Once the mainstay of many airlines' medium and long-haul fleets, sadly, the days of three-engined airliners are all but over. Starting a new series for Simple Flying, where we take a look at the key differences between historic airliners of yesteryear, we kick off with two legendary tri-jets - the McDonnell Douglas DC-10 and the Lockheed L1011 TriStar.

Introducing the two protagonists

Both equipped with three powerful high-bypass ratio turbofan engines, the DC-10 and the Tristar were significant developments of their age. Launched roughly around the same time, the two competing aircraft battled for supremacy in the medium to wide-bodied long-haul market, winning large orders quickly and becoming regular visitors at airports worldwide.

It would be the DC-10 that would ultimately become the better seller of the two models, selling 446 airframes in total versus 250 Tristars. Although the L-1011 was a superb aircraft for its time, it lost out to its rival, which came to the market first a year earlier. As a result, the Tristar missed out on crucial revenue from potential sales that went to the McDonnell Douglas aircraft.

This factor ended up causing the project and, indeed, Lockheed itself huge losses. It sold 250 units, whereas it needed to sell 500 for the project to become profitable. There was also a public relations disaster when Lockheed bribed figures in the Japanese government to partly pay for All Nippon Airways' purchase of the L-1011.

With massive losses and the only engine manufacturer for the Tristar - Rolls-Royce - almost going out of business too, the program was wound up, and Lockheed quit the commercial airliner market to concentrate on their military projects instead.

The DC-10 - a brief history

The design of the DC-10 began in 1966 to meet the requirements of American Airlines for a large capacity widebody airliner. Following an initial order for 25 aircraft plus 25 options from American and 30 plus 30 options from United Airlines, the DC-10 went into production in 1968.

A low-set, swept wing configuration with a pylon-mounted engine under each wing, coupled with all-swept tail surfaces and the third engine mounted at the foot of the vertical stabilizer, the first flight of the DC-10 took place in August 1970. Following receipt of its certificate of airworthiness, the type entered service with American Airlines on August 5th, 1971.

A design flaw in the cargo doors of the DC-10 caused a poor safety record in early operations. Following the accident involving American Airlines flight 191 in May 1979 (the deadliest aviation accident in US history), the Federal Aviation Administration (FAA) temporarily grounded all US-registered DC-10s in June 1979.

In August 1983, McDonnell Douglas announced that production would end due to a lack of orders - the model having acquired widespread public apprehension after the 1979 crash along with its generally poor fuel economy.

The manufacturer ultimately delivered 446 DC-10s of all variants, the last of which was delivered to Nigeria Airways in 1989. However, production of the military variant, the KC10A Extender, a model generally similar in design to its civil stablemate and used for inflight refueling and cargo transport by the US Air Force, continued until the start of 1990.

The Tristar - a brief history

Lockheed's widebody offering came in the form of the model L1011, more commonly known as the Tristar when it was first launched, to meet American Airlines' requirements. Construction began in early 1968, just like the DC-10, and the first flight of the Tristar took place on November 17th, 1970.

The Tristar was a cantilever low-wing monoplane with 35 degrees of wing sweep and powered by three Rolls-Royce RB211 turbofans. At an early stage of development, Lockheed and Rolls-Royce ran into severe financial difficulties, both requiring financial aid from their respective governments to stay afloat before the program could be resumed.

As a result, certification was not obtained until April 14th, 1972, almost a year after that of its arch-rival, the DC-10.

The first revenue flight by a Tristar was flown by the aircraft's launch customer, Eastern Airlines, on April 26th, 1972. Some teething problems followed, primarily with the engines, but in a very short space of time the Tristar was proving popular with operators and passengers alike.

Key differences between the two models

While largely developed in parallel to the same set of requirements from American Airlines, there were some key differences between the two models. We will look at each aspect of these differences in turn, starting with capacity, followed by each model's main technical specifications and performance, powerplants, orders, and finally, the key external differences between the two.

Capacity

Depending on the airline operator, the DC-10 was offered in various configurations but could generally carry between 250 and 380 passengers. Although the maximum number of passengers carried on a DC-10 was 399 in an all-economy layout, the FAA restricted US-registered planes to 380 passengers for safety reasons relating to the availability of emergency exits.

The Tristar was similarly able, designed to carry between 256 and 400 passengers depending on the configuration chosen by the operator. Many Tristars that went into service later on in their lives with charter carriers around the world, such as Caledonian Airways in the UK, often fitted 398 passengers into the aircraft for their all-inclusive, medium-haul route network.

