Every jet engine built since the 1940s runs on the same thermodynamic cycle: pull air in, squeeze it, burn fuel in it, and blow the hot gas out the back. But how that gas is managed — and how much of it bypasses the core entirely — separates a fuel-sipping airliner engine from a fighter engine that can push a jet past Mach 2.
Browse engine profilesAll gas turbine engines operate on the Brayton cycle, which engineers summarise as four strokes: suck, squeeze, bang, blow.
The efficiency of this cycle improves with higher turbine inlet temperature and higher pressure ratio, which is why modern engines run at conditions that would destroy their materials without active cooling.
The turbojet is the simplest configuration: all ingested air passes through the core and all thrust comes from the hot exhaust jet. The Messerschmitt Me 262 used Junkers Jumo 004B turbojets producing 8.8 kN (1,980 lbf) each — modest by later standards but enough to make it the first jet fighter to see combat in 1944.
Pure turbojets are efficient only at high speeds — above Mach 1.5 or so — because the core jet velocity is already high relative to the aircraft. At subsonic speeds, a turbojet wastes energy by accelerating a small mass of air to a very high velocity, when it is thermodynamically cheaper to accelerate a large mass of air to a lower velocity for the same thrust. That insight led directly to the turbofan.
A turbofan adds a large fan at the front of the engine, driven by an extra turbine stage at the rear. This fan accelerates a ring of air that flows around the core rather than through it — the bypass stream. The ratio of bypass mass flow to core mass flow is the bypass ratio (BPR).
The GE9X engines on the Boeing 787-9 and 787-10 have a bypass ratio of 10:1 — for every kilogram of air that enters the core, ten kilograms flow around it. The fan diameter is 3.4 m (134 in). This produces enormous thrust — up to 105,000 lbf per engine — at low exhaust velocities, which means high propulsive efficiency and a noise footprint far below an equivalent turbojet. The Rolls-Royce Trent XWB on the Airbus A350 runs a similar philosophy at BPR 9.3:1 and delivers up to 97,000 lbf.
High-bypass engines are not suitable for supersonic aircraft: the large fan diameter creates prohibitive drag above Mach 1, and the bypass stream cannot be efficiently accelerated to supersonic exhaust velocities.
Fighter engines use bypass ratios of 0.3:1 to 0.5:1. The Pratt & Whitney F119-PW-100 in the F-22 Raptor has a BPR near 0.3:1 and delivers 35,000 lbf with afterburner engaged. Its low bypass means the core jet velocity is high enough for supersonic exhaust — enabling the F-22's Mach 1.82 supercruise without afterburner. The F135-PW-100 in the F-35A Lightning II produces 43,000 lbf with afterburner at a similarly low BPR.
An afterburner is a second combustion stage fitted between the turbine and the exhaust nozzle. The turbine exhaust still contains 15–20% unburnt oxygen, so injecting more fuel into this hot stream and reigniting it produces a dramatic boost in thrust — typically 50–70% more — at the cost of roughly doubling fuel consumption.
Afterburners are only used in military aircraft that need a brief burst of thrust for supersonic acceleration, takeoff from short runways or carriers, or combat manoeuvres. The F119's afterburner pushes the F-22 from its dry thrust of 26,000 lbf to 35,000 lbf. Concorde's Olympus 593 engines used a form of reheat for transonic acceleration through Mach 1 before throttling it back at cruise — one of the few civil applications.
A turboprop extracts nearly all the energy from the hot gas through extra turbine stages, converting it into shaft rotation rather than exhaust velocity. That shaft drives a conventional propeller through a reduction gearbox. Turboprops are thermodynamically efficient at speeds below 450 mph (720 km/h), where a large-diameter propeller can accelerate a wide column of air at low velocity — the same principle as a high-bypass turbofan, but using a propeller instead of a shrouded fan. The Rolls-Royce AE 2100D3 on the C-130J Super Hercules produces 4,591 shp paired with a six-bladed composite Dowty R391 propeller.
A turboshaft is mechanically identical to a turboprop but optimised to deliver all power as shaft output with no useful thrust from the exhaust. The free power turbine is mechanically decoupled from the gas generator turbine, which means rotor speed can vary without changing engine speed — important for helicopter control. The General Electric T700-GE-701D in the UH-60M Black Hawk produces 1,940 shp. The GE CT7-8C in the CH-47F Chinook delivers 4,733 shp per engine, turning rotors that can lift up to 10,886 kg of slung load.
Engine specifications quoted are from publicly available manufacturer and government sources and reflect production variants as of 2026.