The Blackburn B-20 was an

experimental aircraft An experimental aircraft is an aircraft intended for testing new aerospace technologies and design concepts. The term ''research aircraft'' or ''testbed aircraft'', by contrast, generally denotes aircraft modified to perform scientific studies, ...

, first flying in

1940 A calendar from 1940 according to the Gregorian calendar, factoring in the dates of Easter and related holidays, cannot be used again until the year 5280. Events Below, the events of World War II have the "WWII" prefix. January *January ...

, that attempted to drastically increase the performance of

flying boat A flying boat is a type of fixed-winged seaplane with a hull, allowing it to land on water. It differs from a floatplane in that a flying boat's fuselage is purpose-designed for floatation and contains a hull, while floatplanes rely on fusela ...

designs.

Blackburn Aircraft Blackburn () is an industrial town and the administrative centre of the Blackburn with Darwen borough in Lancashire, England. The town is north of the West Pennine Moors on the southern edge of the Ribble Valley, east of Preston and north- ...

undertook an independent design study based on a patent filed by their chief designer, John Douglas Rennie for a retractable pontoon float that formed the planing hull.

Design and development

The B-20 was an attempt to combine the best features of both the

and the

floatplane A floatplane is a type of seaplane with one or more slender floats mounted under the fuselage to provide buoyancy. By contrast, a flying boat uses its fuselage for buoyancy. Either type of seaplane may also have landing gear suitable for land, ...

. 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, somewhat like those on the American Consolidated PBY flying boat design, 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.Buttler Blackburn, along with Supermarine, Shorts and Saunders-Roe tendered designs against Air Ministry Specification R1/36. The Supermarine was chosen initially but Supermarine could not start work soon enough (due to their work on the Spitfire) and what would enter service as the Saunders Roe Lerwick became the chosen aircraft. However, the Ministry was interested enough to authorise and contract for the construction of a prototype of the B-20,

serial number A serial number is a unique identifier assigned incrementally or sequentially to an item, to ''uniquely'' identify it. Serial numbers need not be strictly numerical. They may contain letters and other typographical symbols, or may consist enti ...

''V8914'', to test the concept.

Testing

The prototype, built at Dumbarton, flew for the first time on 26 March 1940. On 7 April, during a test run, the aircraft experienced extreme vibration due to

aileron An aileron (French for "little wing" or "fin") is a hinged flight control surface usually forming part of the trailing edge of each wing of a fixed-wing aircraft. Ailerons are used in pairs to control the aircraft in roll (or movement around ...

flutter Flutter may refer to: Technology * Aeroelastic flutter, a rapid self-feeding motion, potentially destructive, that is excited by aerodynamic forces in aircraft and bridges * Flutter (American company), a gesture recognition technology company acqu ...

and the crew bailed out. Three were lost, the other two were picked up by , a converted merchantman. Development ceased when the first prototype crashed, as Blackburn's resources were dedicated to the war effort. The Ministry felt the concept had been proven and the crash was not due to the pontoon design. The aircraft's wreck still exists, but remains undisturbed as it is designated a War grave. In 1998, one of the engines was raised as it had been caught in a fishing boat's nets and dragged away from the wreck, into shallower water. It is currently an exhibit in the

Dumfries and Galloway Aviation Museum The Dumfries and Galloway Aviation Museum is a volunteer-operated aviation museum located in and around the World War II-era watch tower (control tower) at the former RAF Dumfries, located two miles north east of the centre of Dumfries, Scotla ...

B.40

The B-40 was an improved variant of the B-20 with

Bristol Centaurus The Centaurus was the final development of the Bristol Engine Company's series of sleeve valve radial aircraft engines. The Centaurus is an 18-cylinder, two-row design that eventually delivered over . The engine was introduced into service lat ...

engines to meet a requirement for a small general purpose flying boat and specification R.13/40 was raised for it.Meekcoms/Morgan 1994, p. 287 Two prototypes were ordered in September 1941 but the situation was reconsidered in December. Its range was insufficient improvement over the Sunderland III, performance on one engine was unacceptable, and land-based patrol aircraft were capable of covering longer ranges. Further, there was little value as an experimental design because the principle had been proven in the B.20 and for an aircraft the size of the B.40 there would not be a significant improvement in drag. With no operational requirement for the B.40, it was therefore cancelled.Buttler. ''British Secret Projects Fighters and Bombers 1935–1950'' Midland Publishing

Specifications (B-20, as designed)

Notes

Bibliography

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External links

"A Teaser in Hydraulics"
''Flight'' 1946 p383-384. – details of the float mechanism

and afloa
Dinger's Aviation Pages: Photos and data on Blackburn B20
{{Blackburn aircraft Blackburn aircraft, B-20 1940s British experimental aircraft Floatplanes High-wing aircraft Aircraft first flown in 1940 Twin piston-engined tractor aircraft