Can a sports car be transformed into a monster truck simply by mounting a second engine? That’s the sort of engineering paradox now making the rounds in the U.S. defense community, with recent plans to transform the single-engine F-35 Lightning II into a twin-engine “F-55” generating head-scratching as well as sharp criticism from aero-space experts.
The idea, championed by then-President Donald Trump, would have Lockheed Martin develop a two-engine version of the F-35, ostensibly combining the platform’s flexibility with the redundancy and horsepower of dual propulsion. “It’s going to be also with two engines because the F-35 has a single engine. I don’t like single engines,” Trump announced, reiterating a long-held distrust of single-engine military aircraft. However, as a plain-speaking former Air Force Secretary Frank Kendall put it, “A two engine version of F-35 would be virtually a complete redesign. It’s an option that was never presented and that we never considered, to my knowledge” Kendall told Breaking Defense.
The technical challenges are considerable. Adding a second engine to the F-35 would require a wholesale reengineering of the airframe fuselage, wings, tail, and stealth shaping would all need to be redesigned. “You’re not building a variant—you’re building an entirely new aircraft. These types of proposals are rarely about capability. They’re about keeping development dollars flowing after losing a major program like NGAD,” a source told Defence-Blog. The intricacy is not just structural: stealth capabilities, which depend on accurate shaping and materials, would have to be redone and rechecked, and the installation of a second engine would drastically change the aerodynamics and radar profile of the plane according to Stacie Pettyjohn.
The discussion surrounding the F-55 cannot be disentangled from the larger strategic challenge confronting the Pentagon: how to preserve U.S. air supremacy as competitors introduce more sophisticated fifth-generation fighters. With Lockheed Martin having lost the Next Generation Air Dominance (NGAD) program’s sixth-generation fighter contract to Boeing’s F-47 instead, the company has tried to close the gap by bidding upgraded F-35 variants with some of the NGAD-inspired technologies. But the F-35, though technologically advanced and multi-role capable, is not configured for air superiority. Since the only U.S. aircraft capable of intercepting a high-altitude Chinese spy balloon in 2023 was the F-22 Raptor, the gap in uncompromised air-to-air superiority remains glaring Defense Express noted.
This has sparked renewed interest in reviving the F-22 Raptor production line, possibly overhauling it with NGAD-era technology. However, the hurdles here are no less staggering. The F-22’s unique production facilities and support chain have fallen apart since the final aircraft completed production in 2011. A 2017 Air Force report estimated that it would take more than $50 billion to restart production on 194 more Raptors a cost that has only increased with inflation and obsolescence of technology as outlined in a National Security Journal analysis. Numerous original suppliers have left the market, and central avionics and stealth technologies are no longer current and must be redesigned significantly in order to achieve contemporary standards. The F-22’s operating costs continue to be high, with a per flight hour cost of over $70,000 and a mission-capable rate frequently less than 60 percent.
At the same time, the F-35’s advantages are its sophisticated sensor fusion, electronic warfare, and maintainability, which make it a darling for allied air forces and the backbone of U.S. multi-domain operations. Its versatility of armament air-to-air missiles to nuclear gravity bombs allows it to conduct missions the F-22 cannot, although it lacks raw speed and dogfighting abilities. The F-22, with its top Mach 2.0 top speed and 62,000 feet-per-minute climb rate of climb, is still the Air Force’s lead interceptor, but its usefulness is confined to air superiority missions as outlined in comparative studies.
The future holds the NGAD program, which is a paradigm for change. In place of a monolithic platform, the NGAD is conceptualized as a “system of systems,” centered around a sixth-generation manned fighter surrounded by a cluster of up to 1,000 collaborative combat aircraft (drones), cutting-edge sensors, and open-architecture digital systems. The program uses digital engineering, adaptive propulsion, and modular upgrades to drive development and save costs as per recent program updates. The Air Force is going to buy 200 NGAD fighters and is spending billions on research, development, and risk reduction, looking to have a platform that surpasses both the F-22 and F-35 in survivability, adaptability, and lethality.
The strategic math for U.S. air dominance is therefore at a fork in the road. Rebuilding the F-35 as a twin-engine F-55 would take the same time, capital, and gamble as designing a new plane from the ground up. Ramping up the F-22 line is plagued by supply chain, cost, and technology barriers. The future, however, appears to be winning friends with the next generation where digital design, unmanned teaming, and open architectures will redefine what it means to own the skies.
