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Aviation History
1938
1938 - 1841.PDF
JUNE 30, 1938. •'.- FLIGHT. 631 In the works : Applying the plywood skin to afuselage side in its jig. CONSTRUCTION AND EQUIPMENT /COMPREHENSIVE jigging has permitted ^-/ creditable rapidity oi construction, though the output of the Airspeed factory, which has not yet reached its peak, is not for publica- tion at Air Ministry request. The fuselage of the Oxford is a typical Air- speed semi-monocoque with spruce longerons and stiffeners beneath the plywood covering. The joint between front and rear sections is made at the rear bulkhead; an interesting point is the special reinforcement of the for- ward bulkhead to withstand the shock in the event of the machine turning over during landing. The fuselage sides are made on separate jig3 alongside each other. One requirement of training machines for the Royal Air Force is the ability to be transported easily by road when dismantled. Consequently, the wing of the Oxford is in three parts. It is, of course, a stressed skin ply-covered structure with spars which have spruce flanges and three- ply webs. The spars are positioned on one jig, others being provided for positioning the leading and trailing edges. The three-piece ribs have braced webs and spruce booms. The sturdy centre-section is of similar construction to the outer panels. There are interesting drilling jigs for the centre-section spars with a system of colouring for the various sizes of holes to be drilled. The spars are posi- tioned by horizontal and vertical datum lines. Split flaps extend from aileron to aileron, and are nor- mally operated hydraulically by pressure from an engine- driven pump, though for emergencies there is a hand- operated pump. - . The Tail Unit The elevator is fabric-covered and is built up.from a wooden spar and ribs. The fin is of similar construction, the fin post being built into the fuselage and faired with fabric covering and spruce stringers. Aerodynamic and mass balances are provided for the rudder. Although the skin of the main planes is applied at 45 deg., this measure is not considered worth while for the tailplane. The retractable undercarriage is of Airspeed design, and features a broken radius rod mechanism acting on a braced twin oleo leg chassis and retracting rearward into each nacelle. Although actuation is normally by an engine-driven pump, manual gear is pro- vided to pump the wheels down in the case of engine failure. The brakes on the Avery wheels are operated pneumatically by a lever on each control column. Normal movement of the ruddfr gives differential action by means of the Dunlop relay system. A B.T.H. compressor is driven from the right-hand engine, and maintains a pressure of 200 lb. /sq. in. in a reservoir in the centre section. There are two main fuel tanks, each of 49 gallons capacity, between the centre- section spars; they are interconnected with two auxiliary tanks each holding 29 gallons. Fuel is drawn by the engines from the main tanks, the auxiliary tanks feeding into the main ones by gravity. Oil is carried in two tinned steel tanks (8f gallons each) in the engine nacelles. An oil-cooler of Airspeed design and Gallay construction is used, the cooler being " Flight " photograph. integral with the tank. Cooling air is taken through an inlet inside the engine cowling and conducted by a pipe to the tank of the cooler. The standard power plant of the Oxford is two Arm- strong Siddeley Cheetah X seven-cylinder air-cooled radials geared 1: 1 and with a supercharger gear ratio of 6.5: 1, giving a normal output of 340 h.p. at 2,300 r.p.m. and 7,000ft. Maximum and take-off powers are respectively 350 h.p. at 2,425 r.p.m. and 7,500ft. and 375 h.p. at 2,300 r.p.m. The engines are designed to use the size 2,000-De Havilland variable-pitch airscrews, though these are not yet available in quantity. Machines now being delivered have wooden airscrews. Constant-speed De Havillands can be accommodated. Welded steel construction is used for the nacelles, which are attached to the centre section at four points by means of Lord rubber insulated joints. Claudel Hobson's " M "-type carburettors with variable datum boost control and automatic mixture control are specified. The control pedestal has two throttle control levers and one lever for adjusting mixture strength. This has three positions : '' Automatic weak," " automatic rich '' and "over-ride." When rapid accelerations are expected, the lever is put in '' automatic rich ''; the '' automatic weak '' position is for economical cruising. For take-off the " over-ride" position is used, this actuating an enrichment jet to prevent detonation and to keep the engine at a safe tem- perature. Electric starters, auxiliary hand-turning gear " " Flight " photoaraph. The cockpit roof of the Oxford is of exceptionally good design to permit unobstructed view in all essential directions. In this view the remaining sections of Perspex moulding are seen being put into place and sealed with Bostik compound.
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