Pinnacle of the Propliners
The propliner era of aviation began in the early 1930s and ended in the 1950s with the advent of jet and turboprop powered airliners. It was an extremely important period in aviation that brought many changes to not only how people travelled, but also how many people had access to air travel.
It was during the propliner era that air travel became reachable to the masses. In the interwar period, air travel was primarily the domain of the wealthy. Post WWII developments in aircraft and engine design brought operational costs of large aircraft down and led to airlines creating multiple passenger classes, thus bringing the price of air travel within reach of many more people of other social classes.
It was also during this period that land based aircraft became capable of flying trans-oceanic distances and the era of passenger service by flying boats came to an end. Large land based propliners were faster, more efficient, less maintenance intensive and much less limited in where they could operate from; the flying boat never stood a chance against them.
In general terms, a propliner is defined as a large passenger or cargo aircraft of primarily metal construction powered by two or four piston engines. Turboprop aircraft are not typically included in the propliner category.
One of the early and major players of the propliner era was the Douglas Aircraft Company based in California, USA. The company’s DC-1 of 1933 was one of the very first propliners to fly; the company improved upon it the following year with the DC-2 and in 1935 gave the world the legendary DC-3, widely regarded as the most significant and influential airliner type ever made. 1939 saw the advent of the DC-4, a very capable and well liked transport that served well during WWII and was the most widely used aircraft type of the Berlin Airlift. The DC-6 first flew in 1946 and served well in the Korean War as well as being one of the very first land based airliners to be put on regularly scheduled trans-oceanic routes. The last of the Douglas propliners was the DC-7 of 1953, it showed the limits of what piston powered airliners could do and was not as popular as previous Douglas designs owing to its limitations and the fact that the first generations of jet airliners and turboprop airliners were starting to make their appearances in airline service.
In the overall picture of the propliner era, the DC-6 is widely considered to be the best of the propliner category. The aircraft, particularly in its B model form, was considered to have the best balance of range, speed, efficiency, reliability, handling and passenger comfort of any propliner type.
At that, let’s spend some time with the DC-6:
A Child of Experience
With their reputation as a capable and competent designer of airliners well established during the interwar period, Douglas most certainly were not in uncharted waters for themselves when design of what would become the DC-6 started in 1944.
While the aircraft would claim its greatest fame in airline service, it was born from a military requirement for an improved version of the C-54, the military version of the DC-4.
The improved aircraft was to be longer and more powerful than the C-54 as well as have a pressurised fuselage as a standard feature. In US Army Air Force terminology, the new aircraft was designated XC-112. The XC-112 prototype did not fly until February of 1946 and, with the war over, the military requirement was dropped.
All was not lost for the aircraft, however. Douglas had designed the aircraft to be easily adapted to airline use and several America airlines had placed orders for the new Douglas airliner before the war had ended. Douglas used the XC-112 as a prototype for the DC-6 and in a short time had developed the airliner from the transport. The new airliner first flew in in June of 1946 and deliveries began in November of that year to launch customers, American Airlines and United Airlines.
In spite of a four month grounding of the DC-6 fleet in 1947 due to a series of in-flight fires, fleets of the aircraft were serving airlines in North America, Europe and Asia on regularly scheduled intercontinental and trans-oceanic routes before the 1940s were out.
Military interest in the aircraft was rekindled with the Korean War in the early 1950s. The US Air Force and US Navy both ordered fleets of the aircraft, designated C-118 and R6D respectively, for their logistical needs.
The aircraft served well in Korea and in the wake of that conflict, the type attracted an increase of interest from several militaries worldwide to complement its already well established reputation in international airline service.
Secrets of Success
In a production run spanning 1946 to 1958, more than 700 DC-6 aircraft were made in all variations.
The DC-6 enjoyed a longevity in practical life that none of its contemporaries nor its intended propliner replacement, the DC-7, enjoyed to any equal degree. As of 2018, a few DC-6s are still flying and serving practical purposes.
Over the years, the aircraft served numerous airlines and air transport companies in no fewer than 70 countries and served in the militaries of no fewer than 25 nations. The aircraft enjoyed as much success on second hand markets as it did with original customers and has operated from every continent including both poles.
In light of all that success, one could rightly ask what the DC-6 had to it that allowed it to become the definitive propliner.
Perhaps the best place to start looking is with the aircraft’s origin in a wartime military specification. A military in the midst of active combat will put function over form and simplicity over complexity. Priorities will be on ease of training and maintenance as well as timely production and supply of new aircraft. The design that would become the DC-6 had all of these things going in its favour.
It was not an adventurous design, rather a logical progression of the existing DC-4/C-54 design. As such, the learning curve for any air or ground crew to convert from the DC-4 to the DC-6 was not a steep one; this fact benefitted both civil and military users moving from the DC-4 to the DC-6.
The DC-6 was a relatively simple and strightforward design compared to its nearest contemporary, the Lockheed L-749A Constellation. Both aircraft were well designed and built, but the DC-6 proved more reliable mechanically and more flexible in the variety of roles it could perform. As a result of these qualities, the DC-6 was also more reliable as a money maker for the airlines.
