Profile – Douglas DC-6 and 7

To appreciate the DC-6, one has to go back to the dark days of World War II. The United States, by accident or design, had become the main supplier of transport aircraft to the war effort. The Douglas Company, of Santa Monica, California, was America’s principal transport manufacturer, churning out thousands of C-47 (DC-3) and C-54 (DC-4) aircraft.

Across town at Burbank, Lockheed was working on a new transport aircraft, the C-69, with US Army Air Force backing. The C-69 was to be a vast improvement over the C-54, having more speed and range and the benefits of pressurised comfort. Transcontinental and Western (TWA), which had played such a big part in launching Douglas into the airliner business with the DC-2 and DC-3, had already placed orders for the proposed post-war civil version, the L-049 Constellation.

This was of great concern to TWA competitors, United Air Lines and American Airlines. In those days, the most prestigious air route in the States was the transcontinental service from California to New York. Having the fastest and most modern airline was more important in attracting travellers than the fares charged.

United approached Douglas to come up with a more modern aircraft, faster than the Constellation, with more range and pressurisation. The USAAF already had its pressurised C-69, so were not particularly interested, but after much negotiation, decided to sponsor the Douglas project. The DC-6 was thus on its way. Interestingly, neither the USAAF or its successor, the USAF, operated the aircraft it had paid for until much later, when it ordered a substantial fleet of the improved DC-6A.

The first DC-6, carrying the military designation XC-112, flew on February 15th, 1946 under the command of John Martin. The XC-112 was based largely on the DC-4, retaining the 35. 8 metre wing of the older aircraft. The new pressurised fuselage was two metres longer and operating weights were pushed up. Rectangular windows replaced the DC-4’s oval ones. Some DC-4 operators later painted their aircraft so as to give the illusion of rectangular windows so passengers would think they were in a DC-6.

The most significant change was in the power plants. In place of the DC-4’s Pratt & Whitney R-2000s were four magnificent Pratt & Whitney R-2800-CA15 Double Wasp radials producing 2100 hp each. The R-2800 was one of the great aero engines of all time. Built in vast numbers during the war years, it powered such famous aircraft as the Thunderbolt, Corsair and Hellcat, and was noted for its economy of operation, reliability and durability. It was this engine that made the DC-6 so exceptional.

Deliveries to American and United commenced on November 20th, 1946, nine months after TWA’s Constellations. The Connies had suffered the ignominy of grounding a few months after services started, which detracted from its initial advantage. The DC-6s of United were scheduled to operate the eastbound transcontinental service in only 10 hours, a time that could not be matched by the Lockheed product. Like its competitor, the DC-6 was compelled to make a stop to refuel, normally at Chicago.

Unfortunately, Douglas was to receive a setback in November 1947, when after two in-flight fires leading to the loss of 52 lives, the DC-6 was also grounded. Exhaustive tests revealed that fuel was venting into the cabin heater intake, and after modifications, the aircraft were returned to service in March 1948.

Other airlines were quick to adopt the new transport. National Airlines (now part of Pan Am) used its DC-6s to take on Eastern’s Constellations on the lucrative New York-Miami route. This battle, like the transcontinental, was to see the two airlines leap-frogging each other with improved Lockheed and Douglas products. Delta’s DC-6s challenged Eastern too. This was on the Chicago to Miami service and it was again a classic Lockheed vs Douglas fight that was to drag on through the fifties.

The recently demised Braniff made extensive use of the DC-6 both domestically and on its services into South America, while the US flag carrier specialising in Latin American air travel, Panagra, also found the Douglas product a worthwhile investment.

In Europe, the DC-6 was bought by Scandinavian Airlines System, KLM, Sabena and the Italian airline, LAI. These airlines used the new equipment to build up their international air routes including the all-important transatlantic service.

Flota Aerea Mercante Argentina operated the DC-6 from Buenos Aires to London, Madrid and Rome before being absorbed into Aerolinas Argentinas. Douglas secured an order from Mexicana by offering a more powerful version able to cope with Mexico City’s hot and high conditions. History recently repeated itself when McDonnell-Douglas produced a special version of the DC-10 to meet these same Mexican requirements.

In our part of the world, Philippine Air Lines acquired a fleet of DC-6s and used them to open international services to Europe and across the Pacific to San Francisco. The ill-fated British Commonwealth Pacific Airlines, a joint effort by the British, New Zealand and Australian governments, also purchased four DC-68s for its sole route from Australia to North America. After the San Francisco accident, Qantas took over the service and BCPA’s aircraft were transferred to that other multinational carrier, TEAL, and placed on the New Zealand register. They later served with the RNZAF.

