TECHNICAL FIELD

The application related generally to aircraft engines and, more particularly, to aircraft engines having variable pitch propellers.

BACKGROUND OF THE ART

While existing variable pitch propeller systems were satisfactory to a certain degree, there remained room for improvement. Indeed, in some variable pitch propeller systems, when the engine was operated for a relatively long time at relatively cold temperatures, the oil coming back through the feather valve from the pitch actuator when feathering can be cold and viscous causing pressure losses through the feather valve, and a notable effect on feather rate. This could lead to overdesigning feather valves in a manner to account for this effect, which was otherwise undesirable due to associated additional costs and/or weight.

SUMMARY

In one aspect, there is provided an aircraft engine having a variable pitch propeller, an actuator to control the pitch of blades of the variable pitch propeller, a source of adjustable, actuation hydraulic pressure, a feather valve openable to provide an actuation path of the actuation hydraulic pressure between the source and the actuator, and closeable to block the actuation path and connect the actuator to a drain below the actuation hydraulic pressure, and a bypass path parallel to the actuator path and restricted relative to the actuator path.

In another aspect, there is provided a variable pitch propeller control system for a propeller having an actuator to control the pitch of blades, the variable pitch propeller control system comprising a source of adjustable, actuation hydraulic pressure, a feather valve openable to provide an actuation path of the actuation hydraulic pressure between the source and the actuator, and closeable to connect the actuator to a drain below the actuation hydraulic pressure and close the actuator path, and a bypass path parallel to the actuator path, the bypass path having a restricted flow area relative to a flow area of the actuator path.

In a further aspect, there is provided a method of operating a variable pitch propeller, the method comprising: conveying an actuation hydraulic pressure of hydraulic fluid from a source to an actuator controlling the pitch of blades of the propeller; operating a feather valve to connect the actuator to a drain, thereby releasing the hydraulic pressure in the actuator, and causing a reverse flow of hydraulic fluid from the actuator towards the drain, while simultaneously feeding a limited flow rate of hydraulic fluid, below the actuation hydraulic pressure, from the source to the drain, into the reverse flow and across the feather valve.

