Trijets have always captured my imagination, tracing back to my childhood when I received a children’s book about airplanes. One of the pages presented a comparison between two types of trijets. I was well-acquainted with the McDonnell Douglas DC-10, but the accompanying illustration introduced me to another aircraft: the Lockheed L-1011 Tristar. This comparison allowed me to notice both the differences and similarities between these two aircrafts. As I continued to explore and see more images of the Lockheed L-1011 Tristar, my affection for it grew. Now, it’s a pleasure to discuss this iconic jetliner in more detail.
The Lockheed L-1011 Tristar, a unique creation by Lockheed Corporation, stands as their only venture into commercial jet transport to date. This aircraft earned its name, Tristar, through a staff competition, and soon became synonymous with advanced technology and innovative design. Lockheed, a corporation known for military transport success stories like the C141 Starlifter and the C5 Galaxy, had taken a hiatus from commercial passenger transport production since the L188 Electra in 1961, until the birth of the Tristar.
Design and Technology
Peering into the L-1011 Tristar’s aviation technology offers insights into an aircraft engineered for maximum performance, safety, and convenience.
Engine Configuration and Features
One of the distinct characteristics of the Tristar is its Rolls Royce RB211 engines. These engines are known for their superior fuel economy and notably low noise levels.
The development process was no easy feat. Initially, the RB211 engines featured thrust-spoilers for capturing a quarter of the total engine thrust. However, interference with the flaps reduced the flaps’ braking effectiveness, leading to a shift in design. Lockheed then installed an 11-degree afterbody, enhancing the specific range by 1.5%. Subsequent modifications further improved this to a 15-degree afterbody, boosting the aircraft’s efficiency.
All-Flying Tail
Contrary to the typical trimmable horizontal stabilizer found on many jetliners, the Tristar was equipped with an all-flying tail, or a stabilator. This design integrated a geared elevator that moved concurrently with the stabilator, altering its camber and enhancing the overall effectiveness of the control surface.
This design aimed to eliminate mis-trim and runaway trim problems, enhancing the safety and reliability of the aircraft. However, it’s important to note that the design also presented challenges, as evidenced by incidents such as the jamming of the left elevator on Delta Air Lines Flight 1080 in 1977.
The Fuel and Landing Gear System
The Tristar fuel system was configured in a manner that offered maximum efficiency. The four-wing tank design of the L-1011-1 ensured a balanced supply of fuel. Each inboard tank fed its corresponding wing engine, while the two outboard tanks fed the tail engine.
Lockheed didn’t just pay attention to the fuel system; the landing gear design was also given careful thought. The nose landing gear was designed with two attachment points, forward and aft. This allowed a sufficiently small tug to push or pull the aircraft from directly underneath, a feature meant to allow operations where forward space at airports was limited.
Electrical System, Avionics, and More
The Tristar’s electrical system featured an industry-first integrated drive generator, while the avionics were state-of-the-art for their time. The Flight Management System (FMS) on the L-1011, certified in 1977, offered a suite of advanced features that significantly reduced crew workload and enhanced fuel efficiency.
The Tristar was the first widebody aircraft to receive FAA certification for Cat-IIIC autolanding. This allowed the aircraft to perform entirely blind landings in zero-visibility weather, controlled entirely by the autopilot system. The Tristar used an inertial navigation system for guidance, and incorporated a unique direct lift control (DLC) system for smoother landings.
The Tristar stood out from the crowd with its auxiliary power unit (APU), which could function at heights of up to 30,000 feet, and its four independent hydraulic systems for enhanced redundancy and safety. Moreover, the aircraft used a unique “autoclave” system for bonding fuselage panels, rendering the L-1011 exceptionally resistant to corrosion.
L-1011 Tristar Variants and Specifications
The L-1011 Tristar had different variants, including the -1, -100, and -150, which can be differentiated from later models by the middle engine nacelle design. The earlier versions featured a round intake while later models sported a small vertical fin.
Some L-1011s, including the two delivered to Pacific Southwest Airlines, were configured with internal airstair doors. This feature, intended to enable operations from airfields lacking terminal buildings with jet bridges, was later seen in service with Aeroperú and Worldways Canada.
L-1011-1
Launched in 1972, the L-1011-1 was the first production model designed for short and medium-range flights. Serving as the basis for subsequent variants, it saw orders from numerous airlines, with most sales occurring in the US. A total of 160 units were built before production ceased in 1983.
