The Botha was developed during the mid 1930s in response to Air MinistrySpecification M.15/35, and was ordered straight off the drawing board alongside the competing Bristol Beaufort. On 28 December 1938, the first production aircraft made the type's maiden flight; almost exactly one year later, it enter service with the RAF. During official evaluation testing of the Botha, stability issues were revealed, as well as the fact that it was underpowered. It was only briefly used in frontline operations before being withdrawn to secondary roles during 1941. It continued to be flown in these roles, largely being used for training and as a target tug, before the Botha was fully withdrawn in September 1944.
Development
During September 1935, the British Air Ministry issued specification M.15/35, which called for a new reconnaissance/torpedo bomber to reequip RAF Coastal Command.[1] Among the stipulations set out were a twin-engined arrangement, a crew of three, and the provision of internal stowage to accommodate a single torpedo. Blackburn opted to produce a design to meet this requirement.[1] During early 1936, two submissions that fulfilled this requirement were accepted, one being Blackburn's and the other being the Type 152 from Bristol. The Blackburn design would receive the name Botha after General Botha, while the rival Type 152 would be named Beaufort after the Duke of Beaufort.[1]
Both of the proposed aircraft were originally intended to be powered by the Bristol Perseusradial engine, capable of producing 850hp (634kW).[1] At a late stage, the Air Ministry decided to revise the specification and re-issue it as M.10/36; the principal change was that the aircraft was abruptly required to accommodate a crew of four, along with an enlarged fuselage that increased the aircraft's overall weight. It was also intended that this change would allow the successful design to be ordered straight from the drawing board.[1] A consequence of the weight increase was that both designs suddenly required more power to be able to achieve their envisioned performance; however, while the Taurus, capable of producing up to 1,130hp (840kW), was provided for the Beaufort, the Botha only received the Perseus X, capable of up to 880hp (660kW), due to limited supplies of the Taurus engine.[1]
Early on, Blackburn made several proposals to address the engine shortfall; the adoption of the large Bristol Hercules radial engine was the main element of the proposed Botha II, however, it was not pursued.[1] During December 1936, the Air Ministry ordered 442 Bothas, it placed orders for the competing Beaufort as well. Immediately upon receipt of the order, Blackburn set about establishing two production lines for the Botha at its main factory at Brough and its new facility in Dumbarton, Scotland; additional component manufacturing was performed at the Olympia works in Leeds.[2]
On 28 December 1938, the first flight of the Botha took place at Brough , piloted by H. Bailey.[3] This was the first production aircraft, since there was no prototypes as such.[4] On 25 March 1939 it was delivered to RAF Martlesham Heath for performance and handling trials by the Aeroplane and Armament Experimental Establishment (A&AEE). The first production aircraft was found to have inadequate elevator control; this was rectified on a second aircraft sent for trials by a slight increase in the tailplane area and a larger horn-balanced elevator.[4]
A total of 380 aircraft were produced at Brough, while another 200 Bothas were constructed at Dumbarton for a total of 580.[5] Peak production was attained in June 1940, during that month alone the two sites produced 58 aircraft.[6] Limited modifications were implemented during the production run, such as the addition of a jettisonable main entrance door, non-retractable bulged navigator windows, new flap jacks, and an improved undercarriage retraction mechanism; several proposed changes, such as larger propellers and flame dampers, were not implemented.[7]
Design
In basic configuration, the Blackburn Botha was a twin-engined cantilever monoplane; the high-mounted wing was a deliberate design decision, intended to provide the best possible downward view for its crew.[8] The pilot, seated in a relatively spacious and well-instrumented cabin at the front of the aircraft, had an exceptionally unobstructed forward-facing field of view, although the rearwards view was restricted by the position of the engines. The navigator and wireless operator's positions were within a separate central cabin reached via an entrance door with a built-in stepladder on the starboard side of the fuselage.[8] Crew members could move between their positions via a narrow gangway; the observer had to use this passage to reach the prone bombing position in the aircraft's nose. The final crew member, the gunner, was positioned to the rear of the wing in an egg-shaped power-assisted turret on the upper fuselage.[8]
