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Blackburn B.20

Flying Boat Prototype Aircraft

United Kingdom | 1940

"The Blackburn B.20 aircraft project held a unique, extendable boat-like hull for which to accomplish water landings with."

Authored By: Staff Writer | Last Edited: 05/15/2018 | Content ©www.MilitaryFactory.com | The following text is exclusive to this site; No A.I. was used in the generation of this content.
Britain's long-ranging coastline and free access to surrounding seas made it a priority for its military to field a fleet of capable flying boats in the post-World War 1/pre-World War 2 period. As technology allowed, these platforms became evermore advanced and a critical component to sea-based operations involving both the Royal Navy (RN) and the Royal Air Force (RAF). With the arrival of World War 2 in September of 1939, the fleet proved critical to the scope of both services, helping to stave off defeat and, in turn, helping to secure the ultimate victory of 1945.

Prior to the war in 1936, the RAF put together a new specification covering a compact reconnaissance-minded flying boat aircraft under Specification R.1/36. Flying boats provided two very key qualities in their design: offering excellent over-water range and excellent loitering times once on station. In addition to this, the type held a built-in functionality which allowed it to land and take-off from water - not requiring a prepared runaway to operate from. The one requirement authorities revealed was a minimum speed of 230 miles per hour.

Two companies returned with two very similar designs: Saunders-Roe delivered their "A.36" and Blackburn delivered their "B.20". The Blackburn offering was of particular note for it featured a retractable pontoon assembly built as part of the boat-like hull and this could be operated when landing or taking-off while then being "tucked in" for air travel and thus retaining aerodynamic efficiency.

This unique mechanical system was a solution to a soon-realized problem - protecting the engines from the spray of the salty sea when running along the water. Prior to this period of aviation history, the issue was contained by simply mounting engines atop the upper wing assembly of a biplane arranged aircraft. The shift to the monoplane as the new aircraft standard now meant that engines sat close to the ground, or in this case the water's surface. One option was to create a deep hull/fuselage to help elevate the engines but this reduced aerodynamic efficiency by generating additional drag.

Therefore, the Blackburn B.20 was an interesting response to this challenge and attempted to deal with the issue through a more complex, yet possibly practical, arrangement - retaining the monoplane wings and actively affecting the hull itself in-flight (as needed) instead.

The result was an aircraft that featured qualities more akin to a seaplane or floatplane than a true flying boat. The boat-like hull sat under the fuselage in the usual way but was only called into action when needed and outboard pontoons were used to steady the aircraft on the surface of the water (these also folded away when not in use). The wing mainplanes were mounted high along the sides of the upper fuselage section and the engines were fitted to each wing element near the wingroots. The heavily-framed flightdeck overlooked the nose in traditional fashion and gave the pilots excellent views of the engines installed at the wing leading edges to either side of the cockpit. The fuselage tapered nicely to the rear, the tail unit containing a single, rounded vertical fin and low-set horizontal planes.

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The aircraft's design is attributed to John Douglas Rennie and a prototype went airborne for the first time on March 26th, 1940. However, that April, extreme aileron flutter forced the crew to bail out (three were killed in the action) and the aircraft was a ruled a total loss. Just a handful of test flights were completed with this vehicle, meant to test the validity of the retracting hull idea, and, apparently, RAF authorities had seen enough of the project to end its commitment to the B.20 after the final flight (as such no additional development work was taken up).

As designed, the B.20 carried 2 x Rolls-Royce Vulture X-type, 24-cylinder engines developing 1,720 horsepower each and these were used to drive three-bladed propellers in traditional "puller" fashion. Performance included a maximum speed of 305 miles per hour and a range out to 1,500 miles. Dimensions were a length of 69.7 feet, a wingspan of 82 feet and a height of 25 feet. MTOW was rated at 35,000lb. Armament was to be defensive in nature and made up of a mix of cannon and machine guns to include two powered turrets. The operating crew would have been six men.