L-1011-100
The second model, the L-1011-100, first flew in 1975 and introduced a new center fuel tank and higher gross weights, increasing the aircraft’s range by about 930 miles. Orders were placed by several airlines, including Saudia and Cathay Pacific.
L-1011-50 and L-1011-150
The L-1011-50, an upgraded version of the -1, increased the maximum takeoff weight but did not augment fuel capacity. Similarly, the -150 increased its maximum takeoff weight, improving range, but without an additional center-section fuel tank, its range was still less than the -100.
L-1011-200
Introduced in 1976, the -200 variant utilized Rolls-Royce RB.211-524B engines to enhance performance in hot and high-altitude conditions. Apart from engines, it was essentially identical to the -100. The -200 series had a total production run of 24 new aircraft.
L-1011-250
The -250 upgrade applied to late-model L-1011-1 aircraft and all -100 and -200 aircraft, offering increased maximum takeoff weight and fuel capacity. The more powerful engines enabled the L-1011 to match the performance of the long-range McDonnell Douglas DC-10-30.
L-1011-500
The last variant, the L-1011-500, was a longer-range version first tested in 1978. It had a shortened fuselage length and increased MTOW, allowing for higher fuel loads. It featured more powerful RB.211-524 engines, increased wingspan, and improved systems. It was popular among international operators, but its late introduction gave the similar DC-10-30 an advantage in securing orders from potential customers.
The -500 had an overall length of 164 feet 2 inches and an increased wingspan of 164 feet 4 inches. It introduced aerodynamic improvements such as a modified wing-to-body fairing, extended wingtips, and an active control system (ACS). The more powerful RB211-524B engines were also introduced in this model.
This variant also had an original MTOW of 496,000 pounds, later increased to 510,000 pounds, and had a standard fuel capacity giving it a range of about 5,200 nautical miles with 246 passengers. Passenger capacity varied according to the configuration, with a maximum of 315, but typically, the aircraft accommodated around 250 passengers in a two-class layout. It had fewer exits than the long-body TriStars, reducing the exit limit maximum.
| L-1011-1 | L-1011-200 | L-1011-500 | |
|---|---|---|---|
| Cockpit Crew | 3 (Pilot, Co-pilot, Flight Engineer) | 3 (Pilot, Co-pilot, Flight Engineer) | 3 (Pilot, Co-pilot, Flight Engineer) |
| Interior Width | 18 ft 11 in (5.77 m) | 18 ft 11 in (5.77 m) | 18 ft 11 in (5.77 m) |
| Length | 177 ft 8+1⁄2 in (54.17 m) | 177 ft 8+1⁄2 in (54.17 m) | 164 ft (50.05 m) |
| Wingspan | 155 ft 4 in (47.35 m) | 155 ft 4 in (47.35 m) | 164 ft 4 in (50.09 m) |
| Height | 55 ft 4 in (16.87 m) | 55 ft 4 in (16.87 m) | 55 ft 4 in (16.87 m) |
| Wing Area | 3,456 sq ft (321.1 m2) | 3,456 sq ft (321.1 m2) | 3,541 sq ft (329.0 m2) |
| Maximum Takeoff Weight (MTOW) | 430,000 lb (200,000 kg) | 466,000 lb (211,374 kg) | 510,000 lb (231,332 kg) |
| Operating Empty Weight (OEW) | 241,700 lb (110,000 kg) | 248,400 lb (113,000 kg) | 245,400 lb (111,000 kg) |
| Fuel Capacity | 23,814 US gal (90,150 L) | 26,502 US gal (100,320 L) | 31,642 US gal (119,780 L) |
| Engines (×3) | Rolls-Royce RB211-22 | RB.211-524B | RB.211-524B |
| Thrust (×3) | 42,000 lbf (187 kN) | 50,000 lbf (222 kN) | 50,000 lbf (222 kN) |
| Maximum Operating Speed (Mmo) | Mach 0.90 (516 kn; 956 km/h) | Mach 0.90 (516 kn; 956 km/h) | Mach 0.90 (516 kn; 956 km/h) |
| Cruise Speed | 520 kn (963 km/h) | 515 kn (954 km/h) | 525 kn (972 km/h) |
| Stall Speed | 108 kn (200 km/h) | 110 kn (204 km/h) | 114 kn (211 km/h) |
| Range | 2,680 nmi (4,963 km) | 3,600 nmi (6,667 km) | 5,345 nmi (9,899 km) |
| Ferry Range | 4,250 nmi (7,871 km) | 4,935 nmi (9,140 km) | 6,090 nmi (11,279 km) |
| Service Ceiling | 42,000 ft (12,800 m) | 42,000 ft (12,800 m) | 43,000 ft (13,100 m) |
Comparing the Tristar to the DC-10
When comparing the Lockheed L-1011 Tristar to its contemporary, the McDonnell Douglas DC-10, you’ll find a striking resemblance. The key differentiating factor lies in the configuration of the Number 2 engine, positioned at the rear of the fuselage. Instead of mounting the engine externally as part of the tail, like the McDonnell Douglas, Lockheed preferred an internal fuselage mount, a method resembling the Boeing 727 design.
