HOW IT WORKS BY IAN J. TWOMBLY Cabin heater Only slightly better than freezing IN MOST LIGHT aircraft, the environmental systems are woefully simple. Cabin air is the equivalent of rolling your car window down, only with less air. Cabin heat is only slightly more complicated. By far the most common system for single-engine aircraft consists of taking radiant heat off the engine exhaust and directing it to the cabin. Often this is done with a shroud that surrounds the exhaust manifold. The system is sometimes described as an air-to-air heat exchanger because it may mix some amount of outside air to passively regulate the temperature. From the shroud, there is another hose or series of hoses that goes directly to the firewall of the aircraft to provide heat to the cabin. In simple systems the air is pumped to the floor and a vent on the back of the glareshield for defrost. In more sophisticated systems, ducts runs through the cabin to provide heat to the rear-seat passengers. Pulling the knob on the panel opens a simple valve forward of the firewall that directly controls the amount of air that can enter the cabin. Twin-engine aircraft employ a dedicated fuel-burning heater, usually located in the nose. These systems can be beneficial in that heat is almost instantaneous and often very warm. But some pilots don’t appreciate a fire source in the nose of the aircraft. DUCTS RUN THROUGH THE CABIN TO PROVIDE HEAT TO THE REAR-SEAT PASSENGERS. CARBON MONOXIDE The big disadvantage to using these simple engine heaters is the posSTEVE KARP ide is odorless and colorless, people don’t realize they are being exposed. An inexpensive detector is the only way to protect yourself. They are available at any pilot supply store. sibility of carbon monoxide poisoning. If there’s any crack in the exhaust manifold it’s likely to come directly into the cabin. Because carbon monox- JANUARY 2013 FLIGHT TRAINING / 13