Arado Ar 68

The Arado Ar 68 was a single-engine biplane fighter developed in the early 1930s. It quickly proved to have admirable manoeuvrability characteristics, being quite manoeuvrable but not prone to rotation. During a flight test it overtook a Heinkel He 51 in a mock air combat.  Despite this favourable outcome, some officials expressed concerns over the unforgiving nature of such a high-performance aircraft, to the point that production of the Ar 68 was allegedly almost cancelled altogether. Source wikipedia