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Douglas DC-8

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The Douglas DC-8 is a four engined jet airliner, manufactured between 1959 and 1972.

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Background


NASA Dryden DC-8 Airborne Laboratory, February 1998.
Larger version

At the time the world's first jet airliner was introduced, the de Havilland Comet in 1949, Douglas held a commanding position in the aircraft market. Although Boeing had pointed the way to the modern all-metal airliner in 1933 with the 247[?], it was Douglas that, more than any other company, made the promise a reality. Douglas produced a succession of great piston-engined commercial aircraft through the '30s, '40s and '50s: 138 DC-2s[?], 10,928 DC-3s (mostly for military service in World War II), 1453 DC-4s[?], 537 of the DC-6[?], and 226 DC-7s[?].

Given the success of their designs, Douglas took the view that there was no reason to rush into anything new, as did their rivals Lockheed and Convair. Most air transport manufacturers expected that there would be a transition from piston engines to turbines eventually, but that the switch would be gradual, that it would be to the more fuel-efficient turboprop engines rather than pure jets, and that it would happen later rather than sooner.

In contrast, Boeing took the bold step of starting to plan a pure jet airliner as early as 1949. Boeing's military arm had gained extensive experience with large, long-range jets through the B-47 (first flight 1947) and the B-52 (1952). With thousands of their big jet bombers on order or in service, Boeing had developed a close relationship with the US Air Force Strategic Air Command (SAC), and could count on having the inside running when the time came to replace SAC's fleet of piston engined KC-97[?] tankers.

For Boeing, this was a golden opportunity: an aircraft built to provide air-to-air refueling capacity for strategic bombers could be turned into a commercial transport with very little extra effort. Boeing could now plan on building a commercial jetliner - which might or might not sell - but either way the Air Force would pay for most of the development cost.

De Havilland's pioneering Comet entered airline service in 1952. To begin with, it was a huge success, but a series of fatal crashes in 1953 and 1954 resulted in the type being grounded until the cause could be discovered. Airlines cancelled orders for it, public confidence in the idea of jet transport plummeted, and it would take de Havilland four years to find and fix the problem. (In fact, the cause of the Comet crashes was nothing to do with jet engines as such: it was rapid metal fatigue[?] brought on the stress of cycling a pressurised cabin to high altitudes and back rapidly. The harsh lesson of the Comet disasters was inevitable, but the new understanding of fatigue that the Comet investigation produced would play a vital part in the good safety record of later types like the DC-8.)

Development

In 1952, Douglas remained the most successful of the commercial aircraft manufacturers. They had almost 300 orders on hand for the piston engined DC-6 and its successor, the DC-7, which had yet to fly and was still two years away from commercial service. The Comet disasters and the consequent airline disinterest in jets seemed to demonstrate the wisdom of their tried and true strategy. Nevertheless, with one eye on the USAF tanker market, Douglas secretly began jet transport project definition studies in mid-year, and by mid-1953 had decided on something very like the final form: an 80-seat, low-wing aircraft with four Pratt & Whitney JT3[?] turbojet engines, 30 degree wing sweep, and an internal cabin diameter of exactly 11 feet (3.35m) to allow five abreast seating. Maximum weight was to be 95 tonnes, and range was estimated at somewhere between 3000 and 4000 miles (about 4800 to 6400km).

Douglas were luke-warm about the jet airliner project, but believed that the USAF tanker contract would go to two companies for two different aircraft (as several USAF transport contracts in the past had done). In May 1954, the USAF circulated its requirement for 800 jet tankers to Boeing, Douglas, Convair, Fairchild, Lockheed and Martin. Boeing were already just two months away from having a prototype in the air. Before the year was out, the Air Force had ordered the first of an eventual 808 Boeing KC-135 tankers. Even leaving aside Boeing's ability to supply a jet tanker promptly, the flying boom air-to-air refueling system - as first fitted to the KC-97 - was also a Boeing product: developing the KC-135 had been a very safe bet.

Just four months after issuing the tanker requirement, the USAF ordered 29 KC-135s from Boeing. Donald Douglas[?] was shocked by the rapidity of the decision which, he said, had been taken before the competing companies had been given time to complete their bids, and protested to Washington, but without success. The US Air Force would buy more than 800 strategic tankers over the next ten years, and every one of them from Boeing. In financial terms, the 707 would have an armchair ride, while Douglas would be short of cash from that time on.

