President Donald Trump’s recent call to build a twin-engine variant of the F-35, which he would call the F-55, has caused the defense community to buzz, bringing back to life the questions about the future of American airpower.
In a roundtable with business leaders in Doha, Trump called the concept a “super upgrade” of the F-35, questioning the usefulness of single-engine fighters and hailing the importance of redundancy in safety. He also spoke of a possible “F-22 Super,” a future Raptor variant, indicating his desire to upset long-standing U.S. fighter development strategy.
Trump’s F-55 idea would basically mean placing a second engine on the F-35 airframe, something he contends would greatly enhance the plane’s capability. His argument is straightforward: no engine is bulletproof, and having multiple engines enhances survivability. Trump even used the four engines of a Boeing 747 as an example of redundancy in the aerospace industry.
The response from the defense and aerospace community has been guarded, if not skeptical. Former Air Force Secretary Frank Kendall called the proposal “mystifying” since a twin-engine version of the F-35 would nearly need to be redesigned.
Aerospace analyst Richard Aboulafia was more direct, calling the proposal “not feasible” and likening it to a child’s drawing instead of an actual engineering proposal. Putting in a second engine basically would create a whole new plane, with all the expenses and engineering challenges that come along with it.
Technological challenges are very real. As J.J. Gertler of the Teal Group explains, the F-35’s existing airframe does not have space for a second engine. Redesigning it would involve a greater, stronger frame, new wings, tail, and air intakes, in effect building an entirely different airplane with minimal connection to the original.
Stacie Pettyjohn of the Center for a New American Security further noted that stealth would be especially difficult to maintain, as even slight alterations in the airframe’s shape or material would destroy low observability.
Strategically, the timing and logic of the proposal are questionable. The Air Force already chose the F-47 as its sixth-generation fighter, built from the ground up to replace future operational requirements. Building a twin-engine F-35 may duplicate the mission profile of the F-47, risking redundancy in terms of size, cost, and capabilities.
In addition, the F-35 program itself is already being heavily modernized and upgraded in terms of sustainment. Multi-billion-dollar upgrades are in the pipeline for engines, thermal systems, and power systems, while the Block 4 upgrades offer increased combat capability. Lockheed Martin has also floated a “fifth-generation-plus” variant of the F-35, providing much of the F-47’s future capabilities at lower cost. Yet the program still leaves unanswered questions about sustainment, maintenance responsibility, supply chains, and intellectual property, highlighting the sheer complexity of such a bold fighter program.
For the defense sector, Trump’s remarks are a mixed message. An interest in purchasing and modernizing the F-35 and F-22 might prove helpful to Lockheed Martin and its partners. Yet the technology and strategic difference between the F-55 concept and current modernization plans means that the undertaking is not likely to go further than the concept phase. Aboulafia cautioned that firms pursuing such an effort without government support would be assuming giant, perilous expenses.
The F-55 debate emphasizes a key conflict in U.S. airpower strategy: reconciling the aspiration for aggressive, paradigm-shifting capabilities with technical constraints, cost, and strategic unity. As the Pentagon presses forward to modernize its fighter force and close the F-35’s sustainment issues for the long term, the F-55 reminds us that visionary concepts have to be anchored in technical possibility and workable planning.