For information about the form of substance abuse known as huffing, see inhalant

Inhalant

Inhalants are a broad range of drugs whose volatile vapors are taken in via the nose and trachea. They are taken by volatilization, and do not include drugs that are inhaled after burning or heating...

. For the Transformers character, see Huffer (Transformers)

Huffer (Transformers)

Huffer is the name of several fictional characters in the various Transformers universes. All are Autobots who turn into trucks. Huffer was first introduced in 1984, and was voiced by John Stephenson in the animated series The Transformers....

.

In aviation

Aviation

Aviation is the design, development, production, operation, and use of aircraft, especially heavier-than-air aircraft. Aviation is derived from avis, the Latin word for bird.-History:...

, a huffer is an external engine that creates large volumes of pressurized air used to start large gas turbine

Turbine

A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...

 jet engines on some types of aircraft

Aircraft

An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

.

The huffer works by blowing compressed air via flexible hose to the aircraft's bleed air

Bleed air

Bleed air in gas turbine engines is compressed air taken from within the engine, after the compressor stage and before the fuel is injected in the burners. While in theory bleed air could be drawn in any gas turbine engine, its usage is generally restricted to jet engines used in aircraft...

 system. From there, the air flows via a pilot controlled valve to the engine's starter motor. The starter motor converts the energy of the moving air to rotational torque. The starter motor is linked via shaft to the N2 or core of the engine and spins the compressor and first stage turbine. Once there is enough air flowing through the compressor

Gas compressor

A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume.Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas...

 and the combustion chamber

Combustion chamber

A combustion chamber is the part of an engine in which fuel is burned.-Internal combustion engine:The hot gases produced by the combustion occupy a far greater volume than the original fuel, thus creating an increase in pressure within the limited volume of the chamber...

 to light the engine, fuel in the form of vaporized kerosene

Kerosene

Kerosene, sometimes spelled kerosine in scientific and industrial usage, also known as paraffin or paraffin oil in the United Kingdom, Hong Kong, Ireland and South Africa, is a combustible hydrocarbon liquid. The name is derived from Greek keros...

 starts flowing and an igniter similar to a spark plug

Spark plug

A spark plug is an electrical device that fits into the cylinder head of some internal combustion engines and ignites compressed fuels such as aerosol, gasoline, ethanol, and liquefied petroleum gas by means of an electric spark.Spark plugs have an insulated central electrode which is connected by...

 ignites the fuel. Then fuel flow is increased to spin the engine up to its normal idle speed, at which point the engine is self-sustaining and no longer needs the support of the starter.

In some earlier jet engines, the air from the huffer acted directly on the compressor or turbine blades to cause them to spin without the need for the air starter motor.

Some aircraft turbine engines do not use compressed air to start, but instead are started using an electric starter motor. This is attached to the main turbine shaft and does the same job as the air starter motor. The application of the huffer is primarily seen when an aircraft's Auxiliary Power Unit

Auxiliary power unit

An auxiliary power unit is a device on a vehicle that provides energy for functions other than propulsion. They are commonly found on large aircraft, as well as some large land vehicles.-Function:...

is not working, or to military aircraft, many of which use a huffer to save on weight.