Chapter 20: The Air Inlet

20.1 Purpose and Design

• The air inlet (or intake) is designed to provide a steady, turbulent-free supply of air to the face
• f the compressor.
•  Subsonic Intakes: These are typically divergent ducts. As the aircraft's speed increases, the
• ram air is slowed down and its pressure increases before it reaches the compressor, improving
• efficiency. This is known as ram pressure recovery.
•  Supersonic Intakes: Since an engine compressor cannot handle supersonic airflow,
• supersonic intakes are designed to slow the air down to subsonic speeds before it enters the
• engine. They use a convergent-divergent shape and often employ movable ramps or spikes
• to control the position of shockwaves for efficient deceleration of the air.
•  Icing: Intakes are prone to icing in certain atmospheric conditions. Engine anti-ice systems,
• which use hot bleed air from the compressor, must be used to prevent ice from forming and
• being ingested by the engine.
•  Foreign Object Damage (FOD): The intake is the entry point for any debris (stones, birds,
• etc.) that can severely damage the compressor blades.