The Douglas DC-4, DC-6, and DC-7 signify the really growth with ΥΔΡΑΥΛΙΚΟΣ ΑΘΗΝΑ the quad-motor piston airliner during the nineteen forties and 1950s.
Ever rising acceptance of air transportation sparked by the minimized vacation occasions it available more than existing rail suggests, coupled with enhancements in security and trustworthiness, sparked the need for larger-potential, for a longer time-vary aircraft through the close from the 1930s, specially to meet the nevertheless-elusive intention of supplying nonstop transcontinental assistance.
Based mostly, hence, upon the muse laid by its all-metal, twin-engine DC-3 monoplane, Douglas Plane Firm commenced layout scientific tests of a larger successor following a consortium of 5 US carriers, inclusive of yank, Japanese, Pan Am, TWA, and United, Each individual contributed $a hundred,000 toward the event of a prototype that could incorporate all latest advancements, nevertheless at the same time provide double the volume of powerplants, relaxation over a tricycle undercarriage, and accommodate a larger quantity of travellers.
The conventionally configured consequence, sporting a low, straight wing, a triple vertical tail, 4 1,four hundred-hp Pratt and Whitney Twin Hornet engines, and seating for nearly 52 in the pressurized cabin, to start with took towards the sky on June 21, 1938. Designated DC-4E, it supplied a a hundred ninety-mph cruising pace along with a two,000-mile vary.
Even though the then-mammoth, 65,000-pound airliner included significant advancement, like a perfectly-appointed galley and cigarette smoking and dressing rooms, it represented excessive of a leap to the period, along with the sponsoring carriers requested both equally modifications and a discount in size.
Equally anticipating decrease passenger desire because of the pending war, Douglas redesigned it using a shorter, unpressurized fuselage accommodating forty two, a shorter span, tapered wing, and a far more standard one vertical fin, causing the definitive DC-four.
Environment War II, inside the party, delivered a considerably better impact on the program than predicted. Indeed, following the notorious, December 7, 1941 Japanese attack on Pearl Harbor, the 24 plane that were intermittently requested by American and United ended up requisitioned via the US Army Air Corps for use as transports and the primary of these, draped in army livery, very first flew on February fourteen of the following calendar year, now selected the C-54 Skymaster. Individuals operated with the Navy have been discovered as R5Ds.
The war, not less than in terms of manufacturing, experienced a good influence on the kind, with one,163 military variations eventually built by 1945, when seventy nine further, purely commercial counterparts have been produced immediately after this time. The main, operated by American Overseas Airways, inaugurated the initial publish-war transatlantic assistance with it from The big apple to Hurn, England, by using Gander, Newfoundland, and Shannon, Ireland, in October.
Numerous ex-military services C-54s were also transformed to commercial normal and the type shaped the backbone of numerous Airways’ article-war fleets.
Run by 4 1,450-hp Pratt and Whitney R-2000-2SD-13G Twin Wasp radial engines, the DC-4 featured a ninety three.5-foot All round size, a 117.6-foot wingspan, in addition to a one,462-sq.-foot spot. Carrying a 14,200-pound highest payload, the plane, that has a seventy three,000-pound gross bodyweight, could cruise at 207 mph and fly 1,a hundred and fifty- to 2,one hundred eighty-mile nonstop sectors, relying upon its payload-to-gas ratio.
Both equally profitable and flexible, it could accommodate nearly 86 one-course passengers, rendering it particularly attractive to constitution or nonscheduled carriers, and will alternatively have primary deck cargo after the set up of an upward-opening doorway.
In an effort to cater to anticipated publish-war need and continue to be aggressive with Lockheed’s own equivalent, quad-motor L-649/-749 Constellation airliners, Douglas stretched the DC-four by eighty one inches, in the method confirming that its configuration would function the standard for extensive-vary transports. Although it retained its wing, planform, span, space, and hydraulically actuated, double-slotted flaps, it re-released the pressurization briefly offered by the first DC-4E and elevated its passenger ability to match it.
Trying to contend with TWA’s Constellations, the two American and United respectively placed launch orders for fifty and 35 of what would come to be the DC-6 in late-1944.
Originally meant for that US Military Air Pressure, the sort, at first designated XC-112, initial flew in prototype form run by four two,one hundred-hp Pratt and Whitney R-2800-34 engines on February 15. 1946, but, with resolution of World War II, they no more desired a armed service version, leaving the 1st industrial variant to get on the sky 4 months later on.
