Controlling rate of rotor feather by system secondary to primary blade angle control system

1 . A rotor control system comprising:

a main control valve having an inlet for receiving liquid and an outlet for issuing liquid to a rotor pitch change actuator, wherein the main control valve is configured to control flow of the liquid from the inlet to the outlet to modify pitch angle of rotor blades;

a feathering system including a feather valve having a feather inlet, a feather port, and a drain outlet, the feather system having a first conduit fluidly connecting the outlet of the main control valve to the feather inlet, a second conduit fluidly connecting the feather port with the rotor pitch change actuator, and a drain conduit fluidly connecting the drain outlet of the feathering valve to a drain location for draining the liquid from the rotor pitch change actuator,

wherein the feathering system has a normal operation mode for supplying liquid from the main control valve to the rotor pitch change actuator by allowing flow through the feathering system from the first conduit to the second conduit, the feather valve fluidly connecting the feather inlet to the feather port while disconnecting the feather port from the drain outlet in the normal operation mode, and

wherein the feathering system has a feathering mode for allowing drainage from the rotor pitch change actuator to the drain conduit by connecting the second conduit in fluid communication conduit with the drain conduit for drainage from the drain conduit to an engine oil return system, the feather valve fluidly connecting the feather port to the drain outlet in the feathering mode,

the feathering system further including a feather drain control valve, the drain outlet of the feather valve fluidly connected to the drain location through the feather drain control valve; and

a controller operatively connected to the feather drain control valve, the controller having a processing unit operatively connected to a computer-readable medium having machine readable instructions stored thereon executable by the processing unit for:

upon the feather valve being in the feathering mode caused by an undesired state, determining that the undesired state requiring a need to feather the rotor pitch angle actuator is no longer present; and

causing the feather drain control valve to at least partially restrict a drain flow of the liquid from the feather valve to the drain location.

2 . The system as recited in claim 1 , wherein the machine-readable instructions include instructions configured to cause the controller to:

command the feathering system to drain the second conduit to the drain conduit at the fully open flow initially;

to receive input indicative of exiting the need to feather, commanding the feathering system to at least partially restrict the drain flow by doing at least one of:

modulate drainage from the second conduit to the drain conduit somewhere in the range between fully open flow and fully closing off flow from the second conduit to the drain conduit; or

completely block drainage from the second conduit to the drain conduit with the feature drain control valve being configured as an open/close valve.

3 . The system as recited in claim 2 , wherein modulating drainage includes gradually reducing rate of oil drain from the second conduit to the drain conduit.

4 . The system as recited in claim 3 , wherein modulating drainage includes after gradually reducing rate of oil drain, fully closing off flow draining the rotor pitch angle actuator.

5 . The system as recited in claim 3 , wherein modulating drainage and/or completely blocking drainage is performed under active control.

6 . The system as recited in claim 3 , wherein modulating drainage and/or completely blocking drainage is performed under passive control.

7 . The system as recited in claim 1 , wherein the feathering system includes:

a feather solenoid operatively connected to control a piston of the feather valve for actuating the feather valve between connecting the second conduit in fluid communication with either the first conduit or with the drain conduit, wherein the feather solenoid is in fluid communication with the drain conduit through a branch of the drain conduit.

8 . The system as recited in claim 7 , wherein the feather drain control valve is an open/close valve configured to selectively either allow or block flow through the drain conduit.

9 . The system as recited in claim 7 , wherein the feather drain control valve is an actively controlled metering valve, configured to open, moderate, and close flow through the drain conduit under active control in the feathering mode.

10 . The system as recited in claim 7 , wherein the feather drain control valve is a passively controlled metering valve, configured to passively meter flow in through the drain conduit in the feathering mode.