In the end, a submission from Saunders-Roe, the A.36 "Lerwick", became the more successful of the two offerings but even this design was not an outright success and only twenty-one examples were acquired by the RAF (and some used by the Royal Canadian Air Force (RCAF)). The series gave a poor showing in practical wartime service as they were highly prone to accidents (indeed ten of the lot were lost in this fashion). With service introduction had in 1940, the line was retired as soon as 1942.

The Blackburn B.40 was drawn up as an improved, dimensionally larger, form of the B.20 and this was covered by Specification R.13/40 of 1940. In September of 1941, the RAF commissioned for a pair of B.40 prototypes to be developed but, after review, the type was not deemed worthy of additional work nor funding, leading to its uneventful end in December of that year. This aircraft was to carry 2 x Bristol Centaurus air-cooled radial piston engines and carry a mix of cannon and machine gun armament for defense. Dimensions included a wingspan of 98 feet and an MTOW of 52,000lb. The Short Sunderland ultimately took its place in service (detailed elsewhere on this site).

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Power & Performance
Those special qualities that separate one aircraft design from another. Performance specifications presented assume optimal operating conditions for the Blackburn B.20 Flying Boat Prototype Aircraft.
2 x Rolls-Royce Vulture 24-cylinder X-type engines developing 1,720 horsepower each and driving three-bladed propeller units in puller fashion.
304 mph
490 kph | 265 kts
Max Speed
1,491 miles
2,400 km | 1,296 nm
Operational Range
City-to-City Ranges
Operational range when compared to distances between major cities (in KM).
The nose-to-tail, wingtip-to-wingtip physical qualities of the Blackburn B.20 Flying Boat Prototype Aircraft.
69.6 ft
21.20 m
O/A Length
82.0 ft
(25.00 m)
O/A Width
25.1 ft
(7.65 m)
O/A Height
35,274 lb
(16,000 kg)
Available supported armament and special-mission equipment featured in the design of the Blackburn B.20 Flying Boat Prototype Aircraft .
2 x 0.303 caliber machine guns in nose turret.
2 x 0.303 caliber machine guns in dorsal turret.
4 x 0.303 caliber machine guns in tail turret.

Also an internal bomb load capacity up to 8 x 250lb drop bombs.
Notable series variants as part of the Blackburn B.20 family line.
B.20 - Base Project Designation; single example completed and lost during flight testing; project cancelled.
B.40 - Improved variant fitting Bristol Centaurus engines; two prototypes ordered but project cancelled December of 1941.
Global customers who have evaluated and/or operated the Blackburn B.20. Nations are displayed by flag, each linked to their respective national aircraft listing.

Total Production: 1 Units

Contractor(s): Blackburn Aircraft - UK
National flag of the United Kingdom

[ United Kingdom (cancelled) ]
Relative Max Speed
Hi: 400mph
Lo: 200mph
Aircraft Max Listed Speed (304mph).

Graph Average of 300 MPH.
Era Crossover
Pie graph section
Pie graph section
Showcasing Aircraft Era Crossover (if any)
Production Comparison
Entry compared against Ilyushin IL-2 (military) and Cessna 172 (civilian) total production.
MACH Regime (Sonic)
RANGES (MPH) Subsonic: <614mph | Transonic: 614-921 | Supersonic: 921-3836 | Hypersonic: 3836-7673 | Hi-Hypersonic: 7673-19180 | Reentry: >19030
Aviation Timeline
1 / 1
Image of the Blackburn B.20
Image copyright www.MilitaryFactory.com; No Reproduction Permitted.

Mission Roles
Some designs are single-minded in their approach while others offer a more versatile solution to airborne requirements.
Some designs stand the test of time while others are doomed to never advance beyond the drawing board; let history be their judge.
Going Further...
The Blackburn B.20 Flying Boat Prototype Aircraft appears in the following collections:
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