• Trijets: Flying through engine’s history

    A trijet flying through countryside

Trijets, also known as tri-engines, are aircraft equipped with three engines, one located on each wing and the third in the tail or fuselage. These aeronautical prodigies were extremely sought after during the 1970s and 1990s, when they served large routes with considerable cargo capacity.

However, technological evolution was not favourable to them and they were gradually relegated by twin-engine and four-engine aircraft.

In this post, we invite you on a journey through the timeline of these aircraft, from their conception to the present day and eventual projections.

First steps of the three engines

Firstly, three-engined aircrafts emerged in the 1930s, as a strategy to increase the power and safety of twin-engines. Iconic aircraft of the era include the German Junkers Ju 52, the American Ford Trimotor and the Italian Savoia-Marchetti SM.79.

These propeller-driven aircraft featured a traditional configuration, with two engines in the wings and one in the bow.
As a consequence of the advent of jet engines, the tri-props had to reinvent their design. Particularly, the British Hawker Siddeley Trident, which first took off in 1962, became the commercial pioneer with three jets.

This aircraft had two engines in the wings and a third in the tail, with an air intake on the fuselage. This design set a precedent for later models such as the American Boeing 727 and the Soviet Tupolev Tu-154.

For those interested in a more in-depth look at aircraft engines, we suggest you check out our article dedicated to the subject – it’s a must-read!

Evolution of the trijet

Tri-props enjoyed their heyday between the 1970s and 1990s, when they were commonly employed for transcontinental and transoceanic routes.

Surprisingly, these aircraft had the advantage of being able to reach greater distances than twin jets, without having to adhere to safety restrictions limiting the maximum distance they could fly away from an emergency airport. They also consumed less fuel than four-engines, making them a more cost-effective option.

Some of the most recognisable tri-props of this era include the McDonnell Douglas DC-10 and its successor the MD-11, which could accommodate up to 380 passengers and cover a distance of up to 12,000 km; the Lockheed L-1011 TriStar, distinguished by its comfort and advanced technology; and the Dassault Falcon 900, the world’s smallest private jet equipped with three engines.

  • Three-engine aircraft, American Air force

Pioneering manufacturers

The leading manufacturers in the production of tri-propellant engines are:

  • Boeing: The US giant has built two models of tri-jet: the Boeing 727, which became the best-selling commercial aircraft until the advent of the Boeing 737; and the Boeing 757-200M, a mixed passenger/cargo version of the Boeing 757, which was only produced for the Royal New Zealand Air Force.
  • McDonnell Douglas: The late US firm was the originator of the DC-10 and MD-11, two aircraft popular with commercial airlines and cargo companies. The MD-11 was the last three-engine aircraft produced by McDonnell Douglas before its merger with Boeing in 1997.
  • Lockheed: This US corporation specialising in defence and aerospace designed the L-1011 TriStar, an innovative aircraft that incorporated automatic flight and landing systems, a spacious and quiet passenger cabin, and an aerodynamic design that reduced fuel consumption.
  • EAA three-engined aircraft on the ground
  • Dassault: The French military and business jet producer has developed several three-engine models, including the Falcon 50, Falcon 900 and Falcon 7X. These aircraft are characterised by their luxury, performance and versatility, as they can land on short runways and fly at high altitude.
  • Tupolev: The Russian aircraft design firm has produced two three-engine aircraft. One of them is the Tu-154, the most widely used aircraft in the former Soviet Union. The second one is the Tu-22M, a supersonic bomber that entered service in 1972 and is still operational.

What is happening to the Jetpack today?

At present, jet aircraft are becoming increasingly rare in the skies. The main reason is that modern engines are more powerful, reliable and efficient than those of a few decades ago, which allows twinjets to deliver the same performance as jet aircraft, but at a lower operational and environmental cost.

In addition, safety regulations have been relaxed for twinjets, allowing them to fly further away from alternative airports.

In spite of this, there are currently about 200 tri-jets left in service worldwide, most of them dedicated to cargo transport. Moreover, there are airlines that still rely on them! Like FedEx, UPS, Lufthansa Cargo or KLM. And the most common aircraft are the MD-11 and the Boeing 727.

The future of trijets

As a consequence, the future projection of this type of tri-engine planes is uncertain. On the one hand, it seems unlikely that new models of commercial jet aircraft will be produced. It’s a fact that twin-engines have proven to be more competitive in today’s market.

On the other hand, some military or experimental aircraft projects continue to rely on the three-engine configuration, such as the Northrop Grumman B-21 Raider stealth bomber, which is expected to enter service in the 2020s.

We won’t forget what trijet have meant

Undoubtedly, technology has developed and the market has evolved, three-engine aircraft have become less popular in favour of more efficient options, but we must not forget that they have been an important part of aviation history!

We hope this post has brought you closer to the history of aircraft engines. If you want to know more about this fascinating world, we invite you to continue exploring our blog. See you next time!

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