The propellers fitted to the Conquest are either three bladed Hartzell or four bladed McCauley constant speed propellers. Operation of both types of propellers from inside the cockpit is identical, the only difference between the two being the blade angles at the feather and flight idle position.
Mccauley props | Hartzell Props
The propellers operate on a 'pressure to fine' principle whereby oil pressure is used to drive the propeller into the fine and full reverse positions. This oil pressure is generated by a pump located within the propeller governor. This means that if oil pressure is lost the propeller will naturally move toward the full coarse position.
Propeller Governor located under the starter-generator
The propeller operates in two modes:
- Beta, and
- Propeller governor mode.
In Beta mode the pilot controls the blade angle with the power levers through the propeller pitch control unit during ground operations (Start-Taxi position on the condition levers).
Condition levers shown in the Start-Taxi position
In the propeller governor mode, blade angle is controlled by the propeller governor in response to input from the fuel control unit as determined by the position of the condition levers. The governor operates in the usual operating ranges of Under speed, Over speed and On speed conditions.
When the propeller is Under speed, the governor will react by applying governor pump pressure to the piston in the propeller dome which reduces the blade angle causing an increase in engine RPM toward the selected on-speed condition.
Oil pressure being applied to prop dome during under-speed condition
When the propeller is in over-speed condition the governor will react by allowing oil to drain from the propeller dome to the accessory gear case permitting the spring and counterweights to increase the propeller blade angle causing the engine RPM to decrease toward the selected on-speed condition.
Oil pressure being reduced from prop dome during over-speed condition
During flight at a constant power setting, blade angle is a function of True Airspeed. RPM is a sole function of Blade Angle. Engine RPM signals are transmitted to the electronic fuel computers by the Primary Monopole which is driven by a special gear from the propeller governor.
Propeller governor drives the Primary Monopole which transmits RPM to electronic fuel computers
A propeller pitch control unit controls the propeller in Beta mode (blade angle controlled by the power levers). A sleeve operated by a cam slides on the Beta tube which is attached to the propeller piston.
Beta tube in which oil is fed to/from the prop dome.
The position of the sleeve relative to oil ports in the Beta tube allows oil pressure to be directed to or from the propeller piston, thereby directly changing propeller blade angle.
Propeller shown operating in Beta mode with Beta light on.