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800px-Avia Bk-534 Slovenských vzdušných zbraní

The Avia B-534 is a Czechoslovak biplane produced during the period between the Great War and World War II.

Design and development[]

n 1932, the Czechoslovak aircraft company flew a first prototype of a single-engined fighter biplane, the Avia B-34, designed by František Novotný. After modification, the Czechoslovak Ministry of Defence placed an order for B-34s. A second prototype, the Avia B-34/2, was built, which was intended to be powered by a 600 horsepower (450 kW) Avia Rr 29 radial engine instead of the Hispano-Suiza 12N V12 engine of the first prototype and the initial production series. This engine proved prone to overheating and vibration, however, and it was decided to re-engine the B.34/2 before it flew, fitting it with a Hispano-Suiza 12Ybrs V12 engine.

The Avia B-34/2 made its maiden flight on 25 May 1933. The prototype was sent for testing in September and was redesignated as B-534.1. It was to compete against the Praga E-44 and Letov Š-231.

A second prototype, the B-534/2 was completed in September 1933. It differed from the first prototype in having an enclosed cockpit, a revised tail and undercarriage. On 14 April 1934 test pilot Václav Kočí successfully gained a Czechoslovak national speed record of 365.7 kilometres per hour (227.2 mph).

More testing followed and an initial order for 34 aircraft for the Czechoslovak Air Force, soon increasing to 147, was placed on 17 July 1934. At that time, the B-534 was well ahead of its contemporaries. The United Kingdom was still dependent on Hawker Furies, with the first Gloster Gladiators being produced at this time. The Soviet Union was placing its hope on its Polikarpov aircraft designs. The United States was still using descendants of the Curtiss Hawk series, with the Seversky P-35 and Curtiss P-36 just about to fly as prototypes.

The B-534 was designed as a single-engine biplane fighter

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with a license-built Hispano-Suiza inline powerplant, and fixed landing gear. The air forces of the 1930s were reluctant to abandon the maneuverability and climb rates of biplanes for the speed of monoplanes, even in the face of new and better technology. The success of the Soviet pilots with biplanes may have contributed to this reluctance; they were known to strip their aircraft of sliding canopies, preferring to have the wind in their faces. Aircraft with two fabric-covered wings and fixed landing gear were also less expensive to manufacture.

First deliveries of the B-534 to the Czechoslovak air force began in October 1935, and 666 or so had been completed by 1938. The first 100 of these were of the first series. The second prototype was the blueprint for the I series, although it was built with an open cockpit. These early series aircraft were initially armed with four 7.92mm vz.28 guns. Two were located in the nose either side of the engine in a similar manner to the Avia B-34 and two were fitted in the wings. At an early stage of production it was however recognised that the wing mounted guns were troublesome. Aircraft from serial number B-534.47 were completed without the wing guns, which were also removed from the earlier aircraft. The first to fourth series aircraft were fitted with the Avia licence built version of the Hispano-Suiza 12Ydrs engine. This was a liquid cooled V12 cylinder engine with a capacity of 36.05 litres. On the ground its normal power rating was 650 hp, it could deliver 750 hp for two minutes. At an operational height of 4,000 m (13,123 ft), it could reach 860 hp. Total fuel was 347 litres (76 gal) which was held in two fuselage fuel tanks of 90 and 257 litres.

The II series completed the remainder of the first order from the Czechoslovak Government, These were forty-five aircraft numbered B-534.102 to 147. Like the I series these carried four guns. However the solution to the problems with the wing mounted guns was to move these guns, now upgraded to the vz.30 to the fuselage with the others. The four 7.92 mm (0.312 in) machine guns were located in the sides of the fuselage, firing through the propeller. One very modern innovation was a bubble canopy. This was tested on a small number of the early series aircraft, although certainly not a standard fit.

In 1936 a second order for 46 aircraft were issued by the government. The first 25 of these were the B-534/III version serial numbers B-534: 148–173. Production took place in the second half of 1936. It entered service between March and April 1937. The III series had aerodynamic refinements which saw the streamlining of the front carburator air intake. Mudguard spats were also often added at the factory to the main gear.

The remainder of the second order from 534.174 to 534.193 were the IV series. With later orders the fourth series would occupy the serial numbers .174 and 445 and was therefore the most numerous of the types. The most important change to the earlier series was the enclosed cockpit. The IV series also enjoyed a metal light alloy Letov (Hochfeld) Hd-43 propeller. The various refinements allowed the IV series to have an increased speed of over 200 mph, and this placed it on par with the best of its contemporary biplanes. A common alteration to the IV series was the replacement of the tail skid with a tail wheel. Operational experiences had shown that the spat on the main landing gear could become clogged with mud on grassy airfields and cause take-off and landing problems. The spats were then often removed.

The superb performance of the aircraft was demonstrated at a flying exhibition in 1937. The aircraft was tested against the best in the world at the IV International Air Meeting at Zurich's Dübendorf airport. The B-534 entered three of the competitions. The first of these tested climbing and diving. A GermanBf 109 took first place and a Henschel Hs 123 pilot pushed his biplane to claim second. The B-534 took the next three positions. the 534 outflew every other fighter participating, bar the Messerschmitt Bf 109 – and even then, the Avia was only 11 kph slower than the German aircraft.

The abrupt partition of Czechoslovakia in 1939 prevented the use of the B-534 in combat by the nation that had produced it. By then, high performance monoplanes such as the Bf 109 and Britain's leading models – the Hawker Hurricane and Supermarine Spitfire – were raising the bar of fighter/interceptor standards. Four sub-types were produced during the B-534's production run, all with mostly minor improvements.

One major variation was introduced in this production run. The Bk-534 was designed to carry one 20 mm (0.79 in) cannon firing through the nose and only two 7.92 mm (0.312 in) machine guns to the sides. Developmental problems prevented the cannon from ever being used and, desperate to get more aircraft in the air, Avia decided to use a third machine gun in the nose only weeks before the German annexation of Czechoslovakia. Only three examples with this configuration were completed for the Czech air force, and the remaining production block was finished for the Germans.