09/30/2012. Remarks by Johan Visschedijk: "In developing the B 34, Ing. Frantisek Novotny had considered installation of several alternative engines, versions offered being the B 134 with the 800 hp Walter-built Mistral 14Kbs, the B 234 with the 600 hp Avia Rr 29 nine-cylinder radial, the
B 334 with the 650 hp Armstrong Siddeley Panther and the B 434 with the 690 hp Hispano-Suiza 12Xbrs.
A second prototype, the B 34/2, was completed, this having larger, less angular vertical tail surfaces and armament transferred to wing fairings. It was to have had the Rr 29 engine, but the failure of this power plant resulted in the B 34/2 being re-engined with an Hispano-Suiza 12Ybrs rated at 860 hp at 13,123 ft (4,000 m). The twin-gun armament was reinstated in the fuselage and, with a redesigned rudder, the B 34/2 was flown in August 1933, being subsequently referred to as the B 534/1 after successfully completing official trials.
A further prototype was then built as the B 534/2, this introducing mainwheel fairings, a forward-extended radiator bath, redesigned vertical tail surfaces, raised aft fuselage decking, a cockpit canopy, and the fuselage-mounted guns moved farther aft for CofG reasons. On July 17, 1933, an order was placed for 146 production examples of the B 534. The production B 534 omitted the refinements of wheel spats and cockpit canopy, but was otherwise similar to the B 534/2 prototype.
The Avia-built Hispano-Suiza 12Ydrs engine of 830 hp for take-off was installed and armament comprised four 0.303 in (7.7 mm) Model 28 or 30 guns, two in the fuselage and two in lower-wing fairings, aircraft so armed being referred to as the B 534 Series I (or B 534.I). With the 48th aircraft, all four guns were mounted in the fuselage, this being the first B 534.II and the arrangement being standardized for all subsequent machines.
A further 54 had meanwhile been ordered with an alternative armament as the Bk 534. Similar in other respects to the B 534.II, the Bk 534 was to have had an engine-mounted 0.787 in (20 mm) Oerlikon FFS cannon, machinegun armament being reduced to two Model 30 weapons. Difficulties with the cannon shell feed arrangement eventually led to the Oerlikon being discarded in favor of a third 0.303 in (7.7 mm) weapon.
The Series III production batch of the B 534 (B 534.III), consisting of 26 aircraft, embodied some refinements, these aircraft featuring an enlarged supercharger air intake and originally the wheel spats as flown on the
B 534/2. This, however, was an interim model pending introduction of the definitive Series IV (B 534.IV). Six B 534s essentially similar to the Series III were exported to Greece and fourteen to Yugoslavia.
The Series IV was similar to its immediate predecessor apart from having a metal rather than wooden propeller and in adopting an aft-sliding cockpit canopy with raised fuselage rear decking. A total of 272 B 534.IV fighters was built, these being powered by the Avia-built Hispano-Suiza 12Ydrs engine and mounting four 0.303 in (7.7 mm) guns. Of some 450 B 534s and Bk 534s in the inventory of the Czechoslovak air arm on March 15, 1939, a number was absorbed by the newly-created Slovak Air Force, 78 were sold to Bulgaria and the remainder were taken into the inventory of the Luftwaffe."