Ever wonder how aircraft brakes are cooled? Like automotive brakes, aircraft brakes rely on friction to achieve a lower traveling speed. Friction creates heat, however, and too much heat can damage or destroy an airplane’s braking components.
Overview of Aircraft Brakes
Aircraft brakes consist of disc stacks. Some of these discs rotate, whereas others remain stationary (stators). When the pilot engages the brake pedal, these discs will compress against the wheels, resulting in friction. This friction slows the speed at which the wheels turn and, thus, allows the airplane to decelerate.
Airplanes land at very fast speeds. Depending on factors like the size, weight and runway conditions, they may touch down at speeds of 130 to 160 mph. The disc-based braking system is designed to quickly slow airplanes via friction. Heat, of course, is a byproduct of friction. Some aircraft brakes can exceed temperatures of 1,800 degrees Fahrenheit, which is why cooling is so important.
Ambient Air
Most airplanes use ambient air to cool their brakes. When landing, aircraft brakes are exposed to the surrounding air. Air will flow around the discs, cooling them naturally.
Ambient air is a very basic form of cooling, but it’s surprisingly effective. It doesn’t require any special devices, nor does it consume energy. Instead, it leverages the air around the brakes. As air circulates around the brakes, heat transfer will occur. Heat will transfer from the discs to the surrounding air, thereby cooling the brakes.
Brake Cooling Fans
Some airplanes may use specialized fans to cool their brakes. Known as brake cooling fans, they are designed to force air over the airplane’s brakes.
Brake cooling fans are electric. They are powered by an electric current that spins a set of fan blades. As these blades spin, they force air over the brakes.
When compared to ambient air alone, brake cooling fans offer a faster cooling solution. With that said, not all airplanes are equipped with brake cooling fans, and many airlines only use them when additional cooling power is required to keep brake temperatures within the recommended limits.
Landing Gear Extension
Pilots may leave the airplane’s landing gear extended for a prolonged period to assist with brake cooling. Normally, pilots retract the landing gear immediately after takeoff. If the brakes are hot, however, they may leave them extended for several minutes.
Aircraft brakes cool faster when the landing gear is extended. As part of the landing gear, they are exposed to the air when the landing gear is down and extended. Air will flow past the brakes, effectively cooling them.