The unique Blackburn B20, which was built at Blackburn Aircraft's Dumbarton works, was a twin-engine reconnaissance flying designed to meet Specification R.1/36. It was based upon a patented design study (UK Patent No 433925) by Blackburn's Chief Seaplane Designer Major John Rennie.
It was described as combining the best features of both a flying boat and a floatplane as it boasted a retractable planning bottom surface which could be extended (with retractable wing-tip floats) to provide propeller clearance when on the water. This allowed the hull frontal area and drag to be significantly reduced when the planning surface was retracted, once airborne.
A further advantage of this arrangement was that the length of the pontoon struts was selected to ensure that the wing sat at the optimum incidence for best take-off performance when the aircraft was on the water.
Power was supplied by two Rolls-Royce Vulture, 24 cylinder X-type engines producing 1,20 hp each and Six crew were carried, comprising bomb aimer, first and second pilot, navigator, observer and flight engineer.
The B20 was designed to carry two 0.303 machine guns in the nose and 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 wings. Provisions were made for an additional twin gun dorsal turret.
The prototype (V8914) flew on 26th March 1940 but the aircraft was lost in an accident at the Sound of Bute on the Firth of the Clyde on 7th April 1940, caused by aileron flutter. The crew bailed out but sadly 3 were lost in the tragedy. The wreck still remains and was declared a War Grave in 1998.
Early tests had fully vindicated the main benefits of the retractable pontoon configuration but although design work was initiated on other projects (including a single seat seaplane fighter - the B44) no further designs were built as Blackburn turned it attention to the war effort.
The competition for the original requirement was won by the Supermarine 314 but they could not fulfill any order due to the work on the Spitfire and the Saunders Roe Lerwick became the chosen aircraft.
Variants & Numbers Built
One example only, serial V8914.
|Powerplants||Two 1,720 hp Rolls-Royce Vulture X engines|
|Span||82 ft 2 in with floats retracted|
|Maximum Weight||35,000 lb|
|Capacity and armament||Six crew, provision for six machine guns in pairs (nose, and dorsal and tail turrets) and up to 2,000 lb bomb load carried in bomb compartments in the wing roots.|
|Maximum Speed||288 mph at 5,750 ft; 306 mph at 15,000 ft|
|Cruising Speed||200 mph|
|Endurance / Range||8 hours endurance; maximum range 1,500 miles|
No surviving aircraft, V8914 having been destroyed in an accident on 8th April 1940..