The United States Air Force announced in late January that it was more than tripling the authorized spending ceiling for its Next Generation Adaptive Propulsion (NGAP) program. The service is now authorizing up to $3.5 billion (up from $1 billion) each for work on rival XA102 and XA03 adaptive-cycle turbofan engine prototypes. The engines are being developed by General Electric and Pratt & Whitney, respectively.
The new spending may be a sign the Air Force is inclined to procure a manned Next-Generation Air Dominance (NGAD) sixth-generation jet fighter after all, despite the service’s leaders spending much of 2024 arguing it was unaffordable and possibly unnecessary. The move comes a month after Chinese companies publicly revealed two flying, manned sixth-generation designs.
An F-35A Lightning II, flown by Maj. Kristin “Beo” Wolfe, F-35 A Lightning II Demonstration Team commander, performs aerial displays during the Joint Base Andrews 2022 Air & Space Expo, at JBA, Md., Sept. 18, 2022. Wolfe demonstrated several difficult maneuvers throughout her performance at the Air & Space Expo to provide an opportunity for people to see U.S. military air capabilities in action. (U.S. Air Force photo by Airman 1st Class Ben Cash)
For many years, the Air Force insisted it was moving full-steam ahead to field an NGAD jet specialized in air-to-air combat over long distances that would enter service alongside new ‘buddy’ Loyal Wingman drones. NGAD would replace older F-22 Raptor air-to-air fighters while complementing newer, strike-optimized F-35s. The service even revealed it had test-flown an NGAD prototype in 2020!
But in the spring of 2024, Air Force Secretary C.Q. Brown revealed he would no longer accept the roughly $250-300 million per aircraft cost projected for NGAD—around three times the unit price of an F-35 ($85-120 million). Brown later suggested he’d be open to solutions costing no more than an F-35 does, which seems unlikely for a heavier and more advanced successor.
NGAD was deemed expendable because its separately in-development buddy drones—Collaborative Combat Aircraft (CCA)—could pair with the F-35s. So, he argued, perhaps these pilotless aircraft (projected to cost around $30 million each) could undertake the most dangerous missions at the tip of the spear under the direction of F-35s.
But while CCAs have great potential, the question stands: what are the tradeoffs of relying only on F-35s teamed with CCAs instead of the formerly planned mixed NGAD/F-35+ CCA combo?
Next-Generation Engines
A key anticipated advancement for sixth-generation fighters is the integration of state-of-the-art combined cycle turbofan engines (AKA adaptive- or variable-cycle) able to re-optimize themselves midflight for either low- or high-speed travel by shifting the bypass ratio of air sucked into an engine’s core. This is what the $7.5 billion funding for NGAP is going towards.
Low-bypass engines are more fuel efficient for long-distance/long-endurance missions, while high-bypass turbofans—invariably the kind found on jet fighters—enable much higher speed performance. However, a combined cycle engine can shift the bypass ratio as the situation dictates.
Next-generation engines will also likely support more sustainable supersonic flight performance and generate greater electrical generation and cooling capacity than their predecessor, unlocking the integration of more powerful sensors and digital systems.
U.S. Air Force Maj. Kristin “BEO” Wolfe, F-35A Lightning II Demonstration Team commander, flies over Kennewick, Washington, during the Tri-Cities Water Follies Airshow Over the River, July 30, 2023. The F-35 Demonstration Team participated in the 2023 Tri-Cities Water Follies airshow and various other events in support of their mission to recruit, retain and inspire new and old generations of Airmen. (U.S. Air Force photo by Staff Sgt. Kaitlyn Ergish)
Longer Range, Greater Payload
It was thus expected that NGAD would be built larger to carry more fuel and fly farther into hostile airspace—indeed, its predecessor program was called Penetrating Counter-Air. China’s newly revealed J-36 prototype stealth jet seems very much built with fuel capacity in mind.
In the event of military conflict with China, the geography of US bases in the Pacific will require aircraft to traverse tremendous distances—particularly as the closest bases will be exposed to a high volume of China-based missile strikes, placing aircraft at great risk of destruction on the ground. And due to China’s improving anti-ship capabilities, including special ballistic missiles, US carrier task forces will also prefer to keep their distance from China’s coast to reduce the volume of weapons able to reach them.
Unfortunately, neither the F-22 nor the F-35 is optimized for long-range, with a combat radius in the mid-hundreds of miles on internal fuel. The usual solutions—carrying external fuel tanks underwing and/or in-flight refueling with large tanker aircraft—betray the aircraft’s stealth. For this reason, the Air Force is increasingly interested in stealth tanker aircraft.
