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Aviation History
1956
1956 - 0870.PDF
12 Airliners of the World BOEING 707 the wing, through-bolted to a strong rib. Each beaver tail projects fromthe line of the skin and fades out midway between the wing spars; the lower pair are in tension and the upper in compression, so that themain gear is, in effect, held in a pair of outsize long-nose pliers. Each main leg is pulled inwards by a hydraulic jack mounted in awalking beam hinged to a link anchored to the edge of the fuselage floor. The legs are braced by radius rods which are hinged nutcracker-fashionand broken by ad hoc jacks picking up on the deep fuselage keel web. According to design weight the tyre pressure varhs from 128 to145 lb/sq in. All wheel doors have individual jacks and the nose gear retracts forwards and is steerable by twin cylinders to give a turningradius of 21ft about the inner bogies. Flying Controls. As a result of the great experience with the B-52bomber Boeing have evolved a completely manual system for the 707, which has been described by several airline captains as "perfection."The rudder is a simple surface actuated by aerodynamic tabs via cables incorporating automatic tension-regulating units. The elevators aresimilar and are used in conjunction with the powered (with manual stand-by) trimming tailplane, driven by an electric screw-jack. Lateral control is less conventional, partly owing to the fairly sub-stantial angle of sweep on the wing. At low speeds, lowering of the flaps unlocks low-speed ailerons, which are normal surfaces carried on asub-spar outboard of the wing break at station 725 and operated manu- ally, by tabs. At high speeds these are locked and lateral control iseffected by high-speed ailerons and spoilers. The former are relatively small surfaces between the flap portions, moved manually by springtabs and provided with gust dampers for speeds up to 70 knots. The spoilers are fitted in four sections above each wing. They can be flickedopen together, to act as speed brakes, or differentially, to increase rate of roll; they are permanently linked to the aileron circuit. All flying controls are sealed by a novel arrangement of internalpressure-balance panels. These broadly consist of inter-rib sections of flat plates hinged to chordal extensions from the leading edge of themoving surface and arranged to move with the surface inside balance- chamber boxes formed by the fixed skins and ribs. The fixed structurein the wing behind the rear spar, although secondary, is made rigid to form accurate housings for these panels. The upper fixed skins arestabilized by spanwise bonded channels and the lower skins are honey- comb-filled sandwiches, better able to withstand the intense high-fre-quency buffet from the engines. Double-slotted flaps are fitted in two portions on each wing. Theouter flap sections are driven through screw-jacks and torque tubes geared to a hydraulic motor on the aft face of the lower part of thefuselage rear-spar frame. The inner portions are similarly driven from an independent system, bevel boxes in which also actuate the small split"fillet flaps" at the trailing-edge roots. Emergency actuation is electric. Each flap portion runs out on steel tracks to increase area. Produc-tion 707s have straight (i.e., unrecessed) flap leading edges, with span- wise stringers, a single spar and honeycomb-stabilized skin. Ahead ofthe flaps the underside of the wing is terminated at a cove-lip door which hinges up when the flaps are down; as the flaps return to theirhoused position they engage the door and push it down to seal the chordal gap which would otherwise exist. Position-indicators areprovided for each flap section and lateral control can be retained with any one section asymmetric. POWERPLANTS. On the 707-120 the standard engine is thePratt and Whitney JT3C-4 turbojet, with a wet rating of 13,000 lb. This is a commercial variant of the well-known J57, a large and fairlyweighty engine with tandem compressors operating at the very high pressure ratio of 12.5 : 1. It has a can-annular combustion systemand most of the accessories are grouped under the casing of the rear, high-pressure compressor. Oil is contained in a 5.75 gal saddle tankabove the front low-pressure casing and is cooled in tubular coolers mounted low on each side of the nacelle (in the -80 prototype the oilcoolers are in the fairing on the front of the intake-hub). All TT3C-powered machines will be equipped for water injection foruse on all full-load take-offs at ambient temperatures over about 50 deg F. Approximately 350 gal water will be carried (in a positionyet to be finalized on the -320; on the -120 it will be in the wing tips and centre section) and supplied by electrically-driven pumps taking atotal of 40 kVA. All the water available will be expended in the first two minutes of flight to obviate freezing problems. Very extensive development is continuing with a view to reaching anoptimum design of noise-reducing, thrust-reversing propelling nozzle. In co-operation with the N.A.C.A., Rolls-Royce and other agencies,several attractive arrangements have