How do they start jet engines on airplanes?

Gas turbine engines come in many shapes and sizes, including a normal "jet" engine on an airplane. Jet engines harness the principles of aerodynamics and thermodynamics to generate thrust. But how do jet engines work? The hot gases produced by the burning fuel drive blades and vanes in the same way that wind turns a windmill. The vanes connect to a shaft that also spins the turbine's compressor.


The Mechanics of Jet Engines

A jet engine, also called a gas turbine engine, is a marvel of engineering that converts fuel into high-speed jets of gas, propelling a plane forward at incredible speeds. The operation of a jet engine involves a series of complex processes, each playing a crucial role in generating thrust. Let’s delve deeper into these processes to understand the mechanics behind jet engines:


Air Intake and Compression

The journey of air through a jet engine starts at the front of the engine, where the air intake is located. As the aircraft advances, the engine sucks in incoming air, initiating the propulsion process. This air passes through various stages of both rotating and stationary blades in the compressor, leading to progressively compressed air. This process of compression increases the air's pressure and temperature, preparing it for the next crucial stage in the engine core.


Combustion and Energy Release

The high-pressure, compressed air then flows into the combustion chamber, where it mixes with fuel, typically aviation kerosene. Spark plugs, similar to those in car engines, ignite the mixture, and the fuel burns continuously. This combustion process releases a substantial amount of energy, causing the gases to expand rapidly and create high-speed, hot exhaust gases.


Driving the Turbine and Exhaust

These high-energy gases then propel the turbine blades, causing them to rotate and, in turn, drive the shaft connected to the compressor. This action creates a continuous cycle of operation within the engine core. After passing through the turbine, the gases, now depleted of most of their energy, exit the engine at high speed through a tapering exhaust nozzle. As the hot exhaust gases exit the engine, they create a jet of gas that propels the jet plane forward.


Producing Thrust

The operation of modern jet engines is governed by Newton’s Third Law of Motion: for every action, there is an equal and opposite reaction. As the high-speed jet of gas is expelled from the back of the engine, it generates a forward thrust. This engine thrust is what propels the plane forward, overcoming atmospheric pressure and other resistive forces. The efficiency and power of a jet engine, and consequently the jet power it can produce, are determined by how effectively it can accelerate the exiting gases to the highest possible speed.

Understanding these processes sheds light on the remarkable capabilities of jet planes and explains how jet engines harness the principles of aerodynamics and thermodynamics to generate the thrust that propels a jet plane forward.


This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.

Frequently Answered Questions

Can a jet engine be restarted in flight?
Yes, a jet engine can be restarted in flight.