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Aviation History
1956
1956 - 0896.PDF
FLIGHT 40 Airliners of the World ELECTRA the floor and over the top of the centre-section. The booster operatesport and starboard push-pull rods running straight along the back of the wing box to the tail of the outer nacelles, where they kink rear-wards and finally drive the undersides of the ailerons through bell- cranks. Single cables transmit the manual aileron trim. Each cablebifurcates to drive duplicated screw-jacks attached to the tabs. Under the fuselage is a speed brake consisting of three panels hingedbeneath the wing trailing edge which close flush with the fuselage skin. All three are driven by a single hydraulic motor in the starboard fillet viatorque shafts, bevel gears and screw-jacks. The brakes can be pushed open with the flaps or independently.Each mainplane carries a single section of Fowler flap running on multiple roller carriages in five steel tracks. Operating power is suppliedby duplicated hydraulic motors mounted inboard and driving through torque-tubes and triple-extension, ball-bearing screw-jacks. There aretwo jacks to each flap section, attached to the rear face of the rear spar adjacent to the upper boom and passing through the single spar ofthe flap to pick up between adjacent strengthened plate ribs. As the flaps are pushed down the tracks their angle of incidence steadilyincreases until the roller-carriages hit "quick cams" at the far end, which suddenly depress the flaps to about 70 deg at full extension.Flaps and ailerons are the responsibility of Temco. POWERPLANT. Although such engines as the Rolls-Royce Tyneare obviously suitable and are being studied by Lockheed, the Electra was designed around the Allison 5O1-D13. This engine is rated at3,740 e.h.p. (3,460 s.h.p.) for take-off; a typical cruising rating is 1,850 s.h.p. at 25,000ft. It is a single-shaft turboprop with a pressureratio of 9:1, a cannular combustor and a four-stage turbine. The reduction gear is mounted ahead of, and beneath, the remainder of theengine, driven by a shaft embodying a torquemeter. The siandard airscrew is an Aeroproducts four-blade unit of 13ft 6indiameter, with take-off autofeathering, reverse pitch and provision for automatically increasing blade angle upon receipt of reverse-torquesignals. Electras for K.L.M. will have an advanced airscrew by Hamilton Standard. Each powerplant is supplied as a "quick engine-change" unit com-plete with airscrew; Rohr Aircraft will manufacture the complete installa- tions, including nacelles and tailpipes. The engine itself is hung froma ring on the firewall bulkhead with a steady at the turbine section. Extensions from the front of the wing box form the roof of theundercarriage bay and also carry most of the engine loads. Airscrew thrust and torque are reacted through steel-tube trusses attached atfour points to the main firewall, the two principal members being continued on each side of the engine to the second firewall and thenbeing inclined down to anchors above the wing-box above the under- carriage girder-ribsThe tailpipe is passed back across the wing to a propelling nozzle above the trailing edge. Each pipe lies in a stainless-steel troughsupported by transverse trunnions. The oil tanks are mounted immedi- ately above each engine, and a drum-type oil cooler is mounted inthe lower part of each cowling, with a ram intake beneath the spinner. Accessories are driven from the reduction gear-box and each nacelle isdivided into three fire-zones separated by firewalls, with appropriate fire surveillance and high-rate extinguishing systems. Large hingedpanels on each side provide access to the gear-box, engine and acces- sories and further panels admit to the hot parts of the engine andtailpipe. A considerable proportion of the skin is titanium. Although certain operators may specify a different system, the stan-dard starting arrangement features a fuel/air combustion starter on each engine. Air for this purpose is stored in 3,000 lb/sq in bottles behindthe firewall in the outboard nacelles. The system incorporates com- bustors, fuel pumps and igniters which raise the temperature to 1,000deg F and take the engine to 8,240 r.p.m. before cutting out after 12 sec. During flight the air bottles are recharged (from the pressure remainingafter one start) in 164 min. Air is supplied by a six-cylinder radial compressor in the rear of each inboard nacelle driven by a hydraulicmotor from the undercarriage circuit. One of the drawbacks of the D13 engine is its high rotational speedof 13,820 r.p.m. under all flight conditions. Strenuous efforts are turning it into a satisfactory commercial engine and Allison, who havenever powered commercial aircraft before, are pursuing an aggressive sales policy. The approved overhaul life is hoped to reach 625 hr in The upper curve shows the capacity payload for the Electra before the recent increase in authorized weight to 113J0O0 Ib. The lower curves show operating cost for 66-seat domestic and international versions (D, and IJ and 80-seat versions (D2 and IJ. OO 9 X a a 501-D15 unit—io wun.ii i^x->» •.«.!