The F135 engine powers the global F-35 fleet, but may face a competitor in the future. (Nicolas Myers/US Air Force)

This report was updated 10/15/21 at 12:13 PM et to correct a stat related to GE’s engine.

MIDDLETOWN, Conn.: As the Pentagon looks to increase the power of the F-35 joint strike fighter’s engine while cutting costs, Pratt & Whitney and General Electric could be less than a year away from finding themselves in a rematch over the future of the stealth fighter’s propulsion system.

The Pentagon stopped funding General Electric’s F136 engine in 2011, leaving the Pratt & Whitney F135 as the sole propulsion option for the Lockheed Martin-made F-35. However, the F-35 will need an improved engine to support oncoming Block 4 enhancements that will make the jet more lethal, and department officials are contemplating whether another competition between the former rivals could lead to a massive leap forward in engine capability, at a price the services can afford.

“I love competition,” Lt. Gen. Eric Fick, who leads the Pentagon’s F-35 program office, said Sept. 15. “I’m a big fan of having two viable fighter engine manufacturers in the defense space. What we need to figure out, I think, as an enterprise is: Are we willing to pay the cost associated with [a new engine].”

General Electric Aviation is pitching its XA100 adaptive cycle engine, which the company is developing as part of the US Air Force’s Adaptive Engine Transition Program.

The XA100 is “drop in” compatible with the F-35A conventional variant used by the Air Force and most international customers, as well as the F-35C carrier variant, said David Tweedie, GE’s head of advanced combat engines. However, the XA100 would have to be majorly modified for use on the F-35B, which can vertically take off and land.

While Pratt & Whitney also has an adaptive engine in the works, the company is proposing an upgraded version of the F135 that it believes will offer the Pentagon the most bang for its buck, said Jen Latka, Pratt & Whitney’s vice president for the F135 engine program.

The enhanced F135 would be applicable to all variants of the jet, giving an increase in thrust and power management without forcing the services to field a new engine — or leading to a mixed fleet of adaptive engines and F135s.

The Pentagon’s F-35 joint program office is charged with compiling future engine requirements from the US Air Force, Navy and Marine Corps. Within the next six to 12 months, the office plans to carve out a path forward for either upgrading the F135 or starting an engine competition, Fick said.

Much will depend on whether the Air Force continues financing development of Pratt and GE’s adaptive engines, and whether the service is willing to pay the increased engineering, procurement and sustainment costs associated with having a different engine than the rest of the F-35 enterprise, Fick said.

“We know that beyond Block 4, we are going to need more power” and cooling, he said. “We know that we need to start [determining a path forward] so that we can put a solution set in place for all aircraft, for all customers.”

General Electric’s proposal

Tweedie said GE’s pitch comes down to the a single question: “Do you want an incrementalist approach, or do you want a transformational capability improvement that’s not just good for the next five or 10 years, but for the next 30 or 40 years?”

While engines built for commercial airlines prioritize fuel efficiency and engines built for fighters prioritize thrust, adaptive engines can shift between the two modes — allowing a fighter to use less fuel as it cruises and hence improving its range, but also affording it the thrust it needs during combat.

General Electric’s proposal for the Adaptive Engine Transition Program, the XA100. (General Electric)

GE anticipates that the XA100 will increase the F-35’s range by 30 percent, increase thrust by 10 to 20 percent and improve fuel burn by 25 percent when compared to current engine performance.

In addition, its thermal management capability would be doubled due to the third stream of air flowing through the XA100, which acts as a heatsink for electronics, avionics and mission systems, he said. That would give the F-35 the cooling it needs to accommodate the upgrades planned as part of Block 4, with margin for additional advances, Tweedie said.

However, the XA100 — like other adaptive engines — is still moving through development and won’t be ready until 2027 at best.

The company has built two XA100s and fired up the second engine on Aug. 26 at GE’s facility in Evendale, Ohio. Once that ongoing testing is complete, the Air Force will conduct its own evaluation at Arnold Engineering Development Complex in Tennessee, where it will get “full flight envelope [data] and more precision level performance measurements,” Tweedie said.

After the Air Force wraps up its testing sometime next year, all AETP program milestones will have been achieved, and it will be up to the service to determine whether to start a program of record or to continue development of adaptive engines.

While the Air Force has not laid out an acquisition strategy for an adaptive engine, Tweedie said he’s been encouraged by comments made by Air Force Secretary Frank Kendall and other Air Force leaders who have shown interest in pursuing a new engine for the F-35.

“The $4 billion investment that the Air Force has made [in AETP], we think it provides a trend transformational level of capability improvement,” he said. “We think we offer not only capability, but frankly, the lowest risk approach based on the investment that has been made at this point. So we would eagerly look forward to a head to head competition.”

Pratt & Whitney’s proposal

If the Pentagon decides that it needs a leap-ahead engine for the F-35, Pratt & Whitney will be ready with its own adaptive engine — the XA101, which it is developing as part of the AETP effort.

However, with the Defense Department likely looking at constrained budgets for the foreseeable future, Pratt & Whitney officials think it’s more likely that the department opts for a more economical improvement plan for the F135.

The company delivered a study to the F-35 program office in March that laid out two “enhanced engine proposals.” Officials have not disclosed how much development and nonrecurring engineering will cost.

Pratt & Whitney employees prepare for a test of the F135 engine.

However, once the upgrades are tested and cut into the production line, an enhanced F135 will cost only as much as the original version, and sustainment costs could decrease by as much as $40 billion over the life of the program, according to the company.

Katherine Knapp Carney, the company’s chief engineer for the F135 program, said that its most expansive suite of upgrades would increase the F135’s range and thrust by as much as 10 percent, while doubling the engine’s thermal management capability.

Knapp Carney declined to detail what kind of improvements could be made to the F135 in order to generate those performance improvements, saying that the company needs a requirement from the government before it can detail what upgrades it plans to make.

“There’s a range of options available that we have, from a Pratt & Whitney perspective,” she said during a briefing to reporters at the company’s production facilities in Middletown, CT.

“Our objective is to make sure that we are offering cost-effective solutions for those requirements. So the big piece for us is getting a propulsion requirement defined, and then we can go provide the solution based on the different options that we have available to support those future needs.”