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Aviation History
1958
1958 - 0697.PDF
«I Douglas C-54 (above): "By the end of the war 1,163 of the military versions of the DC-4 had been built." The prototype Boeing 307 on a test flight in Jan- uary 1939 with its starboard Cyclones feathered. board" by several airlines, including American, United andEastern, for use on the U.S. domestic routes. They were to be 42-passenger aircraft in day configuration with sleeping accom-modation for 30 and were to cost $300,000 (£60,000) each. The first DC-4 flew on February 14, 1942, but by then the UnitedStates had entered the war and the orders which had been placed were—after some hesitation—taken over by the United StatesArmy Air Forces. The DC-4 went into military transport service as the C-54 during 1943 and the type soon proved invaluable forlong-haul trans-ocean transport. By the end of the war 1,163 of the military versions of theDC-4 had been built and the type was being used on a large scale to maintain the inter-continental communications of the Allies allover the world. Many C-54s were converted to civil use at the end of hostilities and a further 79 DC-4s were built as civil air-craft before the type was succeeded in production by the DC-6, a somewhat "stretched" and pressurized development (with adifferential of 4.16 lb/sq in) which, after originally being projected as a military transport, first went into service with American Air-lines on April 27, 1947. (Its first flight had been made on February 15, 1946). The DC-4 itself, although projected to havepressurization was, in fact, never so equipped and even the 300 still in service with the airlines today fly unpressurized. The DC-6, as the first purely civil model of the DC-4 series,started a long line of airliner development which has included such successful aeroplanes as the DC-6B, DC-7B and DC-7C. Atotal of some 1,100 "post-DC-4" derivatives have now been built (850 for the airlines) and the later versions are still in large-scaleproduction. The structures of these aeroplanes have been logical and pro-gressive developments of the DC-4. The DC-6 (wing loading: 55-64 lb/sq ft) and subsequent types have double instead of single-slotted flaps, raising the maximum achieved lift-coefficient from about 2.4 to about 2.6. The fuselage has been successively"stretched" in length to provide more capacity, more powerful engines have been installed and the fuel tankage has been increased.In the case of the DC-7C, the wing has also been extended by the addition of a new centre section, bringing the area up to 1,637 sq ft.The loaded weight has grown to 143,000 lb, but with all these developments, the airframe remains basically unchanged. It isprimarily of 24S alloy although some of the later 75S alloy is also used, plus titanium in the latest models. The DC-7C markedanother milestone to air transport development by being the first aeroplane to offer non-stop service with reasonable regularity onthe Blue Riband London - New York route. In April 1939, quite soon after it became clear that the DC-4Ewas to be dropped and Douglas started discussing the DC-4 with the airlines, Lockheeds also began preliminary work on a projectin the same category to a specification issued by T.W.A. for a non-stop coast-to-coast aeroplane. A payload of 6,000 lb wasrequired for a still-air range of 3,500 miles at a speed of more man 250 m.pJi. at 20,000ft. Lockheeds, as we have seen, had been very successful in theyears immediately before the war with their range of small trans- ports which had been complementary to, rather than competitivewith the DC-3. They had had a project in 1939 (the L.44 Excali- bur) for a four-engined aeroplane of approximately DC-3 capacity.However, this was not developed. At about the same time, as a result of the discussions with T.W.A., they decided to competedirectly with Boeing and Douglas in the long-range large aircraft category and their L.049 project, later named the Constellation,evolved closely similar in size to the DC-4. It had a wing span of 123ft and a wing area of 1,650 sq ft. The wing section was ofN.A.C.A. 23 series, 18 per cent thick at the root but N.A.C.A. 4412 (12 per cent thick) at the tip. Fowler flaps gave an effective maxi-mum lift coefficient of about 2.6. The gross weight was initially 68,000 lb and the wing loading 41 lb/sq ft. "The DC-6. as the first purely civil model of the DC-4 series, started a long line of airliner development . . .' Construction of the first Constellation started in 1940 to aninitial order for nine aircraft from T.W.A., whose order was soon increased to 40 when Pan-American also ordered 40. The firstflight was made on January 9, 1943. As with the DC-4, the Con- stellation was taken over by the military and put into service asthe C-69. The first service flight with the U.S.A.A.F. was made on April 17, 1944, when a Constellation flew non-stop fromB,urbank to Washington in just over seven hours. However, the type did not go into full service until 1945, by which time 15 hadbeen delivered. Airline operations started early in 1946. After a number of vicissitudes, which led to short-term groundings (alsosuffered by the DC-6), 135 were established in service by 1948. Structurally, the Constellation's layout differed in detail fromthe DC-4 series, although the basic four-engined low-wing mono- plane configuration with tricycle undercarriage was unchanged.The most obvious difference was that the Constellation had a circular-section "fish-shape" fuselage (of 132in maximum internaldiameter), possibly suggested by the British de Havilland Albatross of 1937. The section provides space for two-and-two 22in seatson each side of a 24in aisle. The Constellation series is also fre- quently used with a rive-abreast (two-and-three) high-density lay-out. The Constellation's attractive shape probably gives some small aerodynamic advantage and by "drooping" the front fuselageshortens the nosewheel leg. However, at the same time, it creates difficulties in the full use of the interior space. It is significantthat the Douglas "parallel-section" formula has now been univer- sally adopted for civil passenger transports. As already mentioned,the tail unit of the Constellation had triple vertical surfaces, in contrast to the single unit of the Douglas types. This also has nowgone out of fashion. Lockheed's latest civil aeroplane, the new turboprop Electra, has both a parallel-section fuselage and a singlefin and rudder. This clear-cut adoption by Lockheed of design features whichDouglas have shown to be more satisfactory is a good example of the far-sighted policy of American manufacturers—which hasbeen particularly evident in their development of transport air- craft—of unhesitatingly changing over to design practices whichcompetitor companies may have demonstrated to be superior to their own. This historical survey has given several instances, andthere is no doubt that the practice has been an important reason for American leadership in airliner development. Equally evidentis the reluctance of manufacturers in other countries—and, per- haps, particularly of the British—to adopt the same enlightenedpolicy. Too often it appears that national pride, or a reluctance (or inability) to learn from other people's successes and mistakes,has led designers along unprofitable lines of development. The readiness of American manufacturers to adopt a design practicewhich one company has shown to have proven advantages is still very evident in their latest aircraft—as, for example, in their newjets. A high order of judgment is obviously required in weighing the case for adopting those innovations in design which are essen-tial to progress against the conservative incorporation of proven features. One must hope that British manufacturers are now, atlast, profiting from the lessons of the past 25 years. But to return to the Constellation. This aircraft was of conven-tional construction in aluminium alloy and was, of course, pres-
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