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102-789: The Douglas DC-8 (sometimes McDonnell Douglas DC-8 ) is an early long-range narrow-body jetliner designed and produced by the American Douglas Aircraft Company . Work began in 1952 towards the United States Air Force 's (USAF) requirement for a jet-powered aerial refueling tanker . After losing the USAF's tanker competition to the rival Boeing KC-135 Stratotanker in May 1954, Douglas announced in June 1955 its derived jetliner project marketed to civil operators. In October 1955, Pan Am made

204-416: A crack growth equation by summing up the width of each increment of crack growth for each loading cycle. Safety or scatter factors are applied to the calculated life to account for any uncertainty and variability associated with fatigue. The rate of growth used in crack growth predictions is typically measured by applying thousands of constant amplitude cycles to a coupon and measuring the rate of growth from

306-408: A high bypass turbofan , which produced 22,000 lbf (98.5 kN) of thrust. The conversions also includes new nacelles and pylons built by Grumman Aerospace . Maximum takeoff weights remained the same, but there was a slight reduction in payload because of the heavier engines. Modifications to create the -71 was more involved because the -61 did not have the improved wings and relocated engines of

408-614: A swept wing enabled a higher cruising speed and better range. First presented in 1950 as the Model 473-60C , Boeing failed to generate any interest from airlines, yet remained confident that the project was worthwhile and pressed ahead with a prototype, the Boeing 367-80 ("Dash-80"). After spending $ 16 million of its own money to build it, the Dash-80 rolled out on May 15, 1954. During mid-1952, Douglas opted to covertly begin work on definition studies for

510-495: A commercial aircraft manufacturer, having received almost 300 orders for its piston-engine DC-6 and its successor, the DC-7, which had yet to fly. The Comet disasters, and the airlines' subsequent lack of interest in jets, seemed to validate the company's decision to remain with propeller -driven aircraft, but its inaction enabled rival manufacturers to take the lead instead. As early as 1949, rival company Boeing had started design work on

612-469: A coupon or a full-scale test article to determine: These tests may form part of the certification process such as for airworthiness certification . Composite materials can offer excellent resistance to fatigue loading. In general, composites exhibit good fracture toughness and, unlike metals, increase fracture toughness with increasing strength. The critical damage size in composites is also greater than that for metals. The primary mode of damage in

714-467: A failure condition. It plots stress amplitude against mean stress with the fatigue limit and the ultimate tensile strength of the material as the two extremes. Alternative failure criteria include Soderberg and Gerber. As coupons sampled from a homogeneous frame will display a variation in their number of cycles to failure, the S-N curve should more properly be a Stress-Cycle-Probability (S-N-P) curve to capture

816-481: A jet-powered transport aircraft. The company's design team examined various arrangements, including some that closely resembled the Comet. By mid-1953, the team had settled on a form similar to the final DC-8; an 80-seat, low-wing aircraft powered by four Pratt & Whitney JT3C turbojet engines, 30° wing sweep, and an internal cabin diameter of 11 feet (3.35 m) to allow five-abreast seating. The use of podded engines

918-458: A large number of DC-8 early models being available, all used the same basic airframe, differing only in engines, weights and details; in contrast, the rival Boeing 707 range offered several fuselage lengths and two wingspans: the original 144-foot (44 m) 707-120, a 135-foot (41 m) version that sacrificed space to gain longer range, and the stretched 707-320, which at 153 feet (47 m) overall had 10 feet (3.0 m) more cabin space than

1020-424: A larger wing for a MTOW up to 350,000 lb (159 t). The DC-8-63 had the long fuselage and the enlarged wing, freighters MTOW reached 355,000 lb (161 t). The DC-8 was produced until 1972 with 556 aircraft built; it was superseded by larger wide-body airliners including Douglas' DC-10 trijet. Noise concerns stimulated demand for a quieter variant; from 1975, Douglas and General Electric offered

1122-480: A metal structure is cracking. For metal, cracks propagate in a relatively well-defined manner with respect to the applied stress, and the critical crack size and rate of crack propagation can be related to specimen data through analytical fracture mechanics. However, with composite structures, there is no single damage mode which dominates. Matrix cracking, delamination, debonding, voids, fiber fracture, and composite cracking can all occur separately and in combination, and

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1224-430: A number of methods to determine the fatigue life of a material: Whether using stress/strain-life approach or using crack growth approach, complex or variable amplitude loading is reduced to a series of fatigue equivalent simple cyclic loadings using a technique such as the rainflow-counting algorithm . A mechanical part is often exposed to a complex, often random , sequence of loads, large and small. In order to assess

1326-672: A pure jet airliner. Boeing's military arm had experience with large long-range jets, such as the B-47 Stratojet and the B-52 Stratofortress strategic bombers. While producing and supporting these bombers for the United States Air Force (USAF), Boeing had developed a close relationship with the USAF's Strategic Air Command (SAC). The company also supplied the SAC's refueling aircraft, the piston-engined KC-97 Stratofreighters , but these proved to be too slow and low flying to easily work with

