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Aviation History
1956
1956 - 0874.PDF
FLIGHT, 6 July 195618 Airliners of the World DOUGLAS DC-8 in excess of cruising i.a.s. On the upper surface of each wing aremounted four small spoilers ahead of the flaps which are flicked open hydraulically—bussed together by cables—after touch-down, the circuitbeing energized by a micro-switch on the nose leg. Their purpose is to destroy lift and improve the traction of the wheel brakes.POWERPLANT. The domestic Model 1881 is powered by the Pratt and Whitney JT3C-4 or -5 (described in the analysis of theprevious aircraft) with a wet rating of from 12,500 to 13,000 lb thrust. Each engine is picked up by two semi-hoops suspended from the twospars of the nacelle pylon. Some 340 gal of water (without methanol) are carried for use during full-load take-offs at more than about 50 deg F.A 10-kVA drive is provided for a water pump for each engine, and the procedure will be to consume all the water in the first two minutes offlight so that none remains to freeze under cruising conditions. The water is carried in the wing tips and centre section. Inter-continental DC-8s will be powered by the Pratt and WhitneyJT4A-3 (commercial J75) or Rolls-Royce Conway RCo.10 by-pass engine; the Bristol Olympus 511 is also obviously suitable. Details ofthese engines are restricted, but their thrust will certainly lie in the range from 15,000 to 19,000 1b. Douglas believe that they are close tothe optimum form of reverse-thrust, sound-suppressing propelling nozzle. Many systems have been investigated, and Douglas are assumingresponsibility for evolution of the best arrangement. They have achieved 40-45 per cent reverse quite readily and have even recorded 58 per cent.The quiet nozzle and thrust-reverse portions are to be combined. Accessories on the Pratt and Whitney engines are mounted beneaththe high-pressure compressor casing. Two drum-type oil coolers are provided, each fed with air from an individual ram intake in the lowerpart of each nacelle. For the British engines fuel/oil heat exchangers will be employed, requiring no auxiliary intake. The complete nacellewill be isolated in the event of fire, and two-shot Freon systems are provided for fire suppression. SYSTEMS. Air Conditioning. Cabin air is bled from the second(h-p.) spool of each engine at around 750 deg F and immediately cooled to about 400 deg F to reduce fire risk. At this temperature,the air is fed to a battery of four Douglas air turbines (maximum, 55,000 r.p.m.) in the nose, where they drive compressors feeding freshair to the cabin. The dP is 8.67-8.73 lb/sq in (6,700ft at 40,000ft) and any one turbo-compressor can maintain it. Behind the nose-under-carriage bay is a closed-circuit Freon refrigeration system supplied by the Carrier Corporation. It is energized by two tiny supersonic rotorsand provides 26-ton refrigeration. Warm air is fed to trunks in the cabin roof, and down multiple ductsin the sides of the fuselage from which it escapes into the honeycomb- filled cabin wall, which consequently acts as a source of radiant heat.The air finally enters the cabin beneath the baggage racks. All the overboard spill from the cabin and air turbines is ejected through apropelling nozzle on the ventral centre-line which Douglas consider to be worth 4 m.p.h. in cruising flight. FneL As already noted, the entire wing between the front andrear spars forms an integral tank terminated at the inner end by the centre-line of the aircraft on the inter-continental DC-8, and by anend-rib on domestic versions. The outer end-rib is spaced about three from the wing tip (station 727). The manufacturing joint ineach wing divides the capacity into what are termed main and auxiliary tanks on each side. Total capacity is 14,650 gal (17,999 gal inModel 1910). Each engine has its own tank system, with cross-feed to the remainder.Feed from the immersed boosters is backed up by further line boosters driven by the engines. Immersed pumps feed to a fuel box (a speciesof header) on each powerplant, and Douglas are guaranteeing a very modest quantity of maximum unusable fuel, without reliance on acces-sory power. Under-wing sockets are provided, through which the system can be pressure-fuelled in 16 minutes. Hydraulics. The inboard engines each drive a multi-plungervariable-stroke pump energizing the hydraulic system to 3,000 lb/sq in. Choice of variable-stroke pumps reduces surge and fatigue problemsand saves about 12 per cent power in allowing the full design pressure to be utilized. An electrically driven stand-by pump is provided, withits own reservoir. The "system compartment" is accessible from a main bogie bay. Services supplied include the landing gear, flaps, spoilers, speedbrakes, wheel brakes, nosewheel steering, engine-starting air com- pressor, tailplane trim and aileron and rudder power. Douglas co-oper-ated with Monsanto Chemicals in the evolution of Skydrol 500 4O.OOO 3O.OOO 20.OOO 3 I 1O.OOO CAPACITY PAYLOAD 35,93Olb \ CAPACITY FUEL" 140,000 Ib 1,000 2,000 3,000 4,000 5,000 6.OOC RANGE (n.m) Payhad/range curve for Model 1910 at 287,500 Ib. which will be standardized; it is a development