F-35s could get new engines as early as 2027

Congress may require the U.S. military to prepare a pair of studies on what it would take to install new engines in current and future F-35 stealth jets later this decade. An all-new powertrain is under development as part of the Adaptive Engine Transition Program, or AETP, with several prototypes already tested. The hope is that the AETP engine or some other alternative would bring a significant performance improvement to the three variants of the F-35, as well as improved efficiency.

Write in Air Force Review Yesterday John Tirpak pointed to the wording of the most recent version of the annual Defense Policy Bill, or National Defense Authorization Act (NDAA), for fiscal year 2022. The bill, which did not yet passed in the Senate, would require the Secretary of the Air Force, in conjunction with the Under Secretary of Defense for Acquisition and Sustainment, present a plan for adding AETP engines to take-off and to the conventional landing of the F-35A. (CTOL) beginning no later than 2027. The Secretary of the Navy, working with the Under Secretary of Defense for Acquisition and Sustainment, would develop a similar, but separate, plan for the addition of an “advanced propulsion system” – which could be the latest AETP Design or upgraded version of the existing Pratt and Whitney F135 variants – to F-35B Short Take-off and Vertical Landing (STOVL) and F-35C, starting again onwards by 2027 at the latest.

US Air Force

The commercial part of the Pratt & Whitney F135 engine powering a US Air Force F-35A.




In either case, the “competitive acquisition strategy” described would cover the addition of AETP engines to existing and new production aircraft. Both reports are expected to be submitted within two weeks of President Joe Biden’s proposed fiscal year 2023 budget request to Congress.

The costs involved in integrating any new powertrain into the three variants of the F-35 could be substantial.

For the Air Force in particular, which is the current largest American operator of joint fighter jets of any type, the question certainly arises as to whether the service has the means to equip all its existing and future jets with AETP engines. completely new. There are already separate concerns about the expense of maintaining existing F-35As, as well as adapting them to the latest Block 4 standard, which includes enhanced radar and electronic warfare capabilities, as well as the ability to carry new weapons.

In the past, Lt. Gen. Eric T. Fick, program manager for the F-35 Joint Program Office, has said the Air Force should cover the development and production costs of integrating the AETP engine in the F-35A.

Currently, prototypes of two options for the AETP, the General Electric XA100 and the Pratt & Whitney XA101, are being tested. Both of these powertrains are expected to increase jet range by around 30% and persistency by around 40%, thanks to a reduction in fuel consumption of around a quarter. Currently, the F-35A has a non-refueling range of about 1,350 miles, which would be increased to about 1,800 miles with the new engine. Acceleration would also be improved with the new engine installed.

The “Adaptive” part of the name refers to the fact that these new engines combine the fuel economy of the types of turbojets used in new generation airliners with the high pressure compression normally found in combat engines. By introducing a third air flow, this can be dynamically modulated between the engine core and the bypass flow, to provide increased thrust during combat conditions and increased fuel efficiency during cruise conditions.

US Air Force

Schematic illustration of an Adaptive Engine Transition Program (AETP) design.




US Air Force




General Electric




In particular, giving the F-35A longer legs would be something that would be of great benefit to the Air Force, as it considers the likelihood that the next major conflict will take place in the Asia-Pacific theater, where the range Limited Lightning II would be a major concern. As the service plans for its next hunter, increased range has already been singled out as a “must have” feature.

Not only would a longer range F-35A be more suited to operations in the Asia-Pacific region, it would also reduce reliance on aerial tankers. The availability of sufficient aerial refueling aircraft has always been a key factor for air combat planners. More recently, however, the survivability of these same tankers has become a real concern, with an interest in more resilient tankers, achieved through poor observability or by other means.

US Air Force / Master Sgt. Jean Nimmo

An F-35A approaches a KC-135 Stratotanker during an aerial refueling near Eglin Air Force Base, Fla.




In addition to improving overall capabilities, a new powertrain would solve a persistent problem of excessive wear of the thermal protective coating on the F-35A’s turbine rotor blades. Earlier this year, it emerged that 46 of the jets did not have functioning engines due to the problem. With the engine maintenance center facing a delay in repair work, frontline F-35 fleets were hit and the Air Force fleet suffered the most severe lack of availability.

In the recent past, Air Force Chief of Staff Gen. Charles Q. Brown Jr. also noted that F135 engines “fail a little faster in some areas”, in particular. due to heavy use and regular deployments. While maintenance modifications are under consideration, Brown also suggested that a solution to the problem might simply be to use the F-35 less, which is not an ideal long-term solution.

US Air Force

Last year, two US Air Force F-35As were in an “undisclosed location” in the Middle East, demonstrating their ability to rapidly move resources in the region to respond to emerging contingencies.




Although the new engine’s timeline is bold, General Electric and Pratt & Whitney said Air Force Review that the 2027 deadline is achievable. Members of Congress who crafted the most recent NDAA appear to be overwhelmingly supportive of the Adaptive Engine Program, with the bill proposing to triple its funding in FY2022 from what was originally requested.

At the same time, as members of Congress push to add the AETP engine to the F-35A, the NDAA project leaves open the possibility of going in a different direction with the F-35B and F-35C. The study for the F-35B and F-35C would include an “analysis of the impact on combat effectiveness and sustainment costs of increased thrust, fuel efficiency and thermal capacity for each variant of the F-35, to include improvements to acceleration, speed, range and overall mission efficiency of each advanced propulsion system. There is no specific mention of AETP.

The requirements of the aircraft carrier operating environment for the F-35C and, most importantly, the swivel nozzle and integrated lift motor for the STOVL F-35B mean that the challenges of integrating a new engine are bigger. Indeed, in the past, General Electric and Pratt & Whitney have stated that their AETP designs are not compatible with the F-35B. With that in mind, the NDAA can expect the Model B to use the upgraded F135 engine, while the F-35C gets the same or a version of the new AETP powertrain.

Sgt. Audrey Rampton / US Navy

An F-35B lands aboard the USS America (LHA 6) in the South China Sea.




The Navy report is also to provide an assessment of how an advanced propulsion system could reduce air refueling requirements and any “overall cost benefit” resulting from “reduced acquisition and sustainment.”

Once the two reports are prepared, Congress will have a timetable “noting the relevant milestones and annual budgetary resource requirements for the implementation of such a strategy”. With an average price tag of $ 20 million for the current F135, one would expect the new engine to be significantly more than that.

If Congress considers the re-engine project worth pursuing, it’s not clear what the next step would be. At the start of the Joint Strike Fighter program, there were two engines, the F135 and the alternative General Electric / Rolls-Royce F136, although the latter was dropped for reasons of cost, which was somewhat controversial.

Rick good friend

A General Electric / Rolls-Royce F136 engine is tested under maximum thrust conditions.




It may be that the Air Force has learned from this lesson and decides that the XA100 and XA101 should both go into production, after which they can compete for contracts, perhaps to power the F-35 or other platforms.

For the F-35, of course, the AETP could still prove to be “one engine too far.” At this point, Pratt & Whitney would be in a good position to launch their upgraded F135 engine, which also promises improvements in thrust and efficiency, but which the company says would be much cheaper than AETP technology.

With significant production ahead for the U.S. Department of Defense and overseas customers, it makes sense that the Joint Strike Fighter’s powertrain keeps pace with technological developments in the same way other aspects of the aircraft are being improved. through upgrades and new iterations. But whether the Air Force, let alone other operators, can foot the bill for integrating this promising new engine technology into the already expensive F-35 is currently questionable.

Contact the author: thomas@thedrive.com