Fighter jet engines are complex machines that enable aircraft to reach incredible speeds.
The modern fighter jet is defined by its engine, which accelerates a tremendous volume of air rearward that it can propel an aircraft weighing as much as 70,000 pounds at supersonic speeds. While different engine models have varying capabilities allowing for such a function, an engine’s core function remains unchanged.
A fighter jet engine operates by intaking air through its inlets, located under the aircraft’s wings or chin. Because fighter jets are often flying at immense speeds, the air must be slowed down before being ingested through the engine. Therefore, during supersonic flight, complex inlet geometries, including ramps, cones, or diverter plates, shock air into submission by reducing it from supersonic to subsonic speeds before the air enters the engine’s core.
This operational concept is borrowed directly from nature, as seen in the Peregrine Falcon, which can fly at speeds in excess of 200 miles per hour in a dive that is far too fast to allow for the ingestion of air. However, the Peregrin has a nostril bone that slows the speed of incoming air, allowing the bird to breathe while diving.
Once the air enters the fighter jet engine, it is squeezed by compressor stages, which are rotating fans and fixed blades in alternating sequence. With each stage, the pressure of the air rises. And in modern jets, the compression ratio can exceed 20:1, meaning the air entering the combustion is dozens of times denser than the air outside.
The compressed air enters the engine’s combustion chamber, where carefully measured streams of jet fuel are sprayed into the air and ignited, creating a continuous flame that is sustained by a perfect calibration of fuel and air. Too little air and the flame would die, whereas too much air and the flame wouldn’t light at all. The combustion is designed to allow only a fraction of the compressed air to mix directly with fuel, while the rest of the air bypasses to cool the chamber walls and shape the flame downstream. The result of combustion is high-pressure gas with temperatures topping 3,000 degrees Fahrenheit, pushing to expand.
The expanding gas then rushes into a turbine section, which is a series of blades much like the compressor, only reversed in function, where energy is extracted from the hot flow, spinning shafts that drive the forward compressor stages and the big front fan. In essence, a model of efficiency involves the back half of the engine powering the front part. And even so, enough energy remains to blast out of the tailpipe at ferocious speeds — creating the thrust necessary to propel flight. Indeed, most of a jet’s thrust comes from the exhaust.
For some modern aircraft, their engine is equipped with an afterburner, located just behind the turbine. The afterburner is a long pipe with spray bars that dump raw fuel into the exhaust. Because the exhaust still contains oxygen-rich air, the fuel ignites, producing a second combustion, which doubles the thrust almost instantly.
About the Author: Harrison Kass
Harrison Kass is a senior defense and national security writer at The National Interest. Kass is an attorney and former political candidate who joined the US Air Force as a pilot trainee before being medically discharged. He focuses on military strategy, aerospace, and global security affairs. He holds a JD from the University of Oregon and a master’s in Global Journalism and International Relations from NYU.
Image: Wikimedia Commons.
.jpg){kind=link}