A fusible plug is a metal cylinder, usually made of materials like bronze, brass, or gunmetal. It has a tapered hole drilled through its length, which is sealed with a metal that melts at low temperatures. When a specific high temperature is reached, this metal flows away. This mechanism acts as a safety valve, particularly in situations where high temperatures, not high pressures, are a concern.
Fusible plugs are often found in aircraft wheels, especially in larger or high-performance models. During braking, especially after a rejected takeoff, thermal loads can significantly increase. This heat can raise the pressure in the tires to dangerous levels, risking a burst. If the temperature in the wheel assembly exceeds safe limits, the core of the fusible plug melts. This melting allows for a relief mechanism that helps the tire deflate safely.
The gas released from the tire, typically nitrogen, is often directed to cool the brake assembly surfaces. This process is vital for maintaining safety during critical flight operations.