« ~~ .e.h.p. and the Electra is structurally and aerodynamically capable of ii«in<r the verv advanced Allison 550, of 5,500 e.h.p., which should be 1958 with 1,000 hr scheduled for 1959. In the latter year the refined 5O1-D15 unit-to which D13s can be converted-will ^deliver•4,050 e.h.p. and the Electra is using the very advanced cleared by 1960.SYSTEMS Cabin Air. Positive-displacement blowers are mounted on the reduction gearboxes of both inner engines, each feeding air atth» ra'e of 55 lb/min. The air ducts pass along the leading edge of the wing and enter an air-conditioning bay in the fuselage at station 502,in Lien me equipment is centralized. Two air-cycle coolers are mounted to port with the fans on top; to starboard is a self-containedFreon system for ground-cooling, energized by the main engines or by electric power. A single hatch in the underside of the fuselage pro-vides access to the bay for a man standing on the ground. N.A.C.A. intakes for the inter-coolers are provided on each side of the fuselageadjacent to the air-conditioning bay, from which the air is dumped overboard through the bottom skin. ... It is probable that the air will be taken into the fuselage beneath the baggage racks and extracted along the port and starboard sides of the roof. The walls are heated by the incoming air, and the floors are also heated, although in certain areas this is likely to be electric. The rear pressure bulkhead carries an inwards-relief valve at the centre with dual outwards-relief valves above. Beneath the port side of the floor at station 250 is a separate heater, fan and filter system serving the flight deck. . ..... - -Fuel. A simple four-tank system is provided with automatic trim- ming and cross-feed. All tankage is integral between the widelyspread wing spars. The inboard tanks, starting at the root end-ribs, each have a capacity of 918 gal, although this could no doubt beincreased if fuel were allowed to permeate the region between the undercarriage rib trusses. The outboard tanks each hold 1,324 gal andare terminated by end-ribs one station in from the tip, to which the float valves are attached. Fuel lines run within the tanks and a ventmanifold and flame trap points aft at each wing-tip. Liberal inspec- tion panels are provided in the integral under-surface. A single pres-sure-fuelling socket is stationed some 6ft from ground-level at the rear end of the starboard inner nacelle, and each tank has standard over-wingfiller caps. Hydraulics. Duplicated fail-safe systems operate at 3,000 Ib/sq in,the two pairs of pumps being mounted one on each engine. Services include undercarriage retraction, speed brakes, flaps, wheel brakes, con-trol boosters and folding stairway. As an example of the duplication provided, the captain's brake pedalsare in a separate system from those of the co-pilot. The hydraulic servicing bay is under the fuselage floor immediately behind the wingbox with a single large access door. Within it are accommodated the aileron booster unit, the brake accumulator, emergency air-sphere forbraking, and centralized shuttle valves; the reservoirs, of unequal size, are mounted at station 749.Electrics. Each engine reduction gearbox carries a 60 kVA alterna- tor supplying current at 208/120 V, three-phase, 400 c.p.s., with auto-matic load-transfer. Priority loads can be maintained on any two alternators. All major components are centralized in a service centrebeneath the floor immediately ahead of the wing. Among the principal electrical loads are those associated with ice protection.Ice Protection. The wing and engine intakes are anti-iced by air bled directly from the Allison compressors. To reduce weight, air isextracted at high pressure and at 600 deg F and piped to the wing root along the front of the wing box. The duct then runs back insidethe leading edge itself down the centre of an inner skin; along the front of the pipe small injection nozzles squirt the hot air against the insideof the skin. The air then runs back across the chord and escapes from flush exits. The system is designed to meet continuous and inter-mittent heavy icing. Airscrew de-icing is electro-thermal and Nesa glass is used in thewindscreen. Originally the tail was to have been de-iced by bleed air, but electro-thermal elements are now specified. Each will extend overthe complete length of tailplane or fin leading edge to 15 per cent chord, the heating being cyclic (8 sec per cycle) at 19 watts/sq in. Flight Equipment. The standardized flight deck, reached after somesix years of committee meetings, follows practices recommended for the S.A.E. Type II S.7 cockpit. The operating crew comprises captain,first officer and an engineer seated behind the pedestal. Behind the captain is a seat for an observer—-or, in over-water Electras, a curtainedcubicle for a navigator. Experience of the mock-up emphasizes that the flight deck is reallyexceptionally wide. All seats are large and adjustable and plenty of thought has been given to crew comfort and kit stowage. Basic electricpanels are at the rear to starboard, with radio and electronics to port. The whole roof between the circuit-windows is occupied by a switchpanel. Emergency controls can be reached by all three crew members. Except for the duplicated H.F. and A.D.F. systems, all aerials areflush. Provision is made for weather radar beneath the hinged and heated nose radome, and other aerials include V.H.F. windows in thefin and D.M.E. on the bottom centre-line around station 274. PAYLOAD ACCOMMODATION. From the flight deck a levelfloor extends to the rear pressure bulkhead at a height of 97.25in from the ground. The entrance vestibule is 38in wide, around which willnormally be carry-on baugage bays, coat closets and two toilets with a water tank above the roof trim. The total usable floor area is 710 sq ft.Fixed light and ventilation panels are provided under the baggage racks at 38in pitch, which will be the seat pitch in most versions.Lockheed are anxious to sell Electras with a new pattern of seat 20in between the arm rests incorporating optional seat-back tables andsteps for access to the baggage racks. In an attempt to quieten the interior, no seats are fitted in the three bays adjacent to the plane ofthe airscrews in anv version contemplated. Standard equipment includes synchro-Dhasing of engine r.n.m., and the clearance between the inboarddiscs and the fuselage is 39.7in. Aft of station 200 is a large under-fioor hold with a door on the JO 500 1,000 1.5OO 2.OOO 2.5OO 3.OOO 3,500 FLIGHT DISTANCE (st.m.)
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