1428-419: A recontoured wing leading edge was later developed to extend the chord 4% and reduce drag at high Mach numbers. On August 21, 1961, a DC-8 broke the sound barrier at Mach 1.012 (660 mph/1,062 km/h) while in a controlled dive through 41,000 feet (12,497 m) and maintained that speed for 16 seconds. The flight was to collect data on a new leading edge design for the wing, and, while doing so,

1530-401: A result of aging, increasing operating costs and strict noise and emissions regulations, the number of active DC-8s continues to decline, with the youngest airframes passed a half-century of age as of 2024. For domestic use, powered by 13,500 lb (60.5 kN) Pratt & Whitney JT3C -6 turbojets with water injection. First Series 10 DC-8 flew on 30 May 1958. The initial DC-8-11 model had

1632-464: A result of plasticity at the crack tip. When the stress intensity exceeds a critical value known as the fracture toughness, unsustainable fast fracture will occur, usually by a process of microvoid coalescence . Prior to final fracture, the fracture surface may contain a mixture of areas of fatigue and fast fracture. The following effects change the rate of growth: The American Society for Testing and Materials defines fatigue life , N f , as

1734-556: A rule that had first been proposed by Arvid Palmgren in 1924. The rule, variously called Miner's rule or the Palmgren–Miner linear damage hypothesis , states that where there are k different stress magnitudes in a spectrum, S i (1 ≤ i ≤ k ), each contributing n i ( S i ) cycles, then if N i ( S i ) is the number of cycles to failure of a constant stress reversal S i (determined by uni-axial fatigue tests), failure occurs when: Usually, for design purposes, C

1836-577: A small fraction of the applied stress . And the fibers in the wake of the crack experience fatigue damage. In many cases, the damage rate is accelerated by deleterious interactions with the environment like oxidation or corrosion of fibers. Following the King Louis-Philippe I 's celebrations at the Palace of Versailles , a train returning to Paris crashed in May 1842 at Meudon after the leading locomotive broke an axle. The carriages behind piled into

1938-485: A success, but the Comet was grounded in 1954 after two fatal accidents which were subsequently attributed to rapid metal fatigue failure of the pressure cabin. Various aircraft manufacturers benefited from the findings and experiences gained from the investigation into Comet losses; specifically, Douglas paid significant attention to detail in the design of the DC-8's pressurized cabin. By 1952, Douglas had continued its success as

2040-481: A water tank. After the equivalent of 3,000 flights, investigators at the Royal Aircraft Establishment (RAE) were able to conclude that the crash had been due to failure of the pressure cabin at the forward Automatic Direction Finder window in the roof. This 'window' was in fact one of two apertures for the aerials of an electronic navigation system in which opaque fibreglass panels took the place of

2142-529: A weight increase to 276,000 pounds (125,190 kg). 33 DC-8-20s were built plus 16 converted DC-8-10s. This model was originally named "DC-8B" but was renamed when the Series 30 was introduced. The first Series 20 DC-8 flew on 29 November 1958 and received FAA certification on 19 January 1960. 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

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2244-401: Is a parameter that scales with tensile strength obtained by fitting experimental data, N f {\displaystyle N_{\text{f}}} is the number of cycles to failure and b {\displaystyle b} is the slope of the log-log curve again determined by curve fitting. In 1954, Coffin and Manson proposed that the fatigue life of a component was related to

2346-407: Is assumed to be 1. This can be thought of as assessing what proportion of life is consumed by a linear combination of stress reversals at varying magnitudes. Although Miner's rule may be a useful approximation in many circumstances, it has several major limitations: Materials fatigue performance is commonly characterized by an S-N curve , also known as a Wöhler curve . This is often plotted with

2448-1460: Is insufficient for fully laden operations and operates at reduced capacity like the Airbus A318 , while the Airbus A321LR could replace the less fuel efficient Boeing 757s used since their production ended in 2004. Boeing will face competition and pricing pressure from the Embraer E-Jet E2 family , Airbus A220 (formerly Bombardier CSeries) and Comac C919 . Between 2016 and 2035, FlightGlobal expects 26,860 single-aisles to be delivered for almost $ 1380 billion, 45% Airbus A320 family ceo and neo and 43% Boeing 737 NG and max. By June 2018, there were 10,572 Airbus A320neo and Boeing 737 MAX orders: 6,068 Airbuses (57%, 2,295 with CFMs, 1,623 with PWs and 2,150 with not yet decided engines) and 4,504 Boeings (43%); 3,446 in Asia-Pacific (33%), 2,349 in Europe (22%), 1,926 in North America (18%), 912 in Latin America (9%), 654 in Middle East (6%), 72 in Africa (1%) and 1,213 not yet bounded (11%). Many airlines have shown interest in

