Heinkel He 51 A-1 single-engine fighter
A single-seat biplane of composite structure with fixed landing gear. This aircraft was designed by Heinkel Flugzeugwerke AG under the guidance of the brothers Siegfried and Walter Günter. The He 51 fighter was a serious upgrade of the single-seat He 49 fighter, which had flown for the first time in November 1932.
The He 49 was a single-strut biplane of composite structure with a BMW liquid-cooled engine. Among German planes of that period, it was set apart by its fuselage, which had extremely clean aerodynamic contours and a retractable radiator.
The designers themselves were not very satisfied with their creation, believing that its characteristics could be significantly improved. A fourth prototype was built, with a new designation: He 51a.
The dimensions and the design of the aircraft remained almost unchanged, but the He 51a was noticeably different from its predecessor in various details. The vertical empennage was completely redesigned. The retractable radiator was replaced with a ducted one. The new ailerons had balance and trim tabs, and the wing pylon's parallel struts were replaced with N-type struts. The pyramidal landing gear with a common axle was replaced with individual V struts featuring hydromechanical shock-absorbers. The struts and the wheels now had fairings, and a tail skid was used instead of a tail wheel. As a whole, the He 51 turned out to be noticeably more elegant, which significantly improved its flight characteristics.
The plane's power unit was a 500 hp Bayerische Motoren Werke BMW VI twelve-cylinder liquid-cooled engine that could provide a power of up to 750 hp during short-term uprating.
The He 51 was armed with two fuselage-mounted synchronous 7.92 mm Rheinmetall-Borsig MG 17 machine guns with 500 rounds each.
The leadership of the German Ministry of Aviation saw the He 51 as an aircraft of extreme importance for the reviving Luftwaffe. In April 1935, the production of He 51 A-1 fighters began. The production aircraft differed from the prototype: it had a cut-down fuselage spine fairing behind the cockpit, a slightly changed tail skid design, and extended engine exhaust pipes.