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Aviation History
1955
1955 - 0361.PDF
FLIGHT, 18 March 1955 361 TWIN PIONEER . . . a 6 lb bottle feeding spray rings. These bottles can also be dis-charged by a pair of inertia crash switches in the belly of the aircraft, both of which are mounted behind frame 90 and bracedoff the lower skin to increase sensitivity to both vertical and horizontal accelerations. Engine oil is supplied from 7-gal Essex Aero magnesiumtanks behind each nacelle firewall, these tanks incorporating a special supply reserved for the constant-speed unit and featheringcircuit. Hot scavenge oil is passed through the throttle manifold for icing protection and is then piped to the oil cooler, which isa Delaney Gallay lOin drum-type unit with steel shutters actuated by a Tekflcx control from the cockpit. Provision is made foroil dilution. The Twin Pioneer uses 100/ 130-octane fuel which is containedin four bag-type tanks manufactured by Fireproof Tanks, Ltd. Two tanks, each of 30 Imperial gallons capacity, are fitted at theinboard ends of the outer wings between the spars; the other pair of tanks, each of 55 gals capacity, are mounted in the centresection. The inner and outer cells on each side of the aircraft behave as a single tank; the filler caps are mounted in the outertanks, and the inner cells each incorporate a Smith's float gauge, an S.P.E. booster pump and a non-return and relief valve. Cross-feed connection is provided, joined at a combined Teleflex- controlled fuel, oil and hydraulic shut-off cock. The high-pressure priming pump, mounted in the starboard nacelle, is a Plessey unit and the majority of the feed lines are Dunlop flexiblehoses. All auxiliary power is provided electrically or hydraulically.Each Leonides drives a Newton HX.2 l,500W D.C. generator, which supplies current nominally at 28V to 38 a-h accumulatorsmounted on sliding racks in the nose. D.C. electric power is supplied to the engine starter motor (if this unit is electric), fuelpumps, tank booster pumps, feathering pumps, passenger-warning sign en the door at frame 90, Rotax retractable landing lamp inthe port wing, navigation and upper and lower identification lights (which have a Rotax flasher unit) and the pump feeding thepair of Dunlop Maxivue windscreen wipers. The main electric control panels are mounted in the "eyebrow position" above thewindscreen; apart from the instrument supplies, which are pro- tected by fuses, all circuits are passed through a Rotax multiplecontact-breaker panel on the starboard side of the door frame at station 90, facing to port. The electric distribution panel is anintegral part of station 90 accessible from the cockpit, and is cooled by a small venturi attached to the outside of the roof. Radio equipment specified for the Twin Pioneer comprises aMarconi AD.115 V.H.F. set (served by a whip aerial), a Marconi AD.7092D A.D.F. (with a flat loop mounted flush with thecentre-section upper skin and covered by a Cobex plastic plate), a Plessey PTR.61 emergency V.H.F. and a Lascom 75M/Cmarker beacon. Optional extras for which provision is made include an H.F. set and a Standard Telephones I.L.S. equipment.Radio control panels are mounted in the cockpit roof and the sets themselves are in the lower part of the nose, the AD.115 beingto port and the remainder to starboard. Instrumentation follows typical British practice, nearly all theequipment being supplied by the Smiths group and the volt- meters and ammeters being Sangamo Weston products withextended scales. A single blind-flying panel is mounted in front of the first pilot, although a duplicate panel can be provided tostarboard if necessary. Engine instruments are mounted centrally, ahead of the main control pedestal. Provision is made for incor-porating a Sperry A.L.la autopilot at customer request; if fitted, this is driven off the pressure side of the vacuum system, thelatter being supplied by a Plessey vacuum pump. A Lockheed Mk 7 pump, driven by the starboard engine anddelivering through a Purolator filter, energizes the hydraulic system to a working pressure of up to 2,500 lb/sq in. Most of thehydraulic accessories are mounted in die starboard nacelle, the header tank being fitted above the starboard oil tank and accom-modating standard mineral oil, with an air space. The principal hydraulic-powered services are the slat and flap rams, and anemergency air bottle charged to 1,800 lb/sq in is mounted above the fuselage in the centre-section, and has sufficient capacity toeffect one complete operation of the slats and flaps. This bottle, which has a gauge and charging point in the starboard nacelle,can be replaced by a separate air /oil accumulator if desired. The wheel brakes are actuated through a separate 1,500 lb/sq insystem, with accumulators in the starboard nacelle. Brake actua- tion is effected by standard Dunlop toe pedals which pressurizelow-pressure cylinders displacing fluid through a quarter-inch line. A ground-test hydraulic hand-pump is fitted on the star-board undercarriage leg, inside the fairing. At present, the Twin Pioneer prototype is unfurnished, butproduction aircraft will be capable of seating up to 16 passengers in forward-facing, single- and double-seat units developed byL. A. Rumbold. These seats, which are stressed to 9 g, are covered with Texalose tropical mesh and, complete with lap A typical section of slatdrive mechanism, showing the driving sprockets, camsand micro-switch, all of which are described onp. 359. straps and life jackets, are exceptionally light, a double-seat weigh-ing only 21 lb. Naturally enough, the interior is designed to be readily convertible to incorporate a pantry, freight-hold, or foruse in all-cargo, executive or ambulance roles, according to requirements.Interior heating is provided by air warmed during passage dirough a new type of Delaney Gallay heat exchanger. One ofthese units is mounted on each side of the nacelle shoulder cowls, surrounding the exhaust collector pipe. Unlike previous designs,the new heat exchanger does not cut through the exhaust pipe at all, but transfers heat through a large area of baffling on bothsides of the wall between the hot and the cold flows (see sketch). Airframe ice protection is an optional extra, and the systemschosen are the T.K.S. fluid type, which can be fitted along the leading-edges of the tail surfaces, outer-wing slats and airscrewblades, or the pulsating rubber overshoe pattern. A particularly notable feature is the degree of interchangeabilityand unhandedness achieved between the various major airframe components. For example, in addition to the previously men-tioned power units and fins and rudders, die slats, outer flaps, main undercarriage, nacelles, oil and outer fuel tanks are allinterchangeable port and starboard. As far as possible, the Twin Pioneer has been designed to permit trouble-free operation withthe minimum of attention. The whole aircraft seems to be straightforward, sound and efficient for its job, and each of theaccessories bears the name of a famous British company. The power units also have been arduously used in all types of air-craft in all parts of the world. Within a very few weeks the first Twin Pioneer will be rolledout from the factory at Prestwick, and it should have logged a considerable number of flying hours before the S.B.A.C. Showin September. As stated previously, this prototype has been built in production jigs, and tooling is now being prepared for afull production run of 200 aircraft. The accompanying diagram shows the approximate schedule of Twin Pioneer output. Thesecond machine is now well advanced and detail parts are coming dirough for several others. Clearly the basic machine offers considerable promise fordevelopment to fill specific roles, such as the carriage of heavy freight, photo-surveying and (if a sufficiendy high ceiling canbe obtained) as a slow-flying radar picket—perhaps for carrier use. The first-named of these roles should be excellently metby the projected freight version with large rear-loading doors, of which a model was exhibited at the last S.B-A.C. Show. Such anaircraft would seem to have even more to offer than the basic design. Cross-sections of the centre section (below) and outer wing, showing the geometry of the auxiliary surfaces. TORQUE TUBE WOODSTRIP FALSE SPAR SLOTTEDAILERON
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