Although outwardly comparable to the DC-four on which it was dependent, the DC-six supplied many style versions. Run alone by 2,a hundred-hp, 18-cylinder, two-row, air-cooled Pratt and Whitney R-2800-CA15 Double Wasp engines showcasing three-bladed, electrically-deiced propellers, As an illustration, it launched rectangular passenger windows along with a squared-off tail. Its wing, empennage, and windshield had been provisioned with thermal anti-icing.
Internally, it featured an electronic autopilot method, an automated tension Regulate technique, air (temperature and humidity) conditioning, radiantly heated floors and walls, and the opportunity to settle for pre-loaded cargo containers.
The eight.10-foot-huge by seven-foot-higher cabin accommodated 46 twenty-inch-broad, Douglas created, four-abreast seats set up in a forty-inch pitch, as well as 6 in an aft lounge.
1st flying on July ten, 1946 and shipped to launch clients American and United for the duration of a joint ceremony on November 27, it was inaugurated into support on April 27 of the next yr, affording 10-hour eastbound and 11-hour westbound transcontinental schedules.
Cabin configurations different As outlined by carrier. American, for example, accommodated fifty four-abreast working day passengers or 24 night sleeper ones in ceiling extendible higher berths with their very own slender, higher fuselage Home windows and forty two-by-seventy six-inch decrease types produced with the seats on their own.
Sabena, the type’s first international operator, provided mixtures of the two.
Other DC-six operators bundled Braniff, Delta, KLM, Linee Aerea Italiane, Nationwide, Panagra (Pan American Grace Airways), and SAS.
With the aircraft’s quite a few data, that on March two, 1950, entailing a three-hour, 8-minute flight from Chicago to Miami operated by Delta at a 376-mph pace, was notable and indicative on the increasing efficiency of the modern pistonliner.
Examination of The fundamental DC-six design and style indicated that it had been structurally effective at carrying extra payload when coupled that has a modest, five-foot fuselage stretch to improve its Heart-of-gravity array and higher horsepower engines, leading to two further more variations.
The primary, a devoted freighter designated the DC-6A Liftmaster, highlighted port, 7.7-by-five.7- ahead and ten.four-by-six.6-foot aft primary deck, upward-opening cargo doorways. Initial traveling on September 29, 1949, it entered assistance with Slick Airways, which in the end flew thirteen, on April 16, 1951.
Eighteen carriers placed 67 orders for the type.
The next, an all-passenger Model dubbed the DC-6B, showcased 54 four-abreast seats, along with a six-place aft lounge, Even though high-density preparations permitted accommodation of approximately 102.
Very first flying on February two, 1951 and moving into assistance with United Airlines two months later on, on April 11, the sort, run by four 2,500-hp R-2800-CB17 Double Wasp engines, highlighted a 105.7-foot overall duration and 117.six-foot wingspan. Carrying a 24,565-pound payload and featuring a 107,000-pound all-up bodyweight, it could cruise at 316 mph and provide three,000- to four,720-mile sectors.
Operated by American, Continental, National, Northeast, Northwest, Pan Am, Trans American, United, and Western from the US, and Alitalia, KLM, Linee Aerea Italiane, Olympic, Sabena, SAS, and Swissair in Europe, it liked a 288-plane creation run.
Giving the lowest seat-mile fees of any then-recent piston airliner, it facilitated significant interior and route overall flexibility, proving particularly interesting to all-vacationer North Atlantic operators. Northeast, one example is, operated its DC-6Bs alongside the East Coastline, funneling travellers from its as soon as classic New England route technique-encompassing Montreal, The big apple, and Washington-to Florida sunspots, though Northwest served the Pacific with its dozen plane. Western operated the kind with the eight-seat forward, 38-seat primary, and 14-seat aft cabin, As well as the regular six-place lounge.
The kind enabled SAS to inaugurate assistance on the Great Circle route, from Copenhagen to L. a., about the North Pole in November of 1954, cutting down travel time by 10 hrs around the standard transatlantic journey by way of New York.
Changing its DC-4s with DC-6Bs, Olympic served European and Eastern Mediterranean Locations with combined, ahead-day and aft-evening sleeper configurations.
Ethiopian Airways operated its DC-6Bs inside of a superior-density arrangement, carrying 102 travellers among its Khartoum foundation in Africa and Athens and Frankfurt in Europe.
LAN-Chile connected the North and South American continents with its aircraft, linking Miami with Lima, Peru.
Australian Nationwide operated four aircraft to towns inside of its household country.
