How Does an Airplane Engine Work? The Basics

What an airplane engine does

An airplane engine supplies the force needed to overcome drag and move an aircraft through the air. The basic principle is Newton’s third law: when an engine pushes air backward, the air exerts an equal and opposite force on the engine, producing forward thrust. The engine does not push directly against the ground or need to “grab” the surrounding air.

Engines also provide power for aircraft systems, either directly or through generators and other equipment. But their defining job is propulsion. The amount and type of thrust needed depend on the aircraft’s size, speed, mission, and design.

How a jet engine makes thrust

Most airliners use turbofan engines, a kind of gas turbine. A turbofan draws in air, compresses some of it, burns fuel in that compressed air, and sends the resulting hot gas through turbines and out the back. The flow of air leaving the engine is faster and carries momentum backward, creating thrust.

Draw in air. The inlet guides outside air into the engine. A large fan at the front of a turbofan accelerates much of this air around the engine core.
Compress the core air. Compressor stages squeeze the air, raising its pressure and temperature. Compressed air supports efficient combustion.
Burn fuel. Fuel is sprayed into the compressed air in a combustion chamber and ignited. Once started, combustion is continuous while the engine runs; it is not a series of explosions like a car’s piston engine.
Drive the turbine. Hot gas expands through turbine blades. The turbine turns shafts connected to the compressor and, in a turbofan, the fan.
Produce the exhaust flow. Remaining gas exits through the rear nozzle. Together, the core exhaust and the fan’s bypass airflow create thrust.

The compressor, combustor, and turbine form the engine’s core, often called the gas generator. The core keeps the cycle running, while the fan moves a large volume of air. In many turbofans, most of the air goes around—not through—the core. This bypass flow contributes much of the thrust and helps make the engine quieter and more efficient at typical airliner speeds than a simple high-speed jet exhaust would be.

Why a propeller engine is different

A propeller engine also moves air backward, but it uses a propeller as its main air-moving device. A piston engine burns fuel and air inside cylinders; the moving pistons turn a crankshaft, which rotates the propeller. The propeller’s blades act like rotating wings, producing thrust as they push air backward.

A turboprop uses a gas turbine rather than pistons to turn a propeller. The turbine extracts energy from hot gas to drive the propeller through a shaft and reduction gearbox. Turboprops are useful for many regional aircraft and other planes that fly at relatively modest speeds. Piston engines are common in smaller general-aviation aircraft. Neither type is simply a miniature airliner jet: each suits different aircraft and operating conditions.

What changes thrust and efficiency

Engine controls adjust how much power or thrust is produced. In a jet, the pilot’s thrust control changes fuel flow and engine operating conditions; the engine’s control system helps maintain safe limits. In a propeller aircraft, power and propeller settings work together, with the exact controls depending on the design.

Thrust and performance also vary with the atmosphere and aircraft speed. At higher altitude, the air is thinner, so an engine takes in less air mass. Temperature, pressure, and the aircraft’s forward speed affect how an engine performs as well. Pilots and aircraft systems account for these factors when setting power and planning climbs, cruise, and takeoff.

Efficiency is not the same as maximum thrust. A turbofan generally achieves good efficiency at airliner speeds by moving a large amount of air backward by a relatively moderate amount. A propeller is also effective at lower speeds. Designs that work well in one speed range may be less suitable in another, which is why aircraft engines are matched to their intended use.

Starting, controlling, and monitoring an engine

A jet turbine needs its compressor turning before stable combustion can begin. An auxiliary power unit or other starter system spins the engine; fuel and ignition are introduced in sequence, and the turbine takes over as the engine reaches self-sustaining operation. A piston engine starts by turning its crankshaft until combustion keeps it running.

During operation, instruments and sensors track conditions such as temperature, rotational speed, and oil pressure. These readings help crews confirm that the engine is within its operating limits. Aircraft engines are designed with multiple systems and inspection procedures, but they still require careful maintenance: wear, contamination, leaks, or damage can affect performance.

Common misconceptions and safety

A jet engine does not need oxygen carried in a tank for ordinary combustion; it takes oxygen from the air it ingests. This is why conventional jet engines cannot operate in space. Nor does an engine “suck” an airplane forward in the everyday sense: thrust comes from accelerating air backward.

Engine failure is a serious event, but it does not automatically mean an aircraft will fall out of the sky. A fixed-wing airplane can glide without engine thrust, and many passenger aircraft have more than one engine. The outcome depends on the aircraft, altitude, conditions, and circumstances. Aircraft are designed and operated under safety requirements that include procedures for engine problems; passengers should follow crew instructions.

Frequently Asked Questions

Do airplane engines burn fuel continuously?

In a running jet turbine, fuel burns continuously in the combustion chamber, rather than in separate timed cylinder events. Piston engines burn fuel-air mixtures in repeating cycles inside their cylinders.

Why do airplane engines have a large fan?

The fan moves a large volume of air around the engine core. In a turbofan, this bypass air supplies a substantial share of the thrust and supports efficient operation at common airliner speeds.

Can a plane fly if its engine stops?

A fixed-wing aircraft can glide when it has no engine thrust, though it will gradually lose altitude. What happens next depends on the aircraft and situation, and trained crews use established procedures.

What is the difference between a turbofan and a turboprop?

Both use gas turbines, but a turbofan’s fan produces thrust directly by accelerating air, while a turboprop turbine primarily turns a propeller. Turbofans are common on airliners; turboprops are suited to many lower-speed aircraft.

Further reading: NASA. Details can change, so check the official page for anything that matters to you. Spotted a mistake? Tell us. How we write an answer.