The dual-engine L-1011 was studied lengthy earlier than ETOPS reshaped aviation. Right here’s why Lockheed’s TwinStar idea by no means flew.
The Lockheed L-1011 TriStar is remembered as one of the vital technologically formidable widebodies of its period. Its quiet cabin, superior autoland functionality, and distinctive S-duct made it one of the vital recognizable airliners of the Seventies and Nineteen Eighties.
However do you know that the TriStar started as a twin-engine idea?
In response to American Airways’ 1966 requirement for a widebody home airliner, Southern California neighbors Lockheed and McDonnell Douglas jumped on the alternative. Whereas McDonnell Douglas started planning for what would ultimately grow to be the DC-10, Lockheed initially studied a twinjet design generally referred to in firm supplies because the CL-1011 (the “CL” stood for California Lockheed). The idea envisioned a short- to medium-haul twin-aisle plane powered by two high-bypass turbofans.
Nonetheless, engine expertise and regulatory constraints formed the ultimate configuration. Powerplant expertise on the time was nonetheless maturing when it comes to thrust and reliability. On the identical time, the FAA’s “60-minute rule” restricted twin-engine plane to routes inside 60 minutes of a diversion airport. For airways looking for most route flexibility, significantly overwater or transcontinental segments, this restriction was vital. Efficiency necessities for hot-and-high airports and shorter runways additionally weighed closely.
Lockheed finally adopted a trijet configuration, including the tail-mounted engine and S-duct that grew to become the TriStar’s signature function.
Revisiting the Twin: Early Seventies Research
By the early Seventies, engine efficiency had improved and airline economics have been shifting. A number of sources point out that Lockheed revisited the thought of a twin-engine spinoff of the TriStar.
One research usually referenced in fanatic and archival discussions is the so-called CL-1600 or Mannequin 1600. This seems to have explored eradicating the middle engine from the present TriStar airframe in pursuit of decrease working prices and simplified upkeep. Interval accounts recommend the corporate believed vital price reductions might be achieved by eliminating one engine and its related programs.
Some secondary sources recommend that such ideas might have been informally mentioned with carriers together with Air Canada, although documentation of formal proposals stays restricted in publicly accessible archives.
These research didn’t progress to a launched program. Eradicating the tail engine from an plane structurally and aerodynamically optimized round a trijet configuration posed nontrivial engineering challenges.
It’s price mentioning that whereas Lockheed was conceptualizing a widebody twin-engine plane based mostly on the TriStar, Airbus Industrie GIE (now Airbus) launched its A300 program. The A300, which carefully resembled what a twin-engine TriStar would have appeared like, first flew in October 1971 and was launched into service with Air France in Could 1974.
It might grow to be the world’s first twin-engine, twin-aisle, widebody airliner, and featured a 2-4-2 seating configuration. It carried between 250-300 passengers, besides as much as practically 370 passengers in a high-density configuration.
The L-1011-600: TwinStar or BiStar
Essentially the most detailed twin-engine proposal related to the TriStar is usually recognized because the L-1011-600, generally referred to in interval illustrations and later discussions because the “TwinStar” or “BiStar.”
Developed within the mid-Seventies as a part of an prolonged household of projected TriStar variants, the -600 was envisioned as a two-engine widebody optimized for shorter-haul routes. The one member of the L-1011 household to succeed in manufacturing was the Lockheed L-1011-500.
Accessible summaries of the -600 idea describe:
Two underwing Rolls-Royce RB211-524 sequence engines within the 50,000-pound thrust classElimination of the middle tail engineWing refinements tailor-made to twinjet operationAlternative vertical stabilizer research, together with a faired-over S-duct configuration and a extra standard twinjet-style fin
Proposed seating seems in most accounts as roughly 174 to 200 passengers, with a projected vary within the neighborhood of two,700 nautical miles. These figures ought to be understood as conceptual targets quite than licensed specs.
Artist renderings, three-view drawings, and desk fashions of the -600 circulated in the course of the research interval. Nonetheless, no launch buyer emerged, and there’s no proof that the design progressed past superior research and advertising and marketing exploration.
So…Why Wasn’t it Constructed?
The explanations span two distinct eras of aviation growth.
Within the Sixties, regulatory restrictions (such because the FAA’s “60 minute rule”) and engine-performance realities favored three- and four-engine configurations for widebody plane. By the point engines such because the RB211-524 made high-capacity twinjets extra viable, the aggressive panorama had modified dramatically.
The Airbus A300 had entered service. The Boeing 767 was on the horizon as a clean-sheet twin optimized from inception for two-engine operation. In the meantime, the TriStar program had confronted vital delays and monetary pressure, together with the well-documented influence of Rolls-Royce’s chapter throughout engine growth.
Airways evaluating fleet choices more and more favored both confirmed current sorts or solely new-generation plane quite than closely re-engineered variants. Lockheed finally selected to withdraw from the business airliner market and focus on navy packages.
Consequently, no twin-engine L-1011 was ever constructed or flown. No manufacturing variant was certificated. Later speculative designations and engine improve eventualities stay hypothetical and are usually not supported by documented Lockheed program launches.
The TriStar’s Legacy — And Its Final Flying Instance
Whereas the TwinStar by no means materialized, the TriStar itself left a exceptional legacy. It’s a legacy we have now lined extensively right here at Avgeekery.
MORE ABOUT THE TRISTAR ON AVGEEKERY
Constructed between 1968 and 1984, Lockheed produced round 250 of the kind, operated by carriers starting from TWA and Delta to Cathay Pacific. Regardless of its superior design, early engine provider delays and related price overruns slowed entry to market and opened the door for rivals just like the McDonnell Douglas DC-10 to win early gross sales. Lockheed by no means managed to succeed in the manufacturing volumes it wanted for business profitability, finally withdrawing from the civilian plane business.
That legacy continues in a novel means: one L-1011 stays airworthy in the present day. The plane often called Stargazer — delivered in 1974 and initially operated by Air Canada — has been modified and operated as a peg-launched rocket mothership underneath firms now a part of Northrop Grumman. As of 2026, Stargazer is the one L-1011 nonetheless flying and frequently performs missions out of Mojave Air and House Port (MHV) in California, carrying Pegasus launch automobiles to altitude earlier than launch.
An Aviation What-If
The dual-engine L-1011 stays certainly one of business aviation’s extra intriguing “what might need been” tales.
The idea was born throughout a transitional second in business aviation when widebody design philosophy was making the transition from tri- and quad-engine configurations towards the twinjet dominance that might outline later a long time. The research have been actual. The renderings existed. The engineering was explored.
However the market moved sooner than the ideas.
In the long run, the TriStar’s third engine grew to become its defining trait, and the dual remained an idea confined to drawings, desk fashions, and the margins of aviation historical past.
