The Blackburn Botha was a reconnaissance/torpedo bomber used by Great Britain during World War Two.
History[]
Origin and Gestation[]
In 1935 specifications were issued for a new torpedo-bomber (TB) and for a general reconnaissance (GR) aircraft, both to be twin-engined shore-based machines of high performance. Some of the resulting designs indicated that a single basic airframe could fulfil both requirements.
Officialdom agreed and observed on December 16, 1935, that the two types were roughly the same weight with the same engines and "...only four squadrons of torpedo bombers needed; is hardly worth creating a new type." The economy of scale was appealing, and it was recommended on January 14, 1936, that the requirements for the two specifications be merged and that prototypes be ordered from preferred contractors. The Chief of Air Staff (CAS) concurred, Blackburn and Bristol being invited to proceed with their 670 h.p. Aquila-powered proposals to com ply with an experimental version of Specification 10/36, issued on May 4. Then, at a design conference on May 7, CA5 declared a preference for the moderately supercharged 850 h.p. Bristol Perseus VI engine.
By May 23, it was clear that the B-26 Botha, designed by G.P. Petty, Blackburn's chief designer, would be ordered. With the intention of speeding up their urgently-needed entry into service, CA5 approved ordering the two designs "off the drawing board" (i.e. without prototypes for initial testing) on June 13. This proved a costly error, as trials of normal prototypes would probably have prevented production orders from being placed with Blackburn (and would have ensured that Bristol made the Taurus engine reliable before mass producing its Beaufort).
In its preamble, Specification 10/36 (formally approved on June 30) declared that only the limited number of aircraft supplied to TB squadrons would be equipped to use atorpedo or 2,000lb bomb. The specification included a high cruising speed - 220 m.p.h. at l0,000ft for TB aircraft, long endurance for GR aircraft, good navigational facilities, suitability for both level and dive~bombing and the ability to maintain height on one engine up to 'l0,000ft with full normal load. Range requirements including 15min at full power at sea level, all at 5,000ft, were 500lb for 1,000 miles for GR work, l,000lb for 1,000 miles for bombing or a torpedo/2000lb bomb for 500 miles. Ranges would be increased by 250 miles in overload condition. Additional fuel in detachable tanks and extra oil would be provided for a range of 1,650 miles at maximum cruising r.p.m.[1]
A crew of four would be carried and one fixed forward and two rear guns in a turret would be provided, all 0.303in, the former with 300 rounds and the latter with 500 rounds per gun. This requirement for a gun turret would have provoked considerable redesign work, as Blackburn had proposed twin Lewis guns in an open mounting.[2]
Blackburn received a requisition to purchase on November 17, with the aircraft to be delivered by March 1939, and by December it was clear that some would be built by Blackburn Denny at Dumbarton Also in November the question of making bombing the primary role of GR squadrons was raised. This change required maximum power to be developed at 15,000ft instead of 5,000ft, which in turn required fully supercharged engines. The change to 880 h.p. Perseus X engines to raise operational height was approved by CAS.[3]
Assumptions and revisions[]
At a meeting onjanuary 15, 1937, Mr Petty forecast that the first aircraft would be ready for flight by the end of the year. Meanwhile, in late January a mock-up conference had been held at Brough, probably limited to the fuselage, so that crew positions and weapons arrangements could be considered and clearly none of the official party was astute enough to visualise the view from the cockpit. Had they done so, the realisation that the intended high wing and under—slung engines would irrevocably obscure any view of the wingtips, would have surely guaranteed that the type would not have been ordered. However, all was obviously thought satisfactory for, onjuly 27, dropping the Beaufort was advocated "as it was late and the Botha was alright".
The choice of the Perseus X led to a revised Specification 'lO/36 being issued in mid-October. Among the revisions imposed were a doubling of the ammunition supply for the rear guns to 1,000 rounds per gun and the inclusion of four small bomb containers among the alternative loads. An internal torpedo carriage was still sought. However, this proved impossible because of the span of the monoplane air tails necessary to cope with the torpedo's unprecedented flight-in-air conditions resulting from the new monoplanes' speed. Another new requirement was provision for fuel jettisoning.
The nose of the Botha did not at first incorporate an optically flat bomb-aiming panel. It was in fact a single conical Novellon moulding, which Blackburn decided in January 1938 to redesign in advance of the first aircraft appearing. Of the original order, 242 would be built at Brough under contract 563935/36, and 244 would be built at Dumbarton under contract 583994/36, with the aircraft from there being test-flown from neighbouring Abbotsinch.
Having two production lines allowed production to build up quickly (58 completed in June 1940). The first two from Brough would be partly hand-built, but with all major parts interchangeable. The third to fifth would be mainlyjig-built and the sixth onwards would be fully tooled to production standard. All the Dumbarton machines would be jig-built. Blackburn forecast completion of the first aircraft in July 1938 and 19 from the two factories by December. However, the RAF resident technical officer did not expect the first machine to appear before October, and believed that, asjigs and tools were "in the early stages" and that only detailed parts had been manufactured so far, the first jig-built machine would not emerge from either factory before February 1939. All deliveries would of course be dependent on the satisfactory completion of flight trials of the first aircraft.
After a few days of ground testing at Brough, Flt Lt Henry Bailey, the company's chief test pilot, eventually took the first Botha, L6104, for its maiden flight on December 28, 1938.[3]