2550-583: Is not a microstructural change within the material, but rather a propagation of dislocations within the material. Instead of a smooth interface, the intrusions and extrusions will cause the surface of the material to resemble the edge of a deck of cards, where not all cards are perfectly aligned. Slip-induced intrusions and extrusions create extremely fine surface structures on the material. With surface structure size inversely related to stress concentration factors, PSB-induced surface slip can cause fractures to initiate. These steps can also be bypassed entirely if

2652-400: Is the fatigue ductility coefficient, c {\displaystyle c} is the fatigue ductility exponent, and N f {\displaystyle N_{f}} is the number of cycles to failure ( 2 N f {\displaystyle 2N_{f}} being the number of reversals to failure). An estimate of the fatigue life of a component can be made using

2754-414: Is to replace the DC-8 with a more capable and fuel-efficient Boeing 777-200ER . The DC-8 was donated to Idaho State University and is preserved at Pocatello Regional Airport . As of October 2015, the DC-8 had been involved in 146 incidents, including 84 hull-loss accidents , with 2,255 fatalities. The DC-8 has also been involved in 46 hijackings with 2 fatalities. The deadliest incident involving

2856-532: Is used. Each coupon or component test generates a point on the plot though in some cases there is a runout where the time to failure exceeds that available for the test (see censoring ). Analysis of fatigue data requires techniques from statistics , especially survival analysis and linear regression . The progression of the S-N curve can be influenced by many factors such as stress ratio (mean stress), loading frequency, temperature , corrosion , residual stresses, and

2958-411: The Airbus A321LR or its A321XLR derivative, and other extended-range models, for thin transatlantic and Asia-Pacific routes. Metal fatigue In materials science , fatigue is the initiation and propagation of cracks in a material due to cyclic loading. Once a fatigue crack has initiated, it grows a small amount with each loading cycle, typically producing striations on some parts of

3060-663: The Boeing 737 Classic , McDonnell-Douglas MD-80 and Airbus A320 were primarily employed in short to medium-haul markets requiring neither the range nor the passenger-carrying capacity of that period's wide-body aircraft. The re-engined Boeing 737 MAX and Airbus A320neo jets offer 500 miles more range, allowing them to operate the 3,000 miles transatlantic flights between the eastern U.S. and Western Europe, previously dominated by wide-body aircraft. Norwegian Air Shuttle , JetBlue and TAP Portugal will open up direct routes bypassing airline hubs for lower fares between cheaper, smaller airports. The Boeing 737NG 3,300-mile range

3162-471: The Port Authority of New York and New Jersey 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

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3264-469: The threshold or after the application of an overload , and the increased rate of crack growth associated with short cracks or after the application of an underload . If the loads are above a certain threshold, microscopic cracks will begin to initiate at stress concentrations such as holes, persistent slip bands (PSBs), composite interfaces or grain boundaries in metals. The stress values that cause fatigue damage are typically much less than

3366-399: The yield strength of the material. Historically, fatigue has been separated into regions of high cycle fatigue that require more than 10 cycles to failure where stress is low and primarily elastic and low cycle fatigue where there is significant plasticity. Experiments have shown that low cycle fatigue is also crack growth. Fatigue failures, both for high and low cycles, all follow

3468-461: The -55 were certified in 1961. The DC-8-51, DC-8-52 and DC-8-53 all had 17,000 lb (76.1 kN) JT3D-1 or 18,000 lb (80.6 kN) JT3D-3B engines, varying mainly in their weights: 276,000 pounds (125,200 kg), 300,000 pounds (136,100 kg) and 315,000 pounds (142,900 kg) respectively. The DC-8-55 arrived in June 1964, retaining the JT3D-3B engines but with strengthened structure from

3570-491: The -62 and -63. All three models were certified in 1982 and a total of 110 60-series Super DC-8s were converted by the time the program ended in 1988. DC-8 series 70 conversions were overseen by Cammacorp with CFMI, McDonnell Douglas, and Grumman Aerospace as partners. Cammacorp was disbanded after the last aircraft was converted. As of January 2024, two DC-8s are in commercial service with Congolese cargo airline Trans Air Cargo . These are DC-8-62s (9S-AJG and 9S-AJO). In

3672-400: The 556 DC-8s made, around 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. Most of the surviving DC-8s are now used as freighters. In May 2009, 97 DC-8s were in service following UPS's decision to retire its remaining fleet of 44. In January 2013, an estimated 36 DC-8s were in use worldwide. As

3774-466: The 707 order book, while Douglas sold 22 DC-8s to Delta, Swissair, TAI, Trans Canada , and UAT. By the start of 1958, Douglas had sold 133 DC-8s compared to Boeing's 150 707s. Donald Douglas proposed to build and test the DC-8 at Santa Monica Airport , which had been the birthplace of the DC-3 and home to a Douglas plant that employed 44,000 workers during World War II. To accommodate the new jet, Douglas asked

3876-552: The CFM56 was up to 23% more fuel-efficient than the JT3D, which reduced operating costs and extended the range. The largest single customer for the Series 70 was United, converting 29 of its Series 61 airliners at a reported cost of $ 400 million. By 2002, of the 1,032 Boeing 707s and 720s manufactured for commercial use, just 80 remained in service – though many of those 707s were converted for USAF use, either in service or for spare parts. Of

