The Heinkel HD 37 was a fighter aircraft, designed in Germany in the late 1920s, but produced in the

USSR The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen nationa ...

for

Soviet Air Force The Soviet Air Forces ( rus, Военно-воздушные силы, r=Voyenno-vozdushnyye sily, VVS; literally "Military Air Forces") were one of the air forces of the Soviet Union. The other was the Soviet Air Defence Forces. The Air Forces ...

service. It was a compact,

single-bay A biplane is a fixed-wing aircraft with two main wings stacked one above the other. The first powered, controlled aeroplane to fly, the Wright Flyer, used a biplane wing arrangement, as did many aircraft in the early years of aviation. While a ...

biplane with staggered wings of unequal

span Span may refer to: Science, technology and engineering * Span (unit), the width of a human hand * Span (engineering), a section between two intermediate supports * Wingspan, the distance between the wingtips of a bird or aircraft * Sorbitan ester ...

, braced by N-type

interplane strut In aeronautics, bracing comprises additional structural members which stiffen the functional airframe to give it rigidity and strength under load. Bracing may be applied both internally and externally, and may take the form of strut, which act in ...

s. The pilot sat in an open cockpit, and the main units of the tailskid undercarriage were linked by a cross-axle.

Design and development

It had been designed for the clandestine air force that the ''

Reichswehr ''Reichswehr'' () was the official name of the German armed forces during the Weimar Republic and the first years of the Third Reich. After Germany was defeated in World War I, the Imperial German Army () was dissolved in order to be reshape ...

'' was training at

Lipetsk Lipetsk ( rus, links=no, Липецк, p=ˈlʲipʲɪtsk), also romanized as Lipeck, is a city and the administrative center of Lipetsk Oblast, Russia, located on the banks of the Voronezh River in the Don basin, southeast of Moscow. Populat ...

, but had been rejected by German officials, who purchased the Fokker D.XIII instead. The Soviet Air Force was experiencing a crisis with the obsolescence of its main fighter, the

Polikarpov I-5 The Polikarpov I-5 was a single-seat biplane which became the primary Soviet fighter between its introduction in 1931 through 1936, after which it became the standard advanced trainer. Following Operation Barbarossa, which destroyed much of the ...

, with no replacement apparently forthcoming from domestic manufacturers. When Heinkel was approached to provide an alternative, the firm was able to offer the HD 37, and the two prototypes were flown to

Moscow Moscow ( , US chiefly ; rus, links=no, Москва, r=Moskva, p=mɐskˈva, a=Москва.ogg) is the capital and largest city of Russia. The city stands on the Moskva River in Central Russia, with a population estimated at 13.0 millio ...

in early 1928. Flight testing produced mixed results. While the basic design was apparently sound, Soviet test pilots reported many deficiencies in handling, and Heinkel was presented with a long list of complex changes to be made. Heinkel responded with the HD 43, and when the same Soviet test pilots found that they liked it even less than the HD 37, attention shifted once again to the previous design by the end of 1929. Early the following year, the Soviet government bought a licence to manufacture the type for the next three years, paying Heinkel 150,000 Marks for it. Manufacturing was carried out by TsKB (''Tsentrahl'noye konstrooktorskoye byuro'' - central construction bureau) and

Polikarpov Polikarpov Design Bureau was a Soviet OKB (design bureau) for aircraft, led by Nikolai Nikolaevich Polikarpov. Dux Factory was acquired by the USSR and became part of Polikarpov. After the death of Polikarpov on 30 July 1944 at the age of 5 ...

, given the designation I-7. Many of the improvements that had been adopted in the creation of the HD 43 were eventually implemented in the I-7 as well, along with other modifications, and by the time the first examples flew in summer 1931, flight test results were positive. Despite on-going difficulties in obtaining materials, 131 examples were produced by 1934. Most of these served briefly with units in

Belarus Belarus,, , ; alternatively and formerly known as Byelorussia (from Russian ). officially the Republic of Belarus,; rus, Республика Беларусь, Respublika Belarus. is a landlocked country in Eastern Europe. It is bordered by ...

, but by the time the last examples were leaving the factory, the type was already obsolete.

Variants

;HD 37a: 1 built. ;HD 37b: 1 built. ;HD 37c: The third sub-series, produced under licence by

after adaptation by TsKB (''Tsentrahl'noye konstrooktorskoye byuro'' - central construction bureau): 132+ built. ;Polikarpov I-7: The licence-built HD 37c adapted by TsKB by fitting a

Mikulin M-17F The Mikulin M-17 was a Soviet-licensed copy of the German BMW VI V-12 liquid-cooled aircraft piston engine, further developed by Alexander Mikulin and used by Soviet aircraft and tanks during World War II. Production began in 1930 and continued th ...

engine,

PV-1 machine gun PV-1 (''Pulemet Vozdushny'', airborne machine gun) is a Soviet air-cooled version of the Russian M1910 Maxim for mounting on aircraft. It was designed between 1926 and 1927. The first prototypes were produced and accepted into service in 1928.Ш� ...

Design and development

Variants

Operators

Specifications (I-7)

References

Further reading