All modern aircraft have a braking system that assists with deceleration and stopping on the ground, as well as holding the plane in place during an engine run-up. Though they may work similarly to brakes employed in many automobiles, there are some crucial differences to account for. Firstly, as an oddly shaped vehicle, aircraft typically place their brakes directly on the wheels beneath the vessel body. However, they are usually only fitted to the rear wheels where they can best provide leverage for stopping the vehicle. Aside from their placement, it is also useful for aircraft owners and operators to understand some of the physics behind such braking systems, along with what major types are available when replacements are required.
The Physics of Braking
At a glance, braking refers to the way a vehicle will slow and stop the movement of its wheels by forcing them to stop rotating. The vehicle is able to do this by contacting its wheels with a semi-metallic or ceramic brake pad that presses against the rotating tires, creating a large amount of friction. In this way, kinetic energy of the wheels can then be dissipated as heat caused by the friction of the two surfaces pressing against each other. Therefore, with enough time and energy applied to the brakes, even huge, fast-moving vehicles like airplanes can come to a full stop simply by converting their kinetic energy to heat. Nevertheless, the large frictional forces generated during braking cause the pads to wear quickly, so regular inspection and maintenance of the system is required to ensure that all brakes continue to work as intended. Additionally, because they are such large and powerful vehicles, aircraft typically use hydraulically actuated brakes.
Types of Brakes
Disc brakes are the most common braking system in use today and consist of a disc which rotates with the wheel and a stationary brake caliper that actuates onto the disc to facilitate a braking force. In specific, the caliper is an assembly that contains the brake pads and piston(s), and the pads are connected to the piston(s) which actuates under hydraulic pressure applied via a toe brake or brake lever in the cockpit. On smaller aircraft, there will often only be a single disc used per wheel, while on larger vessels, there are often multiple discs.
Expander Tube Brakes
Expander tube brakes are an old technology that were used primarily on aircraft manufactured between 1930 and 1950. They are a low-pressure braking system that has now largely been replaced by disc brakes, but may still be around in vintage vessels. Their basic design consists of a lightweight frame attached to the outer section of a rubber tube. The frame and tube sit inside a wheel drum, and a set of brake blocks are attached to the frame to provide a braking surface. As such, when the rubber tube is inflated during braking, it pushes the brake pads onto the inside of a wheel drum, generating the necessary friction to slow the aircraft. Similar to the disc brakes, expander tube brakes are inflated through hydraulic action. Springs installed in the system can then return the expander tube to its deflated position when braking force is removed by the pilot.
Brake Actuation Systems
Both expander tubes and disc brakes rely on some form of actuation system to apply the necessary force to their brake pads. Depending on the size and complexity of an aircraft, there are different types of brake actuation systems that can be used. For example, light aircraft often lack a hydraulic system; therefore, they use an independent brake system. In these systems, the braking pressure at the wheel is fully controlled by the amount of force that the pilot applies on the brake pedal. On larger aircraft that use a booster brake system, the brakes are assisted by the hydraulic system already in place on the aircraft. Finally, on very large aircraft, there are typically power brake systems which are still controlled by the pilot’s movements, but are fully powered by an electrically controlled hydraulic system.
Altogether, airplanes use a variety of braking systems which all function on the same working principle, but with varying levels of hydraulic assistance. No matter the type of braking equipment used, it is always important to conduct regular inspection and maintenance to ensure that all applicable brakes remain working as designed. If you have found a need for replacement bearings, fasteners, connectors, or other parts after conducting inspections, you can always rely on Civil Aviation 360 as a trusted source for high-quality components. Backed by a widespread supply network and robust market expertise, we find competitive solutions for our customers’ fulfillment needs!
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