3978-704: The Comet remained grounded, the French 90-passenger twin jet Sud Aviation Caravelle prototype had just flown for the first time, and the Boeing 707 was not expected to be available until late 1958. The major airlines were reluctant to commit themselves to the huge financial and technical challenges of jet aircraft; however, none could afford not to buy jets if their competitors did. There the matter rested until October 1955, when Pan American World Airways placed simultaneous orders with Boeing for 20 707s and Douglas for 25 DC-8s. To buy one expensive and untried jet-powered aircraft type

4080-515: The DC-8 became the first civilian jet – and the first jet airliner – to make a supersonic flight. The aircraft was DC-8-43 registered as CF-CPG , later delivered to Canadian Pacific Air Lines . The aircraft, crewed by Captain William Magruder, First Officer Paul Patten, Flight Engineer Joseph Tomich and Flight Test Engineer Richard Edwards, took off from Edwards Air Force Base in California and

4182-407: The DC-8 was Nigeria Airways Flight 2120 which crashed on July 11, 1991, with 261 fatalities. The following museums have DC-8s on display or in storage: Related development Aircraft of comparable role, configuration, and era Related lists Narrow-body aircraft Historically, beginning in the late 1960s and continuing through the 1990s, twin engine narrow-body aircraft, such as

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4284-522: The DC-8, a feat that was eased by its fuselage keeping the same dimensions across its length. In April 1965, the company announced belated fuselage stretches for the DC-8 with three new models known as the Super Sixties . The DC-8 program had been in danger of closing with fewer than 300 aircraft sold, but the Super Sixties brought fresh life to it. By the time production of the DC-8 ceased in 1972, 262 of

4386-401: The DC-8. Douglas' refusal to offer different fuselage sizes made it less adaptable and compelled airlines such as Delta and United to look elsewhere for short to medium range types. Delta ordered Convair 880s while United chose the newly developed short-fuselage 707-020. United prevailed on Boeing to rename the new variant the Boeing 720 in case the public thought they were dissatisfied with

4488-500: The DC-8. Pan Am never reordered the DC-8 and Douglas gradually lost market share to Boeing. In 1962, DC-8 sales dropped to just 26 aircraft that year, followed by 21 in 1963 and 14 in 1964; many of these later deliveries were of the Jet Trader model rather than the more-prestigious passenger versions. In 1967, Douglas merged with McDonnell Aircraft , becoming McDonnell Douglas . During the early 1960s, Douglas began considering stretching

4590-484: The Series 30, and by Rolls-Royce Conway turbofans for the Series 40. The Pratt & Whitney JT3D powered the later DC-8-50 and Super 60 (DC-8-61, -62, and -63) as well as freighter versions, and reached a MTOW of 325,000 lb (147 t). A stretched DC-8 variant was not initially considered, leading some airlines to order the competing Boeing 707 instead. The improved Series 60 was announced in April 1965. The DC-8-61

4692-472: The Series 70 retrofit, powered by the quieter and more fuel-efficient CFM56 turbofan engine. It largely exited passenger service during the 1980s and 1990s, but some re-engined DC-8s remain in use as freighters. At the end of World War II, Douglas was a dominant North American aircraft producer in the commercial aviation market, only being rivaled by Boeing , releasing the innovative all-metal Model 247 airliner in 1933, and produced prodigious quantities of

4794-663: The Super Sixties had been completed, almost half of all models produced. With the ability to seat 269 passengers, the DC-8 Series 61 and 63 had the largest passenger-carrying capacity available. That remained so until the Boeing 747 arrived in 1970. The DC-8-62 featured a shorter fuselage when compared with the Series 61 and 63, but was capable of nonstop long-range operations. All of the earlier jetliners were relatively noisy by modern standards. Increasing traffic densities and changing public attitudes led to complaints about aircraft noise and moves to introduce restrictions. As early as 1966

4896-480: The U.S, the DC-8 has been retired from commercial service entirely; only one example maintains active registration (with one flying). Samaritan's Purse (a faith-based humanitarian relief organization) has operated a DC-8-72 Combi (acquired from Air Transport International ) since 2015. In 2024, NASA retired N817NA, a DC-8-72 flying laboratory that has supported research in meteorology, oceanography, geography, and various other scientific disciplines since 1986. NASA

4998-581: The advantage that they can predict the intermediate size of cracks. This information can be used to schedule inspections on a structure to ensure safety whereas strain/life methods only give a life until failure. Dependable design against fatigue-failure requires thorough education and supervised experience in structural engineering , mechanical engineering , or materials science . There are at least five principal approaches to life assurance for mechanical parts that display increasing degrees of sophistication: Fatigue testing can be used for components such as

5100-419: The air. Just four months after issuing the tanker requirement, the USAF ordered the first 29 KC-135 Stratotankers from Boeing. Donald Douglas was reportedly shocked by the rapidity of the decision which, he claimed, had been made before the competing companies even had time to complete their bids. He protested to Washington, but without success. Having already started on the DC-8 project, Douglas decided that

