EVENDALE, Ohio—General Electric [GE] believes that a new engine for Block 5 and beyond of the U.S. Air Force F-35A fighter will be a sine qua non for the service in fielding those fighters with distance, acceleration, thermal management, and loiter time enhancements needed for long-range deterrence in the Indo-Pacific theater.

The Air Force’s fiscal 2024 budget funds the Engine Core Upgrade (ECU) for Raytheon Technologies’ [RTX] Pratt & Whitney F135 engine for the F-35 and zeroes the Advanced Engine Transition Program (AETP) effort to develop leap ahead engines with higher thrust, better thermal management, and increased fuel efficiency, but GE says that 500 employees, including 400 engineers, continue their work on the company’s XA100 AETP engine.

Congress may decide to restore AETP funding. Last October, Ohio Sens. Rob Portman (R) and Sherrod Brown (D) and Rep. Brad Wenstrup (R-Ohio) spearheaded a letter by four dozen lawmakers to top DoD officials to urge the Pentagon to fund advanced propulsion for fighter aircraft in the fiscal 2024 budget request (Defense Daily, Oct. 11, 2022).

Air Force Secretary Frank Kendall has said that the service may have pursued AETP for the F-35 in fiscal 2024, “if the [AETP development] cost had been lower.”

“We were disappointed that the Air Force did not request funding for the adaptive cycle engine,” said David Tweedie, vice president and general manager for advanced products at GE Edison Works. “That doesn’t change our perspective.”

General Electric’s aerospace subsidiary here has tested the XA100 engine at the company’s altitude test chamber, which is capable of putting jet engines through their paces at speeds of up to Mach 2.8 and 28,000 feet altitude.

GE tested the first XA100 prototype in Evendale from December, 2020 through the spring of 2021 in what the company has said was “the most heavily instrumented engine test in both GE and U.S. Air Force history.” Phase 1 testing of the second XA100 prototype, the final for AETP, began in Evendale in August, 2021 and concluded in November that year. Phase 2 testing of the second XA100 prototype at the Air Force’s Arnold Engineering Development Complex in Tullahoma, Tenn. began in March, 2022 and ended in August, 2022 after which GE brought the second XA100 prototype back to Evendale (Defense Daily, Sept. 13, 2022).

“At that point in time, we believed we had met the primary objectives of the AETP program in terms of building/testing to demonstrate the capability,” Tweedie said. GE has begun Phase 3 testing of the second prototype XA100 in Evendale to push the design envelope and ready the engine for possible production, he said.

The company hosted reporters at its Evendale facility on May 1 and 2 for briefings and a look at the XA100 nearly two months after GE gave a sneak peak of the XA100 to some outsiders—investor analysts—on March 8. Also present this week were former Air Force Chief of Staff T. Michael Moseley, retired Marine Corps Maj. Gen. Arnold Punaro, chairman of the Punaro Group LLC and a former staff director for the Senate Armed Services Committee, John Venable, a retired Air Force F-16 pilot and senior research fellow for defense policy at the Heritage Foundation, and Stacie Pettyjohn, director of the defense program at the Center for a New American Security and a former RAND Project Air Force analyst.

Punaro said that he has been a GE consultant, while Moseley said that he has not and that he decided to speak to reporters at Evendale because he believes that the Air Force needs an advanced propulsion engine for future operations.

Launched in 2016, AETP followed Air Force engine developments in the Adaptive Versatile Engine Technology (ADVENT) program, begun in 2007, and the Adaptive Engine Technology Development (AETD) program, started in 2012. In June 2016, Pratt & Whitney and GE each received contracts worth more than $1 billion for AETP. Pratt & Whitney tested its XA101 adatpive cycle engine under AETP.

GE has said that the Air Force has spent more than $4 billion on adaptive cycle engine development.

The Air Force has estimated a development cost of nearly $6.7 billion for AETP but has not released a breakout of such estimated costs (Defense Daily, June 30, 2022).

Air Force leaders have lauded the advances in GE’s XA100 for AETP but said that they simply could not continue the program, given the fiscal 2024 budget constraints.

ECU is to field in Block 4 F-35s, which may start delivery next year.

But GE said that Block 5 F-35s, which may field around 2030, will need the thrust, range, fuel efficiency, and cooling afforded by the XA100 engine. GE has said that “only XA100 can meet those demands by 2028 and for decades to come.”

GE has said that the XA100 will provide 30 percent more range than the F135, 20 percent more acceleration, and twice the thermal management. As an adaptive cycle engine, the XA100 is to switch automatically, as needed, between high thrust mode for maximum power during basic fighter maneuevers, for example, and high efficiency mode to extend aircraft range.

The XA100 adds a third airstream for engine cooling. In addition, ceramic matrix composites (CMCs)—an innovation started in the military realm and migrated and matured for the A320 and 737 commercial airliners–replace a significant number of metal parts in the XA100 and allow 500 degrees more heat resistance at one-third the weight of metal components, GE said.

The dry weight of the F135 for the Air Force and Navy variants of the F-35 is 6,400 pounds, while the dry weight of the engine for the Marine Corps F-35B is 10,400 pounds due to the lift system. The XA100 is above the 6,600 pound AETP specification, but GE engineers have reduced weight, and the company believes the XA100 will meet the weight specification.

Moseley likened the F-35’s need for an advanced propulsion engine, like the XA100, to the need that the Army Air Forces had for the Rolls-Royce Merlin V-1650 engine, built under license by Packard Motors in the United States, to replace the Allison V-1710 engine for P-51 Mustang fighters in World War II to allow the Mustang to fly long-range bomber escort missions above 15,000 feet and reduce drastically the loss of 8th Air Force bombers.

“How can we manifest a return on that [AETP] investment with these engines?” Moseley asked. “We’ve got two engine suppliers who’ve designed the prototype engines that represent the best path. I think the answer to this is, ‘Compete them.’ I think the answer is, ‘Put them on an airplane, and let’s go fly.'”

“In the previous engine wars, we saw a 20 percent decrease in F-16 engine price,” he said.

Supporters of a second engine for the F-35 have pointed to the “Great Engine War” between Pratt & Whitney and General Electric for the F-16 in the 1980s, which they said helped reduce engine costs and improve reliability through Pentagon competitive awards.