The Future of Trijets in Modern Aviation

The trijet, a configuration of three engines on an aircraft, has played a significant role in aviation history, particularly with aircraft like the Dassault Falcon 7X and Falcon 8X. However, the question remains: will trijets ever return to commercial aviation?

Current Trijet Models in Production

Currently, two trijets are still in production:

Dassault Falcon 7X: This corporate jet utilizes a unique S-duct engine as one of its three engines, contributing to its lower ground clearance and easier loading, valuable features for private jets catering to VIP transport. However, the maintenance of this S-duct engine may not be as straightforward as simpler engine designs. Falcon 8X and Falcon 900: Both are corporate jets with a slightly larger configuration, often used for VIP transport with full seating, carrying less than 20 passengers. Due to their inconsistent passenger-to-thrust ratios and cost factors, these options are generally not economically viable for regular commercial flights.

Engine Technology and Design Philosophy

Engineers continuously strive to create the best design possible with the technology available at the time. In the 1960s, the Boeing 747–100 faced limitations in engine technology, necessitating the use of the Pratt Whitney JT9D-3A engines, which provided 43,500 pounds of thrust each. Four of these engines were required for the 747–100 to achieve the necessary thrust of 174,000 pounds, carrying 366 passengers.

Today, jet engine technology has advanced significantly. The Boeing 777X, for instance, features two GE9X engines with 110,000 pounds of thrust each, totaling 220,000 pounds of thrust, and carries 426 passengers. The 747–8 offers a more efficient passenger-to-thrust ratio of 1.75 passengers per 1,000 pounds of thrust, with 266,000 pounds of total thrust, flying 466 passengers. The ratio stands at an even more economical 1.93 passengers per 1,000 pounds of thrust with a 777.

Hybrid Configurations and Partial Electrification

There have been discussions about innovative hybrid configurations, where the third engine could be used exclusively for takeoff climb and go-around capability, and shut down during cruise. This concept presents potential in a partly electric aircraft, where more efficient but less powerful electric fans could be used for cruise operation, reducing fuel consumption and operational costs.

Looking to the Future

The return of trijets to commercial aviation seems unlikely. The inclusion of four engines has become more practical with the availability of larger and more reliable engines. Two engines are now acceptable for ETOPS, ensuring safe long-distance flights over water. The potential costs, complexity, and maintenance of three engines in today's highly cost-conscious airline operations make it an undesirable choice.

While the trijet configuration has been a vital part of aviation history, its place in modern commercial aviation appears to be limited to niche applications or specialized uses, such as the Falcon series for private jets and VIP transport. Future advancements in engine technology and aircraft design are likely to further limit the chances of trijets returning to the skies in the commercial sector.