Attached to the turbine is a shaft which is joined by gears to the main engine shaft, and that begins spinning as well. There, an electric spark ignites the air and fuel mixture, and the exhaust passes from the combustor out through a turbine consisting of still more blades, speeding up the engine until it reaches idle, the point at which it is self-sustaining. Thrust is produced when the pilot adds more fuel, which speeds up the engine even more, increasing its power output.
Related Questions Can helicopters fly upside down? How does a jet engine work? When the proper pressure is reached, fuel is added and ignited. Since an electric motor is nearly identical to a power generator, many aircraft combine the functions into one device. Hydraulic motors have also been used to start jet engines. This system is used in small turboshaft or turbojet engines, especially those found in helicopters or cruise missiles. By far, the most common type of jet engine startup is the air-start.
The air starter uses some source of already moving high-speed air, forces it over the compressor and turbine blades, which then gets the engine running when fuel is added. Where does the high-speed air come from? If an airplane has more than one engine, it can get the air from another engine.
Some high-pressure air is often ducted from an engine for other uses. This is known as bleed air, and bleed air is often used to help start a turbine engine. But to use bleed air to start a jet engine, another jet engine needs to be already running. Many planes have an APU, or auxiliary power unit, built into the plane. Airliners often have their APUs mounted in the tail cone. The APU is really just a tiny jet engine.
An alternative to using the APU is a ground-based unit, also called the huffer cart. These ground carts are trailers found around airports parked next to the plane to help it during ground starts.
These come in several forms, but the biggest ones are basically mobile APUs. The proper name for them is a GPU, or ground power unit. If an engine is shut down in-flight for any reason—be it a malfunction, training, or fuel savings—it can be restarted quickly. Since the relative wind to the aircraft is still spinning the fan and compressor blades, chances are introducing fuel back into the system will result in a restart. If the turbine speed is insufficient, it can be increased by putting the plane into a dive to increase airspeed.
Editorial Team Turbojet Engine Diagram. Battery: Older or smaller jet engines were started directly using electrical power, either from a battery or an external power unit. Jet fuel starter: This is also a gas-generating turbine, but unlike an APU, it does not function independently of the engines.
The JFS is directly linked to the engine it is starting and can't be used for any purpose other than starting the engine. Cross-bleed start: With this method, bleed air from an already-running engine is used to start another engine. This is a common feature on multi-engine aircraft and is a technique used to restart a failed engine. Air start unit: The so-called "start cart" is a wheeled airport utility that can be carted over to an aircraft.
It provides high pressure air to the engine to start it. This helps save the battery from wear due to repeated use.
Start carts are at every major airport. This question originally appeared on Quora - the place to gain and share knowledge, empowering people to learn from others and better understand the world. More questions:.
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