5202-436: The applied load. This causes the amplitude of the applied stress to increase given the new restraints on strain. These newly formed cell structures will eventually break down with the formation of persistent slip bands (PSBs). Slip in the material is localized at these PSBs, and the exaggerated slip can now serve as a stress concentrator for a crack to form. Nucleation and growth of a crack to a detectable size accounts for most of

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5304-402: The best option was to press on than abandon the project. Following consultations with the airlines, several design changes were made, such as the fuselage being widened by 15 inches (38 cm) to permit six-abreast seating, which in turn led to larger wings and tail surfaces being adopted along with a lengthening of the fuselage. The existence of the DC-8 was formally announced on 7 June 1955; at

5406-499: The change in compliance of the coupon or by measuring the growth of the crack on the surface of the coupon. Standard methods for measuring the rate of growth have been developed by ASTM International. Crack growth equations such as the Paris–Erdoğan equation are used to predict the life of a component. They can be used to predict the growth of a crack from 10 um to failure. For normal manufacturing finishes this may cover most of

5508-479: The city of Santa Monica, California to lengthen the airport's 5,000-foot (1,500-meter) runway. Following complaints by neighboring residents, the city refused, so Douglas moved its airliner production line to Long Beach Airport . In September 1956, production of the first prototype commenced. The first DC-8 N8008D was rolled out of the new Long Beach factory on 9 April 1958 and flew for the first time, in Series 10 form, on 30 May for two hours and seven minutes with

5610-413: The cracking process. It is for this reason that cyclic fatigue failures seem to occur so suddenly where the bulk of the changes in the material are not visible without destructive testing. Even in normally ductile materials, fatigue failures will resemble sudden brittle failures. PSB-induced slip planes result in intrusions and extrusions along the surface of a material, often occurring in pairs. This slip

5712-429: The cracks form at a pre-existing stress concentrator such as from an inclusion in the material or from a geometric stress concentrator caused by a sharp internal corner or fillet. Most of the fatigue life is generally consumed in the crack growth phase. The rate of growth is primarily driven by the range of cyclic loading although additional factors such as mean stress, environment, overloads and underloads can also affect

5814-457: The cracks reach a critical size they propagate quickly during stage II crack growth in a direction perpendicular to the applied force. These cracks can eventually lead to the ultimate failure of the material, often in a brittle catastrophic fashion. The formation of initial cracks preceding fatigue failure is a separate process consisting of four discrete steps in metallic samples. The material will develop cell structures and harden in response to

5916-466: The crew being led by A.G. Heimerdinger. Later that year, an enlarged version of the Comet finally returned to service, but had arrived too late to secure a substantial portion of the market: de Havilland secured just 25 orders. In August, Boeing had begun delivering 707s to Pan Am. Douglas made a massive effort to close the gap with Boeing, using no fewer than ten aircraft for flight testing to achieve Federal Aviation Administration (FAA) certification for

6018-435: The cyclic stress ( S ) against the cycles to failure ( N ) on a logarithmic scale . S-N curves are derived from tests on samples of the material to be characterized (often called coupons or specimens) where a regular sinusoidal stress is applied by a testing machine which also counts the number of cycles to failure. This process is sometimes known as coupon testing . For greater accuracy but lower generality component testing

6120-403: The early 1970s, several airlines approached McDonnell Douglas with requests for noise reduction modifications to their DC-8s. While third parties had developed aftermarket hushkits , there was initially no meaningful action taken by Douglas to fulfil these requests and effectively enable the DC-8 to remain in service. Finally, in 1975, General Electric began discussions with major airlines to fit

6222-401: The fatigue life of a component where growth can start from the first cycle. The conditions at the crack tip of a component are usually related to the conditions of test coupon using a characterising parameter such as the stress intensity, J-integral or crack tip opening displacement . All these techniques aim to match the crack tip conditions on the component to that of test coupons which give

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6324-522: The first of the many DC-8 variants in August 1959. Several modifications proved to be necessary: the original air brakes on the lower rear fuselage were found to be ineffective and were deleted as engine thrust reversers had become available; unique leading-edge slots were added to improve low-speed lift; the prototype was 25 kn (46 km/h) short of its promised cruising speed and a new, slightly larger wingtip had to be developed to reduce drag . Also,

6426-485: The first order along with the competing Boeing 707 , and many other airlines soon followed. The first DC-8 was rolled out in Long Beach Airport on April 9, 1958, and flew for the first time on May 30. Following Federal Aviation Administration (FAA) certification in August 1959, the DC-8 entered service with Delta Air Lines on September 18. Permitting six-abreast seating, the four-engined , low-wing jet aircraft

6528-399: The fracture surface. The crack will continue to grow until it reaches a critical size, which occurs when the stress intensity factor of the crack exceeds the fracture toughness of the material, producing rapid propagation and typically complete fracture of the structure. Fatigue has traditionally been associated with the failure of metal components which led to the term metal fatigue . In

