Showing content mapped to EASA Part-66. Change authority in the header.
Propeller fundamentals
A propeller is a rotating aerofoil that converts engine torque into thrust. Geometric pitch is the distance advanced in one revolution in theory; effective pitch is the actual distance; the difference is slip. Blades are twisted (washout) so the angle of attack is roughly constant along the span because tip speed is much higher than root speed.
Forces on a propeller
Centrifugal twisting moment tries to reduce blade angle (fine); aerodynamic twisting moment tries to increase it (coarse). Centrifugal force is the largest static load. Torque reaction, gyroscopic precession, asymmetric blade effect (P-factor) and slipstream all affect aircraft handling.
Pitch control systems
Fixed pitch is efficient only at one condition. Variable-pitch/constant-speed propellers use a governor that senses RPM with flyweights and meters oil to the pitch-change mechanism to hold the selected RPM. Single-acting units use oil against a spring/counterweight; double-acting use oil on both sides. Feathering turns blades edge-on to minimise drag after an engine failure; reverse pitch provides braking on landing. Beta range gives direct blade-angle control on the ground.
Synchronising & synchrophasing
Synchronising matches the RPM of all propellers to remove beat noise. Synchrophasing additionally holds a fixed blade-phase relationship between propellers to minimise cabin noise and vibration. Auto-feather and negative-torque sensing systems protect against drag from a failed engine.
Ice protection & installation
Propeller de-icing may be electrical (heating elements bonded to blade leading edges, cycled by a timer through slip rings and brushes) or fluid (glycol slinger ring). Installation includes correct flange fitting, torque, and static/dynamic balancing to reduce vibration.
Inspection & maintenance
Inspect for nicks, gouges, cracks, corrosion, delamination on composite blades, and blade track. Damage is blended out within the manual's limits and re-protected; never straighten a bent aluminium blade in the field. Track is checked with a fixed reference and must be within limits (typically 1/16 in). Overhaul is calendar and hours driven; a propeller strike requires engine and propeller inspection per the manufacturer's instructions.