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Aviation History
1955
1955 - 0080.PDF
80 FUEL IN OUTER WNG(R1053 Imp <jal EACH MAINTENANCE LINKED HYDRAHATCH DRAUUCALIY. WITH MMB DOORS' BOOlE IDUNLOt BRAKES BACKGROUND TO THE SPERREN . . . at speeds up to 500 m.pJi. T.A.S. or 450 m.p.h. E.A.S., at variousvalues of g and angles of incidence. Photography indicated that the system would be acceptable. Full-scale trials were then undertaken with the aid of theR.A.E.'s large Merlin-driven blower tunnel (Flight, September 10th, 1954), in the course of which flight-test personnel wereblown out of the cabin and into a net. Finally, when the proto- types had been built, actual flight trials were completed, dummiesbeing released through the chute during various conditions of manoeuvre at high airspeeds with the bomb doors closed or open.An equipped mock-up of the standardized crew compartment was made at Rochester, and this was used as a familiarization andtraining model for V-bomber crews. The structure of the S.A.4 could scarcely be more conventionalin its essentials, although, as will be described, a number of steps which broke new ground had to be taken. The fuselage is builtin nose, centre and tail portions, each terminating in a double frame of extruded section. The frames, spaced at an averagedistance of 20in, are cut to accept the longitudinal stiffeners, each third stiffener (on the average) being joined to the frames. Theskin panels are butt-jointed and riveted to internal butt-straps with a braided cord sandwiched between each strap and the skin. The basis of the wing is a box spar, formed from a front andrear girder connected by sheet drag-members notched to accept the spanwise stiffeners. The inner wing, out to rib five, is verymassive, the basic stressing assuming a box form outboard of the nacelles, two spars at the nacelle and an imperfect box (with a cut-out for the main undercarriage) inboard. The principal innovations during construction of the airframewere the use of D.T.D. 687 aluminium alloy (a high-strength material which, unlike the familiar D.T.D. 610, tends to shatterwhen overloaded), the employment of hot dimpling for skin per- forations and the method developed by Shorts of milling externalrivet heads and so ensuring the finest possible exterior finish. When the company made their big move from Rochester toBelfast in 1947 the S.A.4 design was in full swing. The move undoubtedly set back the progress of the design by a least fourmonths, but this was partly compensated for by the fact that, at Belfast, the company were able to erect a really large structuraltest rig capable of accepting a complete S.A.4 fuselage with stub wings. Actually, three sets of airframe parts for the S.A.4were made, and one set was used solely for structural testing. Initially, a complete nose section was submerged in a specialtank and tested for both cabin-pressure and aerodynamic loads. With a design pressure-differential of 9 lb/sq in, the crew com-partment was stressed to an ultimate strength equivalent to a differential of twice this value. During the tank testing, thepressure was increased beyond 18 lb/sq. in and, at 23 Ib/sq in differential, a minor distortion of the jettison hatch over the firstpilot's ejection seat occurred. This was certainly one of the first tests in the world to impose such differentials.
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