|First flight||8 January 1932|
|Primary user||Polish civilian aviation (LOT Polish Airlines)|
In spite of buying a party of three-engine Fokker F.VIIb/3m aircraft, LOT Polish Airlines soon started looking for more modern design and organized a design contest in 1928. The contest was won by the Polish engineer Zygmunt Bruner, working in the French Bernard works, with his design T-600. It was all-metal high-wing three-engine monoplane, similar to Ford Trimotor. State Aviation Works PZL decided to take over its development, and a group of engineers was sent to Paris and worked the design in 1929, under direction of Zygmunt Bruner. There were also carried out aerodynamic trials of a plane model. Detailed technical drawings were worked in PZL in Warsaw in 1930, under direction of Stanisław Prauss, and a prototype was built, designated PZL.4 (this designation was used before for a single-engine design worked out for a passenger plane contest in 1928, won by PWS-20).
The PZL.4 was a high-wing cantilever monoplane of metal construction, with closed cab and three engines. The fuselage was rectangular in cross-section, made of duralumin and covered with duralumin sheet. The two-spar wings and tailfins were covered with Wibault-pattern ribbed duralumin sheet. The wings had squared-off wingtips. A crew of two (pilot and mechanic), were accommodated in front, before the wing, equipped with twin controls. Behind and slightly below under the wing, there was a cabin for 10 passengers in three compartments in the fuselage. The cabin had wide rectangular windows, sloped outwards for a better view, and door on the left side. The cabin had places for a baggage behind it and below a floor.
Three 9-cylinder radial engines Wright Whirlwind J-5 produced by the Polish Skoda Works division) mounted in the fuselage front and in wing nacelles provided (240 hp takeoff power, 220 hp nominal power. The engines were fitted with Townend rings and three-blade metal propellers, later two-blade wooden propellers of a fixed pitch. A conventional fixed landing gear, with a rear wheel, main gear wheels' diameter 1.15 m was also fitted. The fuel tanks located in the central wing section had 915 l, providing (cruise fuel consumption 180 l/h).
The prototype was flown on 8 January 1932 in Warsaw by Bolesław Orliński (markings SP-AGY). In June 1932 it took part in an international air meeting in Warsaw. From autumn 1932 to 1935 it was evaluated by LOT Polish Airlines, but it was found unsatisfactory. The empty weight was bigger by 730 kg, than designed, which decreased performance. As a result, its performance was inferior to Fokker F.VIIb/3m, with the same engines. Proposals to use Gnome-Rhone K-7 300 hp or Pratt-Whitney Wasp 450 hp engines were rejected by LOT (the latter engines would demand strengthening of construction).
The prototype was withdrawn from service in 1936 and scrapped in 1937.
- Crew: 2, pilot and mechanic
- Capacity: 10
- Length: 16.5 m ()
- Wingspan: 24.4 m ()
- Height: 3.3 m ()
- Wing area: 77 m² (ft²)
- Empty weight: 4081 kg ()
- Loaded weight: 5586 kg ()
- Useful load: 1505 kg ()
- Powerplant: 3 × Wright Whirlwind J-5 air-cooled 9-cylinder radial, 240 hp () each
- Maximum speed: 190 km/h
- Cruise speed: 170 km/h
- Stall speed: <105 km/h ()
- Range: 800 km ()
- Service ceiling: 2800 m ()
- Rate of climb: 2.3 m/s ()
- Wing loading: 72.6 kg/m² ()
- Glass, Andrzej. Polskie konstrukcje lotnicze 1893-1939 (Polish Aviation Constructions 1893-1939, in Polish). Warsaw: WKiŁ, 1977 (Polish language, no ISBN).
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