Second-hand buyers of the DC-6 were many and some are still giving sterling service today.

The USAF bought a single DC-6 for use as a Presidential transport. Named the “Independence’, it is now part of the National Air and Space Museum collection.

In 1946, Douglas were offering the DC-6 at $US590,000. The 175th and last DC-6 was delivered to Braniff in November 1951. United sold its last of the original model in 1968.

With the availability of more power in the form of the 2400 hp R-2800-CB16, Douglas decided to stretch the DC-6 by 12 metres and increase both the operating weights and fuel capacity. The improvements were first applied to an all-cargo model, the DC-6A, which had two main deck cargo doors, metal plugs over the windows and a heavier, reinforced floor. The first DC-6A flew on 29th September 1949.

Douglas soon realised the potential of the bigger DC-6 in the passenger role, particularly as arch-rival Lockheed had now developed the Super Constellation. So in February 1951, it flew the first of the most familiar of the whole DC-6 series, the DC-6B. Despite the DC-6A having flown 18 months before the new aircraft, both types entered airline service in the same month, April 1951. It was the DC-68 that was to be the zenith of Douglas’ big piston airliners. New standards in reliability and economy were set by this aircraft, standards that would not be surpassed until the jet age.

American Airlines was the first airline to place the DC-6B into service and Douglas soon secured almost absolute domination of the US market. Only the loyal Lockheed operator, TWA, of all the US trunk operators, did not buy the DC-68. America’s flag carriers also rushed to buy them, with Braniff and Panagra using these aircraft to South America. Pan Am selected the DC-68 to inaugurate tourist-class services across the Atlantic, made possible by the aircraft’s low operating costs. The DC-68 can lay claim to starting the revolution in low cost international travel that was later carried to extremes by widebody DC-10s and 747s in the seventies.

The most numerous of all the DC-6 variants, 288 DC-6Bs were built at a 1951 cost of $US1,100,000 each. They were deployed by airlines worldwide.

The two French independents, UAT and TAI, used DC-688 on their long haul networks. TAI operated them on the very long Paris to Bora Bora route from September 1958. This service is still operated today by UTA, the descendant of TAI, using 747s. It forms part of the longest air route in the world – Paris to Los Angeles via Sydney.

SAS used its aircraft for pioneering polar air services. On 15th November 1954, the tri-national Scandinavian airline inaugurated the first Great Circle air service over the Arctic from Copenhagen to Los Angeles via Sondre Stromfjord and Winnipeg.

Seven months later, Canadian Pacific started trans-polar services from Vancouver to Amsterdam, and again the reliable DC-6B was chosen. Both the national airlines of the low countries, KLM and Sabena also opted for DC-6Bs. In Southern Europe, Olympic Airlines became one of the last purchasers of new DC-6Bs when it ordered four in mid-1957. These aircraft were finally withdrawn in 1972.

L AN-Chile used its aircraft for many years on trans-Pacific services from Santiago to Fiji. Asian airlines to have acquired DC-6Bs included Cathay Pacific, Taiwan’s Civil Air Transport and Japan Air Lines.

Douglas even secured a sale behind the Iron Curtain when Jugoslav Air Transport bought a couple.

Locally, Australian National Airways was the main operator of the type. The DC-6B’s excellent range compared with the Viscount meant it was extensively used on transcontinental and New Guinea air routes.

The civil DC-6A, on the other hand, was built in relatively small numbers. Only some 74 were built, the last being delivered on 10th February, 1959. This was the last piston-engined airliner to be delivered by Douglas and one of the last aircraft built at the company’s Santa Monica plant, birthplace of the DC-1.

DC-6As were sold to both passenger airlines, like Pan Am and KLM, and specialist all cargo operators like Slick Airways of San Francisco. Some aircraft were convertible passenger/cargo aircraft, sometimes designated DC-6Cs. Douglas considered these convertibles to be DC-6As for they had all the important features of these aircraft.

Many DC-6As were adapted for passenger operation by the removal of window plugs, and conversely, a large number of DC-6Bs (and DC-6s) were modified for all cargo operation. The only DC-6A registered in Australia was also the only DC-6 series aircraft bought by TAA, VH-TAD. It operated here only as a passenger aircraft.

