Exhaust duct arrangement in Aircraft:
Exhaust ducts are invariably positioned to ensure that on the ground as the hot gases are directed away from the maintenance crews and aircraft structure. This is usually achieved by angling the exhaust duct upwards. Figure. represents a typical duct arrangement.The exhaust ducts are subjected to high temperatures, so the following design features must be considered:
• Leaf springs are fitted to allow for longitudinal expansion of the exhaust duct.• The flexible bellows allow for slight variations during the assembly of the duct to the engine flange.• Flame traps may be fitted to joints to provide protection if the joint leaks.
The exhaust duct is normally insulated to prevent the heat from affecting the aircraft structure or adjacent components. This can be a double duct with cool air being passed between the ducts or by the use of insulation blankets.An exhaust door may be fitted to reduce cold soak or to prevent rain or snow entering the duct. The door must be open before the engine can start and will close after a time delay on shut down.