Definition
The opposition a material offers to the establishment of magnetic flux through it. Reluctance in a magnetic circuit is analogous to resistance in an electrical circuit; the higher the reluctance, the less magnetic flux a given magnetomotive force will produce.
Plain English
How hard it is to push a magnetic field through something. Iron has low reluctance, so a magnetic field passes through it easily. Air has high reluctance, so the same magnetic field has a much harder time getting through.
Context Anchor
Seen in aircraft electrical and ignition system discussions, especially when describing magnetic cores, coils, generators, alternators, and magnetic sensors.
Derivation
From the Latin reluctari, meaning 'to struggle against' or 'resist.' The word captures the idea of a material struggling against the magnetic field that is trying to pass through it.
Why Pilots Care
Core materials in magnetos and generators are chosen for low reluctance so magnetic flux can build efficiently and produce reliable ignition and electrical power.
Analogy
Think of reluctance like the resistance you feel pushing water through different materials. Water flows easily through a wide pipe (low reluctance) but struggles through a sponge (high reluctance). Magnetic flux behaves the same way through different materials.
Intuition Check
Reluctance does not mean a person is unwilling here. In aircraft electrical use, it means resistance to a magnetic field passing through a material or path.
Example Sentence 1
The iron core of the magneto provides a low-reluctance path for the magnetic flux, allowing a strong field to build up around the coil.
Example Sentence 2
High reluctance in the magnetic path reduces output from the aircraft alternator.