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Aviation History
1969
1969 - 0129.PDF
FLIGHT International, 16 January 1969 107 efficiency; but, says Boeing, considerations of construction, bi-axial crack containment and the minimising of the technical risk dictated the selection of the more conventional structural concept. The forebody skin and stiffeners are annealed titanium 6A1-4V. The aft upper crown structure makes use of annealed skins and heat-treated stiffeners to provide the optimum strength design compatible with the fail-safe requirements. The side shear panels over the wing and the lower panels of body fore and aft of the wing and through the wing centre section use titanium 6A1-4V integrally stiffened skins to optimise the compression and shear design allowables. Basic arrangement of the fin and tailplane primary structure is of a multi-spar sandwich form. The basic material is titanium 6A1-4V. The internal spar is of welded sine wave construction. The cover panels are titanium 6A1-4V stressed skin, and their widths were selected to satisfy fail-safe require ments; they are mechanically attached as individual panels to the in-spar structure. Leading-edge wedges and trailing-edge control surfaces are of titanium stressed-skin panels, truss ribs and titanium •sfressed-skin or brazed steel wedges. The aft body structure is a frame stabilised sandwich shell using titanium 6A1-4V stressed-skin panels in the primary load-carrying structure. The aft body fairing is a frame stabilised titanium honeycomb shell made by adhesive bonding using polyimide adhesive. The main undercarriage is a conventional two-leg arrange ment with each leg carrying a 12-wheel bogie sized to provide the equivalent flotation of the DC-8-63. Each leg is attached to the wing structure and retracts forward into a cavity in the wing. During retraction the bogie stays in a horizontal position to minimise the frontal area (even so, there is a blister fairing on the top surface). The basic structural material of the gear is 4340 modified steel heat-treated to 270,0OOlb/sq in-300,0001b/sq in—a material currently used on subsonic jets. Components such as the torque links, side struts and drag struts will use titanium 6A1-4V or titanium 6A1-6V-2SN. Propulsion System The propulsion pod consists of an inlet, the engine, nozzle and thrust reverser. The inlet is axisym- metric and has a translating centrebody, movable cowl throat doors, and cowl by-pass doors. The thrust reverser is part of the ejector nozzle assembly. The axisymmetric translating centrebody inlet comprises a movable centrebody, cowl throat doors and by-pass doors to obtain proper inlet/engine airflow matching during all flight conditions. A boundary-layer bleed system is installed in the inlet to provide shock/boundary layer interaction control and to improve the overall diffusio'n efficiency. Shock stabilisation devices (vortex valves) are installed in the inlet throat to provide inlet stability to downstream disturbances. The boundary layer bleed scoops on the forebody provide boundary layer control and increased buzz suppression capability. Basic operational modes of the translating centrebody inlet are shown in Fig 1. During take-off the centrebody is fully extended, the throat doors are closed and the take-off doors are open to reduce the cowl lip suction and to provide cooling air for the secondary air system. In the external compression mode of operation up to Mach 1.75, the centre- body is fully extended and the throat doors are open to CENTERBOOY BLEED EXIT TYR Fig I (below) Basic operational modes of the translating centrebody inlet. Reading downwards: Take-off, external compression (Mach US), internal compression (Mach 1.75), windmill brake Fig 2 (right) Centrebody inlet: bleed system Fig 3 (below, right) Design total pressure recovery of the centrebody inlet during climb arid acceleration" 1-00 P •80-• •76 •72 •68 VORTEX VALVE - SECONDARY AIR DUCT - CLIMB AND ACCELERATION — DESIGN RECOVERY TEST DATA © Vio SCALE C INLET H1/18 SCALE C INLET £1/18 SCALE H INLET 0-5 10 1-5 MACH NUMBER 2-0 2-5
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