Despite the seeming similarities, the two manufacturers undertook drastically different approaches to overcome design challenges. McDonnell Douglas, under significant budget constraints, borrowed heavily from their DC-8 jet airliner’s technology. Lockheed, on the contrary, ventured into new territory by employing groundbreaking technology wherever possible, even inventing it when it didn’t exist.
This audacious approach led to several noticeable enhancements. The Tristar was a notably quieter aircraft, a quality that led Eastern Air Lines to affectionately name their L-1011s, ‘WhisperLiners’. Among the various differentiating technologies that the Tristar introduced were the advanced auto-pilot rated for Cat-IIIc auto landing, the Direct Lift Control system that ensured smoother landing approaches, and the Auto Clave, a system for bonding fuselage panels rendering them highly resistant to corrosion.
| Characteristics | Lockheed L-1011 TriStar 500 | McDonnell-Douglas DC-10-30 |
|---|---|---|
| Length | 50.05 m (164 ft) | 55.50 m (182 ft 1 in) |
| Wingspan | 50.09 m (164 ft 4 in) | 50.40 m (165 ft 4 in) |
| Wingarea | 329.00 m² (3,541 ft²) | 367.70 m² (3,958 ft²) |
| Height | 16.87 m (55 ft 4 in) | 17.70 m (58 ft 1 in) |
| Engines | 3 | 3 |
| Thrust per engine | 222 kN (50,000 lbf) | 240 kN (54,000 lbf) |
| Total thrust | 666 kN (150,000 lbf) | 720 kN (162,000 lbf) |
| MTOW (Maximum Takeoff Weight) | 231,332 kgs (510,000 lbs) | 263,085 kgs (580,000 lbs) |
| Range | 9,899 km (5,345 nm) | 7,415 km (4,004 nm) |
| Cruise Speed | M0.84 | M0.84 |
| Capacity | 230 passengers | 250 passengers |
History of the L-1011 Tristar
In the late 1960s, American Airlines approached aircraft manufacturers, including Douglas and Lockheed, with the need for a new widebody jet that was smaller than the Boeing 747 but could manage intercontinental routes. Lockheed responded with a design for a large twin-engined aircraft. However, international operations required an adjustment to a three-engine design to comply with the ETOPS30 (Extended Operations) restriction.
In spite of all its technological advances, the Tristar was more expensive than its rival, the DC 10. This pricing put the Tristar in a difficult market position, as for a slightly higher price, buyers could opt for a Boeing 747.
Another challenge the Tristar faced was Lockheed’s firm decision to stick with one engine choice only – the Rolls Royce RB211. Despite the RB211 concept’s superiority, its development cost led to financial trouble for Rolls Royce, even leading to the British government intervening with subsidies to continue its development.
Even with the struggles, the Tristar took its maiden flight on November 16, 1970, received FAA certification by April 14, 1972, and was delivered to Eastern Air Lines by April 26, 1972. The same year, Lockheed took the L1011 Tristar on tour, with famous Lockheed test pilot Tony LeVier at the helm. This tour became renowned for a landmark event where the aircraft, under autopilot control, completed a flight from Palmdale to Dulles in just 4 hours and 13 minutes, without a single human touch.
Produced from 1968 to 1984, Lockheed manufactured a total of 250 Tristars, falling short of the required 500 to break even. This shortfall led Lockheed to withdraw from the commercial aviation market post-Tristar, marking a pivotal point in the industry’s landscape.
First love never dies. I fell in love with airplanes and aviation when I was a kid. My dream was to become a pilot, but destiny led me to another path: to be an aviation digital media content creator and a small business owner. My passion for aviation inspires me to bring you quality content through my website and social accounts. Aviation is indeed in my blood and blog!
