What is the Largest Theoretical Size of a Trijet, Inspired by the Lockheed L-1011 TriStar's Legacy?

With the current state of technology, the largest commercial jet engine, the GE-9X turbofan, presents a formidable challenge for trijet designs. Two GE-9X engines powering a gigantic 777 passenger jet is impressive enough, but the potential for a trijet with three such powerful engines is even more awe-inspiring. In fact, it has been estimated that three GE-9X engines could produce 400kn more thrust than the four GENX engines powering the 747–8, suggesting the possibility of a plane so large that it could be the biggest airliner ever built.

Theoretical Limits and Practicality

It's important to recognize that there is no one theoretical maximum size for an aircraft. Instead, current trends favor twin-engined designs due to engine advancements. Today, engines have become larger and more powerful, making redundancy with additional engines unnecessary. The shift towards larger engines using just three units can potentially lead to massive trijet designs. However, the real-world limitations become overwhelming as the physical size of the aircraft grows beyond what current airport infrastructure can accommodate.

The Role of Engine Technology

The GE-9X turbofan represents the pinnacle of contemporary engine technology. When considering a trijet configuration, using three powerful GE-9X engines, the theoretical maximum size of an aircraft could be dramatically increased. Such an aircraft, with sufficient thrust from these engines, could potentially surpass the size of any aircraft ever constructed.

Practical Challenges and Limitations

While the idea of a trijet with three GE-9X engines is fascinating, reality imposes strict boundaries on aircraft design. The size limitations are often dictated by practical considerations such as airport infrastructure and operational logistics. Increasing the size of an aircraft necessitates larger wings and therefore new airports. This is why the Airbus A380 team meticulously designed the aircraft to a size comparable to a Boeing 747, ensuring it could fit into existing airports.

Engine Thrust and Airline Considerations

Engine thrust is a critical factor in determining the maximum size of an aircraft. If two GE-9X engines can power a 777 with plenty of power to spare, the possibility of three engines producing even greater thrust suggests the potential for a much larger aircraft. However, the real-world challenges are substantial. The wings of such a plane would need to be significantly enlarged, potentially making the aircraft too large for many current airports.

Wheel Loading and Infrastructure

Increasing the size of an aircraft also mandates greater wheel loading, which in turn requires new airport runways and taxiway infrastructure. This necessitates the addition of extra wheels or bogies to distribute the weight more evenly. Furthermore, the complexity of emergency egress and the certification requirements for passenger safety add to the design challenges.

Conclusion

In summary, the largest theoretical size of a trijet, inspired by the technological prowess of the GE-9X turbofan, opens the door to designers and engineers. However, the practical limitations posed by airport infrastructure and operational constraints mean that such a design would require a complete rethinking of current airport technology and infrastructure. The legacy of the Lockheed L-1011 TriStar serves as a reminder of the potential and the challenges in pushing the boundaries of air travel.