Air Conditioning
Heating and ventilation of the (unpressurised) cabin, bleed-air/combustion heaters and vapour-cycle cooling.
Air conditioning, summary notes
- Most helicopters are UNPRESSURISED, so 'air conditioning' means heating and ventilation rather than a pressurisation pack; cabin comfort is managed with fresh-air vents and a heating source.
- Heating is provided by engine BLEED AIR through a heat exchanger, or by a separate combustion heater on piston/some turbine helicopters; a cracked heat source is a carbon-monoxide risk, as on a piston aeroplane.
- Where cooling is fitted it is usually a VAPOUR-CYCLE (refrigerant) air-conditioning system rather than the air-cycle machine used on pressurised jets.
- Temperature and airflow are controlled by mixing/valve arrangements; demist air is supplied to the windscreen.
- Because there is no pressurisation, there is no cabin-altitude control, outflow valve or differential-pressure limit to manage.
- ⚠ Exam trap: helicopters are generally UNPRESSURISED, air conditioning is heating/ventilation (bleed-air or combustion heater), and any cooling is usually a vapour-cycle system, NOT an air-cycle pressurisation pack.
Why does a typical helicopter not have an air-cycle machine and outflow valve like an airliner?
An air-cycle machine and outflow valve exist to cool and control the pressure of a pressurised cabin. Helicopters generally operate at low altitude and are unpressurised, so there is no cabin differential pressure to manage. Comfort is handled by simple ventilation and a heater (bleed-air or combustion), with a vapour-cycle cooling system if cooling is needed.
Air conditioning concept map
Air Conditioning
Air conditioning quiz
Air Conditioning, quiz
1. Most helicopters are
Unpressurised, so air conditioning means heating/ventilationPressurised in the same way as a jet transport, with packs and an outflow valve fittedSealed and airtight, so that the cabin can hold a differential pressure at altitude2. Cabin heating is commonly provided by
Engine bleed air or a combustion heaterAn air-cycle machine packThe battery3. Where cabin cooling is fitted, it is usually a
Vapour-cycle (refrigerant) systemAir-cycle pressurisation packBleed-air only system4. Because the helicopter is unpressurised, there is no
Outflow valve or differential-pressure controlVentilationHeating5. A cracked combustion heater or exhaust heat exchanger is a hazard because it can
Admit carbon monoxide to the cabinImprove heatingCool the engine6. Demist air is supplied to the
WindshieldFuel tankRotor head7. Compared with an airliner's air conditioning, a helicopter's is generally
Simpler (heating/ventilation only)More complexIdentical8. Fresh-air ventilation on a helicopter is provided by
Adjustable cabin vents/scoopsThe outflow valveThe hydraulic system