Section 17.2

Propeller Construction

Blade materials, hub and spinner, leading-edge protection and propeller balancing.

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Main ideas

Blade materials: wood (older/light aircraft), aluminium alloy (the most common) and modern composites (light, strong and damage-tolerant). Propellers are fixed-pitch, ground-adjustable or controllable/constant-speed.
Blade features: the root and shank, the aerofoil section with leading and trailing edges, the tip, and blade 'stations' measured from the hub; a blade cuff can be fitted to improve airflow and cooling at the root.
The hub retains the blades and, on variable-pitch propellers, carries the bearings and pitch-change mechanism; a spinner fairs the hub for airflow and appearance.
Wooden and composite blades have a metal leading-edge sheath ('tipping') to protect against erosion from rain, grit and stones; drain holes prevent water building up.
Every propeller must be balanced — statically and dynamically — because it is a large rotating mass; imbalance causes vibration that fatigues the engine and airframe.
⚠ Exam trap: metal leading-edge sheaths/tipping protect WOODEN and COMPOSITE blades from erosion; aluminium alloy is the most common blade material; a propeller must be both statically and dynamically balanced.

Solved examples

Why do wooden and composite propeller blades have a thin metal strip bonded along the leading edge?
The leading edge meets rain, dust and small stones at high speed, which would quickly erode a wood or composite surface and change the aerofoil. A metal sheath ('tipping') protects the leading edge from this erosion, greatly extending blade life; small drain holes stop water collecting behind it.

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