The system incorporates a ventilating air system, fuel system, and ignition system to heat various components of an aircraft. In order to heat incoming air from the ventilating system, the combustion unit integrates an independent combustion system within a shroud in a heater unit, where fuel and air are mixed and ignited within an inner chamber. Air intended for combustion is provided by a blower, which pulls air from outside the aircraft and ensures the air is pressurized to the correct specifications.
Ram air is collected when the aircraft is grounded, through a ventilating air fan. The ram air is circulated around the combustion chamber and outer shroud, allowing it to heat through convection. Following this process, the heated air is then directed to the cabin. Exhaust from the same process is expelled from the aircraft.
A combustion unit is extremely versatile, which is why it is used on a variety of aircraft. Most are controlled and monitored by a pilot through a cabin heat switch and thermostat and incorporate various redundant safety features. These might include an overheat switch or duct limit. As is recommended for any other aircraft system, it is important to follow aircraft manufacturer instructions and protocols in the maintenance of exhaust or combustion heaters.
This way, if an opening should occur, the higher-pressure ventilating air flows into combustion chamber walls instead of allowing dangerous combustion gases to flow out into the ventilating air stream. Heating Systems Better by Design Janitrol Aero cabin heating systems are manufactured to handle the most demanding conditions.
Learn More. Performance Design Technology. Find A Distributor Shop Now. A combustion heater is an airtight burner chamber with a stainless-steel jacket. Fuel from the aircraft fuel system is ignited and burns to provide heat. Ventilation air is forced over the airtight burn chamber picking up heat, which is then dispersed into the cabin area.
When the heater control switch is turned on, airflow, ignition, and fuel are supplied to the heater. Airflow and ignition are constant within the burner chamber while the heater control switch is on. When heat is required, the temperature control is advanced, activating the thermostat.
The thermostat which senses ventilation air temperature turns on the fuel solenoid allowing fuel to spray into the burner chamber. Fuel mixes with air inside the chamber and is ignited by the spark plug, producing heat. The by-product, carbon monoxide, leaves the aircraft through the heater exhaust pipe.
Air flowing over the outside of the burner chamber and inside the jacket of the heater absorbs the heat and carries it through ducts into the cabin. As the thermostat reaches its preset temperature, it turns off the fuel solenoid and stops the flow of fuel into the burner chamber. For this reason, they are not very common. However, their use on the ground when powered by a ground electrical power source preheats the cabin before passengers board and does not tax the electrical system.
Most single-engine light aircraft use exhaust shroud heating systems to heat the cabin. The air is warmed by the exhaust and directed through a firewall heater valve into the cabin. This simple solution requires no electrical or engine power and it makes use of heat that would otherwise be wasted.
Figure 1. The basic arrangement of an aircraft exhaust shroud heater. Figure 2. The environmental system of a single-engine Piper aircraft with an exhaust shroud heating system.
A major concern of exhaust shroud heat systems is the possibility that exhaust gases could contaminate the cabin air. Even the slightest crack in an exhaust manifold could send enough carbon monoxide into the cabin to be fatal. Strict inspection procedures are in place to minimize this threat. Most involve pressurizing the exhaust system with air, while inspecting for leaks with a soapy solution. Some require the exhaust to be removed and pressurized while submerged under water to detect any leaks.
Frequency of exhaust heat leak detection can be every hours. Occasionally, the exhaust system is slightly modified in a shroud heat configuration. For example, an exhaust muffler may have numerous welded studs attached, which increase heat transfer to the cabin air.
Each weld point is a location for a potential leak. Figure 3. An exhaust manifold with its shroud removed showing numerous welded studs used to increase heat transfer from the exhaust to the ambient air going to the cabin.
Regardless of age or condition, aircraft with exhaust shroud heating systems should contain a carbon monoxide detection device in the cockpit. An aircraft combustion heater is used on many small to medium sized aircraft. Combustion heaters are manufactured by a few different companies that supply the aviation industry. Most are similar to the description that follows. The most up to date units have electronic ignition and temperature control switches. Combustion heaters are similar to exhaust shroud heaters in that ambient air is heated and sent to the cabin.
The source of heat in this case is an independent combustion chamber located inside the cylindrical outer shroud of the heater unit.
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