been investigated, and at least one nozzle has been flown on the -80. Engine starting can be effectedelectrically or by a monofuel or pneumatic turbo-starter. Power for the -220 and -320 aircraft will be provided by the Prattand Whitney JT4A-3, a commercial development of the large and weighty J75 turbojet rated at approximately 16,000 lb thrust. Ingeometry this engine resembles the JT3C and the nacelle configuration will be similar, although each equipped nacelle will weigh at least FLIGHT, 6 July 1956 TOILETS GALLEY IOOOO 2,000 3,000 4.OOO 5OOO 5OO 1.5OO 2.5OO 3,5OO 4.5OO RANGE (n m) Payload/range: long-range cruise upper limit 40,000ft; allowances tor t-o, climb and acceleration, no credit for descent; no wind, N.A.C.A. standard day; reserves 17,000 Ib (320), 16,000 lb (120). Costs: 1955 A.T.A. on 7-year depreciation; overseas with flight crew of four. 2,000 lb more. Boeing have also prepared specifications for aircraftpowered by the Rolls-Royce Conway (707-420 and -520) and Bristol Olympus 511. SYSTEMS. Air Conditioning. At the junction of each strut leading-edge and main engine intake a ram intake is provided admitting air to turbo-compressor sets driven by air bled from the first spool of theengines. The fresh air from these units is ducted along the face of the front spar to the centre section, where it turns aft and passes to a primaryheat exchanger served by ram intakes at the forward end of the belly fairings over the main-gear bays. The cabin air can then pass eitherdirect to distribution manifolds or by way of an air-cycle cooling unit, secondary heat exchanger and water-separator. The secondary heatexchanger is fed from a bifurcation in the same belly intake; its air is dumped overboard immediately forward of the rear spar and a vacuumground-cooling connection is provided at the same point. Cabin manifolds run longitudinally from the central bay and feedbranches between each pair of frames. Air passes between each window sandwich and enters the cabin beneath the baggage racks, a separateduct feeding the flight deck. Used air is extracted at floor-level, taken to freight-hold floor-level and passed back to the central bay. Outflowvalves are situated at the front-spar bulkhead (2), rear-spar bulkhead (1) and under the centre-line near the rear door (1). Fuel. Reading in from the port tip the tankage comprises: atank (not used for storage); port reserve tank (361 gal) from the outer end of the low-speed aileron to inboard of the outer strut (through thebreak at sta.725); No. 1 tank (1,946 gal) to a point inboard of the inner strut; No. 2 tank (1,894 gal) to the root rib; the centre section (4,460 gal);and corresponding tanks to starboard. Except for the centre-section tank all tankage is integral. Dry bays (i.e., without fuel) are provided immediately inboard of eachstrut. Pressure-fuelling sockets are provided beneath the wing together with gravity fillers above tanks 1, 2, 3 and 4. Electric dump pumps canrapidly evacuate the centre-section tank in the event of an emergency at an early stage in the flight plan. Shut-off valves, pressure switchesand defuelling connections are provided in the inner dry bays. The tanks are vented through the spanwise stringer channels. Hydraulics. A pump on each engine energizes a 3,000 lb/sq insystem filled with low-temperature Skydrol 500 fluid. Hydraulic ser- vices are provided for the flaps, undercarriage, spoilers, wheel brakes,nosewheel steering and (if fitted) windscreen wipers. Centralized hydraulic panels are provided in the main undercarriage bays. Electrics. A 30 kVA alternator is mounted on each engine, driventhrough a Sundstrand hydraulic coupling. All power is generated at 115V, three-phase, 400 c.p.s., and the four alternators can be paralleledor, in the event of a malfunction, can individually serve specific loads, such as the fuel booster pumps, stand-by hydraulics and flap motors.Ice Protection. Hot air for this purpose is extracted "from the delivery of the high-pressure spool of the JT3C at about 700 deg F,and ducted along the leading edge of the wing, heating being continuous. A further supply of bleed air is passed around the engine intakes. Electricheater mats are fitted on the leading edge of the tailplane and Nesa glass is fitted in the forward-facing nanels of the flight deck. FLIGHT EQUIPMENT. The cockpit is somewhat smaller than onthe spacious Boeing 377, but it is well-planned to S.A.E. recommenda- tions and has found favour with the hundred-plus airline captains whohave flown the -80. A seat for a flight engineer is provided behind the pedestal, his panels being to starboard. One window on each sideforms a direct-vision panel, large enough to serve for emergency crew- escaDe. At the time of writing hydraulic wipers are specified. The following is a selection of standard radio equipment: R.C.A.search radar AVQ-10 in the nose, with a glide-slope horseshoe mounted immediately above; Doppler true-airspeed aerials at the bottom of thefront pressure bulkhead; an A.T.C. transponder 'n the flight-deck roof; TOILETS FORWARD ENTRANCE x LOUNGE LOUNGE \AFT ENTRANCE
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