The two aircraft were well liked by both crews and passengers and several airlines operated both types; typically using the Constellation and its better range for longer, intercontinental routes and the DC-6 with its better economics for regional and continental work. While the dawn of the jet age marked the end of the Constellation in widespread airline service, the DC-6 marched on strongly and held its own against jets in the fleets of smaller airlines and cargo operators. Later in life, the DC-6 was widely used in aerial firefighting.
Another aspect of the the DC-6’s success was the choice of engine, the Pratt and Whitney R-2800 Double Wasp. The R-2800 family of engines started in 1937 and became legendary through WWII for their power and reliability. By the time the baseline DC-6 emerged, Pratt and Whitney had developed the R-2800 to a point where it could generate 2,400 horsepower. With the introduction of the DC-6B, Pratt and Whitney had introduced a version of the engine with a 2,500 horsepower output.
Using a quartet of these high performing R-2800 engines gave the DC-6 and impressive lifting ability that kept it in demand for years.
Additionally, compared to the Wright R-3350 engine that powered the Constellation and DC-7, the R-2800 was notably less complex to service and less temperamental and more economical in operations.
A Hauler with More
Aside of its decades of service to many as a workhorse passenger and cargo aircraft, the DC-6 put some other more varied work on its resumé as well.
In Vietnam, a variant of the aircraft known as the MC-118 was used for medical evacuation purposes.
Through the 1950s, the aircraft was used by the CIA for a number of clandestine flights over China and Tibet.
During the 1960s, a pair of specially modified DC-6s were operated by Perdue University in Indiana as airborne transmitters for an educational television program called MPATI, or Midwest Program for Airborne Television Instruction. The priciple of the program was to broadcast educational television to remote regions of the central part of the continental United States. Flying a figure 8 pattern approximately 7 kilometers above Montpelier, Indiana; the aircraft could broadcast to an area of approximately 320 kilometers in radius. During the program, these aircraft broadcast signals to areas in Illinois, Indiana, Wisconsin, Ohio, Michigan, and Kentucky.
Well into the 2000s, the DC-6 could be seen operating in the aerial firefighting role. The Conair company of Canada was a significant user of the type in this way and used the DC-6 in the role until 2012. During their years with the DC-6, Conair deployed their fleet as far afield as Australia to fight wildfires. The DC-6, with a capacity for over 11,000 litres of water or fire retardant, earned much respect in that role.
The DC-6 has also made many film and television appearances over the years.
The DC-6 Family
The DC-6 family contained three core members from which all other variations were developed.
The Baseline DC-6 debuted in 1946 and was a pure passenger carrier available in domestic and trans-oceanic variants. It featured a fuselage 2 metres longer than the DC-4 and more powerful engines.
The VC-118 was a single baseline DC-6 fitted as a presidential transport for the US Air Force.
The DC-6A was the freighter specialist of the family. It featured a slight fuselage stretch over the Baseline DC-6, more powerful engines, strengthened floor, a large cargo door and an elevator capable of lifting 1,800 kg.
The DC-6C was a cargo conversion variant of the family and considered a sub-variant of the DC-6A. It was designed for quick conversion between passenger and cargo configurations.
When taken into US military service, the US Air Force and US Navy had their own individual designation systems for aircraft. To the USAF, the DC-6A was the C-118A while it was the R6D-1 to the USN.
Both the air force and navy had special VIP staff transport variants of the DC-6A, known as the VC-118A and R6D-1Z respectively.
In 1962, the US military introduced a common designation system based on the USAF model. Under the new system, the R6D-1 and R6D-1Z were redesignated C-118B and VC-118B respectively
The most numerous, and by many accounts the best, member of the DC-6 family was the B model. The DC-6B was a passenger variant based on the DC-6A. The A version’s cargo door was deleted and, Like the baseline DC-6, the B version was available in domestic and trans-oceanic versions.
What Remains and Learning More
Several DC-6s are known to remain intact around the world, though the bulk of them are in museums or in storage.
Through an internet search, I could find that in 2017 there were at least 20 DC-6s on civil registers worldwide. Of those, it appeared that around 11 were regular flyers.
The bulk of the flying examples belong to the fleet of Everts Air Cargo in Alaska. According to some references, Everts predicts they have enough spare parts on hand to keep their DC-6 fleet flying at least until 2020.
One of the biggest obstacles to keeping large piston engined aircraft airworthy is the availability of appropriate fuel facilities. Few modern airports keep adequate amounts of avgas readily available for aircraft the size of a DC-6 or the avgas related equipment to fill the DC-6’s large fuel tanks in an efficient manner.
As with so many vintage aircraft, it will be the financial resources and interests of those operating the DC-6 to determine how much longer we’ll be able to see one fly.
For the moment, it seems your best bet to see one fly is to travel to where they still live.
The following links will give you more information about the DC-6
This link will take you to the Delta Flight Museum’s page on the DC-6. It gives some good insights into what made the aircraft attractive to the airline business:
This link will take you to a page with some great information and photos of DC-6 firefighting aircraft in action:
This is the page for the DC-6 of the Red Bull fleet. The only DC-6 to ever be registered in Austria and seemingly the only actively flying one in Europe as of 2018:
While a bit dated in spots, this site has some very good information about the DC-6 in Africa and the disposition of many of the ones that operated there:
This link will give you more information about Perdue University’s MPATI program which made use of two DC-6s in the 1960s: