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Aviation History
1963
1963 - 1690.PDF
500 FLIGHT Internationa], 19 September 1963 ELFAST . . . The SC.5//0 fight-deck mock-up, with pilots' seats removed. This picture emphasizes the ordered and spacious layout; all instruments and controls are below eye-level, and everything possible has been done to improve flight-deck efficiency and comfort Britannia know-how whenever possible, and a very significant contribution has been made by this policy in easing the achieve ment of a reliable and proven aircraft. Port and starboard wings differ from those of the Britannia only in fairly small details. One of the chief differences is that the main torque box is an integral tank throughout, whereas in the Britannia bag tanks are employed inboard. Canadair Ltd turned the Britannia wing into an all-wet wing for the CL-44 freighter, and their design experience was made available to the Belfast company. Throughout, a three-way flow of information was main tained between Bristol, Montreal and Belfast. Wing scantlings are often greater than in the Britannia because of the increased maximum and zero-fuel weights, but the section profile and jigging is unchanged. The wings have, in fact, been made at Bristol and shipped to Belfast. Addition of the 16ft 6in centre section has increased wing area by some 20 per cent compared with that of the Bristol or Canadair aircraft. The ailerons are almost unchanged, and the flap span is thus more than 8ft greater on each side. The double-slotted flaps differ in a reduction in maximum travel from 45° to 40° to improve baulked landings at the very high MLW of 215,0001b. This re duced travel has been made possible by an improvement in flap performance, partly by elimination of nacelle discontinuities and partly by other means (for example, minimizing leakage around the flap ends). The four sections of flap are hung as in the Britannia and driven by two hydraulic motors in the centre section via torque shafts and ball-screwjacks. This is a much lighter drive than the electric actuation of the Britannia, and failure of either motor results in the other continuing to drive at half speed. Opening up the engines in a baulked landing automatically retracts the flaps to 35°. Fuselage design is complicated by the number and size of cut outs, but is a conventional conservatively stressed cylinder designed to a dP of 6.551b/sq in. A target safe life of 15,000 pressure cycles has been chosen, and a complete fuselage with applied wing, undercarriage and tail loads is currently undergoing fatigue tests in a water tank. The fact that no such testing is required on the wing and tail as such is one of the greatest benefits of the Belfast's ancestry. As the structural drawings show, most of the fuselage frames and stringers are rolled Z-sections, while those bearing increased loads are box beams. The rear ramp and door and the large side door are designed to fail-safe principles with multiple latches. Wherever possible L.72 single-heat-treat material is used, and the whole structure is remarkably free from forgings, or machined members. Extrusions, of J section, form the basis of the freight floor, and metal honeycomb panels are laid on top, but almost all other members are standard sections or sheet. Tail structure again follows Britannia practice, but areas are increased. The extra vertical area counteracts the greater yawing moment resulting from loss of an outer engine (both engine power and distance from the centreline are increased), and improves VMC, while the additional horizontal area handles the greater moments resulting from limiting e.g. positions. The inboard tail- plane leading edge has a modified reverse-camber profile, since it operates in a region of downwash which becomes severe with the application of full flap. Flying Controls Although the manual servo-tab system of the Britannia has been retained, notable improvements have been made. This is especially true of lateral control, where rolling power has been greatly in creased by adopting simple spoilers broadly similar to the type designed by Canadair for the CL-28 and CL-44. These surfaces operate only to assist roll control, and the jacks are electrically signalled whenever aileron tab movement exceeds 3°—except with the application of flap, or upon pilot selection, when the spoilers respond to all roll demands. An equally significant improvement is that the use of rotary torque shafts to transmit control movements has given way to push/ pull rods and cables, the circuits being designed with great care to eliminate friction and backlash. Where a cable passes through the pressure hull the carbon-steel cable runs in a p.t.f.e. fairlead. Throughout hydraulic flutter dampers, of the type fitted to the CV-880 and 990, replace the earlier irreversible screwjack drive to the surface tabs and the tab mass balances, and non-linear gearing is achieved not by elliptical cam-gears but by mechanical linkages. A simple system diagram appears on page 502. As in the Bristol and Canadair aircraft, the port aileron is linked with the rudder to counteract adverse rolling due to rudder de flection, and the elevator is linked to the flaps to cancel trim changes due to flap operation. An element of spring-tab type of operation has been introduced in the rudder circuit to curtail power at nig speeds. Feel in the elevator circuit results from a centering spring and q-pots, while aileron feel is almost wholly aerodynarfli; The autopilot is discussed under the Systems heading "Flight Dec . Undercarriage A particularly neat landing gear has been designed by Elec ^ Hydraulics Ltd for this aeroplane, the weight being taken by main tyres in bogies which fold about skewed axes into un?res^s0 ized boxes on the flanks of the centre fuselage. These boxes provide valuable stowage volume for the bulky air-condltl'fthe system and a.p.u., which in passenger aircraft can go benea main floor. The basic geometry of the main gear was suggeste Short & Harland; the nose unit is based on that of the Bntanw
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