Sorry LowNSlow it is not the Heinkel He-51.
S'land is close enough with the Heinkel He-43 otherwise known as the Heinkel HD-43.
The three view drawing shown is in fact the Heinkel HD-37.
On 21 Jan 1928 the Soviet Government ordered two single seat fighter prototypes from Ernst Heinkel Flugzeugwerke GmbH at Warnemunde. German firms were not allowed to develop military aircraft but Heinkel managed to design , build and test prototypes secrectly on a small scale without interference from the control authorities.
The HD37 was a small and compact fighter biplane was euphemistically described as an aircraft 'for high speed and altitude research'. After evaluation of the HD-37 two modified aircraft were ordered these were the HD-43. The HD-43's fuselage was a little longer and the cockpit and wings were moved back, it was also a little lighter than the HD-37.
Soviet test pilots found that they liked the HD-43 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 to be carried out by TsKB, and the designation I-7 was assigned.