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What was unusual about the Ar 66's tail?
Short answer
The horizontal stabilisers, the aircraft's most distinctive feature: mounted unusually high, on the top surface of the fuselage, and in an unusually forward position. The first prototype, the Ar 66a, flew in 1932, and the fuselage was made of welded steel tube covered in fabric.

High, forward-mounted stabilisers
The most distinctive feature of the Ar 66 was its horizontal stabilisers, placed at an unusual height and mounted on the top surface of the fuselage in an unusually forward position.
A mixed structure of steel, wood and fabric
The fuselage had an oval cross-section and was built from welded steel tube, covered in fabric. Both wings shared the same span and an 8° sweep, with a structure of double pine spars, lime-wood ribs and fabric covering. Both the upper and lower wings were fitted with several balanced ailerons. The steel-tube landing gear attached to the fuselage in a "V" shape and used high-pressure rubber suspension.
Development paid for by Arado
Early development work on what would become the Ar 66 was funded from Arado's own resources. In 1932, the first prototype, designated Ar 66a, made its maiden flight. By the end of September that year the prototype had demonstrated performance superior to that of two competing aircraft.
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