U-2, Po-2 trainer by N.N.Polikarpov

U-2 form Kril'ja Rodini No10 1987

This classic primary trainer has one of the world richest aircraft history. Since the first series aircraft flight (January 7, 1928) it was widely used for more than 35 years. The plane was renamed to Po-2 (Polikarpov, the second model) in 1944, after death of N.N.Polikarpov .
Undemanding to service, U-2/Po-2 could operate from any sufficient spot.. In September 29 - October 6 1932 U-2 flown by V.K.Gribovskij tugged G-9 glider (pilot V.A.Stepanchenok) along 1700km route Tambov - Voronezh - Ejsk in 19 flight hours. Despite retirement of Po-2 started in June 1959, it service continued. Some even were built of spares by aeroclubs. The F-AZPO is still flying over Belgium with its original engine... During The Great Patriotic War peaceful biplane turned into terrifying night bomber. German fighters were praised with Iron Cross for shooting down this small plane named "Rusfaner"! All those roles (not planned during aircraft development!) prove superior quality of the design Combat carrer of this plane continued after WW2. It took part in Korean war also as night bomber and also became a serious problem for american fighter pilots. Many invaders found ther deach with the help of Po-2 precise strikes. (Nevertheless it was replaced in this role by more modern piston engine planes such as Yak-11 and La-11)
As a trainer, it was intended to replace aging U-1 (Avro504) trainer and other old machines used in this role. As industry recovered from the Civil War wounds, unified primary pilot training schedule became a necessity. Old 120hp M-2 (used on the U-1) was unreliable and had too short lifetime. But new generation 100hp M-11 was in production since 1926, specially intended for trainer aircraft.
Requirements to the new trainer were formulated by NTK UVVS under supervision of S.V.Ilyushin. Aircraft had to be safe to fly, with speed no more than 120km/h. This allowed to exclude non-productive high-speed taxing on U-1 with 'stripped' wing (with deleted skean) while pilots education process. After graduating the U-2 courses, pilots had to try perfect advanced P-2 with 300hp engine.
Success came soon, but start was disappointing. First U-2 was built with thick (14%) wing (with high lift at low speed in mind), had very simple and strong airframe. At that time there was such an approach that trainer airplane must be as cheap as possible and it's parts wide unification had to be implemented. So the prototype had similar upper and lower wings, similar stabilizer consoles. Plus Polikarpov tried to avoid curves in shapes where possible. All this resulted into failure. U-2 appeared heavy and had bad aerodynamucs. It took him 11.5 min to climb at 1000m and 29 min at 2000m. The overload of trainer structure was obtained equal 120 kg! Inspite satisfying velosity requirements the aircraft was rebuilt. It had numerous similarities to other aircraft designed by N.N.Polikarpov team. The most distinctive difference was very large rudder. U-2 was also aerodynamically refined compared to its predecessors. First flight was performed by M.M.Gromov on January 7, 1928. Standard skis from the U-1 were installed. Later other pilots tried U-2 in air, and everyone was impressed by excellent handling of new aircraft. U-2 had feature absolutely new for the time - static longitudinal stability. In case of large climb angle and following speed lose aircraft normally stalled, with risk of lost control and spin. U-2 just dropped nose and than continued steady descent (in case of low engine power), or accelerated and continue climb. Aircraft could be send into spin only intentionally (and it was not so easy!). And it was enough to hold controls in neutral position to get out of spin. It was even possible to let U-2 fly without hands on controls... In 1928 aircraft was presented on Berlin Airshow.
Mass production had started in 1930 at 'Krasnyj Letchik' (The Red Pilot) factory and had been finished in 1953 only, when requirements to primary pilot training changed again. More than 33,000 were build.
Actual number is almost impossible to figure out, because many were built by aeroclubs, repair shops and even enthusiasts. Small scale production lasted at least until 1959!

more info

Dozens of production and experimental variants were built. Among them - several agricultural, paramedic and limousine.
  • Po-2 "with thick wing"- first unsuccessfull prototype
  • U-2VS - night bomber

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  • References:
  • "History of aircraft construction in the USSR" by V.B.Shavrov, Moscow, Mashinostrojenije, 3d edition,Vol.1 p.414-418;
  • Technical information
    Type U-2
    Function Prototype Primary trainer
    Year 1928 1930
    Crew 2
    Engines 1*100hp M-11
    Length 8.17m
    Wingspan 11.4/10.6m 11.4/11.4m
    Wing area 33.15m2
    Empty weight 635kg
    Loaded weight 890kg
    Wing Load (kg/m2) 26.8
    Power load (kg/hp) 8.9
    Speed at 0m 156km/h 150km/h
    Speed at 3000m 120km/h 111km/h
    Landing Speed 65km/h
    Landing Roll 100m 10sec 120m 11sec
    Takeoff Roll 70m 8sec
    Turn time 17sec
    Range 400km
    Flight Endurance 3h30min
    Ceiling 4000m 3820m
    1000m 5.6min 6.0min
    2000m 13.0min 14.0min
    3000m 23.0min 25.0min
    Fuel+Oil 71+10kg
    Created November 28, 2002
    by Alexandre Ju.Savine
    and Sergey V.Andreev;