External cooling

Cooling of the external skin of an aero-engine is achieved by suitable design of the aircraft airframe; the layout will depend upon where the engine is fitted and what kind of engine compartment is used. Normally, the cooling and ventilating of an engine bay or pod is achieved by ducting atmospheric air round the engine and spilling it back to atmosphere through suitably placed outlets (see figure). The air is usually taken from a ram inlet but provision is also made to provide a cooling and ventilating airflow during ground running periods. Another function of the cooling airflow is to remove flammable vapours from the engine compartment to reduce the fire risk.