Propeller Construction
Blade materials, hub and spinner, leading-edge protection and propeller balancing.
Propeller construction, summary notes
- 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.
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.
Construction concept map
Propeller Construction
Propeller construction quiz
Propeller Construction, quiz
1. The leading edge of a metal propeller blade is often protected by:
A metal sheath or erosion stripA layer of paint onlyNothing, it is left bare2. Propeller blades are tracked to check that:
Each blade tip follows the same path of rotationThe blades are the same colourThe spinner is centred3. The most common propeller blade material is:
Aluminium alloyCast ironLead4. A metal leading-edge sheath (tipping) is fitted to:
Wooden and composite blades to resist erosionAluminium blades onlyThe spinner5. A propeller must be balanced:
Both statically and dynamicallyStatically onlyNot at all6. The spinner on a propeller:
Fairs the hub for smooth airflowChanges blade pitchDe-ices the blades7. A blade 'station' is:
A position measured along the blade from the hubA ground test rigA type of governor8. A blade cuff is fitted to:
Improve airflow/cooling at the blade rootLock the pitchFeather the blade