World War 2 In Review

Blackburn B.20: British Experimental Flying Boat Aircraft

An excellent view of the Blackburn B.20 flying boat highlighting the aircraft’s extended hull, retracted wingtip floats, and well-engineered cowlings for the Vulture engine.

The Blackburn B.20 was an experimental aircraft, first flying in 1940, that attempted to drastically increase the performance of flying boat designs. Blackburn Aircraft 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 flying boat and the floatplane. 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.

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 authorize and contract for the construction of a prototype of the B.20, serial number 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 flutter and the crew bailed out. Three were lost, the other two were picked up by HMS Transylvania, 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.

B.40

The B.40 was an improved variant of the B.20 with Bristol Centaurus engines to meet a requirement for a small general purpose flying boat and specification R.13/40 was raised for it. 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.

Type: Prototype flying boat

National origin: United Kingdom

Manufacturer: Blackburn Aircraft

Designer: John Douglas Rennie

Primary user: Royal Air Force

Number built: 1

First flight: 26 March 1940

Specifications (B-20, as designed)

Crew: 6

Length: 69 ft 8 in (21.23 m)

Wingspan: 82 ft 0 in (24.99 m) floats retracted

Height: 25 ft 2 in (7.67 m) hull extended

Wing area: 1,066 sq ft (99.0 m2)

Maximum takeoff weight: 35,000 lb (15,876 kg)

Powerplant: 2 × Rolls-Royce Vulture X-24 liquid-cooled piston engines, 1,720 hp (1,280 kW) each

Propellers: 3-bladed Rotol constant-speed feathering propellers

Maximum speed: 306 mph (492 km/h, 266 kn) at 15,000 ft (4,572 m)

Range: 1,500 mi (2,400 km, 1,300 nmi)

Armament:

Guns: provision for two turrets and other defensive positions

Bombs: bomb-cells in center section

Bibliography

"Blackburn B.20". British Aircraft Directory. 20 July 2003.

Bussy, Geoffrey (2006). "Blackburn's Amazing B.20 Flying Boat". Air Enthusiast (124). Stamford, UK: Key Publishing: 28–29.

Buttler, Tony (2004). British Secret Projects: Fighters & Bombers 1935–1950. Hinckley, UK: Midland Publishing.

Jackson, A. J. (1989). Blackburn Aircraft Since 1909. London: Putnam.

Meekcoms, K. J.; Morgan, E. B. (1994). The British Aircraft Specification File. Tonbridge, UK: Air-Britain.

Townend, David R (2010). Clipped Wings – World War Two Edition. Markham, UK: Aerofile Publications.

This side view of the B.20 illustrates how the hull moved forward as it was extended. The rear member of each of the four hull mounts was a hydraulic cylinder that actuated the extension and retraction of the hull.

The B.20 on the water looked a little ungainly with its hull extended. Note the access ladder between the hull and the fuselage.

The B.20 providing a good view of the wing float design. Note the Short Sunderland and what appears to be a Short Empire framed nicely between the B.20’s hull and fuselage.

Rear view of the B.20 helps visualize the defense the four .303 machine guns in the turret would have provided.

Blackburn B.20.

The diagram for J.D. Rennie's patent for a retractable bottom for a flying boat (patent number 433925). Note that at this stage it was envisaged that the wing floats would retract into the rear of the engine nacelles.

Major John Douglas Rennie, Chief flying boat designer for the Blackburn Aircraft company and designer of the B.20.

The Blackburn B20. It is likely to be a composite image, airbrushed to show the B.20 as it would have appeared in flight.

The B.20 pontoon, showing the ladder to gain entrance. There were another two hatches in the "floor" of the aircraft to allow escape onto the pontoon in an emergency. Mooring equipment (boat hooks and anchors) was stored under panels in the pontoon. The fuel tanks were accommodated in the center of the pontoon which made fuel replenishment much simpler than on a traditional flying boat.

Flt Lt Henry "Harry" Bailey, A.M.I.C.E., A.F.R.Ae.S, pilot of the B.20, who lost his life in the crash.

How a Hercules powered version of the Blackburn B.20 might have looked.

How the B.20 might have looked in the air-sea rescue role. Its speed would have made its chance of survival in this task over the North Sea much greater than the types which actually carried it out. The pontoon float would have greatly simplified the task of picking up survivors.

Blackburn B.20.

On the water, B.20 prototype V8914 showing retracting wingtip floats. Mooring could be done from the deck of the retractable pontoon.

Giussano-class Cruisers: Italian Light Cruisers

Cruiser Alberto da Giussano.

The Alberto di Giussano class of light cruisers were a sub-class of the Condottieri class built before World War II for the Italian Regia Marina, to gain predominance in the Mediterranean Sea. They were designed by general Giuseppe Vian and were named after Condottieri (military commanders) of the Italian Medieval and Renaissance periods.

