14.3 and 14.4 Propeller systems, starting and ignition (B2)

Scope

Both level 2 for B2/B2L.

• 14.3 Propeller systems: propeller speed indication; speed control and pitch change — electrical/electronic; synchronising and synchrophasing; electrical anti-icing/de-icing.
• 14.4 Starting and ignition: engine start systems and components; ignition systems and components; maintenance safety requirements.

Propeller basics for B2

• Fixed-pitch — blade angle fixed; rpm varies with throttle and airspeed.
• Constant-speed (variable-pitch) — a governor changes blade angle to hold the selected rpm: if rpm rises, pitch increases (coarser) to absorb more power; if rpm falls, pitch decreases (finer).
• Feathering — blades turned edge-on to the airflow (about 90°) after engine failure to minimise drag and stop windmilling.
• Reverse / beta — negative blade angles for ground braking and manoeuvring on turboprops.

Propeller speed indication

• Propeller rpm (Np) sensed by magnetic pickups at a toothed wheel or by a tacho-generator, displayed in rpm or %.
• On turboprops the propeller speed and torque are the main power indications; beta light shows the propeller is in the beta range.