Propeller pitch control system for aircraft turboprop engines

A propeller pitch control system for a turboprop engine of an aircraft, comprising:

• an engine control unit operable to determine a phase of flight of the aircraft and configured to supply control commands;
• and
• a pitch control unit coupled to receive the control commands from the engine control unit, the pitch control unit comprising:
• a housing having a slot formed therein and including an inlet port, a drain pressure port, a control pressure chamber, and a piston sleeve, the inlet port for receiving hydraulic fluid, the drain pressure port vented to atmospheric pressure;
• a beta piston disposed within the piston sleeve and axially movable therein between a fully extended position and a fully retracted position, the beta piston having a first end section, a second end section, an inner surface, an outer surface, and a control pressure port, at least a portion of the second end section disposed within the control pressure chamber, the second end section having an outer surface and being frustoconical in cross-section, the inner surface defining a beta tube control volume, the control pressure port extending between the inner surface and the outer surface and fluidly communicating the inlet port with the beta tube control volume;
• an anti-rotation pin coupled to the second end section of the beta piston and extending into the slot, whereby rotation of the beta piston is prevented;
• a position sensor having a sensor housing and a sensor shaft, the shaft extending from, and movable relative to, the housing and spring biased to continuously engage the outer surface of the second end section, whereby axial movement of the second end section causes the sensor shaft to move relative to the sensor housing;
• a beta tube disposed within the beta tube control volume and rotatable relative to the beta piston, the beta tube axially movable in the beta tube control volume based, at least in part, on fluid pressure within the beta tube control volume;
• and
• an electrohydraulic valve coupled to the housing and including a supply nozzle, a drain nozzle, a control pressure port, a movable flapper disposed between the supply nozzle and the drain nozzle, and a torque motor coupled to the flapper, the supply nozzle in fluid communication with the inlet port, the drain nozzle in fluid communication with the drain pressure port, the control pressure port in fluid communication with the control pressure chamber, the torque motor coupled to receive commands from the engine control unit and responsive to the commands to move the flapper between the supply nozzle and the drain nozzle to modulate fluid pressure in the control pressure chamber, to thereby move the beta piston to the fully extended position, the fully retracted position, or any one of numerous positions between the fully extended and fully retracted positions,
• wherein:
• the beta piston, the piston sleeve, and the beta tube are configured to form a half-area force balanced architecture,
• when the beta piston is in the fully retracted position, the second end section engages a wall of the control pressure chamber, and
• the engine control unit only commands the electrohydraulic valve to move the beta piston from the fully retracted position when the engine control unit determines the aircraft is conducting pre-takeoff roll taxiing operations or is conducting post landing touchdown operations.

A propeller pitch control unit, comprising:

• a housing including an inlet port, a drain pressure port, a control pressure chamber, and a piston sleeve, the inlet port for receiving hydraulic fluid, the drain pressure port vented to atmospheric pressure;
• a beta piston disposed within the piston sleeve and axially movable therein between a fully extended position and a fully retracted position, the beta piston having an outer diameter (DBP_OUTER) that defines a first area (A1) and including a first end section, a second end section, an inner surface, an outer surface, and a control pressure port, at least a portion of the second end section disposed within the control pressure chamber, the inner surface defining a beta tube control volume, the control pressure port extending between the inner surface and the outer surface and fluidly communicating the inlet port with the beta tube control volume;
• and
• a beta tube disposed within the beta tube control volume and rotatable relative to the beta piston, the beta tube axially movable in the beta tube control volume based, at least in part, on fluid pressure within the beta tube control volume, the beta tube having an outer diameter (DBT_OUTER) that defines a second area (A2),
• wherein:
• a difference between the first area (A1) and the second area (A2) is approximately equal to a third area (A3), and
• the third area (A3) is equal to the second area (A2).