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Aviation History
1947
1947 - 0517.PDF
APRIL IOTH, 1947 FLIGHT 309 In considering the wings, it is found that here more than anywhere does the Ambassador differ from accepted de- sign practice. First, the skin panels are thick, being designed to take, with the stringers, some 87 per cent of the whig bending loads; secondly, centre-section/outer wing jointing is solely through the skins, the spars having no bolted joint; thirdly, the main fuel tankage is integral at the inner end of each wing panel. Since this is purely a structural appraisal of the Ambassa- dor we are not concerned here with the accommodation layout as such ; suffice to say that the flight deck is well proportioned and the space available for passenger accom- modation seems very much larger than would appear from an external view of the aircraft. Fuselage Structure * In section the greater part of the fuselage is circular with a "flattened" base curvature, the intersection of the arcs producing chines which extend roughly from the control cabin back to the rear baggage door, the angle dying into the changing sectional contours of the nose and tail regions. Structurally the fuselage is fairly conven- tional with rolled channel frames which are notched for the Z-section stringers, to which they are secured with shear cleats. Stringers are separated in groups of four by T-section extruded stringer/longerons, and the frames are quadrantly stiffened by angle strips on free flanges and webs. Reinforcement at the chines is provided by doubling strips which are not continuous but are inter- costal to the floor frames, and attached to them with angle clips. Naturally enough, the fuselage frames at spar stations are very massive and take the form of built-up box mem- bers which run from the base of the centre-section spars down to the chines, the proportions of these members having been governed by their requirement to take the wing loads in the event of a belly landing. Wing/fuselage attachment is primarily made by means 01 duplicated strap-fittings port and starboard to each spar and spar frame, the respective pick-up points forming triangles. The outboard (vertical) fittings take lift loads, and the inboard (diagonal) fittings take side loads. Drag loads are taken as shear by the rivets attaching heavy-gauge flanged-angle members which pick-up to the inside of the fuselage skin and the under-surface of the centre-section where these two intersect. In the same connection, fore and aft -box section members riveted to the webs of the three central ribs in the centre-section terminate in fork-and-lug anchorages to the fuselage roof structure forward am! learward of the centre section; their function is to tranMiiii longitudinal loads across the fuselage where it is cut away for the centre- section. A dado in the fonn of a boxed duct runs along each fuselage wall, the shelf top being about six inches below the base line of the windows. This is a ventilating duct, and a pointer to detail design which exemplifies the striv- ing for efficiency so notable in the Ambassador is that, where the duct intersects the fuselagi <-jiar frames, the webs are cut away in the form of a \Y bracing, and each bracing "strut" is fitted with a streamlined capping of laminated wood to reduce drag and, therefore, etlert tin- least flow losses in the duct. The fuselage cross-sectional contour changes rapidly to- ward the tail, but the structure remains essentially the same, and although the frames are very light and their webs are pierced by lightening holes, by contrast the stringer spacing is quite close. A non-stressed bulkhead separates the main cabin from the rear baggage compart- ment, the floor of which is raised about four inches above the main level. Passenger entry is through an upward- opening door at the rear of the cabin on the port side, ingenious jury struts being integral fixtures. Access to the baggage compartment from outside is via a door about 3ft square just above floor level to starboard. Pressurized Second Prototype Although the first prototype is not being built for cabin pressurizing, the second aircraft will be so constructed. In point of fact, structurally there will be little difference, the basic design being the same: it merely means th,at the first machine will not have pressure bulkheads, seal- ing measures, etc. Headroom in the cabin beneath the wing is a minimum of 6ft 4Jin, the cabin roof being swept gracefully down to the under-surface of the. centre-section. This portion of the wing is 35ft in span, and it is built up on two plate web spars with extruded L-section booms: the free flanges of the latter are of constant thickness across the fuselage INTEGRAL FUEL TANK JOINTBETWEEN OUTER &CEN'HRE Transfer struts terminating in fork-and-lug anchorages bridge the cut-out in the fuselage at the centre-section and so transmit fore and aft resolved loads. Structure of outer wing showing fuel tank ; and detail at joint showing rack spar-fittings, joint plates with spanwise bolts and spools, and arrangement of leading edge for thermal de-icing.
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