Blackburn B-20 and B-40

Six-seat experimental reconnaissance flying boat with retractable-hull, to Specification R.1/36 to meet the requirements of OR.32. It was an all metal high wing cantilever monoplane with a cantilever tailplane high on the rear fuselage along with a single fin and rudder. While on the water, the B-20 was essentially a floatplane, using a large float under the fuselage for buoyancy, and two smaller floats near the wingtips for stability. In flight, the main float retracted upwards towards the fuselage, fitting into a "notch" to become streamlined as a part of the fuselage. The wing floats folded outwards to become the wingtips. This configuration gave the correct wing incidence for takeoff and for flight and in the latter a much reduced drag compared to the deep hulls of flying boats.
The aircraft was designed to carry two 0.303 machine guns in the nose, with two more in a tail-mounted turret (which was carried in mock-up form on the prototype). Four 500 lb bombs could be carried in bomb compartments in the wing roots. Provisions were made for an additional twin gun dorsal turret. Two 1,720 h.p. Rolls-Royce Vulture X powerplants driving 3-bladed Rotol constant-speed feathering propellers.

B-20 Specification
Span*	Length	Height**	Wing Area	Empty Wt	Max AUW	Cruise Speed	Maximum Speed	Range	Service Ceiling
82 ft 2 in	69 ft 8 in	25 ft 2 in	1066 sq ft		35000 lb	200 mph/ 174 kn	306 mph/ 266 kn	1500 mi
25.04 m	21.23 m	7.67 m	99.03 m2		15876 kg	322 km/h	492 km/h	2414 km

Proposed improved version of the B-20 to meet a requirement for a small general purpose flying boat to Specification R.13/40. Two Bristol Centaurus powerplants.