(Avia) BH-21 @·AIRCRAFTUBE

  • Avia BH-21 Avia BH-21
    Avia BH-21
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    I
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  • Zdeněk Lhota and a BH-21<br>(Letectví, October 1925) Zdeněk Lhota and a BH-21<br>(Letectví, October 1925)
    Zdeněk Lhota and a BH-21
    (Letectví, October 1925)
  • On skis On skis
    On skis
  • NACA Aircraft Circular No. 22 (1926) NACA Aircraft Circular No. 22 (1926)
    NACA Aircraft Circular No. 22 (1926)

Avia BH-21

The Avia BH-21 was a single-seat fighter biplane designed by Pavel Beneš and Miroslav Hajn and built by the Czechoslovak manufacturer Avia. First flown in January 1925, it was the first Czechoslovak fighter produced in large numbers and became, together with the Letov Š-20, the standard equipment of the Czechoslovak fighter units in the second half of the 1920s. It was also licence-built in Belgium for the Aéronautique Militaire. Robust and highly manoeuvrable, it was renowned for its aerobatic qualities, and a racing version won several national air races in 1925.

Design and development

The BH-21 descended from the Avia BH-17, a conventional biplane designed in the early 1920s in response to a requirement of the Czechoslovak Ministry of National Defence for a new fighter to replace the ageing SPADs then in service. The BH-17 was one of five Avia proposals (three of them biplanes) competing against designs from Letov and Aero. It was selected after a thorough evaluation and a small batch was ordered, but service testing revealed several shortcomings, notably with the fuel system. In 1924 the design was therefore reworked: the interplane bracing was simplified and straightened and the pilot's field of view was improved. The modified aircraft was redesignated BH-21 and made its first flight near Prague in January 1925.

The fuselage, of rectangular section, had a wooden structure made of four longerons joined by uprights and cross members. It was entirely covered with plywood, which made it rigid enough to dispense with bracing wires. Small inspection windows allowed the double control cables to be checked. Instead of a conventional fin, the fuselage ended in a vertical ridge carrying a slightly balanced rudder with a fabric-covered steel-tube frame. The horizontal stabilizer was made of wood and plywood, while the two-piece elevator was fabric-covered. The relatively roomy cockpit, placed behind the wings, had an adjustable seat and room for a back-type parachute.

The staggered wings had a slightly shorter upper span than the lower one, which improved both the pilot's view and the efficiency of the ailerons, fitted to the lower wing. The one-piece upper wing rested on a steel-tube cabane, while the two halves of the lower wing were attached directly to the lower longerons. On each side, the wings were connected by streamlined N-shaped steel struts and two pairs of cables. Each wing had two box spars, plywood-webbed wooden ribs and a plywood skin stiff enough to need no internal bracing. The airframe was stressed to a load factor of 12.5 g.

The BH-21 was powered by a 300 hp (224 kW) Hispano-Suiza 8Fb water-cooled V-8 engine, built under licence by Škoda, enclosed in an aluminium cowling and mounted on a wooden bed fixed to the longerons. A honeycomb radiator made by Avia was fitted under the fuselage and could be raised or lowered in flight to regulate the engine temperature. The main fuel tank, in the bottom of the fuselage, was made of thin aluminium sheets assembled by a patented soldering process and covered with rubber to protect it against incendiary bullets; a pump fed a gravity tank in the centre of the upper wing. The fuel load allowed about three hours of normal flight, or two hours at full throttle. The undercarriage, of mixed wood and metal construction, used rubber-cord shock absorbers. Armament consisted of two synchronised 7.7 mm Vickers machine guns in the upper front fuselage.

Operational history

Czechoslovakia

Series production began in 1925 and 139 aircraft, designated B-21 in military service, were delivered to the Czechoslovak Air Force, where they equipped the fighter squadrons (letky) of the air regiments. Its excellent handling allowed ordinary squadron pilots to practise advanced aerobatics, and the BH-21 contributed greatly to the reputation of Czechoslovak aerobatic flying. The most famous example was B.21.96, painted red and nicknamed "Rudý ďábel" (Red Devil), flown by the aerobatic pilot Captain František Malkovský, who was killed in it at Karlovy Vary on 8 June 1930. The BH-21 remained in front-line service until the end of the 1920s, then finished its career in training units. It never fought and was withdrawn well before the Second World War, but it paved the way for the more advanced Avia BH-33 and Avia B-34.

Belgium

In June 1925 the BH-21 was successful in fighter trials held in Belgium. In 1926 the Belgian Ministry of Defence bought three fighters for evaluation, the Dewoitine D.19, the Avia BH-21 and a Jupiter-powered Dewoitine D.9, which were tested directly by the operational squadrons. The BH-21 was chosen, partly because its Hispano-Suiza engine was already held in stock by the Belgian forces, and partly for its outstanding aerobatic qualities. One aircraft was built by Avia, followed by licence production by SABCA (Société Anonyme Belge de Constructions Aéronautiques) and by SEGA (Société d'Études Générales d'Aviation) in Gosselies, for a total of about 45 aircraft (39 SABCA and 5 SEGA according to most sources, 34 SABCA according to Belgian Wings), serialled T-1 to T-43.

