Definition
The increase in size or volume of a material as its temperature rises. In aircraft brake and landing gear systems, thermal expansion refers specifically to the swelling of brake fluid and components when heat is generated by repeated or heavy braking, which can cause brakes to drag or lock if the system has no provision to absorb the expanded volume.
Plain English
When something gets hot, it gets slightly bigger. In an airplane's brakes, hard or repeated braking heats the fluid and metal parts, and that heat makes them expand.
Context Anchor
Seen in landing gear discussions where heat or outside temperature changes can affect tire pressure, shock strut servicing, or trapped hydraulic fluid.
Derivation
From Latin thermos (heat) and expandere (to spread out). The term simply names what heat does to most materials: it makes them spread out and take up more space.
Why Pilots Care
Affects tire pressure readings, hydraulic fluid volume, and metal part clearances, all of which must be accounted for during preflight and maintenance.
Analogy
A tightly capped plastic bottle left in the sun can feel firmer because the warmed air inside is pushing harder. Landing gear components can show the same basic effect when heat raises pressure inside a closed space.
Grounding Statement
If a tire, fluid line, or shock strut warms up and the material inside cannot freely spread out, the pressure inside can rise.
Intuition Check
Thermal expansion does not mean a part is leaking or being pumped up. It means heat is causing the material inside or the part itself to take up more space, which can raise pressure if it is confined.
Example Sentence 1
After a series of short taxi stops with heavy braking, thermal expansion in the brake fluid caused the brakes to drag slightly.
Example Sentence 2
Mechanics allow for thermal expansion when torquing landing gear bolts in varying temperatures to maintain proper clearances.