Through the 1950s Douglas and Lockheed engaged in a rivalry to create the ultimate propliner as each company successively improved its product line to appeal to the rapidly expanding passenger market. Douglas' DC-6 led to the more powerful DC-7 and even with this aircraft, the design was pushed even further with the DC-7C. In addition to more power and fuselage stretch, the "Seven Seas" also had a constant-chord wing-root section added inboard of the engines. Not only did this move the loud radials five feet further away from the passenger cabin, it also increased the aspect ratio of the wing, reduced drag, and provided more space for internal fuel. The DC-7C could now outperform Lockheed's flagship propliner, the L-1049G Super Constellation, in terms of speed, range, and payload, allowing all-year round nonstop trans-Atlantic service. Not to be outdone, Lockheed briefly considered a turboprop Constellation, the L-1449, using the new Pratt & Whitney T34 engine (which was used on the Douglas C-133 Cargomaster). While military Constellations did flight test both the T34 installation and the Allison 501 turboprop (military versions of which were used on the C-130 Hercules and P-3 Orion), Pratt & Whitney balked at the use of the T34 as they felt Lockheed was pushing the engine too far.
Scrapping the L-1449 out of the dispute with Pratt & Whitney, Lockheed took the new wing design it had developed for the turboprop L-1449 and grafted it on a stretched L-1049 Super Constellation fuselage to give birth to what many consider to be one of the ultimate piston engine airliners, the L-1649 Starliner. The wing was modified to accept the powerful Wright R-3350-18EA Turbo Compound radial engines which were originally developed to power the Navy's Lockheed P-2 Neptune patrol bomber. The 18-cylinder R-3350 instead of using a turbocharger for high altitude performance had power recovery turbines instead (PRTs)- one PRT collected the exhaust gases from six cylinders to deliver more power back to the engine crankshaft, providing a 500 horsepower boost. The same engines were used on the DC-7C as well. The long wing of the Starliner gave it the highest aspect ratio wing of any propliner, 12:1, and this translated to improved performance over the DC-7C. Nearly 2,000 gallons more of fuel could be carried compared to the Super Constellation. Like the DC-7C, the longer wing put the inboard engine nacelles further away from the passenger cabin.
The Starliner made its first flight from Burbank on 10 October 1956. Amazingly, only three Starliners were used for a short 251-hour flight test program to get airworthiness approval on 19 March 1957. With a cost of $3 million per aircraft, TWA inaugurated L-1649 Starliner services on 1 June 1957, exactly one year to the day that the Douglas DC-7C was introduced into service. Though the DC-7C was faster, the Starliner had a longer range as well as a quiet and smooth ride thanks to increased sound insulation in the cabin and a flexible wing that dampened inflight turbulence. TWA marketed its Starliners as "Jetstream Starliners" and on marketing artwork, the wingspan of the Starliner was exaggerated to make the engines appear further from the fuselage than they were. In addition, artists cleverly depicted the Starliner without propellers, much to the ire of competing airlines that cried foul over the advertising campaign they called deceptive. TWA's famous inflight Ambassador Service was upgraded for the Starliners. The passenger seats were called "Siesta Sleeper Seats" that had pull out foot rests and a deep seatback recline that were nearly as comfortable as the sleeper berths which of course were still available on the Starliner's long routes. In the lounge area of each Starliner were cabin wall murals created specifically for TWA's aircraft by the artist Mario Zamparelli that showcased TWA's overseas destinations.
The long range of the L-1649 Starliner allowed TWA to open up polar routes from the US West Coast to Europe. The inaugural TWA polar flight, Polar Flight 801, set a world record for the longest piston engine airliner flight on 2 October 1957 when flying westbound from London to San Francisco, encountered strong headwinds that resulted in a marathon 23-hour 19-minute nonstop flight. As impressive as the capabilities of the Starliner were, only TWA, Air France, and Lufthansa would be first-liner operators as few of the world's airlines had a route network and passenger traffic that made the Starliner economical. The Starliner only flew first line services for less than three years before getting displaced by the Boeing 707 and as a result of coming to market one year later than the Douglas DC-7C, only 44 Starliners were built compared to 121 DC-7Cs. When the final L-1649 Starliner was rolled out of the Burbank factory on 12 February 1958 for Lufthansa, it wasn't just the last Starliner but it was the end of the line for the Constellation family that stretched back to 1943.
One interesting side note from TWA's operation of the Starliner came about due to reliability issues with the R-3350 Turbo Compound engines. While they were some of the most powerful piston engines ever flown, they were a maintenance nightmare compounded by the intricate plumbing work of the three power recovery turbines. In fact, TWA mechanics joked that PRT actually stood for "Parts Recovery Turbine". To minimize the disruption caused by engine failures, TWA acquired a military surplus Fairchild C-82 Packet transport that had a Westinghouse J34 engine in a dorsal nacelle as a jet booster. Nicknamed "Ontos" (the Greek word for "thing"), the C-82 could carry whole R-3350 Turbo Compound engines and a maintenance team to outlying stations where a Starliner might be stranded. Even though the Starliner would be phased out of TWA service, the airline kept Ontos in service to carry spare jet engines for the Boeing 707 and even the Boeing 747, finally retiring the odd bird in January 1972.
Source: From Props to Jets: Commercial Aviation's Transition to the Jet Age 1952-1962 by Craig Kodera, Mike Machat, and Jon Proctor. Specialty Press, 2010, p77-85.