Frequently revolutionary routes, SAS inaugurated the 1st scheduled, spherical-the-earth assistance on Might 29, 1953, necessitating just around eighty three hours for the worldwide circumnavigation.
A succeeding, convertible DC-6C variant, While only garnering 7 orders, included equally DC-6A and -6B characteristics, facilitating key deck mixtures of travellers and cargo, starting from seventy six of the former, their baggage, and a couple of,400 lbs of typical freight to an all-cargo load of virtually 13 tons, by means of a moveable, four-posture bulkhead. First delivered to Searching Clan Airways on August seven, 1958, it was subsequently joined by existing plane transformed to this typical both by Douglas or its approved modification Heart, Pacific Aeromotive.
Sabena created two plane with swing tails to permit it to support outsize cargo pieces provided that 60 feet.
Various navy variations ended up eventually also crafted. The 1st of a hundred purchased C-118s, primarily based upon the DC-6A, flew on July fifteen, 1962 and was operated via the Army Air Transportation Command (MATS), which was afterwards renamed the Navy Airlift Command, while the Navy ordered 65 R6D-1s, which on their own were being redesignated C-118Bs. A singular VC-118, making use of a DC-six generation slot reserved for American Airlines, turned President Truman’s plane named the “Independence” when it had been sent on July one, 1947.
Retaining rate with unrelenting passenger increases, however remaining competitive with Lockheed’s have, multiply stretched Constellation that may before long surface in L-1049 and L-1649 Starliner designs, Douglas examined a still-larger sized DC-6B by-product able to supplying nonstop westbound transcontinental provider and possibly transoceanic types, once again dependent upon impetus from American Airways, which put its initial agreement in December of 1951 for what would become the final word evolution on the quad-engine pistonliner.
First flying two decades later on, on May possibly 18, and The natural way designated DC-seven, it released a forty two-inch ahead-of-the-wing fuselage extend to both accommodate an extra seat row or maybe more cargo, and resulted in a very 62-passenger inside subdivided into eight-ahead, 38-major, and sixteen-aft seat cabins, respectively divided by lavatories as well as a galley/buffet. The latter, as with all former types, was provisioned with the aft, port passenger doorway. Optionally higher densities entailed in between eighty and ninety nine. Sleeper or day and night time blended preparations could also be chosen, With all the travellers accommodated in 4 aft higher and lower berths.
Delta Air Strains, such as, carried 8 passengers inside of a ahead “Sky Place,” forty two in the most crucial cabin, fourteen while in the rear part, and five inside the tail within the DC-7s it operated in between Chicago and Miami.
Even though the kind utilized the same wing released from the DC-4 with its highest, 50-degree, trailing edge flap journey, the Beforehand reputable Pratt and Whitney R-2800 engines experienced achieved their peak of growth, Hence demanding a different kind to cater to the upper gross weights required for increased vary and payload. In this case, the eighteen-cylinder, 3,250-hp air-cooled Wright R-3350 Turbo Compound driving four-bladed, governor-controlled, hydraulically positioned Hamilton Conventional propellers was chosen. Due to interior engines’ proximity for the fuselage, they have been restricted to 13.five-foot diameters, and because of their increased size, they, combined with the outer types, have been housed in redesigned nacelles. Though they provided a twenty-per cent rise in output compared to the Pratt and Whitney engines powering the DC-six, they available similar gasoline consumption.
The hydraulically actuated, ahead-retracting tricycle undercarriage, consisting of a single nose wheel and twin major wheels, was retained, Even though the major equipment could possibly be independently extended to function a speed brake at 300 mph IAS or 410 mph at 20,000 ft to reinforce speedy, but controlled descents.
CAA Qualified on November twelve, 1953 after a 204-flgiht examination software executed over a 6-month period, the DC-7 was inaugurated into services seventeen days later on with American Airlines, for The 1st time permitting bi-directional, east- and westbound transcontinental operations.
A few other carriers, together with Delta, Nationwide, and United, positioned orders, bringing total creation to one zero five.
So as to stay clear of confusion with its existing DC-6A Liftmaster, Douglas applied the “B,” or “DC-7B,” designation to denote the main variant from the baseline design, In this instance a still better gross body weight and more time-variety aircraft which was sparked by Pan Am’s late-1953 purchase for seven with intercontinental variety.
Introducing optional, external, selection-extending saddle fuel tanks mounted within the higher percentage of the engine nacelles, provision for propeller spinners, improved wing flaps, and gross weights as superior as 126,000 lbs ., the sort 1st flew on April 21, 1955. It had been certified the next thirty day period, on Might 27, and entered company with Pan Am over the transatlantic, Big apple-London route one particular thirty day period after that, on June 13.
