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Aviation History
1958
1958 - 0143.PDF
PLIGHT, 31 January 1958 THE VULCAN STORY... 147 wing. Tunnel testing with the 707 was conducted at angles ofattack up to 60 deg, and even at this fantastic inclination the lift was still approximately 90 per cent of the maximum value. Thestall itself was found to take place at around 28 deg, and to have little significance so far from the operating range-Available range of e.g. was found to be about eight per cent of the mean chord, the aft limit being set by the longitudinalstability and the forward limit by the difficulty experienced by the pilot in raising the nose during take-off. Owing to theirdifferent control systems the aft limit for the 707A was not the same as it was for the 707B, but both aircraft have been flownquite satisfactorily with negative static margins. Avro's chief aerodynamicist, Mr. Peter Sutcliffe, has pointed out that "eightper cent may not seem a large range, but it must be remembered that the mean chord of the wing is much greater than that of thecorresponding conventional wing of medium aspect ratio, and that the actual e.g. range in terms of distance is in line withnormal values." Even after the first 698 had flown, the value of its miniaturecounterparts—the 707A in particular—in no way decreased. The small research aircraft were found to be capable of collectingdata much more rapidly than would have been possible with the 698 itself, and it was found that, after making the necessarycorrections, 707A data could be applied to the 698 with a very high degree of accuracy. For example, a major modification tothe wing—which is described later—was initially proven on the 707A and incorporated in a developed form on the 698.This brings the story up to the roll-out of the first prototype Avro 698—which was thereupon named Vulcan—and its sub-sequent first flight at the company airfield at Woodford, Cheshire, on August 30, 1952, in the hands of "Roly" Falk. The serialnumber of this aircraft is VX 770 and it has always been dis- tinctively finished in glossy white paint. Owing to the unavailability of the Bristol B.E. 10 (which bythis time had been named Olympus*), VX 770 was initially fitted with four 6,500 lb-thrust Rolls-Royce Avons. The aircraft per-formed admirably from the outset, and a mere two days after its first flight Falk flew it into the Farnborough Show—where,as we reported at the time, "it stole the show and opened the eyes of the world." VX 770 has now flown many hundreds ofhours, and was later fitted with 7,500 lb-thrust Armstrong Siddeley Sapphire engines; it is now flying with Rolls-RoyceConway by-pass turbojets of almost three times the original thrust. On September 3, 1953, the aircraft was joined by its sistership VX 777, powered by four Bristol Olympus 100-series engines and thus almost representative of the production aircraft. Com-pared with VX 770 the second prototype has a fuselage a few inches longer to obviate the necessity of shortening the noseundercarriage before retraction. Both prototypes were built in the experimental shop at Chadderton, using full jigging for certainairframe portions and a large number of production tools. They were then taken by road to Woodford, as a photograph in ourissue of April 25, 1952, suggested. *Described in our issue oj December 9, 1955. Taken in the autumn of 1951, this photograph shows a fully repre- sentative Ayro 698 model in the lift R.A.E. high-speed tunnel. The first "high-speed" Ayro 707A, which flew in July F95F. It is not yet permissible to publish a full description of theVulcan, but a great deal may be said to outline the characteristics of the aircraft before once more taking up the thread ofdevelopment. Structurally the Vulcan is remarkably conventional, but itsunusual shape has complicated the sub-division of the airframe for production convenience. Much the largest component is thecentre section, in the form of a rectangular box joining the port and starboard wings and housing the weapons bay and power-plants. Basically the wing is built on principles forming a logical exten-sion of those used in the Lancaster, there being two main spars and no particularly unusual features. In the centre section thespars are joined by massive bridge pieces separated by the length of the weapons bay. Above the weapons bay there is no majorstructure and so frontal area has been reduced to that of either the fuselage or wing but never both together. The main load-bearing structure in the centre section comprises the front and rear spars, which are continuous from port to starboard, togetherwith three ribs on each side which partition off the powerplants. Almost the whole underside in this area is formed from detach-able panels or doors, and so major loads are carried around this region through the spars; nevertheless, loads over the uppersurface are largely carried across the upper skin and bomb arches. Although it obviously may not be described in detail, theweapons bay is clearly a single capacious volume occupying almost the full section of the fuselage and closed by two pairs offolding doors. Ahead of the bomb-bay is the fuselage fuel area. At the forward end of the tankage is a flat vertical bulkheadcarrying the nose undercarriage and forming the rear pressure bulkhead of the crew compartment. Of circular section, the crew compartment is pressurized byengine bleed. The structure comprises channel-section formers and stringers of top-hat section, together with four heavier longi-tudinal members. A jettisonable canopy is mounted above the flight deck and on the undersurface is a streamlined blister for thebomb aimer. Behind the latter is the powered entrance door which creates a dead-air region for the emergency exit of thethree crew members on the lower deck. The forward pressure bulkhead is a convex pressing with a central hole for groundaccess to the large radar equipment mounted in the extreme nose. The whole undersurface of the latter is a radome madeby Avro of dielectric sandwich material. The rear fuselage is a relatively rudimentary structure of light stringers and skin,housing the rudder power units and braking parachute and carrying further radar devices within a dielectric tail cone. Each wing is a basically triangular structure bordered by thespars, with secondary leading and trailing edge assemblies. The leading edges are required to have high dimensional accuracyand surface finish and are accordingly constructed in envelope jigs, as shown in our issue of December 13. The leading-edgeribs are located perpendicular to the front spar, and the interior of the profile contains a contoured corrugated section leavingchordal passages for de-icing air. Each leading edge carries considerable torsional loads. Manufactured at Woodford, the main inter-spar triangular boxof each wing contains closely spaced ribs, each perpendicular to the hinge-line of the control surfaces. Six of the ribs in eachwing are reinforced to carry the control surfaces and provision is also made for a considerable quantity of fuel within the wing,although details of this may not be published. A high proportion of the structure is in high-strength light alloy, the manufacturebeing described in a special article on December 13. The skin is applied in strips, shown in the drawing on pages 144-5,arranged parallel to the front spar. These are reinforced by extrusions of D.T.D.683 which are joined to the tops of the ribsby tiny forged links. Metal honeycomb sandwich is employed around the cut-outsfor the main undercarriage boxes and for the shrouds ahead of the
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