6630-442: The freighter versions and 325,000-pound (147,420 kg) maximum weight. 142 DC-8-50s were built plus the 20 converted from Series 10/30/40. The Series 50 first flew on 20 December 1960 and received FAA certification on 1 May 1961. The DC-8-71, DC-8-72, and DC-8-73 were straightforward conversions of the -61, -62 and -63 primarily involving the replacement of the JT3D engines with the more fuel-efficient CFM International CFM56 -2,

6732-409: The hole created by punch riveting caused manufacturing defect cracks which may have caused the start of fatigue cracks around the rivet. The Comet's pressure cabin had been designed to a safety factor comfortably in excess of that required by British Civil Airworthiness Requirements (2.5 times the cabin proof test pressure as opposed to the requirement of 1.33 times and an ultimate load of 2.0 times

6834-426: The idea that the metal had somehow "crystallized". The notion was based on the crystalline appearance of the fast fracture region of the crack surface, but ignored the fact that the metal was already highly crystalline. Two de Havilland Comet passenger jets broke up in mid-air and crashed within a few months of each other in 1954. As a result, systematic tests were conducted on a fuselage immersed and pressurised in

6936-473: The jet airliner project, it 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 Aircraft , Lockheed Corporation , and Martin Marietta . At the time, Boeing was only two months away from having its prototype in

7038-408: The new and vastly-quieter Franco-American CFM56 engine to both DC-8s and 707s. MDC remained reluctant but eventually came on board in the late 1970s and helped develop the Series 70. The Super Seventies proved to be a great success, being 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,

7140-454: The new jet bombers. The B-52, in particular, had to descend from its cruising altitude and then slow almost to its stall speed to refuel from the KC-97. Believing that a requirement for a jet-powered tanker was a certainty, Boeing started work on a new jet aircraft for this role that could be adapted into an airliner. As an airliner, it would have similar seating capacity to the Comet, but the use of

7242-444: The nineteenth century, the sudden failing of metal railway axles was thought to be caused by the metal crystallising because of the brittle appearance of the fracture surface, but this has since been disproved. Most materials, such as composites, plastics and ceramics, seem to experience some sort of fatigue-related failure. To aid in predicting the fatigue life of a component, fatigue tests are carried out using coupons to measure

7344-499: The number of stress cycles of a specified character that a specimen sustains before failure of a specified nature occurs. For some materials, notably steel and titanium , there is a theoretical value for stress amplitude below which the material will not fail for any number of cycles, called a fatigue limit or endurance limit . However, in practice, several bodies of work done at greater numbers of cycles suggest that fatigue limits do not exist for any metals. Engineers have used

7446-528: The original wingtips used on the prototype, and all remaining DC-8 Series 10 aircraft were upgraded to DC-8-12 standard. The DC-8-12 featured the new low-drag wingtips and leading-edge slots , 80 inches long between the engines on each wing and 34 inches long inboard of the inner engines. These unique devices were covered by doors on the upper and lower wing surfaces that opened for low-speed flight and closed for cruise. The maximum weight increased from 265,000 to 273,000 pounds (120,200 to 123,800 kg). This model

7548-505: The plastic strain amplitude Δ ε p / 2 {\displaystyle \Delta \varepsilon _{\text{p}}/2} and is given by Basquin's equation for the elastic strain amplitude is where E {\displaystyle E} is Young's modulus . The relation for high cycle fatigue can be expressed using the elastic strain amplitude where σ f ′ {\displaystyle \sigma _{\text{f}}^{\prime }}

7650-461: The plastic strain amplitude using Combining the elastic and plastic portions gives the total strain amplitude accounting for both low and high cycle fatigue where σ f ′ {\displaystyle \sigma _{f}'} is the fatigue strength coefficient, b {\displaystyle b} is the fatigue strength exponent, ε f ′ {\displaystyle \varepsilon _{f}'}

7752-404: The predominance of one or more is highly dependent on the laminate orientations and loading conditions. In addition, the unique joints and attachments used for composite structures often introduce modes of failure different from those typified by the laminate itself. The composite damage propagates in a less regular manner and damage modes can change. Experience with composites indicates that

7854-480: The presence of notches. A constant fatigue life (CFL) diagram is useful for the study of stress ratio effect. The Goodman line is a method used to estimate the influence of the mean stress on the fatigue strength . A Constant Fatigue Life (CFL) diagram is useful for stress ratio effect on S-N curve. Also, in the presence of a steady stress superimposed on the cyclic loading, the Goodman relation can be used to estimate

7956-453: The presence of stress concentrations, the total strain can be used instead of stress as a similitude parameter. This is known as the strain-life method. The total strain amplitude Δ ε / 2 {\displaystyle \Delta \varepsilon /2} is the sum of the elastic strain amplitude Δ ε e / 2 {\displaystyle \Delta \varepsilon _{\text{e}}/2} and