Having started on the DC-8 project, Douglas decided that it was better to press on than give up. Consultations with the airlines resulted in a number of design changes: the fuselage was widened by 15 inches (38cm) to make room for six abreast seating and make it slightly wider than the 707. This led to larger wings and tail surfaces and a longer fuselage. The cost of the program was enormous; it was at that time the most expensive venture of any kind ever taken on by a single company. Donald Douglas provided $450 million towards it out of his own pocket.

The DC-8 was officially announced in July 1955. Four versions were offered to begin with, all based on the same 45.9m long airframe with a 43m wingspan, but varying in engines and fuel capacity with maximum weights between 120 and 130 tonnes. First flight was planned for December 1957 and entry into revenue service for 1959. Well aware that they were lagging behind Boeing, Douglas began a major push to market the product.

Worldwide, piston engined airliners still ruled. The French 90 passenger twin jet Sud Aviation Caravelle[?] prototype had just flown for the first time, the Comet was still grounded, and the 707 was not expected to be available until late 1958. The transition, when it came, looked likely to be one to turboprops rather than turbojets. The pioneering 40-60 seat Vickers Viscount[?] was already in service and proving enormously popular with both passengers and airlines - it was much faster, quieter, and more comfortable than piston engined types. Another British aircraft, the 90 seat Bristol Britannia[?] was establishing a reputation, and Douglas' main rival in the large piston engined passenger aircraft market, Lockheed, had committed to the short/medium range 80-100 seat turboprop Electra[?], with a launch order from American Airlines for 35 and other major orders flowing in. The major airlines were reluctant to commit themselves to the huge financial and technical challenge of jet aircraft. On the other hand, no-one could afford not' to buy jets if their competitors did. And there the matter rested until October 1955, when the ever aggressive Pan American[?] placed a simultaneous order with Boeing for 20 707s, and with Douglas for 25 DC-8s. To buy one expensive and untried jet-powered aircraft type was brave, to buy both was extraordinary.

In the closing months of 1955, other airlines rushed to follow suit: Air France, American, Braniff, Continental and Sabena ordered 707s; United[?], National, KLM, Eastern, JAL and SAS chose the DC-8. In 1956 Air India, BOAC, Lufthansa, Qantas and TWA added over 50 to the 707 order book , while Douglas sold 22 DC-8s to Delta, Swissair, TAI, Trans-Canada, and UAT. With KC-135 orders helping defray development costs, Boeing could offer lower prices, and also promise earlier delivery slots - though not as early as anticipated because the DC-8 with its wider fuselage had constrained Boeing to take time out the redesign the KC-135 with a wider fuselage again, and the first production-ready 707 did not fly until December 1957.

By the start of 1958 Douglas had sold 133 DC-8s as against Boeing's 150 707s, a substantial achievement under the circumstances. Nevertheless, the pattern from that time on would be for the DC-8 to sell in modest but substantial numbers, while Boeing sold roughly twice as many 707s. The first DC-8 was rolled out of the specially built new factory at Long Beach in April 1958 and flew for the first time in May. Later that year an enlarged version of the Comet finally returned to service - but too late to take a substantial portion of the market: de Havviland had just 25 orders - and in October Boeing began delivering 707s to Pan Am.

Douglas made a massive effort to close the gap, using no less than 10 individual aircraft for flight testing to achieve FAA certification for the first of the many DC-8 variants in August 1959. Much had needed to be done: the original air brakes on the lower rear fuselage were found ineffective and were simply deleted as engine thrust reversers had become available; leading-edge slots were added to improve low-speed lift; the prototype was 25 knots short of its promised cruising speed and a new, slightly larger wingtip had to be developed to reduce drag.

The DC-8 entered revenue service with both Delta and United in September 1959. By March of 1960, Douglas had reached their planned production rate of 8 DC-8s a month.

Early Models

  • DC-8 Series 10 Designed for US domestic use and powered by 60.5kN Pratt & Whitney JT3C-6 turbojets. The initial DC-8-11 had the original, high-drag wingtips and all were subsequently converted to DC-8-12 standard. The DC-8-12 had the new wingtips and leading-edge slots and increased maximum weight from 120 tonnes to 123 tonnes. 28 DC-8-10s were manufactured.

