The Heinkel He 51 was a German single‑seat biplane fighter developed in the early 1930s as a direct descendant of the He 49 series; it featured an all‑metal structure with fabric covering, a BMW VI liquid‑cooled V12 engine and twin 7.92 mm machine guns, and entered pre‑production flight tests in 1933 with deliveries from 1934 onward.
Design and Development
Designed by Walter and Siegfried Günter at Heinkel as a modernisation of earlier streamlined fighters, the He 51 evolved through prototype refinements (new vertical tail, revised wings, undercarriage and radiator) into the A and B production series; early handling and structural issues prompted strengthening changes in the B series and minor production refinements such as a centreline drop tank provision and improved landing‑gear bracing.
Operational Service
The He 51 served as one of the backbone fighters of the nascent Luftwaffe but was effectively obsolete on arrival compared with emerging monoplanes; its most intensive combat use came with the Condor Legion in the Spanish Civil War from 1936, where initial success against older Republican types was quickly reversed after the arrival of Soviet Polikarpov I‑15 and I‑16 fighters and fast Tupolev SB bombers, forcing the He 51 out of air superiority work and into night operations and a prominent ground‑attack role.
Production and Variants
Total production ran to roughly 700 airframes across the A, B and C series, plus floatplane and experimental high‑altitude prototypes; major production blocks were the A‑1 (early fighters), the strengthened B‑1 (the largest run), the B‑2 floatplane and the C‑1/C‑2 ground‑attack adaptations, while one‑off high‑altitude experiments such as the B‑3 and the He 52 prototype explored extending the design’s performance envelope.
Later Use and Legacy
Withdrawn from frontline Luftwaffe fighter duties by the late 1930s, the He 51 continued in training, liaison and close‑support roles and remained in Spanish service longer (designated A.1), where it influenced close‑air‑support doctrine; its principal legacy lies in the combat lessons gained in Spain and the tactical development of ground‑attack methods later used by the Luftwaffe in World War II.
