2 and Po-2 bombers and trainers combined
are between 20,000 and 30,000 with production ending as early as
1952. Correct figures are hard to come by since low-rate production
by small repair shops and air clubs likely continued until
1959.
The aircraft was designed by Nikolai
Polikarpov to replace the U-1 trainer (a copy of the British Avro
504), itself known as Avrushka to the Soviets. Its name was changed
to Po-2 in 1944, after Polikarpov's death, according to the new
Soviet naming system, usually using the first two letters of the
designer's family name, or the design bureau that created it.
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 7
January 1928 piloted by M.M. Gromov. Aircraft from the
pre-production series were tested at the end of 1928 and serial
production started in 1929 in Factory number 23 in Leningrad.
Production in the Soviet Union ended in 1953, but license-built
CSS-13 were still produced in Poland until 1959.
From the beginning, the U-2 became the basic Soviet civil and
military trainer aircraft, mass-produced in a "Red Flyer" factory
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. Manufacturing of the Po-2
in the USSR ceased in 1949, but until 1959 a number were assembled
in Aeroflot repair workshops.
During the defence of Odessa, in September 1941, the U-2 was
used as a reconnaissance aircraft and as a light, short-range,
bomber. The bombs, dropped from a civil aircraft piloted by Pyotr
Bevz, were the first to fall on enemy artillery positions. From
1942 it was adapted as a light night ground attack aircraft.
Nikolay Polikarpov supported the project, and under his
leadership, the U-2VS (voyskovaya seriya - Military series) was
created. This was a light night bomber, fitted with bomb carriers
beneath the lower wing, to carry 50 or 100 kg (110 or 220 lbs)
bombs up to a total weight of 350 kg (771 lb) and armed with ShKAS
or DA machine guns in the observer's cockpit.
Wehrmacht troops nicknamed it Nahmaschine (sewing machine) for
its rattling sound and Finnish troops called it Hermosaha (Nerve
saw)[citation needed] as the Soviets flew nocturnal missions at low
altitudes: the engine had a very peculiar sound, which was
described as nerve-wracking, therefore the name. Luftwaffe pilots
were soon given special instructions for engaging these aircraft.
The material effects of these missions may be regarded as minor,
but the psychological effect on German troops was noticeable. They
typically attacked by surprise in the middle of the night, denying
German troops sleep and keeping them on their guard, contributing
to the already high stress of combat on the Eastern front. The
usual tactic involved flying only a few meters above the ground,
rising for the final approach, throttling back 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 two main
factors: the pilots flew at treetop level where they were hard to
see or engage and the stall speed of both the Messerschmitt Bf 109
and the Focke-Wulf Fw 190 was similar to the U-2s maximum speed,
making it difficult for the fighters to keep a Po-2 in weapons
range for an adequate period of time.[6] The success of the Soviet
night harassment units inspired the Luftwaffe to set up similar
Storkampfstaffel "harassment combat squadrons" on the Eastern Front
using their own obsolete 1930s-era, open cockpit biplane and
parasol monoplane aircraft, eventually building up to larger
Nachtschlachtgruppe (night attack group) units of a few squadrons
each.
The U-2 became known as the aircraft used by the 588th Night
Bomber Regiment, composed of an all-women pilot and ground crew
complement. The unit was notorious for daring low-altitude night
raids on German rear-area positions. Veteran pilots Yekaterina
Ryabova and Nadezhda Popova on one occasion flew eighteen 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/Nocnye 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 by the end of the war and took
part in the Battle of Berlin.
The Polish Air Force used these slow and manoeuvrable aircraft
for air reconnaissance and COIN operations against UPA bands in
mountainous area of Bieszczady. Pilots and navigators were
dispatched to look for concentrations of UPA forces and if needed,
engage them with machine guns and grenades. On several occasions,
the UPA managed to bring down some of the Po-2s, but never captured
or operated them.
North Korean forces used the Po-2 in a similar role during 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 United Nations bases. During one such attack, a lone Po-2
attacked Pyongyang airfield in northwestern Korea. Concentrating on
the 8th Fighter-Bomber Group's parking ramp, the Po-2 dropped a
string of fragmentation bombs squarely across the group's lineup of
P-51 Mustangs. Eleven Mustangs were damaged, three so badly that
they were destroyed when Pyongyang was abandoned several days
later.
On 17 June 1951, at 01:30 hours, Suwon Air Base was bombed by
two Po-2s. Each biplane dropped a pair of fragmentation bombs. One
scored a hit on the 802nd Engineer Aviation Battalion's motor pool,
damaging some equipment. Two bombs burst on the flight line of the
335th Fighter Interceptor Squadron. One F-86A Sabre (FU-334 /
49-1334) was struck on the wing and began burning. The fire took
hold, gutting the aircraft. Prompt action by personnel who moved
aircraft away from the burning Sabre preventing further loss. Yet
eight other Sabres had been damaged in the brief attack, four
seriously. One F-86 pilot was among the wounded. The North Koreans
subsequently credited Lt. La Woon Yung with this damaging
attack.
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. As Korean war U.S. veteran Leo Fournier remarked about
"Bedcheck Charlie" in his memoirs: "... no one could get at him. He
just flew too low and too slow." 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. The Po-2 is also the
only biplane, who credited a documented jet-kill as one Lockheed
F-94 Starfire was lost while slowing down to 110 mph – below
it's stall speed – during an intercept in order to engage the
low flying Po-2.
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 an 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 stabilizing 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
stretchers, 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. A total of 861 were built between
1934 and 1939.
U-2SPL: This limousine version was fitted with rear cabin for two
passengers.
U-2UT: Two-seat training aircraft, powered by an 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) seven
cylinder M-48 radial engine.
U-4: Cleaned-up version with slimmer fuselage; not built in large
numbers.
- (Total U-2 manufacture: 33,000)
Po-2:Post-war basic trainer variant.
Po-2A: Post-war agricultural variant.
Po-2GN: "Voice from the sky" propaganda aircraft, fitted with a
loud speaker.
Po-2L : Limousine version with an enclosed passenger cabin.
Po-2P : Post-war floatplane version; built in small numbers.
Po-2S: Post-war air ambulance variant, with a closed rear cab.
Po-2S-1: Post-war ambulance version, similar to the pre-war
U-2S.
Po-2S-2: Post-war ambulance version, powered by a M-11D radial
piston engine.
Po-2S-3: Post-war ambulance version, which had two underwing
containers, each one was designed to transport one stretcher
patient. Also known as the Po-2SKF.
Po-2ShS: Staff communications aircraft, fitted with an enclosed
cabin for the pilot and two or three passengers.
Po-2SP: Post-war aerial photography, geographic survey
aircraft.
RV-23: This floatplane version of the U-2 was built in 1937. It was
used in a number of seaplane altitude record attempts. The RV-23
was powered by a 529 kW (710 hp) Wright R-1820-F3 Cyclone radial
piston engine.
CSS-13: Polish licence version, built in Poland in WSK-Okecie and
WSK-Mielec after World War II (about 500 built in
1948–1956).
CSS S-13: Polish ambulance version with a closed rear cab and
cockpit and Townend ring (53 built in WSK-Okecie in 1954-1955, 38
converted to S-13).
E-23: Research version, built in the Soviet Union in 1934, for
research into inverted flight.