The P.Z.L. P.42 was a single development aircraft used to help with the design of the P.46 Sum (Sheat-fish), the planned replacement for the P.23 Karas.
The P.23 was an all-metal three-seat low wing monoplane, powered by a single Polish Skoda licence built Bristol Pegasus radial engine. It had a fixed undercarriage, with the bombs carried between the wheels. The pilot had a fully enclosed glazed cockpit, with the observer in a separate cockpit just behind and the rear gunner in an open cockpit. It had a sizable ventral gondola, which carried another rear firing gun and the bomb aiming position. It had been designed as a multipurpose ‘liniowe’ (front line aircraft), but during the development of the P.46 this was changed, and the aircraft was to be built in separate bomber or reconnaissance versions.
The P.46 was to be an improved version of the P.23, stressed to take engines of up to 1,200hp, with the same basic design but with aerodynamic refinements, in particular around the gondola.
The P.42 was produced by modifying the first production P.23 Karas B while it was still on the production line. The normal ventral gondola was removed, and was replaced with a retractable gondola. This was meant to be activated by the weight of the bomb-aimer/ gunner as he moved into position. It was also given a new twin fin and rudder and a P.Z.L. produced Pegasus VIIIA.
This aircraft made its first flight in April 1936. The gravity operated gondola wasn’t satisfactory, so it was replaced with a hydraulically operated system on the production aircraft.
After the trials were over the P.42 was converted back into a standard Karas B and went to the Polish Air Force, and was used with training units of C.W.L. Deblin. The machine was destroyed during the German invasion in 1939. The first two prototypes of the P.46 had been completed by the time the Germans invaded in 1939, but full production had been delayed to allow the resources to be used for more fighters.