Fly Cool with Aircraft Cowl Flaps

Aircraft engines create an immense amount of heat throughout their flight hours. High temperatures necessitate the presence of cooling instruments. An important member of these components is the cowl flap. Dare I reference the Star Wars prequels, an activated cowl flap resembles a mini version of the walkway extended from Padme’s J-type Star Skiff ship in the last scene of Revenge of the Sith. Though a cowl flap doesn’t sound as flashy, the lowering mechanism works almost identically, and is a valuable cooling component.

A cowl flap acts an open-air duct located at the bottom of the engine cowling, as opposed to an extendable walkway. It is one of the key mechanisms that aids in keeping an aircraft engine from overheating. Their specified design enables a cooling and depressurizing effect using the flow of air. Cowl flaps and inlets are most valuable during high power events, like takeoff and sudden increases in thrust. During these occasions, the engine is at its highest temperatures, as the heightened airspeed does not allow the same airflow that is achieved at low power cruising speed.          

There are two main types of cowl flap configurations, but they essentially follow the same series of cooling process functions. Incoming air travels through the engine cowl, and mixes with hot air from the combustion unit. The cooled air then circulates around the engine and exits the compartment through the underside of the engine cowling. With this design, the cowl flap allows the deflection of slipstream airflow. Following this step, a low-pressure environment is invariably formed around the engine, which then draws the air to coincidently cool cylinder components.

On most aircraft models equipped with a cowl flap, the design will include position control, or engagement of the flap, that can be activated by the pilot directly using mechanical or electrical controls. This construction is commonly seen on radial engine aircraft. Their small size and lower speed requirements allow the cowl flap to be a practical cooling addition.

Modern airliners, however, have phased out this version of the cowl flap, in favor of a permanent cowl component. Larger engines generate more heat and cannot afford the drag created by a lowered mechanism protruding from the airframe. Instead, aircraft of this nature are equipped with a more aerodynamic inlet, that functions as a permanently exposed flap on the underside of the engine cowling.

From radial aircraft to commercial airliners, the cowl flap mechanism is one of the many invaluable aircraft components designed to keep you flying cool.  


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