Technical specifications and performance

The maximum cruising speed of the DC-10 series 30 was 564 mph (908 kph). The service ceiling was 33,400 feet (10,180m), and the aircraft's range with a maximum payload was 4,605 miles (7,411 km). The DC-10 was 182 ft 1 in long (55.50 m) with a wing span of 165 ft 4 in (50.41 m) and a height of 58 ft 1 in (17.70 m). The Dc-10s wing area was 3,958 sq ft (367.70m).

The DC-10 series 30 had a maximum cabin width of 19 ft 9 in (6.02 m) and offered a maximum take-off weight of 572,000 lbs (259,459 kg).

In terms of the Tristar, the series 500 long-range variant had a cruising speed of 605 mph (974 kph). The service ceiling was 42,000ft (12,800m), and the aircraft's range with a maximum payload was 5,998 miles (9,653 km).

The Tristar 500 was 164 ft 2 in long (50.05 m) with a wing span of 155 ft 4 in (47.35 m) and a height of 55 ft 4 in (16.87 m). The Tristar's wing area was 3,456 sq ft (321.06 sq m). The Tristar 500 had a maximum cabin width of 18 ft 11 in (5.76 m) and offered a maximum take-off weight of 496,000 lbs (231,332 kg).

Powerplants

While the DC-10 was generally offered with a single choice of engine in the form of the General Electric CF-6 turbofan engine, the later series 40 variant (built purely for the intercontinental market) had the Pratt & Whitney JT-9D powerplants, which offered higher overall thrust of 49,400 lbs (235.8kN).

The Tristar, like its contemporary, had just a single choice of powerplant in the form of the Rolls-Royce RB211-22, later upgraded to the RB211-524 engine.

Order books

As we have seen, the DC-10 did better in terms of commercial sales than its competitor, selling 446 models of all variants. The DC-10's primary customers were American Airlines, United Airlines, and Western Airlines, alongside KLM and Swissair in Europe.

The aircraft had a very successful later life as a freighter, particularly with FedEx, which converted many MD-10s to have upgraded cockpits, which eradicated the need for a flight engineer. The military variant, the KC-10A, has been extensively used by the US Air Force but has largely been replaced by the Boeing KC-767, based on the 767-200 passenger aircraft.

The Tristar sold just 250 airframes of all models. The aircraft's launch customer was Eastern Airlines, but with that carrier's bankruptcy, its fleet of Tristars quickly found other homes. TWA and Air Canada were also early customers, with British Airways operating a relatively large fleet of Tristars throughout the 1980s.

Other significant operators of the Tristar included Cathay Pacific, Pan Am, Royal Jordanian, Gulf Air, Hawaiian Airlines, and All Nippon Airways.

External differences

Although similar in design and specification, the two models had specific differences that would distinguish them from each other when parked at neighboring gates. The most notable external difference was the design of the third tail-mounted engine. While the DC-10 sported a horizontal engine directly over the rear fuselage and underneath the vertical stabilizer, the Tristar's tail engine was of an S-shaped design.

The engine intake was set above the fuselage, but the engine exhaust housing snaked down through the rear fuselage and out via a tailpipe located at the furthermost end of the empennage, giving a generally smoother look and sleeker lines to that of the DC-10.

Other notable differences were that the DC-10 sported a more blunt front end with a less protruding nose section than the Tristar. The latter also offered much larger fuselage windows than the DC-10.

One of the differences between the later DC-10 series 30 and Tristar was that the DC-10 took on the three-leg main undercarriage configuration, adopting a third center gear leg directly underneath the center fuselage to cope with the higher gross weight offered by the DC-10 series 30 (and later the series 40).

Lastly, the Tristar's two wing-mounted engines were on much more forward-protruding engine pylons than those found on the DC-10. Those readers who remember the Tristar may also recall the plumes of gray smoke drifting across airfields as Tristar flight crews would start their engines on colder mornings - a particular characteristic of the mighty Tristar!

In summary

The two airliners competed in the same market for the same orders from the same airlines. However, the DC-10 won the day after the Tristar suffered heavily due to the production and certification delays following the financial issues suffered by both Lockheed and Rolls-Royce.

That said, both models, although now long gone from regular commercial passenger service, enjoyed successful carriers with their respective carriers, carrying many millions of passengers across the world on flights for both business and pleasure.

Do you have memories of flying either on the DC-10 or the Tristar? Do share your experiences with these classic airliners with us in the comments.

Sources: Aircraft.fandom.com, Aviation Safety Network