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Aviation History
1958
1958-1- - 0139.PDF
FLIGHT, 25 July 1958 DC-8 Douglas Aircraft Company, Santa Monica, California 141 LIKE its Seattle contemporary, the Douglas DC-8 has blos-somed into many different versions as its operational scope^ has been widened. Since the aircraft was first announced, its weight has increased from a maximum of 257,000 lb to amaximum of 310,000 lb, although—unlike the Boeing 707 series —the airframe dimensions have remained unchanged since 1956and do not vary between domestic and international models. Off to a later start than Boeing and without their competitor's directmilitary backing, Douglas are determined to show that with their long commercial experience they can produce from their ownresources an airframe at least equally good, and in many respects more advanced. Thus Douglas have invested considerably morethan $200m in wages, engineering, tools and facilities, including a new building solely for DC-8 assembly. The magnitude of the task which Douglas have set themselvesis illustrated by a slight falling behind schedule which occurred over the first flight target. This took place on May 30, abouttwo months behind the anticipated date; but Douglas are con- fident that the certification date of October 1959 for the first DC-8swith JT3C powerplants will not be delayed. An unprecedented number of aircraft—four with JT3Cs, three with JT4As and twowith Conways—are to be employed on certification trials, and by November 1959 and February 1960 both JT4 and Conway versionsshould be certificated and production models of each ready for airline deliveries. There are two basic DC-8 models, which are distinguished bythe designations Domestic and Intercontinental. Within this broad division there are six distinct variants. The Domestic versionspowered by either Pratt and Whitney JT3C-6s or by JT4A-3s, have a design gross weight of 265,000 lb, and the four Intercon-tinental versions comprise an aircraft with a gross weight of 287,500 lb with either JT4As or Rolls-Royce Conways, and thesame choice of engines in combination with a long-range DC-8 weighing no less than 310,000 lb. Douglas have studied very intensively the problems of sup-pressing noise level; the first aircraft to fly was equipped with suppressors designed by Rolls-Royce but Douglas have invested$4m and 360,000 engineering man-hours of their own. The final design will include a clam-shell type thrust reverser as part of thesuppressor unit. COMMERCIAL HISTORY The first DC-8 order wasplaced by PanAm, who bought 25 in October 1955. Later, this order was revised so that four aircraft would go to Panair doBrasil and another four to Panagra in 1960, leaving PanAm 17 to be delivered in 1959 and 1960. The following subsequent orders have brought DC-8 salesto 147: United, 40 (originally 30) in October 1955; National, 6 in November 1955; K.L.M., 8 in November 1955; Eastern, 20(originally 18) in December 1955; Japan Air Lines, 4 in Decem- ber 1955; S.A.S., 7 in December 1955; Swissair, 3 in January1956; Delta, 8 in May 1956; T.C.A., 6 with Conways in May 1956; U.A.T., 2 in November 1956; T.A.I., 2 in November 1956;Olympic, 2 in July 1957; Trans-Caribbean, 1 in January 1958; Alitalia, 6 with Conways in March 1958; Iberia, 2 and Northwest,5 (these last two orders not yet haying been finalised). Domestic models of the DC-8 are due for delivery in the latter part of 1959,while the international versions will be delivered through 1960 and 1961. _ AIRFRAME The structure of the DC-8 is relatively sophis- ticated; advanced bonding and riveting techniques, titanium panel- ling, roll-tapered light alloy skinning and rip-stop construction techniques are widely used. Strict limits have been set on stress levels, with particular emphasis on the elimination of stress con- centrations. Adherence to the philosophy of alternative load paths is illustrated by the third spar introduced into the wing torsion box. Fuselage Geometrically the double-bubble section is formed from a 73.Sin upper radius and 68.7in lower. The untapered por- tion is nearly 100ft long. Lap-jointed skin panels are laid over z-section stringers riveted to channel frames at 20in pitch. Alldoors are of a Douglas design and are double hinged, so that a plug type arrangement can be used but the door can be liftedinwards and slid out edgeways. Cargo doors are mounted on tracks and slide upwards and inwards. The windows are also ofunusual shape, the low sides being formed from arcs that give dimensions of 16in high by 14in wide at the major and minoraxes; the four arcs are joined by a smaller radius. Wing An unusual profile has been adopted which changesradically from root to tip, but allows a 30 deg sweep to be adopted and postpones the drag rise. All three main spars have heavysheet webs carrying vertical stiffeners, and are arranged to lie so that outboard of the outer engines, where the bending momentis low, front and centre spars converge to leave a two-spar arrange- ment out to the tip. The wings are joined on the aircraft centreline with a butt strap and are then continuous to the tip; a manu- facturing break is provided but is not intended to be broken downafter the aircraft is complete. The box formed between the front and rear spars, Y-section compression stringers, I-section lowerstringers and skins is an integral fuel tank where the ribs act as fuel baffles. The three-spar construction of the wing is continuedin the fin and tailplane. The latter has a three-plank integrally stiffened structure between front and rear spars and much of theskin is stabilized by bonding. The fin is remarkable chiefly for the 8ft of glassfibre structure (including spars) which forms thedielectric tip. The engine pylons sweep inwards, following the spanwise flow, and the two main spars pick up on a stiff ribbetween the front and rear wing spars. The complete assembly is built by Ryan and the pod access doors and pylon trailing edgesare entirely panelled in titanium. Undercarriage Each forged main leg carries an articulatedfour-wheeled bogie, which allows the aircraft to be pivoted about a point 4.5ft from the inside gear. The undercarriage track is20ft 9jin. Bendix main and nose wheels are shod with Goodyear or other manufacturers' tyres inflated to 131 lb/sq in for aircraftwith a maximum weight of 287,000 lb. Nose wheel tyres are 34Xllin and mainwheel tyres 44Xl6in. All undercarriage legsare arranged to fall by gravity in the event of hydraulic failure and the main legs are covered by three doors when retracted; themain door enclosing the wheels is closed when the undercarriage is down. Rudder pedals are used to steer the nose undercarriage up to10 deg from centre, and a hand wheel for 78 deg thereafter. When the nosewheel has been swivelled through 40 deg, the articulatedmain gear bogie can be unlocked for taxying. POWERPLANT A choice of three engines is offered: Prattand Whitney JT3C-6s with a wet rating of 13,400 lb for the domestic variant and JT4As or Rolls-Royce Conways for theIntercontinental. JT4A-3s, with a dry rating of about 17,000 lb thrust, or Conway 507s with a dry rating of 16,500 will be usedwith the 287,500 lb airframe, but the long-range aircraft will use the higher powered JT4A-9s or Conway RCo.l2s. Provision ismade for 350 gal of water to be carried in the wing tips and centre section and a lOkVA drive powers the associated water injectionpump. The first DC-8 to fly was equipped with a Greatrex-type noise suppressor of Rolls-Royce design, but later models willadopt a combined silencer /clam-shell door thrust reverser which Douglas have been developing; the company have invested heavilyin research to obtain suitable equipment. SYSTEMS Fuel Intercontinental and Domestic versionsdiffer in that, in the latter, the inboard end of the integral tank terminates outboard of the centre line of the fuselage. Respectivecapacities are 18,000 Imp. gal and 14,650 Imp. gal, but the 310,000 lb Intercontinental aircraft carries 19,400 Imp. gal totalfuel. The integral tank is divided at the manufacturing joint into main and auxiliary sections and each engine has its own fueland tank system with inter-connecting crossfeed. Pressure refuel-
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