of the well-known non-flam fluid used on the DC-7, capable of operation down to — 100 deg F.Electrics. All electrical power is generated at 115/208 V, three- phase, 400 cp.s. by 20 (or 30) kVA alternators on each engine with Sund-strand hydraulic drives. The system, for which Jack and Heintz are responsible, has a heavy overload capacity, is fully paralleled andcompletely automatic in isolating defective portions of circuit, and is also "modularized" for easy maintenance. Transformer-rectifier sets,rated at 25 amp, supply small quantities of D.C. current to certain instruments and electronic services. No storage batteries are associatedwith the system at any point. Ice Protection. All aerodynamic surfaces, together with thenacelle pylons, are de-iced by hot air bled from the engines. The double-skin leading edges are fed with air from multiple-branch mani-folds which exhaust into a curved diaphragm behind each leading edge. The air then escapes into the space forward of the front spar on eachsurface, and thence to atmosphere. The engine and air-conditioning intakes and the radome are protected by the same basic system. Intense heat is applied for short periods on a cyclic basis, this beingconsidered preferable to continuous (anti-icing) heating in preventing ice from re-forming further back on the surface concerned. (Theintakes of the engines are an exception in that they are continuously anti-iced.) The entire span of the wing and tail surfaces is treatedfrom root to tip. At no point is there a pipe temperature in excess of 400 deg F. FLIGHT EQUIPMENT. Normal operating crew comprises cap-tain, first officer and engineer (who, having virtually no powerplant duties, is a "systems manager"), with a seat for a supernumerary observer;in addition provision is made for a navigator on over-water DC-8s. If required the aircraft can be flown by a crew of two. Cockpit glazingcomprises multi-layer panels (Nesa glass, Vinyl, thick glass, air-space, thick glass, Vinyl and Nesa glass, in that order), two of the largestopening to provide direct vision. Rain is cleared by air jets supplied from the air-conditioning bay in the nose. Among the very full radio equipment is search radar, housed in aheated nose radome. Aerials are generally suppressed, the fin incor- porating V.O.R. windows in structural dielectric and the whole upperpart of the vertical tail being isolated to form an aerial of the correct impedence and radiation pattern. Standard equipment includes dupli-cated h.f. and v.h.f. communication, duplicated A.D.F. and glide-slope, marker beacon, Loran, radar transponder and "Hi-range" radio alti-meter, together with flight interphone and p.a. system. PAYLOAD ACCOMMODATION. The total usable length ofpassenger cabin is approximately 97ft; interior floor-width is 130in and height from floor to ceiling about 95in at the centre-line (100.5in to theouter skin). Within this space the following features facilitate a wide variety of interior layouts; seats and partitions mounted on standardrails; readily changeable reading lights and cold-air outlets; passenger and service doors and emergency exits at both ends; removable berthsintegrated with the baggage racks; buffets at both ends; radiant heat and conditioned air outlets distributed along the whole usable length; andrest rooms, or lounges, at both ends. The arrangements shown in the large drawing and the floor plan are typical. Another configurationwhich has found favour is to use alternate twin and triple seats, to allow cabin staff to pass easily. Such an arrangement provides for100 passengers; in all-six-abreast seating a total of 131 can be carried. The two large freight holds under the floor have a combined capacityof 1,415 cu ft. The door arrangement has already been described. It is intended that luggage and freight off-loading shall be capablewithin six minutes, the overall turn-around time being 30 min. COMMERCIAL HISTORY. Douglas were already deeply engagedin work on the Model 1881 long before its existence was announced one year ago. The first order was that of Pan American, who bought 25 inOctober 1955 for £57m; this order was subsequently revised to read: Pan American, 21 for delivery starting in December 1959, and Panagra,4 (with JT4A engine) for delivery from early 1960. Subsequent orders have been as follows:— United, October 1955, 15 with JT4 and 15 with JT3 (for subsequentre-enginmg) for delivery from May 1959 at £62.5m; National, November 1955, 6 with JT3 from mid-1959 at £ 13.2m; K.L.M.,November 1955, 8 with JT4A (option on further 4) from early 1960 at over £18m with spares; Eastern, December 1955, 6 with JT3 fromMay 1959 and 12 with JT4 from March 1960 (option on another 8 with JT4 from autumn 1961) at a total (with option) of £59m withspares; Japan Air Lines, December 1955, 4 with JT4A from first half of 1960 at £9.8m; S.A.S., December 1955, 7 with JT4A from 1960 at£18m; Swissair, January 1956, 2 with JT4A from spring 1960 at £5 83m; Delta February 1956, 6 with JT3 from June 1, 1959, at£1f9m,;.i?nd T.C.A., May 1956, 4 with Rolls-Royce Conway from early 1960 at £7.88m, with an option on 2 more.
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