Definition
A numerical value that expresses how much a material changes in size for each one-degree change in temperature. Each material has its own coefficient — metals like aluminum expand more than steel for the same temperature rise, and this value is used to predict and account for that change in engineering, fabrication, and maintenance.
Plain English
A number that tells you how much a material grows or shrinks when it gets hotter or colder. Different materials have different numbers — some stretch a lot with heat, others barely move.
Context Anchor
Seen in aviation maintenance when working with metals, engine parts, close-fitting parts, and materials exposed to large temperature changes.
Derivation
From Latin coefficere, meaning 'to work together,' and expandere, 'to spread out.' A coefficient is a fixed number that works alongside another value (here, temperature) to produce a result (the change in size).
Why Pilots Care
Aircraft are built from many materials joined together. If a technician ignores how much each part expands or contracts with temperature, fits can loosen, fasteners can fail, and components can bind or crack. Understanding this property is essential for safe repairs and proper assembly.
Analogy
A bridge has small gaps so it can grow slightly on a hot day and shrink on a cold day. Aircraft parts can do the same thing, but the amount depends on the material.
Grounding Statement
If an aluminum part and a steel part are heated by the same amount, they may not grow by the same amount because their coefficients of expansion are different.
Intuition Check
Expansion here does not mean a part permanently gets bigger. It means a predictable size change caused by temperature, usually growing with heat and shrinking again with cold.
Example Sentence 1
Aluminum has a higher coefficient of expansion than steel, so the technician allowed extra clearance when fitting the two parts together.
Example Sentence 2
Different metals expand at different rates, so the coefficient of expansion must be matched in engine assemblies to keep clearances correct at operating temperature.