Both the USAF and US Navy acquired large fleets of DC-6As. Later designated C-118B, the USN’s 65 aircraft were first ordered under the old naval designation system as the R6D-1. These were used as logistics, VIP and staff transports. The USAF purchased 101 for logistic and personnel transport and later acquired another 40 from the USN. The military DC-6As had the more powerful of the two ·engine options available on the DC-6B, the 2500 hp R2800-52W (civil designation R2800-CB17).

Many ex-USAF and USN C-118s are now flying with cargo operators, having only recently been disposed of by the US armed services.

Following the introduction of jets, the DC-6s and DC-6Bs were soon displaced from the fleets of the world’s major airlines. The change to jets was a hasty exercise as airlines felt compelled to introduce competitive equipment as quickly as possible. In 1961, the only airline reporting a profit on the No. 1 international route, the North Atlantic, was Loftleider with its DC-6Bs.

The virtues of the DC-6 series were recognised by a myriad of small airlines and cargo operators, and even today there are many DC-6s plying the airways of the world. Some thirty years after the first flight of the XC-112, 130 were still flying. By comparison, there was only a handful of Lockheed Constellations and Super Constellations airworthy.

While the DC-6B is considered to be the best of Douglas’ long-running series of piston-engined airliners, it was not the ultimate development of the DC-4. That distinction was to go to an aircraft developed to meet the challenge brought about by the ever-longer legs of the Constellation – the DC-7.

The DC-7 was an aircraft that Douglas did not particularly want, though it did end up producing a profit for the company. Its existence was due in part to the availability of a new engine and the insistence of one of its major DC-6 customers.

TWA had ordered a new version of the Constellation, the L. 1049C, able to maintain, regardless of winds, scheduled services non-stop across the United States in either direction. This new model was developed to take advantage of the turbo-compound version of the Wright R-3500 eighteen-cylinder radial.

The R-3500, which Lockheed had been using on the Constellation all along, developed up to 2500 hp. The turbo-compound version with its exhaust-driven turbines coupled to the engine crankshaft, increased this by 30%. The new engine had been first used on the Neptune maritime patrol aircraft.

American Airlines was very concerned by this development and started pressing Douglas to match the Lockheed product. Douglas was more concerned that any new aircraft developed would affect DC-6 sales. This concern that one company product could affect the sales of another appears to be a Douglas trait. The DC-8 was dropped from production because it was thought it would take away DC-10 sales.

When America offered to pay $40 million for 25 aircraft, thus meeting most of the development costs, Douglas committed the new aircraft to production. Power came from four 3250 hp Wright R-3500-18DA-2 engines.

The DC-7 retained the same wing as the DC-6, which was in fact the DC-4 wing, but the fuselage was stretched by another metre. Strangely, fuel capacity was the same as the DC-6B at 20,914 litres, so the DC-7 actually had less absolute range than the R-2800-powered aircraft. It was the higher gross weight of the DC-7 that gave it the payload/range performance for sustained non-stop transcontinental services. It slashed two hours off the elapsed time for this route compared with the DC-68. The DC-7 flew for the first time on 18th May, 1953.

American took delivery of the first aircraft and were soon joined by United, which also used the aircraft on its Hawaiian services. United bought no less than 57 of these aircraft, with Delta and National the only other operators buying new aircraft.

Unfortunately for the DC-7, its engines were never as reliable as the faithful R-2800, and the aircraft soon developed a reputation for engine problems. Lockheed’s aircraft also had to bear this burden. 105 DC-7s were built.

The first development of the DC-7 was the DC-78, which had a higher gross weight and more fuel, some 24,453 litres. The extra fuel was housed in tanks in the engine nacelles and the longer nacelles were the only external difference between the two aircraft. Oddly, DC-7Bs delivered to American domestic carriers and the flag carrier Panagra did not have these extra tanks, but did retain the longer nacelles. The DC-78 was the fastest DC-4 development with a cruise speed of 360 mph.

Two airlines took delivery of new long-range DC-7Bs. Pan Arn bought an interim fleet of seven aircraft, which were introduced on non-stop New York-London services on 13th June, 1955. The only non-US original buyer of the DC-78 was South African Airways, which operated them for many years across the Indian Ocean to Perth in competition with Qantas’ Super Constellations and Electras. Douglas built 112 DC-7Bs.

