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Blackburn B.20

The Blackburn B.20 was an attempt at fixing some of the problems associated with flying boat design. With medium-sized aircraft, keeping the propellors clear of water and spray posed a challenge. The optimal wing angles of incidence for take-off and cruising flight usually did not coincide either. Blackburn's head of seaplane design, Major J. D. Rennie, patented (Patent # 433925) a possible solution to these challenges. The B.20 maritime reconnaissance prototype embodied these ideas. The lower portion of the hull could be lowered, effectively making the B.20 a floatplane. The extended lower hull kept the engines and props clear of water, and it was also set at such an angle that the wing's incidence was optimal for take-off. Once airborne, the hull could be retracted flush with the fuselage to present the streamlined shape of a conventional flying boat. The design also featured floats which retracted outward to form the wingtips.

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Blackburn B.20

Performance of the B.20 was satisfactory, and work was begun on a developed prototype. No armament was installed in the B.20, although provision was made for it. A crew of seven could be carried, and there was enough room for sleeping quarters, a wardroom, workroom, galley and head for extended missions. Unfortunately, Rennie's concept never entered service use. The B.20 prototype was lost during a test flight, possibly due to an engine malfunction or aileron flutter. Due to wartime demands, no further development was undertaken, and the end of World War II saw the dawn of jetliners and the decline of the flying boat.

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Blackburn B.20


Specifications B.20
Designer(s) Major J. D. Rennie
Mission Type Experimental flying boat; maritime reconnaissance, patrol
(Specification R.1/36)
Powerplant 2 x 1,720 hp Rolls-Royce Vulture 24 cyl. X-type inline pistons
(incl. retracted wingtip floats)
82 ft - 82 ft 2 in (25 m - 25.04 m)
Length 69 ft 7.5 in (21.22 m)
Height On beaching gear, pontoon extended: 25 ft 2 in (7.65 m)
Hull depth, pontoon retracted: 11 ft 8 in (3.55 m)
Hull depth, pontoon extended: 16 ft 4.5 in (5 m)
Wing area
(incl. retracted wingtip floats)
1,066 sq ft (99.03 m2)
Empty ?
Normal Take-off 35,000 lb (15,876 kg)
Max ?
Max speed 268 mph @ sl (429 km/hr) (est.)
288 mph @ 5,750 ft (461 km/hr @ 1,755 m) (est.)
306 mph @ 15,000 ft (490 km/hr @ 4,575 m) (est., with armament installed)
322 mph @ 15,000 ft (518 km/hr @ 4,575 m) (est. without armament installed)
Cruise speed ?
Initial climb rate ?
Service ceiling ?
Range 1,500 miles (2,414 km) (est., with armament installed)
Endurance ?
Armament (not installed, but provision for)
  • 2 x 0.303 in machine guns in powered nose turret
  • 2 x 0.303 in machine guns in powered dorsal turret
  • 4 x 0.303 in machine guns in powered tail turret
  • 8 x 250 lb (113 kg) bombs in wing cells inboard of engines
  • Crew Seven:
    • Bombardier
    • Pilots
    • Co-pilot
    • Navigator
    • Radio Operator
    • Observer
    • Flight Engineer
    Sleeping accomodations for six
    User UK (not operational)
    Number built One, plus one partially built
    Construction Numbers ?
    Serial Numbers V8914
    Unofficial Nickname Nutcracker
    Test Pilot(s) Blackburn: Flt. Lt. Harry Bailey

    Click to enlarge

    Related aircraft concept: Ursinus Fighter Seaplane

    Web Links


    1. Bridgman, Leonard, ed. Jane's Fighting Aircraft of World War II. Studio Editions, Ltd, London, 1990. ISBN 1-85170-199-0.
    2. Casey, Louis S. and John Batchelor. The Illustrated History of Seaplanes and Flying Boats. Exeter Books, New York, 1980. ISBN 0-89673-041-7
    3. Munson, Kenneth. Flying Boats and Seaplanes since 1910. Macmillan, New York, 1971. Library of Congress Catalog Card Number 73-142284.
    4. Bowers, Peter M. Unconventional Aircraft. Tab Books, Blue Ridge Summit, PA, 1984. ISBN 0-8306-2384-1.
    5. Updated Information and other Sources:

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    © 1997-2005, Robert Beechy
    Originally posted 31 October 1998
    Modified: 01/01/2005