  • DC-8 Series 20 Higher powered 70.8kN Pratt & Whitney JT4A-3 turbojets allowed a weight increase to 125 tonnes. 34 DC-8-20s were manufactured.

  • DC-8 Series 30 Designed for intercontinental routes, the three Series 30 variants combined JT4A engines with a one-third increase in fuel capacity and strengthened fuselage and landing gear. The DC-8-31 was certified in March 1960 with 75.2kN JT4A-9 engines for 136 tonnes maximum weight. The DC-8-32 was similar bar allowing 140 tonne weight. The DC-8-33 of November 1960 added 78.4kN JT4A-11 turbojets, a modification to the flap linkage to allow a 1.5 degree setting for more efficient cruise, stronger landing gear, and 143 tonne maximum weight. Many -31 and -32 DC-8s were upgraded to this standard. 57 DC-8-30s were manufactured.

  • DC-8 Series 40 The first turbofan powered airliner in the world, the -40 was essentially the same as the -30 but with 78.4kN Rolls Royce Conway[?] turbofans for better efficiency, less noise and less smoke. The Conway was a significant improvement over the turbojets that preceded it, but the Series 40 sold poorly both because of the traditional reluctance of US airlines to buy a foreign product, and because the still more advanced Pratt & Whitney JT3D[?] turbofan was due in early 1961. The DC-8-41 and DC-8-42 had weights of 136 and 140 tonnes, the 143 tonne DC-8-43 had the 1.5 degree flap setting of the -33 and introduced a new 4% leading edge wing extension to allow a small fuel capacity increase and a significant drag reduction - the new wing design improved range by 8%, lifting capacity by 3 tonnes, and cruising speed by better than 10 knots. It would be included in all future DC-8s. 32 DC-8-40s were manufactured.

  • DC-8 Series 50 The definitive short fuselage DC-8 with the same engine that powered the vast majority of 707s, the JT3D. Many earlier DC-8s were converted to this standard. All bar the -55 were certified in 1961. The DC-8-51, DC-8-52 and DC-8-53 all had 76.1kN JT3D-1 or 80.6kN JT3D-3B engines, varying mainly in their weights: 126, 138 and 142 tonnes respectively. The DC-8-53 arrived in June 1964, retaining the JT8D-3B engines but with strengthened structure from the freighter versions and 147 tonne maximum weight. 88 DC-8-50s were manufactured.

  • DC-8 Jet Trader Douglas approved development of specialised freighter versions of the DC-8 in May 1961, based on the Series 50. An original plan to fit a fixed bulkhead seperating the forward two-thirds of the cabin for freight, leaving the rear cabin for 54 passenger seats was soon replaced by a more practical one to use a moveable bulkhead and allow anywhere between 25 and 114 seats with the remainder set aside for cargo. A large cargo door was fitted into the forward fuselage, the cabin floor reinforced, and the rear pressure bulkhead moved by nearly 2m to make more space. Airlines were offered the option of a windowless cabin, though only one, United, took this up with an order for 15 in 1964. The DC-8F-54 had a maximum takeoff weight of 143 tonnes, the DC-8F-55 147 tonnes. Both used 80.6kN JT3D-3B powerplants.

Despite the large number of DC-8 models available, all used the same basic airframe, differing only in engines, weights and details. In contrast, Boeing's rival 707 range offered several fuselage lengths, the original 44m 707-120, a 41m version that sacrificed space to gain longer range, and the stretched 707-320, which at 46.5m overall had 3m more cabin space than the DC-8. Douglas steadfastly refused to create stretched or shortened versions of the DC-8, and gradually lost market share to Boeing. After an excellent start, 1962 DC-8 sales dropped to just 26, followed by 21 in 1963 and 14 in '64, and most of these were for the Jet Trader, not the more prestigous passenger versions.

Super Sixties

In April 1965, Douglas finally announced belated fuselage stretches for the DC-8; with not just one but three new models, known as the Super Sixties. The DC-8 programme had been in danger of closing with less than 300 aircraft sold, but the Super Sixties brought fresh life to it. By the time production ceased in 1972, 262 of the stretched DC-8s had been made. With the ability to seat just over 250 passengers, the DC-8 was easily the largest airliner available, and remained so until the Boeing 747 arived in 1970.

