17B (B3) Pitch control, synchronising and propeller ice protection

Scope (B3, level 2)

• 17.3 Pitch control: speed control and pitch change — mechanical and electrical/electronic; feathering and reverse pitch; overspeed protection.
• 17.4 Synchronising: synchronising and synchrophasing equipment.
• 17.5 Ice protection: fluid and electrical de-icing equipment.

On B3 aircraft you will mostly meet single-engine constant-speed propellers; light piston twins under 2,000 kg (with feathering propellers) and electrically adjustable propellers also exist.

Why vary the pitch?

A fixed-pitch propeller is efficient at only one combination of airspeed and rpm. Varying blade angle lets the engine run at its best rpm for take-off (fine pitch, high rpm, full power) and cruise (coarser pitch, lower rpm, lower fuel burn and noise).

Type	Control
Two-position	Fine for take-off/climb, coarse for cruise
Manually variable (in-flight adjustable)	Pilot changes blade angle directly, electrically or hydraulically; rpm still varies with speed and power
Constant-speed	Governor automatically changes blade angle to keep the selected rpm

Constant-speed operation

Two controls: throttle → manifold pressure; propeller lever → rpm (speeder-spring tension).

Typical power management sequence (to avoid high MAP at low rpm, which over-stresses the engine):

• Increasing power: first increase rpm (propeller lever forward), then MAP (throttle).
• Decreasing power: first reduce MAP, then rpm.