Military


DC-8

The DC-8 is one of the earliest jet-powered commercial passenger aircraft. In the decade following its maiden flight, the DC-8 established commercial transport world records for speed, altitude, distance and payload. From its inception, the four-engine DC-8 embodied advanced aerodynamic and structural concepts, as well as internal systems designed for maximum service reliability, operational convenience and passenger comfort.

The second long-range, high-passenger-capacity transport that, along with the Boeing 707, initiated the jet revolution in air transportation was the McDonnell Douglas DC-8 (originally the Douglas DC-8). This aircraft was ordered by Pan American World Airlines in 1955, and first flight was made in 1958. The aircraft entered airline service in August 1959. The DC-8 was built in many different versions; one of the principal modifications incorporated in the aircraft was a stretched fuselage to provide increased passenger capacity. Over 550 DC-8 aircraft were built before production was terminated in 1972.

In most essential respects, the basic configuration of the McDonnell Douglas DC-8 is the same as that of the Boeing 707. Early versions of the two aircraft were indistinguishable except to someone familiar with them [the 707 had a shorter nose and a profusion of windows]. There were, of course, many differences in the detailed aerodynamic and structural design and in the systems employed on the aircraft.

The Douglas DC-8 transport program was a successful example of the use of the area rule for local interference drag analysis. During a prototype flight investigation of a new long duct nacelle for the DC-8, flight results obtained with a proposed new nacelle afterbody resulted in a much greater interference drag than had been indicated by wind-tunnel tests. In fact, the penalty measured in flight was double the wind-tunnel value for representative cruise conditions. Examination of pressure distributions on the nacelle in the channel between the wing and nacelle indicated that the shock in the channel was significantly stronger and farther aft in flight than in the wind tunnel; this caused very high levels of drag. The difference between the tunnel and flight results was attributed to the differences in boundary-layer growth because of corresponding differences in Reynolds number. Applications of Whitcomb's local area-rule methodology resulted in fairing candidates that eliminated the problem. The successful application of the area-rule process and the elimination of what would have been a major performance penalty for the long duct nacelle configuration provided Douglas with the confidence and enabling technology to proceed with the new versions of the DC-8, the highly successful "Super Sixties" (DC-8-62 and DC-8-63).

A capacity for improved power, payload and range capabilities was inherent in the DC-8 design. Four basic models were produced: the Series 10 through 50, in passenger, freighter and convertible freighter versions; and the Super 60 Series 61, 62 and 63, with freighter models of each. The last of 556 aircraft was delivered on May 13, 1972, marking the end of 15 years of production, at which time there were 48 operators in 28 nations.

Development of the Super 60 Series in 1965, with increased size, capacity and efficiency, demonstrated the capacity for growth in the DC-8 design. The Super 61 & 62 can carry up to 258 passengers. The Super 63, which combined the fuselage extension and payload capacity of the Super 61 with the long-range, aerodynamic and power plant improvements of the Super 62, carries a maximum capacity of 259 passengers and baggage 4,500 statute miles (7,242 km), or lesser loads even greater distances. As compared with earlier versions of the DC-8, the fuselage of the Super 63 was stretched by the addition of a 20-foot section ahead of the wing and a 17.8-foot section aft of the wing. Also, the wing span of the aircraft has been increased 6 feet over that of the original DC-8. The DC8 Super 63F/63CF is able to carry up to 116,000 pounds (52,617 kg) of freight.

The DC-8 Series 70 is a re-engined version of the popular Super 60 Series, substituting CFM56 engines for the latter's Pratt & Whitney engines. The result is an aircraft that retains the Super 60 operating weights, but with a longer range due to the newer, more fuel-efficient turbofans. The Series 70 was also able to meet later, more stringent noise regulation that were implemented in the 1980s.

The wing and engine locations are similar to those used on the 707 however, the aspect ratio and sweepback angle are slightly different. The main landing gear consists of two struts to which are mounted four-wheel bogies; the two rear wheels of each bogie can be put in a free swiveling mode to assist in making sharp turns on the ground. The main landing gear is mounted on the wing and retracts inward into the fuselage. The two-wheel nose gear retracts in a forward direction.

The aerodynamic efficiency of the DC-8 is indicated by the maximum value of the lift-drag ratio, which is estimated to be about 17.9. The value of (L/D)max, is lower for the DC-8 Super 63 than for the 707 because of the DC-8's longer fuselage and consequently increased ratio of wetted area to wing area. The relationship between wetted area, wing area, and (L/D)max, is discussed in chapter 3 of reference 176. The loss in aerodynamic efficiency associated with the long fuselage is more than compensated by the increased passenger-carrying capacity and consequent reduction in direct operating costs per seat mile.