The ultimate development of the DC-4 was the DC-7C. It was the only aircraft in the whole DC-6/DC-7C series to carry a name. This was a play on the aircraft’s designation and very appropriate to its role – Seven Seas.

The DC-7C was developed to meet a Pan Am requirement for an aircraft capable of scheduled non-stop transatlantic services in either direction regardless of winds. Douglas got the jump on Lockheed in this regard, for the latter’s long-range Constellation development, the Starliner, required an all-new wing. By the time the Starliner appeared, the jets were almost upon us and only a handful were built.

The Santa Monica manufacturer also had to do some work on the DC-7 wing to produce the DC-7C. The span was increased by three metres by adding sections at the root. Not only was fuel capacity and aspect ratio increased but the extension also moved the engines further from the fuselage, reducing noise and vibration in the cabin. The fuselage was stretched by a further 1. 1 metres and the DC-7Cwassome 5. 6 metres longer than the DC-4. Up went the gross weight and so did power to compensate. The DC-7C had four 3400 hp R-3350-18EA-1s driving four-blade propellers.

Pan Am introduced the DC-7C into service on 1st June, 1956, forcing several other airliners to follow suit. On the glamorous transatlantic route, BOAC rushed to buy a fleet of Seven Seas just to remain competitive. Its own turboprop Britannias were suffering teething problems and the airline had found itself without an aircraft that could maintain the now essential non-stop schedules.

KLM switched from the Super Constellation to the DC-7C to meet the challenge and a number of airlines quite happy with DC-6Bs, like Alitalia, SAS and Swissair also purchased fleets of the long-range transports.

SAS took advantage of the DC-7Cs long range and inaugurated the first truly polar service on 24th February, 1957 from Copenhagen to Tokyo. Later Los Angeles was added to SAS’s polar network. There was only one stop on these flights, at Anchorage, and the aircraft actually circled the pole en route.

On the Pacific, Japan Air Lines and Northwest found themselves with DC-7Cs to match Pan Am. Elsewhere in the world, the French independent, TAI, acquired a fleet which was used for many years on services through Australia to the South Pacific.

The last of 121DC-7Cs was delivered to KLM on 10th December 1958. The aircraft sold for $ 2. 6 million in 1958.

The unreliability of the R-3350 and the introduction of jets and big turboprops in 1958 led to the early retirement of the series. Many, like BOAC’s, were converted to cargo operation but generally, their high operating costs and mechanical headaches meant they would not lead the long lives of their predecessors, the DC-6s. Nevertheless, there are still some DC-7s flying today.

Military use of the DC-7 was restricted to the French Air Force, which operated them as airborne observation platforms in connection with nuclear weapon testing in the South Pacific. These aircraft were extensively modified with many external radomes and sensors.

It was planned to produce a turboprop-powered DC-7 under the designation DC-7D. The favoured engine was the 5800 hp, Rolls Royce Tyne. However, the changing face of air travel forced Douglas to take on a new challenger to its supremacy as the supplier of airliners to the world. Boeing had announced its plans to produce the jet-powered 707, so Douglas proceeded straight to the DC-8 without ever building a turboprop airliner.

The jet age brought to a close one of the most famous production lines in aviation history. Douglas stopped building aircraft at Santa Monica with the end of the DC-6 and DC-7 programs.

The development of the DC-4 in the DC-7C proved that the basic design had remarkable growth built into it. Until the DC-7C, all the derivatives had retained the basic DC-4 wing, which in itself is extraordinary. The DC-4grossedat 73,000lbs, the DC-78at 126,000!

Anyone who has flown in a DC-68 or one of its sisters would have fond memories of this aircraft. It was smooth, relaxed and relatively quiet. The level of reliability obtained in the DC-68 was unmatched by any other piston-engined airliner.

Collectively, the DC-6, DC-7 and Constellation airliners set off the chain of events that ended the days of the great ocean liners as a means of transportation. Inside the States, they brought to a close the railway era and established air transport as the norm for long-distance travel.

The significance in the history of air travel of the DC-6 series cannot be understated, for it played the leading role in the metamorphosis of air transport from an expensive and adventurous way to travel to an everyday occurrence for millions of people. There is one final comment to make about the DC-6 and its developments. Except for the 1947 fires, the aircraft remained remarkably free from adverse publicity. It never suffered from protracted development problems, political controversy or intrigue. Neither did it have glory in war or break new technological ground.

It was totally an airline’s airliner.