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Staying Cool Under Pressure by Elliott Cox
Spring is the time of year here in the Carolinas when we have ice on the windshields in the morning and heat shimmers from the roads in the afternoon, and we’re constantly adjusting the settings on our
thermostats to stay comfortable. A properly functioning environmental system can make flying in the heat of the summer much more enjoyable.
There are two types of environmental systems com- monly used in airplanes. Vapor cycle systems are used in piston aircraft, turboprops, and smaller turbine airplanes. Air cycle systems are used in most turbine airplanes equipped with an APU.
Vapor cycle systems operate like the air conditioning systems in your house or car. These use refrigerant,
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PHOTOS BY ELLIOTT COX
typically R-134a, in a closed system to remove heat from one area (the cabin) and exhaust it to a different place (overboard.) The refrigerant is compressed, causing it to heat up and become vapor. The superheated vapor is sent through a condenser, where a fan blows air over the coils and cooling fins to cool the vapor inside. If you’ve ever held your hand over a running home air conditioner, the hot air you feel blowing out is the product of the fan blowing air over the condenser.
When the refrigerant vapor cools, it returns to a liquid state and flows through an evaporator. The evaporator is also made of coils and cooling fins and works like a condenser. The difference is instead of outside air blow- ing over the coils, recirculated cabin air is blown over the
An Environmental Control Unit in a Cessna Citation XLS+