The forward fuselage was reminiscent of the Blackburn Skua, and had a flush-rivettedAlclad plated covering, while the rear portion of the fuselage was a metal skin over a tubular metal structure.[8] Flight surfaces such as the rudder, elevator, and ailerons had fabric coverings. The centre section of the wing housed the three main fuel tanks, with a normal combined maximum capacity of 435.75 gallons; this could be increased to 565.75 gallons for special operations.[9]Hydraulically-actuated split flaps were present on the central section of the wing's trailing edge, while balanced ailerons were fitted on the sharply-tapered outer wing panels. The fin and tailplane were unbraced cantilevers with stressed-skin construction.[4]
The undercarriage consisted of two oleo-pneumatic legs that retracted rearwards into the nacelles, which were fitted with spring-loaded doors; hand-operated hydraulic brakes were fitted.[4] As built, the Botha I was powered by a pair of Bristol Perseus Xradial engines, each driving a de Havilland Type 5/11 Hydromatic three-bladed constant-speed propeller. The engines, mounted on the central section of the wing in wide-chord cowlings, were fitted with controllable cooling grills.[4] A special cell in the fuselage could accommodate a single torpedo, a single 500lb bomb, or two 250lb bombs; additional bombs could be carried on external bomb racks on the mainplane. Other armaments included the pilot's forward-firing .303-inch Vickers machine gun and the twin Lewis guns installed in the turret. Comprehensive marine gear, including a collapsible dinghy, was also provided.[4]
The RAF's first Botha was delivered to No. 5 Maintenance Unit at RAF Kemble, Gloucestershire on 12 December 1939.[10] Service testing of the Botha was marred by a series of accidents, although no common cause was ever discovered according to the aviation author Aubrey Joseph Jackson; nor did he consider the loss rate to be excessive for the era.[11] However, the aircraft was commonly considered to be somewhat underpowered.[12]
According to aviation author Roger Haywood, concerns were raised regarding its poor lateral stability, while the crew's view to the side or rearward was virtually non-existent owing to the positioning of the engines, the poor view making the aircraft "useless as a GR [General Reconnaissance] aircraft". Although the Botha passed torpedo and mine-dropping tests, the aircraft's poor general performance resulted in the decision in April 1940 to issue the Botha only to four general reconnaissance squadrons equipped with the Avro Anson, rather than the torpedo bomber squadrons previously planned.[13]
During June 1940, the Botha entered squadron service with No. 608 Squadron and began conducting convoy escort duties two months later. This was the only squadron to fly the type operationally.[14] While flying these patrols, the typical bomb load carried was three 100lb (50kg) anti-submarine bombs plus two 250lb (110kg) general-purpose bombs.[15] According to Jackson, operational need for aircraft such as the Botha had greatly diminished following the Fall of France that year.[16]
Efforts aimed at addressing some of the aircraft's shortcomings led to both the airframe and engines being subject to further development work. However, the Air Staff decided to withdraw the Botha from frontline service and transfer the surviving aircraft to secondary duties. Accordingly, numerous training units received the type; at one point in 1941, one unit had over a hundred Bothas on its inventory.[17] However, the combination of inexperienced pilots and its unfavourable flight characteristics resulted in further casualties. Some Bothas were converted to target tugs, these aircraft being redesignated as TT Mk.I. In August 1943, the type was officially declared obsolete, with many aircraft being broken up either on site or after their return to Blackburn.[18] During September 1944, the Botha was fully retired from RAF service.[19]
Orthographic projection of the Botha, with inset detail showing the asymmetrical nose glazing.
Data fromBlackburn aircraft since 1909,[20] The Hamlyn Concise Guide to British Aircraft of World War II [5]
General characteristics
Crew: 4
Length: 51ft 0.5in (15.558m)
Wingspan: 59ft 0in (17.98m)
Height: 14ft 7.5in (4.458m)
Wing area: 518sqft (48.1m2)
Empty weight: 12,036lb (5,459kg)
Gross weight: 18,450lb (8,369kg)
Fuel capacity: 435.75impgal (523USgal; 1,981L) normal fuel in three wing tanks and a distributor/collector tank, with 565.75impgal (679USgal; 2,572L) available for special operations.
Powerplant: 2 × Bristol Perseus XA nine-cylinder air-cooled radial piston engines, 930hp (690kW) each
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