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A repeat of one of the historical moments in the competition between the two major U.S. aero-engine firms—Pratt &amp; Whitney and GE Aviation—is shaping up.&nbsp;This time the battle is over which company will build the U.S. Air Force (USAF) adaptive-cycle&nbsp;engine.
GE designed, built, and tested the XA100 under the Adaptive Engine Transition Program (AETP). As one GE representative explained, it represents the basis for the sixth generation of propulsion systems for the U.S. military.&nbsp;The resulting production standard model derived from the XA100 would be the company’s bid for the USAF project.
Both the GE XA100 and Pratt’s analogous program, the XA101, serve as prototypes for the variable-cycle engine to power the USAF Next Generation Air Dominance (NGAD) fighter.&nbsp;The two firms developed the design under the Next Generation Adaptive Propulsion (NGAP) engine program.&nbsp;At the same time Boeing, Lockheed Martin, and Northrop Grumman are carrying out propulsion integration contracts.
One of the two engine models will power the NGAD.&nbsp;The sixth-generation fighter aircraft will replace the F-22A, expected to begin its sunset years at the end of the decade.&nbsp;The aircraft, however, will likely set records in terms of the price per unit due to the multitude of complex technologies integral to its design.
That fact might mean the aircraft does not get built in very large numbers and, like the F-22, it might not be sold to any export customers either.&nbsp;However, the engine needs to be built in far greater quantity than the NGAD program will require to “adequately amortize the immense investment in the development of this engine,” said one long-time defense analyst specializing in low-observable aircraft who spoke to AIN on the condition of anonymity.
“What the engine needs is to be utilized in a secondary application on a fighter that is to be built over a far longer production run,” he added. “This means it needs to become the second—or rather the ‘new’ engine for F-35.”&nbsp;A decision to integrate a new engine into the F-35 would make it part of the aircraft’s configuration from the Block IV variants and beyond.
In the 1980s, the two jet engine houses fought the “Great Engine War,” which was a battle by GE to get their design on board the F-16.&nbsp;Until the C/D series of the famous U.S. fighter, Pratt’s F100 engine enjoyed a monopoly on the aircraft.&nbsp;GE proposed a fighter engine-compatible version of the engine it had designed for the B-1 bomber, originally called the F101 Derivative Fighter Engine (DFE) and later re-designated the F110.
GE then saw decades of orders for the F110, which became the engine of choice for the USAF F-16s and numerous export customer nations.&nbsp;The latest versions of the engine produce 32,500 pounds of thrust.&nbsp;(A non-afterburning version of the engine designated F118 powered the B-2 Stealth Bomber.)
The production configuration engine developed from the XA100 or XA101 program, therefore, was proposed as a replacement for the Pratt F135 that powers the F-35 today.&nbsp;The issue—as with almost every major configuration change made in the history of an aircraft—centers on money.&nbsp;Current Air Force Secretary&nbsp;Frank Kendall&nbsp;has stated that developing and installing a new adaptive-cycle engine could cost as much as $6 billion to the F-35 program.
Outside of the economies of scale created by a much larger production run, two lines of argument dictate an engine change for the F-35.
One involves the performance enhancements for the F-35 created by a next-generation-technology engine.&nbsp;An adaptive-cycle engine can reconfigure itself midflight, which can improve specific fuel consumption by 25 percent and increase thrust by up to 20 percent as well.&nbsp;The F-35’s growth weight, which designers expect with any aircraft program over time, will require some increase in performance to retain the current thrust-to-weight ratio.
The other train of thought centers on finding a solution to problems with the F-135.&nbsp;Deliveries halted in December 2022 due to the crash of an F-35B.&nbsp;Pratt isolated the problem as one of vibration, officially labeled “harmonic resonance,” as the cause. A modification to reduce the problem has gained approval to resume production, but a plan to retrofit the engines already in service remains a requirement.
There are those, however, who discount the need for a new engine.&nbsp;Pratt’s own F135 program director, Jennifer Latka, has argued that adaptive-cycle engines are not compatible with the F-35 and should be reserved for the NGAD.&nbsp;Pratt, instead, has proposed a design change in the form of an engine core upgrade&nbsp;for the F135.
But GE insists that the F-135 engine, which is itself an adaptation of the F-22’s F119 engine, is not adequate, and the adaptive-cycle engine should become the new propulsion system solution in its place.&nbsp;The Great Engine War might resume before we know it.

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