Huffer

A huffer is an external engine used to start large gas turbine jet engines on some types of aircraft.

The huffer works by blowing compressed air through the engine's turbines, which causes them to spin. Once there is enough air blowing through the compressor and the combustion chamber to light the engine, fuel in the form of vapourised kerosine starts flowing and an igniter similar to a spark plug ignites the fuel. Then fuel flow is increased to spin the engine up to its operating speed, at which point it starts producing thrust. When this happens, obesrvers can sometimes hear a pop and see smoke come out of the back of the engine.

Some aircraft engines do not use huffers, but instead are started using a starter motor, usually electric. This is attached to the main turbine shaft and does the same job as the huffer. The application of the huffer is mainly restricted to very large engines such as those on a Boeing 747, where very large starter motors would be impractical, or to military aircraft, many of which use a huffer to save on weight.

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