Between the World Wars, the world powers started a rush to gain the supremacy on the seas. In 1926, France started to produce the Le Fantasque class of destroyers, which were superior in displacement and firepower to other destroyers of that period. To counter the French menace, the Regia Marina decided to produce a new class of cruiser that would be of intermediate size between the new French destroyer class and cruisers. The Italian ships equated to the British Leander-class cruisers.

There were four ships, all laid down in 1928: Alberto di Giussano, Alberico da Barbiano, Bartolomeo Colleoni and Giovanni delle Bande Nere.

Meant to hunt down and overwhelm the big French destroyers, the emphasis on firepower and speed resulted in these ships being virtually unprotected against gunfire and underwater threats; this was a major factor in all four ships being sunk by torpedoes.

Name: Giussano class

Operators: Regia Marina

Built: 1928–1930

In commission: 1931–1942

Completed: 4

Lost: 4

Type: Cruiser

Displacement:

6,570 tonnes (6,470 long tons) standard

6,954 tonnes (6,844 long tons) full load

Length: 169.3 m (555 ft)

Beam: 15.5 m (51 ft)

Draft: 5.3 m (17 ft)

Propulsion: 95,000 hp (71,000 kW)

Speed:

37 knots (69 km/h; 43 mph)

(42 knots (78 km/h; 48 mph) in trials)

Range: 3,800 nmi (7,000 km) at 18 kn (33 km/h; 21 mph)

Complement: 507

Armament:

8 × 152 mm (6 in) /53 guns in 4 twin mountings

6 × 100 mm (4 in) / 47 caliber guns in 3 twin mountings

8 × 37 mm (1.5 in) 54-cal. guns

8 × 13.2 mm machine-guns

4 × 533 mm (21 in) torpedo tubes

Armor:

Decks: 20 mm (0.79 in)

Belt: 24 mm (0.94 in)

Turrets: 23 mm (0.91 in)

Tower: 40 mm (1.6 in)

Aircraft carried: 2 × CANT 25AR (later Ro.43) seaplanes

Aviation facilities: 1 × catapult launcher

Ships of the Alberto di Giussano Class
Ship	Builder	Laid down	Launched	Completed	Fate
Alberico da Barbiano	Ansaldo, Genoa	16 April 1928	23 August 1930	9 June 1931	Sunk 13 December 1941, by a group of Royal Navy and Dutch destroyers during the Battle of Cape Bon.
Alberto di Giussano	Ansaldo, Genoa	29 March 1928	27 April 1930	5 February 1931
Bartolomeo Colleoni	Ansaldo, Genoa	21 June 1928	21 December 1930	10 February 1932	Sunk 19 July 1940, during the Battle of Cape Spada.
Giovanni delle Bande Nere	R. C. di Castellammare di Stabia	31 October 1928	27 April 1930	27 April 1931	Sunk 1 April 1942, torpedoed by British submarine HMS Urge while off Stromboli.

References

Gay, Franco; Gay, Valerio (1987). The Cruiser Bartolomeo Colleoni. London: Conway Maritime Press.

Fraccaroli, Aldo (1968). Italian Warships of World War 2. London: Ian Allan.

Further Reading

Cernuschi, Enrico (2022). "Esploratori of the Regia Marina, 1906—1939". In Jordan, John (ed.). Warship 2022. Oxford: Osprey Publishing. pp. 147–160.

Cruiser Giovanni dalle Bande Nere, Bartolomeo Colleoni, Alberto di Giussano, Luigi Cadorna, Armando Diaz, Genoa, May 1938.

Cruisers Alberico da Barbiano and Alberto di Giussano docked side by side in the 1930s.

Cruiser Bartolomeo Colleoni in Venice.

Cruiser Alberto da Giussano.

Cruiser Alberto Di Giussano at Venice in the late 1930s.

Cruiser Alberto da Giussano.

Cruiser Alberto da Giussano, 1935.

Cruiser Alberto da Giussano.

Cruiser Alberto da Giussano, off Genoa, September 19, 1930.

Cruiser Alberto da Giussano, Messina, late summer 1941.

Cruiser Alberico da Barbiano.

Cruiser Bartolomeo Colleoni.

Cruiser Bartolomeo Colleoni, April 30, 1934.

Cruiser Bartolomeo Colleoni, Genoa, May 30, 1938.

Large ships from left to right: USS Augusta (CA-31), HMS Birmingham (British Light Cruiser, 1937), Lamotte-Picquet (French Light Cruiser, 1926), USS Chaumont (AP-5), Bartolomeo Colleoni (Italian Cruiser). "Man of War Row" in the Whangpoo (Huangpu) River, Shanghai, China. The Siccawei Observatory signal tower is in the left foreground. Taken off the Bund at Shanghai, China late May or early June 1939.

Cruiser Bartolomeo Colleoni under attack from HMAS Sydney and destroyer flotilla.

Cruiser Colleoni under shell fire.

Cruiser Colleoni under fire.

Cruiser Bartolomeo Colleoni.

Cruiser Colleoni with smoke pouring from her superstructure. She is on fire and her bow has been destroyed after receiving several hits during an encounter with HMAS Sydney on 19 July 1940.