8058-533: The probability of failure after a given number of cycles of a certain stress. With body-centered cubic materials (bcc), the Wöhler curve often becomes a horizontal line with decreasing stress amplitude, i.e. there is a fatigue strength that can be assigned to these materials. With face-centered cubic metals (fcc), the Wöhler curve generally drops continuously, so that only a fatigue limit can be assigned to these materials. When strains are no longer elastic, such as in

8160-403: The rate of crack growth by applying constant amplitude cyclic loading and averaging the measured growth of a crack over thousands of cycles. However, there are also a number of special cases that need to be considered where the rate of crack growth is significantly different compared to that obtained from constant amplitude testing, such as the reduced rate of growth that occurs for small loads near

8262-530: The rate of crack growth. Additional models may be necessary to include retardation and acceleration effects associated with overloads or underloads in the loading sequence. In addition, small crack growth data may be needed to match the increased rate of growth seen with small cracks. Typically, a cycle counting technique such as rainflow-cycle counting is used to extract the cycles from a complex sequence. This technique, along with others, has been shown to work with crack growth methods. Crack growth methods have

8364-402: The rate of damage propagation in does not exhibit the two distinct regions of initiation and propagation like metals. The crack initiation range in metals is propagation, and there is a significant quantitative difference in rate while the difference appears to be less apparent with composites. Fatigue cracks of composites may form in the matrix and propagate slowly since the matrix carries such

8466-439: The rate of growth. Crack growth may stop if the loads are small enough to fall below a critical threshold. Fatigue cracks can grow from material or manufacturing defects from as small as 10 μm. When the rate of growth becomes large enough, fatigue striations can be seen on the fracture surface. Striations mark the position of the crack tip and the width of each striation represents the growth from one loading cycle. Striations are

8568-513: The result of a broken locomotive axle. Rankine's investigation of broken axles in Britain highlighted the importance of stress concentration, and the mechanism of crack growth with repeated loading. His and other papers suggesting a crack growth mechanism through repeated stressing, however, were ignored, and fatigue failures occurred at an ever-increasing rate on the expanding railway system. Other spurious theories seemed to be more acceptable, such as

8670-548: The rugged four-engined B-17 Flying Fortress and sophisticated, pressurized long-range B-29 Superfortress . Douglas produced a succession of piston-engined aircraft ( DC-2 , DC-3 , DC-4 , DC-5 , DC-6 , and DC-7 ) through the 1930s, 1940s, and 1950s. While de Havilland flew the world's first jet airliner, the Comet , in May 1949, Douglas initially refrained from developing a jet airliner. De Havilland's pioneering Comet entered airline service in May 1952. Initially, it appeared to be

8772-538: The safe life of such a part using the fatigue damage or stress/strain-life methods the following series of steps is usually performed: Since S-N curves are typically generated for uniaxial loading, some equivalence rule is needed whenever the loading is multiaxial. For simple, proportional loading histories (lateral load in a constant ratio with the axial), Sines rule may be applied. For more complex situations, such as non-proportional loading, critical plane analysis must be applied. In 1945, Milton A. Miner popularised

8874-428: The same basic steps: crack initiation, crack growth stages I and II, and finally ultimate failure. To begin the process, cracks must nucleate within a material. This process can occur either at stress risers in metallic samples or at areas with a high void density in polymer samples. These cracks propagate slowly at first during stage I crack growth along crystallographic planes, where shear stresses are highest. Once

8976-459: The time of the announcement, the development costs had been forecast to be roughly $ 450 million. Four versions were offered to begin with, all with the same 150-foot-6-inch (45.87 m) long airframe with a 141-foot-1-inch (43.00 m) wingspan, but varying in engines and fuel capacity, and with maximum weights of about 240,000–260,000 lb (109–118 metric tons). Douglas steadfastly refused to offer different fuselage sizes. The maiden flight

9078-401: The window 'glass'. The failure was a result of metal fatigue caused by the repeated pressurisation and de-pressurisation of the aircraft cabin. Also, the supports around the windows were riveted, not bonded, as the original specifications for the aircraft had called for. The problem was exacerbated by the punch rivet construction technique employed. Unlike drill riveting, the imperfect nature of

9180-539: The wrecked engines and caught fire. At least 55 passengers were killed trapped in the locked carriages, including the explorer Jules Dumont d'Urville . This accident is known in France as the "Catastrophe ferroviaire de Meudon" . The accident was witnessed by the British locomotive engineer Joseph Locke and widely reported in Britain. It was discussed extensively by engineers, who sought an explanation. The derailment had been

9282-474: Was accompanied to altitude by a F-104 Starfighter supersonic chase aircraft flown by Chuck Yeager . On September 18, 1959, the DC-8 entered service with Delta Air Lines and United Airlines. According to the Delta Air Lines website, the air carrier was the first to operate the DC-8 in scheduled passenger service. By March 1960, Douglas had reached its planned production rate of eight DC-8s per month. Despite

