By Logan Williams, Warrior Editorial Fellow
In the middle of Summer 2023, the United States Air Force inexplicably cancelled a Pentagon-funded research program designed to create a cutting-edge, new turbofan jet engine for the F-35 Lightning fifth-generation fighter jet. This new jet engine was truly revolutionary — it was exactly the sort of technological frontier that the Pentagon’s financing should enable our defense industrial base to cross.
Yet, after nearly ten years of research, and billions of dollars, the Air Force decided that it was time to quit.
First, to understand the true brilliance of this new jet engine, it is necessary to understand how turbofan engine technology works.
Jet engines operate in four basic stages. First, air enters the intake towards the front of the engine; some of this air enters the core of the engine, and the rest is shifted to a duct which runs just outside the engine core. The air in this duct runs around the engine, providing cooling before escaping out the rear.
The air that enters the engine core undergoes the rest of the multi-stage process. First, it is forced into a combustion chamber by a number of compressor fans, which compress the air to up to 12-times its original density. Inside the combustion chamber, fuel is injected into the pressurized, high-temp air, and then the combination is ignited, causing an exponential increase in temperature – and therefore, in pressure – as well as the release of additional gasses. This air is then forced through the exhaust system, which is much smaller than the intake, and then expelled from the engine. It is the expulsion of this air which provides the forward thrust for a jet to fly.
Why does this matter? The amount of air which enters the combustion chamber, and thus, the amount of air which is directed through the bypass duct, determines the way in which an engine functions.
A jet engine which limits the bypass of air, such as those used for fighter jets, must use more fuel to increase the heat and temperature of the air in the engine core, to cause greater air compression, and therefore, greater thrust upon exhaust. These low-bypass engines are optimal for supersonic flight.
High-bypass engines take in a large mass of air, and allows a greater bypass, which is used to cool the engine and exhaust gasses, as well as to generate additional thrust. In high-bypass engines, the bypass air is used as the primary source of engine thrust, whereas the engine core uses less fuel to move air at a lower rate of acceleration. This is a far more fuel efficient process, but it also results in a limited aircraft speed — thus, it is ideal for subsonic flight.
Additionally, another important metric for thrust generation is the fan pressure ratio, the ratio between discharge air pressure to inlet air pressure. A higher ratio, as in greater pressure at discharge compared to inlet, produces greater thrust by forcing exhaust through a smaller nozzle. This increases the compression of the exhaust gasses just prior to discharge, and thereby, the force generated at expansion when the gas exits the exhaust system, greatly increases.
In theory, altering either of these ratios can produce an engine optimized for performance or efficiency.
AETP Program – Adaptive Engine Technology
This is exactly what the new adaptive engine technology (AETP) was designed to accomplish. The adaptive engine platform uses a third air-stream architecture, which allows for greater thrust and/or fuel efficiency. Typically, jet engines have just two air-streams: the air in the engine’s core and bypass air. Adaptive engines, such as General Electric’s XA-100, utilize a third air-stream which can be used to bolster bypass air (and thus, fuel/propulsive efficiency), or it can be directed through the engine core to increase thrust. Most importantly, this change occurs in flight, automatically, as the war-fighter’s needs change.
For simplicity’s sake, imagine this new engine as similar to your car’s transmission, which switches gears as the vehicle accelerates, to reduce engine strain and fuel consumption.
This adaptive engine would have increased the F-35 fighter jet’s thrust by approximately 20-percent, and it would have increased the aircraft’s range (as well as combat radius) by approximately 35-percent.
Recently, Warrior Maven published various articles about several deficiencies in the United States’ present air power regime, which is based upon a paradigm in which the United States Air Force has been largely uncontested in war for over half a century. These articles included an exploration of the F-16 fighter jet’s usefulness in an Indo-Pacific conflict (or a lack of usefulness, as such), a criticism of the USAF’s dependency on aerial refueling, and an article calling for a new, mass-producible, long-range fighter jet.
This new adaptive engine would have gone a long way to overcoming the tyranny of geography/distance within the Indo-Pacific, by increasing the F-35’s combat radius – and thereby, reducing the USAF’ logistical deficiencies, by decreasing that airframe’s dependence upon aerial refueling capabilities. Additionally, adaptive engine technology could have served as the foundation of a new, extended combat radius fighter jet — and the increased, broad deployment of an adaptive engine would likely have reduced its per-unit manufacturing cost.
Instead, the Pentagon opted for an underwhelming upgrade to the F-35’s current Pratt & Whitney F135 engine, an upgrade which provides few benefits compared to a complete engine replacement with an AETP engine platform. This decision doesn’t just reduce the F-35’s capabilities, but some analysts believe that it will have a dire effect upon the defense-industrial base (DIB), drastically reducing innovation, and causing certain sectors of that DIB to begin to collapse.
It is often said that the United States military apparatus is best served by prioritizing capability over capacity, or put more simply, quality over quantity. This doctrine has been disproved by the United States’ valiant support of the Ukrainian freedom fighters, which has strained the United States’ reserves of crucial weapons — ingenious capabilities don’t matter if the DIB cannot produce capacity, as well. However, the United States’ military apparatus’ decision to cancel the AETP program presents an even worse trade-off — it didn’t place an emphasis upon capability or capacity, rather, it placed cash above all else.
Policy-makers and other stakeholders need to understand that competition with China requires a massive investment. The People’s Republic of China is able to utilize civil-military fusion, poor labor standards, state-owned enterprisies, and other totalitarian measures to conduct a military build-up
in a quick and cost-effective manner — the United States can never pursue these options, as a liberal, democratic, constitutional Republic. The United States’ deterrence of China necessitates ever-increasing expenditures; any attempt to achieve re-militarization on-the-cheap, through half-measures, is a recipe for a disastrous failure.
These technological decisions, as well as the speed with which policy-makers accept the necessity of spending enormous sums, are what will determine the United States’ ability to compete and to defend the freedom and well-being of its allies against the impending Chinese threat.
Logan Williams currently studies at the University of Connecticut. He is an International Affairs Researcher; Work Published in Newspapers, Magazines, and Journals, Such As: Geopolitics Magazine, Modern Diplomacy, Tufts University’s The Fletcher Forum of World Affairs, Democracy Paradox, Diario Las Américas, International Affairs Forum, Fair Observer, History Is Now Magazine, UNC at Chapel Hill’s American Diplomacy, The Center for Military Modernization’s Warrior Maven Magazine,
