The P.Z.L. 3 was a Polish design for a heavy bomber that never got past the design stage, but that influenced the very similar Potez 41 in France, which did reach the prototype stage.
The design of a heavy bomber to replace the Fokker F.VIIb-3M was one of the first tasks given to the newly formed P.Z.L. They gave the task to Wladyslaw Zalewski, who had already put some thought into bomber design in the mid 1920s coming up with an advanced three engined design (the Pteranodon) that won him a prize of 5,000 zloty in 1925.
Zalewski produced the design for the P.Z.L. 3 over the winter of 1928-29. It was to be a low wing cantilver monoplane, using some of the same ideas as the Pteranodon. The fuselage would have a rectangular structure with a rounded top and bottom, constructed from duralumin. The aircraft had three cockpits – an open bomb-aimer/ gunner’s position in the nose, an enclosed cockpit in front of the wing with side-by-side seating for the pilot and co-pilot/ mechanic, and a dorsal gunners position. The nose and dorsal gun positions could carry single or twin Lewis guns on Scarff mountings, while a ventral gun position was provided just behind the wing. An internal bomb bay could carry up to 6,613lb (3,000kg) of bombs.
It was to be powered by four Bristol Jupiter engines, two mounted below the leading edge of the wing and two mounted on turrets above the wing, in an attempt to smooth the airflow around the wing. The wings were thick enough to contain a tunnel leading to the base of each turret, then up the interior of the turret to allow easy in-flight repairs. The undercarriage would be mounted in streamlined fairings, below each of the engine turrets.
This radical design didn’t go down well with Colonel Rayski, commander of the Polish Airforce, who demanded that Zalewski build aircraft ‘which he saw’ – ie using existing ideas. Somewhat ironically Zalewski responded by moving both engines to the top of the turret, with each carrying one pusher and one tractor. He justified this as being similar to the design on the Dornier Do X, and this satisfied Rayski.
Wind tunnel tests were carried out on a scale model in 1929 and produced good results. The Department of Aeronautics ordered a prototype and hinted that 30 production aircraft might follow. Detailed design work began in 1930, but the impact of the Great Depression meant that the money was no longer there, and the project was cancelled on 31 December 1931. Zalewski was so frustrated by this that he resigned from P.Z.L and never designed another aircraft to a government requirement.
This didn’t entire mark the end of the design. At the time French engineers from Potez were working in Poland, and they were given access to the design. A few years later they produced the very similar Potez 41, which shared the same basic layout with a low monoplane wing, slab sided fuselage and four engines carried in pairs on turrets above the wing. Only one prototype of this design was produced.
Stats are designer’s estimates
Engine: Four Bristol Jupiter nine-cylinder radial air-cooled engines
Power: 500hp each
Crew: 4 or 5
Span: 118ft 1.5in
Length: 72ft 2.75in
Empty Weight: 16,543lb
Gross Weight: 27,557lb
Maximum Speed: 173.9mph at sea level
Guns: single or twin Lewis guns in nose, dorsal and ventral positions
Bomb load: 6,613lb