How do the turbine fans in a jet engine start spinning, I know there's no electric motor to get them started

Question

How do the turbine fans in a jet engine start spinning, I know there's no electric motor to get them started

Answer 1

There are two ways of starting a turbine engine, depending on its size.

Smaller turbine engines (found on most business jets and smaller airliners) have a starter/generator.  Depending on the position of switches and the active function on the Generator Control Unit, the generator can function as a starter to get the turbine spinning.  This is accomplished electrically using the battery, a ground power cart, an APU, or (after one engine is started) the other generator.

Larger turbine engines start spinning pneumatically.  It uses air pressure to spin the turbine for starting.  The air pressure usually comes from the APU for the first engine, and the operating engine for the second engine (crossbleed start).  If the APU is not available, the plane can use air pressure from a ground source, called a "huffer".

For planes with an APU, the APU is started electrically.  It's nothing more than a small jet engine used to supply air and electricity to the plane before the engines are started, and like mentioned, to start the engines.

Answer 2

Typically on twin engine business jets they have a self contained APU (auxillary power unit) when these run prior to start-up they provide the necessary power to spool up the engines, and yes there is a light weight starter, but you have to get the fan spinning at a certain percentage to engage the ignitor plugs which in turn gives the engine the ground idle speed, all based upon inlet temps, pressure ratio's, and the like. When you see some aircraft on the ramp you might notice you hear the airplanes turbines running, what you actually hear is the APU, mounted near the back of the jet near the tail cone..

Answer 3

All good answers above. Bigger jets use their Auxiliary Power Unit (APU) for power as the starter for the engines.

Smaller jets use a starter/generator which gets its power from the aircraft's main batteries or a GPU (Ground Power Unit which either delivers power from the terminal to the aircraft, or generates its own power). Once one engine is starter, the use the generator of the already running engine to power up the other engine(s).

Answer 4

Actually on most aircraft there is an electric motor to get them started turning. Usually this is a starter/generator, so once the aircraft's engine start turning on their own, the mode is switched to provide electric to the aircraft. The power to turn the engine's over is either provided by a battery system (saab 340), or an APU. If the APU is in/op the aircraft, or if a GPU (ground power unit) is available, either will provide the power needed to turn over the engine, almost all transport catagory a/c are capable of using a GPU or APU.. On some larger aircraft, they can also use an air start, which is nothing more than a large air compressor to get the turbines to start turning, and then they can light the burners, this is the common way for a Dc-8-61.

Answer 5

Compressed air is shot into the engine to start it spinning.  this comes either from an APU, another engine, or from a Huffer (ground air)