Increased fuel load would likely come bundled with increased weapon load, as the trend towards beyond-visual-range air-to-air combat observable in Ukraine suggests potentially numerous long-range missiles are needed to achieve a satisfactory probability of kill. There are, however, alternatives to large fighters, such as redistributing long-range missile payloads to other aircraft ranging from manned bombers to CCA drones.
Other Proposed Capabilities of Sixth-Generation Aircraft
Sixth-gen airframes might see further stealth optimization—not just of radar-absorbent materials but potentially by eliminating tail control surfaces, as was done for the B-2 and B-21 bombers and China’s new J-36 prototype. This could /reduce ‘all-aspect’ radar observability when scanned from side and rear (useful for a penetrating fighter!) and also helps decrease observability versus low-band surveillance radars potentially able to detect the presence of stealth fighters imprecisely. There may also be greater efforts to minimize thermal, optical, and electromagnetic signatures.
However, many other characteristics associated with sixth-generation aircraft are arguably less airframe-dependent: more powerful yet discrete multi-spectral sensors, advanced AI assistance, networked communications, advanced pilot haptics potentially including brain-to-computer neural interface (already planned for Tempest) and better weapons.
Though important, many of these technologies are likely backwards compatible with 4th- and 5th-generation aircraft, if admittedly at non-trivial costs.
A U.S. Air Force F-22 Raptor assigned to the 3rd Wing conducts flight operations at Joint Base Elmendorf-Richardson, Sept. 28, 2023. The F-22 Raptor is a critical component of the Global Strike Task Force, and is designed to project air dominance rapidly and at great distances to defeat threats. (U.S. Air Force photo by Senior Airman Julia Lebens)
That said, more powerful computers and sensors do have some hardware issues arising from the cooling and electrical generation stresses they induce. Indeed, capacity limits have already necessitated cooling and electricity generation upgrades on F-35 fighters. Raising the capacity ceiling is a major potential benefit of NGAP.
It All Comes Down to Money
Appealing as it is to contemplate the capabilities of advanced jet engines, they’re a moot point if they never find their way onto an operational combat aircraft. And at the moment, the Air Force has yet to commit to buying one it can’t afford anyway.
It looks impossible due to with current funding, as there’s already a multi-way tug-of-war between recapitalization of ground-based nuclear missile silos, procurement of B-21 stealth bombers and multiple increments of CCA combat drones, and investment in space capabilities, a likely pet project for new air force secretary Troy Meink, whose later career primarily concerned space-based intelligence.
Within the Trump administration, there’s potential for a clash between hawks prioritizing overmatch of China across the technological spectrum versus the tech-bro wing disdainful of procuring manned combat aircraft versus spending on drones, satellites, and AI (which the tech-bros happen to have business interests in). Of course, the military-aerospace industrial complex also has powerful lobbies, so the question surrounding NGAD could see the clash of ideologies of air warfare and rival corporate interests.
But as far as NGAP is concerned, it could still wind up in a second fighter design—the Navy’s F/A-XX carrier-based fighter, which is still under development to eventually replace the service’s 4.5-generation Super Hornet jets.
(Jan 31, 2009) An F/A-18 Super Hornet assigned to the “Tomcatters” of Strike Fighter Squadron (VFA) 31 launches from the flight deck of USS Theodore Roosevelt (CVN 71). The Nimitz-class aircraft carrier and embarked Carrier Air Wing (CVW) 8 are operating in the 5th Fleet area of responsibility and are focused on reassuring regional partners of the United States’ commitment to security, which promotes stability and global prosperity (U.S. Navy photo by Mass Communication Specialist 3rd Class Jonathan Snyder/Released)
If FA-XX makes it to production, the Air Force could eventually procure a land-based version. Of course, the Air Force didn’t want a Navy design, given the billions it sank into separately developing NGAD. Furthermore, the inter-service F-35 doesn’t offer an encouraging model due to associated R&D traumas and a disappointing low degree of parts commonality. However, the biggest contributors to those problems were compromises and technical challenges needed to realize the Marine Corps’ F-35B jump jet model. By contrast, de-navalizing FA-XX could prove much cheaper.
That option, aside from increased funding for NGAP, will continue to receive scrutiny as the military and aerospace sector try to discern whether an Air Force sixth-generation jet will get funded or not in the second Trump administration.
About the Author: Sébastien Roblin
Sébastien Roblin holds a Master’s Degree in Conflict Resolution from Georgetown University and served as a university instructor for the Peace Corps in China. He has also worked in education, editing, and refugee resettlement in France and the United States.