9384-458: Was brave: to buy both was, at the time, unheard of. In the closing months of 1955, other airlines rushed to follow suit: Air France , American Airlines, Braniff International Airways , Continental Airlines , and Sabena ordered 707s; United Airlines , National Airlines , KLM , Eastern Air Lines , Japan Air Lines , and Scandinavian Airlines System (SAS) chose the DC-8. In 1956, Air India, BOAC , Lufthansa , Qantas , and TWA added over 50 to

9486-778: Was certified in March 1960 with 16,800 lb (75.2 kN) JT4A-9 engines for 300,000-pound (136,080 kg) maximum takeoff weight. The DC-8-32 was similar but allowed 310,000-pound (140,600 kg) weight. The DC-8-33 of November 1960 substituted 17,500 lb (78.4 kN) JT4A-11 turbojets, a modification to the flap linkage to allow a 1.5° setting for more efficient cruise, stronger landing gear, and 315,000-pound (142,880 kg) maximum weight. Many -31 and -32 DC-8s were upgraded to this standard. A total of 57 DC-8-30s were produced (five of which were later upgraded to DC-8-50 standard). The Series 30 DC-8 first flew on 21 February 1959 and received FAA certification on 1 February 1960. The DC-8-40

9588-480: Was due in early 1961. The DC-8-41 and DC-8-42 had weights of 300,000 and 310,000 pounds (140,000 and 140,000 kg) respectively, the 315,000-pound (142,880 kg) DC-8-43 had the 1.5° flap setting of the -33 and introduced a 4% leading-edge wing extension to reduce drag and increase fuel capacity slightly – the new wing improved range by 8%, lifting capacity by 6,600 lb (3 metric tons), and cruising speed by better than 10 knots (19 km/h; 12 mph). It

9690-405: Was essentially the -30 but with 17,500 lb (78.4 kN) Rolls-Royce Conway 509 turbofan engines for better efficiency, less noise and less smoke. The Conway was an improvement over the turbojets that preceded it, but the Series 40 sold poorly because of the traditional reluctance of U.S. airlines to buy a foreign product and because the still-more-advanced Pratt & Whitney JT3D turbofan

9792-442: Was in service and proving popular with passengers and airlines: it was faster, quieter, and more comfortable than piston-engined types. Another British rival was the 90-seat Bristol Britannia , and Douglas's main rival in the large airliner market, Lockheed Corporation , had committed to the short to medium range 80–100-seat turboprop Electra , with a launch order from American Airlines for 35 and other orders flowing in. Meanwhile,

9894-457: Was initially produced in four 151 ft (46 m) long variants. The DC-8-10 was powered by Pratt & Whitney JT3C turbojets, and had a 273,000 lb (124 t) MTOW ; the DC-8-20 had more powerful JT4A turbojets, for a 276,000 lb (125 t) MTOW. The intercontinental models had more fuel capacity, and had an MTOW of up to 315,000 lb (143 t); it was powered by JT4As for

9996-617: Was originally named "DC-8A" until the series 30 was introduced. 30 DC-8-10s were built: 23 for United and six for Delta, plus the prototype. By the mid-sixties, United had converted 16 of its 21 surviving aircraft to DC-8-20 standard and the other five to -50s. Delta converted its six to DC-8-50s. The prototype was itself also converted to a DC-8-50. It received FAA certification on 31 August 1958, entering service with United Airlines and Delta Air Lines on 18 September 1959. Higher-powered 15,800 lb (70.8 kN) thrust Pratt & Whitney JT4A -3 turbojets (without water injection) allowed

10098-403: Was planned for December 1957, with entry into revenue service in 1959. Aware that the program was lagging behind Boeing, Douglas began a major marketing push to promote its new jetliner. Douglas' previous thinking about the airliner market seemed to be coming true; the transition to turbine power looked likely to be to turboprops rather than turbojets. The pioneering 40–60-seat Vickers Viscount

10200-405: Was seen as highly beneficial for maintenance purposes as well as to increase wing volume for accommodating fuel. The fuselage featured a double-bubble cross-section that produced relatively low drag while providing for a relatively spacious passenger cabin along with a large cargo deck that was sufficiently tall as to permit ground crews to stand up within it. While Douglas remained lukewarm about

10302-483: Was stretched by 36 ft (11 m) for 180–220 seats in mixed-class and a MTOW of 325,000 lb (147 t). It first flew on March 14, 1966, was certified on September 2, 1966, and entered service with United Airlines in February 1967. The long-range DC-8-62 followed in April 1967, stretched by 7 ft (2.1 m), could seat up to 189 passengers over 5,200 nautical miles [nmi] (9,600 km; 6,000 mi) with

10404-463: Was used on all later DC-8s. The first DC-8-40 was delivered in 1960; 32 were built (of which three would eventually be converted to DC-8-50s). The Series 40 DC-8 first flew on 23 July 1959 and received FAA certification on 24 March 1960. The definitive short-fuselage DC-8 came with the same engine that powered the vast majority of 707s, the JT3D . Twenty earlier DC-8s were converted to this standard. All but

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