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Aviation History
1955
1955 - 0360.PDF
360 FLIGHT, 18 March 1955 TWIN PIONEER ... section. This jack drives chains and sprockets which transmitrotary motion to a line of torque tubes along the rear face of the rear spar which, in turn, carry sprockets driving the flap chains.The torque-tube sections are connected with Mqllart Hooke-type joints which permit relatively large changes in alignment betweenadjacent sections. At the joints between the centre section and outer wing, the adjacent tube-ends carry simple cranks, a dowel onone crank locating in a hole on the other. Each flap section carries a number of pulleys on its upper sur-face which run in accurately machined tracks projecting from behind the rear wing spar. These tracks—supplied for the proto-type fay the Reynolds Tube Company—are H-S«tion extrusions; in the outer wings they are riveted to gusset plates, and the moreheavily loaded tracks in the centre section are braced to the rear spar by tubular members and by lateral supports attached toheavy ribs. One major difference between the outer wing of the TwinPioneer and the wings of the Pioneer lies in the relative sizes of the ailerons and flaps. The twin-engined machine has considerablylarger ailerons, which have necessitated a reduction in span of the outer flap sections. The ailerons are of the slotted, non-drooping type, and have metal D-noses with inset hinges, adjust- able balance, and—on the prototype at least—fabric covering aftof the spar (this is the only fabric on the aircraft). The control system is described later. The engine nacelles are monocoque structures made as com-plete assemblies of basically circular cross-section, recessed into the underside of the centre section. Conventional channel-frameZ-stringer construction is employed, with the addition of four stiffening longerons made from strip. Each nacelle incorporatestwo sheet-metal bulkheads, reinforced by vertical angle sections, riveted to the front and rear spars and carrying vertical loads. Inside each nacelle are machined fittings and a trunnion pick-up for the top of the main undercarriage leg. Each leg is a large extruded light-alloy tube, supplied by the NorthernAluminium Company. At the lower end of each leg is a machined fork fitting, to which is attached a pair of tubularextruded bracing struts leading to Ferrobestos-bushed lugs attached to strong points at two fuselage frames. (It is intendedthat both the main leg and the struts will eventually be faired within an unstressed casing of streamlined section.) The main-leg fork fitting also serves as the lower anchor for the inner end of the main outer-wing bracing strut. Into the lower end of each leg is inserted an Electro-Hydraulicsshock-absorbing oleo leg carrying an axle on which are mounted twin magnesium wheels. Each wheel has a Dunlop single-disc An airframe like that of the Twin Pioneer requires very little special tooling. This is a forward fuselage in its jig. 8O - u zo o I 19 J 6 1957 1958 The present schedule for Twin Pioneer output calls for a total of 100 machines delivered by the end of 1958. This diagram does not include the prototype. hydraulic brake and a Dunlop dimpled tyre of size 6.50 x 10.The total travel of the oleo is about 13.3in, the static deflection being about 9in. Electro-Hydraulics also supply the tail-wheelunit, which is a castoring assembly mounted in a box structure at the extreme rear end of the fuselage. It employs levered-suspen-sion, and has a pair of wheels taking smooth Dunlop 5.50 x 4 tyres. As is usual in fixed-wing aircraft capable of flying at low air-speeds, the Twin Pioneer has a relatively large tail. The empennage is made as a complete unit, which is lowered on to thefuselage and attached by four through-bolts with tapered split bushes. The tailplane and three fins are all straightforwardtwo-spar structures with pressed ribs. The outer fins are inter- changeable, the holes for the tailplane spars being covered onthe outer faces by blanking plates. The port and starboard elevators and all three rudders are simple metal assemblies witha minimum number of ribs and swaged 28-gauge skin. All the control surfaces are carried by pre-packed self-aligningball races. The elevators are hung from folded-channel-section outriggers mounted off the rear spar of the tailplane, the controlrods running between the legs of these outriggers along the rear spar itself. Fin drag loads are transmitted through angle-platesriveted to the tailplane ahead of the front spar; the joints between the fins and tailplane are sealed by inserted rubber mouldings butthe junction between the tailplane and fuselage has a large- radius fairing. Between the elevators is a fixed portion of trailing-edge, which carries the rear navigation light and can be removed by undoing bolts and anchor nuts. Beneath this fixed portionis the fuselage tail-cone, which is attached by Dzus fasteners and can be removed to provide access to the tail controls. The flying controls in the cockpit are duplicated and comprisespectacles on cantilevered arms passing outboard of the pilots' legs and parallel-action pedals incorporating toe brakes. Fromthe cockpit, control movements are transmitted by push-pull rods up to the roof and back to the level of the emergency roof-hatch. Multiplying levers then increase the linear movements (so dial, owing to the large cable travel, percentage stretch isreduced) and pass the control to cables leading to the tail and ailerons. The ailerons, centre rudder and elevators are operatedby the cables directly and the outer rudders are moved by quarter- inch H.T.S. push-pull rods on the rear face of the tailplane spar. Trim tabs are fitted to both elevators, the centre rudder andport aileron. They are actuated by screw-jacks driven by Teleflex from standard S.B.A.C. wheels in the cockpit. Thecontrol cables to the main surfaces are guided by fibre pulleys running in ball bearings, or by metal pulleys at locations where,owing to crank movements, side loads are experienced. The power units are Alvis Leonides 503/8 9-cylinder radialswith a maximum rating of 570 h.p. each; these engines are very similar to those of the Pioneer C.C.l except for the use of a0.5:1 reduction gear. Each drives a de Havilland three-blade constant-speed airscrew of lift diameter, and is supplied equippedas a complete engine-change unit, interchangeable port and star- board. The attachment pick-ups consist of four bolts with splittaper-bushes, electrical and other connections being grouped at quick-disconnect sockets on the firewall. Starting can be facilitated either by a Plessey-Coffmann cart-ridge or by an electric starter, the latter (if fitted) doubling as the feathering-pump motor. Fire protection is provided by tworings of Graviner pyrotechnic cord, one around the periphery of the cylinder baffles and the other immediately forward of thefirewall. Signals from these detector rings discharge methyl bromide extinguisher bottles, two of which are fitted in eachnacelle—a 1 lb bottle discharging into the induction manifold and
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