Only operated by an individual foreign carrier-namely, South African Airways on intercontinental sectors, for example from Johannesburg to London-the DC-7B was primarily purchased by US operators, which include American, Continental, Delta, Eastern, Nationwide, Pan Am alone, and Panagra, which served South American destinations with it. Just one hundred twelve were developed.
As well as four common DC-7s, National was equipped to fulfill passenger need on its Florida routes with an extra four DC-7Bs.
Japanese, also serving Florida Locations and hitherto functioning earlier Constellation versions, ordered 50 DC-7Bs, configuring the initial thirty with 64 seats, but introducing large-density, all-coach, ninety three-passenger interiors with the final twenty.
Delta equally operated its 11 aircraft with different densities, from 69 to 90.
Even though the DC-7B made available the required transatlantic assortment, as evidenced by Pan Am’s very own operations, winds sometimes dictated the need for refueling stops in Gander, Yet again prompting Douglas to structure a Variation with even increased functionality, and this became the DC-7C, the definitive and ultimate expression of piston airliner enhancement.
Besides incorporating An additional fuselage extend-In this instance, of 42 inches-it was the initial to hire a modification of The essential DC-four wing. Entailing a ten-foot extension through five-foot plugs inserted among the interior motor nacelles as well as the fuselage, it showcased a 127.six-foot span, a 1,637-sq.-foot spot, a heightened, 9.93 part ratio, and will accommodate 1,000 supplemental, variety-translating lbs . of gas. Various in potential from 4,512 to six,378 US gallons carried in both equally the larger volume wing and within the enlarged motor nacelles’ saddle tanks, it permitted 3,610- to 5,642-mile ranges being flown. Because of the five-foot higher length among the inner powerplants as well as fuselage, the cabin, equipped to support up to 105 travellers, was quieter, whilst the clearance also facilitated the usage of 14-foot-diameter propellers.
Run by 4 three,400-hp Wright R-3350-EA1 or -EA4 piston radials, the DC-7C could have a 21,five hundred-pound payload and had a 143,000-pound gross pounds. Cruise velocity was 345 mph and service ceiling was as superior as 21,700 feet.
Serving as a true intercontinental airliner, it had been able to full-payload, east- and westbound transatlantic operations from any wind condition.
According to Harry Gann within the Douglas DC-six and DC-seven (Specialty Push, 1999, p.74), “In a superb marketing ploy, the DC-7C was named the ‘7 Seas.’ The DC-7C was the final word progress with the Douglas four-engine transports and it carried the majority in the North Atlantic and polar website traffic till the introduction in the Boeing 707 in 1959.”
Initially traveling on December twenty, 1955, it entered provider with Pan Am the following calendar year, on June 1. Although it turned its major operator, with 26 aircraft, and 3 other US carriers requested the sort, it observed substantial international airline support With all the likes of Alitalia, BOAC, Mexicana de Aviacion, Japan Air Traces, KLM, Panair do Brasil, Sabena, SAS, and Swissair.
SAS accomplished a file flight with the sort when it flew it six,005 miles on November 17, 1956, demanding 21 hrs, forty four minutes with the trip.
five. Threshold into the Jet Age
Synonymous with stretched-fuselage aircraft, which resulted inside the DC-one to DC-three after which the DC-4 to DC-7 number of piston airliners, Douglas future regarded as a powerplant kind adjust instead so as to continue to be competitive with the rising turboprop Vickers V.700 and.800 and Lockheed L-188 Electra plane, conducting a variety of the two DC-6 and DC-7 airframe scientific tests that integrated this technologies. The most significant was the proposed DC-7D.
Run by 4 Rolls Royce RB.109s, it would’ve released One more, 40-inch fuselage extend in addition to a swept vertical tail.
Inspite of strong interest from prolonged loyal American Airlines, Douglas couldn’t show the financial feasibility with the undertaking, although it would most probably have already been the 1st lengthy-vary turbine-powered airliner to get appeared, and elected instead to bypass this technological know-how and right away develop a pure-jet layout, the DC-eight, deemed the DC-seven’s up coming-generation successor.
Primarily based upon the overpowering passenger acceptance of, and thus need for, this vibrationless, velocity-fostering powerplant, Douglas-in addition to Boeing and, to the lesser degree, de Havilland with their respective 707 and DH.106 Comet plane–presented the threshold to this subsequent stage of airliner progress, accelerating the substitution of both piston and turboprop plane on all but brief-vary routes.