The first aircraft entered service in 1927 with the I/2 Aé group at Schaffen-Diest, then with the II/2 Aé at Nivelles, alongside the Nieuport-Delage NiD 29s they were supposed to replace. They equipped the 1/I/2 Aé (Comet), 2/I/2 Aé (Thistle), 5/II/2 Aé (Red Cocotte) and 7/II/2 Aé (White Cocotte) squadrons. From July 1931 they were progressively replaced by the Fairey Firefly IIM; some BH-21s were then transferred to the flying school at Wevelgem, where the last were retired in 1934.

Variants

  • BH-21 : Single-seat fighter, main production version.
  • BH-21J : One BH-21 fitted with a Bristol Jupiter radial engine; it led to the development of the Avia BH-33.
  • BH-21R : Single-seat racer with clipped wings and a boosted Hispano-Suiza 8Fb engine of 400 hp (298 kW). It won several national air races in 1925.
  • BH-22 : Unarmed advanced and aerobatic trainer derived from the BH-21, powered by a 180 hp Hispano-Suiza 8Aa, with reduced wing stagger. About 30 built; two were modified for night training as BH-22N, later BH-23.

Operators

  • Belgium : Aéronautique Militaire (Belgian Air Force).
  • Czechoslovakia : Czechoslovak Air Force.

Accidents and incidents

  • 27 July 1928 : The Avia-built T-1 of the 5/II/2 Aé crashed at Nivelles, killing 1st Sergeant Gaston Verton.
  • 5 July 1929 : B.21.6 crashed south-east of Cheb airfield (Czechoslovakia); its pilot, Captain Eduard Seidl, was seriously injured and died of the consequences in 1936.
  • 8 June 1930 : Captain František Malkovský was killed at Karlovy Vary in the crash of his B.21.96 "Red Devil".
  • 9 January 1931 : T-8 of the 7/II/2 Aé crashed at Haut-Ittre; Sergeant Georges Van Pottelberghe died of his injuries the next day.
  • 2 July 1931 : T-17 of the 5/II/2 Aé was destroyed in a mid-air collision at Thines; Adjutant Ernest Verhoeven was killed.

References

  • Green, William; Swanborough, Gordon (1994). The Complete Book of Fighters. Godalming, UK: Salamander Books. pp. 33-35. ISBN 1-85833-777-1.
  • Serryer, J. (21 May 1926). "L'avion de chasse Avia". Les Ailes (205): 2-3.
  • "Avia pursuit airplane B.H. 21". National Advisory Committee for Aeronautics, Aircraft Circular No. 22, 1 November 1926.
  • Wauthy, Jean-Luc; de Neve, Florian (1995). "Les aéronefs de la Force Aérienne Belge". Le Fana de l'Aviation.
  • Krumbach, Jan (1986). "Avia BH-21". Ilustrovaná historie letectví 2. Prague: Naše vojsko. pp. 3-43.
  • Belgian Wings : Avia BH-21 (www.belgian-wings.be).

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This text is available under the Creative Commons Attribution-ShareAlike License
Source : Article Avia BH-21 of Wikipedia ( authors )

Avia BH-21

  • Role : Fighter.
  • Manufacturer : Avia (licence production by SABCA and SEGA in Belgium).
  • Designers : Pavel Beneš and Miroslav Hajn.
  • First flight : January 1925.
  • Status : retired.
  • Primary users :
    • Czechoslovak Air Force.
    • Belgian Aéronautique Militaire.
  • Produced : 1925 to 1928.
  • Number built : 184 (139 for Czechoslovakia, 45 for Belgium).
  • Variants :
    • Avia BH-21J.
    • Avia BH-21R.
    • Avia BH-22.
  • Developed from : Avia BH-17.
  • Developed into :

    • Specifications (BH-21)

  • Crew: one.
  • Length: 22 ft 6 in (6.87 m).
  • Wingspan: 29 ft 2 in (8.90 m), upper wing slightly less.
  • Height: 9 ft 0 in (2.74 m).
  • Wing area: 237 sq ft (22 m²).
  • Empty weight: 1,687 lb (765 kg).
  • Gross weight: 2,370 lb (1,075 kg).
  • Fuel capacity: 310 lb (140 kg).
  • Powerplant: One Hispano-Suiza 8Fb water-cooled V-8 piston engine (licence-built by Škoda).
  • Power: 300 hp (224 kW) at 1,850 rpm.
  • Propellers: 2-bladed wooden propeller.
  • Maximum speed: 152 mph (245 km/h, 132 kts) at 9,800 ft (3,000 m).
  • Stall speed: 56 mph (90 km/h, 49 kts).
  • Range: 370 to 400 mi (600 to 650 km).
  • Endurance: 2 to 3 hours.
  • Service ceiling: 27,900 ft (8,500 m).
  • Time to altitude: 16,400 ft (5,000 m) in 14 min 7 s.
  • Armament: 2 × synchronised 7.7 mm (.303 in) Vickers machine guns in the upper front fuselage.

— — — = = — — —

This text is available under the Creative Commons Attribution-ShareAlike License
Source : Article Avia BH-21 of Wikipedia ( authors )
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