Chyetverikov ARK-3

The Chyetverikov ARK-3 ("ARKtichyeskii" - arctic) was a multi-role flying boat designed for Arctic operations that was built in the Soviet Union from 1933. It featured a conventional flying boat hull, with high cantilever wings equipped with floats at mid-span. The two piston engines were mounted in tractor-pusher fashion on a pylon above the fuselage.
Development.
In 1933 Chyetverikov had the design for a compact twin engined flying-boat ready for further development, which he proposed to the Glavsyevmorput ("Glavsyevmorput" – chief administration of northern sea routes) as a multi-role Arctic aircraft, and an order for a prototype was made, setting up Chyetverikov in his own OKB (design bureau).
The ARK-3 was of mixed construction, with a long Duralumin stressed skin fuselage; wooden wings of MOS-27 aerofoil section; duralumin tubing tail surfaces; and ailerons with fabric covering. The dual control enclosed cockpit housed two pilots sided by side with two gunners/observers in bow and dorsal positions. Strut-supported wooden floats, at approximately half-span; and a pylon-supported engine nacelle housing tandem radial engines with Townend ring cowlings; completed the structural elements, built with a safety factor of 5.5.
Flight- and sea trials in 1936 revealed weaknesses in the bows, floats and engine nacelle pylon, which were all strengthened. Performance was deemed to be good, prompting an order for a second prototype with the fuselage lengthened by to and a slightly enlarged wing; this was designated ARK-3-2 and the first prototype was re-designated ARK-3-1. A production order for five aircraft was placed, with production commencing immediately.
On 14 July 1937 the ARK-3-1 was destroyed following a structural failure; the ARK-3-2 was destroyed exactly one year later and the programme was cancelled.