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Aviation History
1958
1958 - 0318.PDF
332 Design and Development of a Very Famous Aeroplane •T • ^HEI Bo JL so Canberras in the Second Tactical Air Force and inBomber Command are being given a nuclear capacity"— s says the Memorandum published with this year's AirEstimates. It is now fourteen years since the first design thoughts were given to this aeroplane, and nine years since it first flew.Quite clearly the Canberra is not "played out," for it continues in full production for both the Royal Air Force and for overseascustomers, and even its earliest versions are still in front-line service in all parts of the world. It is, in fact, a very remarkablemachine. More than most British jet aircraft, the Canberra has had, andstill has, a classic development life—or in more expressive jargon, "stretch." The Mk 9 photographic-reconnaissance aircraft, withits new wing and advanced Rolls-Royce Avons, will, we may reasonably expect, have a higher over-target altitude than anyother Western aircraft of its type; and even the existing versions are quite capable of setting new world records. Last month aCanberra Trainer set a new point-to-point speed record by flying the 2,058 miles from Washington, D.C., to Caracas, Venezuela,in four hours eleven minutes, while six months ago, on August 28, 1957, a B.Mk 2, fitted with a Napier Double Scorpion rocket engine,raised the world altitude record for aeroplanes to 70,310ft (and on several occasions has been higher). This, then, is the measure of English Electric's first post-waraeroplane: in service with eight countries, produced in three, and current holder of 20 international class records—which is morethan any other jet aeroplane in the world. It all began in 1944, when Mr. W. E. W. Petter investigateda proposal of Sir Ralph Sorley (then controller of R. and D. at the Ministry of Aircraft Production) for a jet-propelled aircraftto succeed the Whirlwind and Typhoon in the low-level fighter/ bomber role.* When Mr. Petter joined the English Electric com-pany in 1944, he found there virtually no design organization capable of undertaking a new aircraft project. Throughout thewar—in fact, for a year before it began—the company had been concerned only with the manufacture of other people's aircraft(770 Hampdens, 2,250 Halifaxes—and later, almost 1,400 Vam- pires). Under Air. Petter's leadership the small design team whichhad dealt with modifications to these aircraft was steadily built up and, with very few people and without any of the facilitiesnormally available to a design team, they began the investigation of various configurations to satisfy the new requirement of a high-altitude bomber (it was not until much later that the ground-attack role for the Canberra was to be revived). The approved policywas, first, to make use of all the technical data which could be reasonably well established at that time and, second, to "push"the design to the limit of this knowledge. By June 1945 the design had evolved into a mid-wing monoplane,powered by a single, very large turbojet, and crewed by a pilot and navigator (with alternative seating positions, either side-by-side or back-to-back). Even at this embryonic stage the aircraft bore a resemblance to the now famjliar Canberra form, Therewas the long fuselage of circular section, the businesslike-looking tailplane and fin, and the large one-piece elliptical cockpit canopy. A particularly interesting difference between this early designand die Canberra proper lay in the powerplant—just one giant engine. "After some consideration with Rolls-Royce," the brochureon this aircraft states, "the conclusion was reached that an engine *From a lecture by F. D. Crowe, B.Sc, A.F.R.Ae.S., Chkf Designer(Canberra), Aircraft Division, The English Electric Company, Ltd., given before the Belfast Association of Engineers on February 26, 19S8. May 1949 at Warton, Lanes: the shiny blue A.I is towed out of the hangar for the first time, with a ground-running intake on. of 66 inches in diameter appeared to be a feasible proposition."It was to be a two-stage centrifugal engine, which, "with reason- able certainty" could produce the necessary static thrust of atleast 12,000 lb. This single unit was decided upon after a careful study had been made of the other engines then available. Theaircraft was obviously going to be in the 40,000-lb. class, and, to obtain the required cruising speed of 500 m.p.h. at 35,000 to40,000ft, it was clear that three engines of any existing type would be needed. The diameter of each of these was about 48in, sothat—assuming fuselage-mounted engines-—the cross-sectional area of the body would have been appreciably in excess of that requiredfor the crew and load. Even when diese engines had been developed it was still considered that two would have been needed.Some saving of frontal area might have been achieved by stagger- ing die engines one behind the other (shades of the P.l's propul-sion system?) and considerable attention was given to this idea, but the fuselage still came out much fatter than that requiredfor a single 12,000-lb engine. With a single engine there were, too, very considerable weight savings in the long jet-pipes andthe fuel and control systems. Having decided to use a single engine, it became feasible toemploy a fuselage of circular section; this fitted in well with the design of the pressure-cabin at the front, and followed on naturallyto the circular engine and tailpipe. The circular section was also relatively easy to design and produce, and it lent itself to low dragat the wing and tail intersections. This balanced layout bestowed a useful load-carrying section between the pressure cabin and thepowerplant. The top half of this section was logically devoted to fuel tanks and the lower half to bombs, in one or other of thefollowing combinations: 6 x 1,000 lb, 1 x 4,000 lb and 2 x 1,000 lb or 8 X 500 lb. A second fuel tank was situated in the rear fuselagearound the jet-pipe to avoid any e.g. change when fuel was used. Thus all the fuel was located in the fuselage, leaving a considerablespace in the wing leading-edge for further fuel during the develop- ment life of die aircraft. (This was, in fact, actually done: thesole Mk 5 was the first to have integral wing tanks, followed by the B.6, PR.7, B.8 and PR.9 models of much later vintage.) This, then, was the first "crystallized" design—or rather partlycrystallized, for a month later a new brochure came out, showing the aircraft with two engines buried in the wing-roots. It was,again quoting die brochure, the rapid development of jet power units diat led the English Electric team to re-examine its designand convert it into "an improved proposal of the same general size and type." The new engines were two axial Rolls-Royce AJ.65s,forerunners of die Avon. These were of considerably smaller frontal area dian die giant centrifugal and could thus be almostcompletely buried in die wing root. Admittedly die wing profile had to be swollen to 15 per cent at the root, but the intakes wereso designed dial die effective thickness of the wing nowhere exceeded 12 per cent. The main undercarriage units were movednearer to the centre-line of die aircraft and so benefited from the advantage of the extra wing depth. This period provides a classic example of design-evolution, andwas an essential step towards die final Canberra configuration. In particular, the advantages of two engines were recognized—albeit slightly grudgingly, for the brochure says that, although the revised design had twin-engine reliability, it did not altogedierconcede that such a precaution was necessary widi jet engines! This powerplant disposition also provided greater flexibility for
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