The wing is equipped with trailing-edge double-slotted flaps and slats over the inboard sections of the leading edge. These high-lift devices provide a lift coefficient that gives a stalling speed of 123 miles per hour at the maximum landing wing loading. The lateral control system consists of inboard and outboard ailerons that are connected by a torque tube that acts as a torsion spring. The inboard sections are power operated. The outboard sections only operate at the lower values of the dynamic pressure where they are needed. As the dynamic pressure increases, the aerodynamic resisting moment of the aileron becomes greater in relation to the torque that can be transmitted through the torsion bar; hence, the aileron deflection is reduced.

The amount of deflection of the outboard aileron varies smoothly with variation in dynamic pressure and, therefore, provides the desired variation of aerodynamic control moment with speed and altitude. The rudder is also power operated. Both the rudder and the ailerons have a manual reversion mode in the form of aerodynamic servotabs. Elevator control is manual and makes use of an aerodynamic servotab. The variable-incidence horizontal tail is power operated and is used for longitudinal trim. Wing spoilers are automatically deployed on landing by nose-wheel contact with the runway.

The gross weight of the DC-8 Super 63 is 358 000 pounds; in an all-tourist configuration, the aircraft seats 259 passengers in a 6-abreast arrangement. With a maximum payload of 67 735 pounds, the range is 4882 miles; and with maximum fuel, a payload of 37 101 pounds can be carried for a distance of 6997 miles. The cruising speeds of the DC-8 are about the same as those of the 707.

A number of DC-8 aircraft have been retrofitted with modern CFM-56 high-bypass-ratio turbofan engines. Manufactured by GE Snecma, these engines have 22 000 pounds thrust and a bypass ratio of 6.0. The modified aircraft are designated DC-8-71, DC-8-72, and DC-8-73 depending upon the 60-series aircraft from which they were derived. Improved performance and economy together with reduced noise are advantages resulting from installation of the new engines. Characteristics of these modified aircraft may be found in reference 150. With retrofit of the new engines, the DC-8 has indeed received a new lease on life. Along with the 707, the DC-8 has indeed received a new lease on life. Along with the 707, the DC-8 has been a workhorse of great productivity for many years; and although out of production, it will continue to be operated for a long time to come.

The DC-8 in Military Service

The Civil Reserve Air Fleet (CRAF) represents approximately one-half of the AMC's total strategic war time airlift capability - 24% of the cargo capability; 95% of the passenger capability; and 100% of strategic intertheater aeromedical capability. While the DC-8 is no longer utilized for passengers, cargo verisions are used to carry 14 or 18 463L Pallets.

The US Army's largest peacetime loss occured on Dec. 12, 1985, when a chartered DC-8 plane carrying 248 members of the 101st Airborne Division and eight crew members crashed at Gander, Newfoundland. After stopping in Gander, Newfoundland for fuel, the chartered Arrow Air Douglas DC-8 jet crashed shortly after takeoff. The planes wreckage, along with the badly burned and dismembered bodies of its passengers and crew were strewn over a three-quarter mile area of frozen forest. In the end, despite the severe damage incurred by the overwhelming violence of the plane crash and fire, all of the deceased were positively identified and accorded a decent burial---with all due honors.

Since 1951, Thule Air Base in Greenland has provided America with early warning capability. Because of Thule's location, actually getting there can be somewhat tricky. Thule's main passenger service is via DC-8 (cargo/passenger) aircraft operated by Air Transport International (ATI). The plane normally departs McGuire AFB, NJ, on Wednesday night at 2300 (show-time is 2100) and flies to Baltimore-Washington International (BWI) airport. The DC-8 then departs BWI at 0200 on Thursday morning (show-time is 2000 on Wednesday) for the approximately 6 hour flight to Thule. Make sure you dress warmly and in layers since the plane can get fairly cold.

If the weather is bad in Thule, the flight may be diverted to St. Johns, Newfoundland; Sondrestrom AB (Kangerlusssuaq), Greenland; Keflavik, Iceland; or Frobisher Bay. All of these places are expensive, so travellers need to make sure they have a government credit card or at least $200 in cash or traveler's checks. ATI provides services similar to commercial international flights. Two flight attendants are on-board to meet in-flight needs. In addition, there will be two movies and two meals (one large and one snack). Blankets and pillows are available as comfort items. Passengers try to get a little sleep on the plane because there is mandatory in-processing as soon as they arrive at Thule.



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