  • DC-8 Series 61 was designed for high capacity and medium range. It had the same weights and engines as the -53, and sacrificed range to gain capacity. Having decided to stretch the DC-8, Douglas did not do the job by halves: they inserted a 6m plug in the forward fuselage and a 5m plug aft, taking overall length to 57m and giving the aircraft a very long, lean look that was (and still is) unique. Bending forces required strengthening of the structure, but the basic DC-8 design already had sufficent ground clearance to permit the one-third increase in cabin size without requiring longer landing gear. It was certificated in September 1966, typically carried 210 passengers or 269 in high-density configuration, and 88 were sold.

  • The long-range DC-8 Series 62 followed in April 1967. It had a much more modest stretch of just 2m (with 1m plugs fore and aft), the same JT8D-3B engines as the -53 and the -61, and a number of modifications to provide greater range. One metre wingtip extensions reduced drag and added fuel capacity, and Douglas redesigned the the engine pods, extending the pylons and substituting new shorter, neater nacelles, all in the cause of drag reduction. Slightly heavier than the -53 or the -61 at 151 tonnes, and able to seat 159 passengers, the -62 had a range with full payload of about 5200nm, or about the same as the -53 but with 40 extra passengers. 67 were built.

  • The DC-8 Series 63 was the final new build variant and entered service in June 1968. It combined the aerodynamic refinements and increased fuel capacity of the -62 with the very long fuselage of the -61, and added 85kN JT3D-7 turbofans, giving a maximum take off weight of almost 159 tonnes and a range with full payload of 4110nm. 107 were built, a little over half of them convertibles or dedicated freighters.

Despite fair sales for the DC-8 and excellent results from the twin-jet DC-9 programme, in 1967 Douglas were forced to merge with McDonnell[?] to become McDonnell Douglas (MDC).

Super Seventies

All the earlier jetliners were very noisy by modern standards, and the DC-8 more so than any. Increasing traffic densities and changing public attitudes led to complaints about aircraft noise and moves to introduce restrictions. As early as 1966, the New York Port Authority expressed concern about the noise to be expected from the then still unbuilt DC-8-61, and operators had to agree to operate it from New York at lower weights to reduce noise. By the early 1970s, legislation for aircraft noise standards was being introduced in many countries, and the 60 Series DC-8s were particularly at risk of being banned from major airports.

In the early 1970s, several airlines approached McDonnell Douglas for noise reduction modifications to the DC-8, but nothing was done. Third-parties had developed aftermarket hushkits but there was no real move to keep the DC-8 in service until 1975 when General Electric began discussions with major airlines with a view to fitting the new and vastly quieter Franco-American CFM-56[?] to both DC-8s and 707s. MDC remained reluctant but eventually came on board in the late 1970s and helped develop the 70 Series DC-8s.

  • The DC-8-72 and the DC-8-73 were straightforward conversions of the -62 and -63, replacing the JT3D engines with 98.5kN CFM56-2 high bypass turbofans in new housings built by Grumman. The DC-8-71 achieved the same end but required considerably more modification as the -61 did not already have the improved wings and relocated engines of the -62 and -63. Maximum takeoff weights remained the same but there was a slight reduction in payload because of the heavier engines. All three models were certificated in 1982 and in total 110 Sixty Series DC-8s were converted by the time the programme ended in 1986.

The Super Seventies were a great success: roughly 70% quieter than the 60 Series and, at the time of their introduction, the world's quietest four-engined airliner. As well as being quieter and more powerful, the CFM56 was roughly 20% more fuel efficient than the JT3D, which reduced operating costs and extended range.

Over its production life, the DC-8 was often seen, unfairly, as little more than a copy of the 707, and it was outsold by roughly two to one. But in the longer term the DC-8 proved its value. By 2002, of the 1032 707s and 720s[?] manufactured for commercial use, just 80 remained in service. Of the 554 DC-8s made, almost 200 were still in commercial service in 2002, including about 25 50 Series, 82 of the stretched 60 Series, and 96 out of the 110 re-engined 70 Series.



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