Blade pitch control system

Abstract

A method of operating a blade pitch change system of a gas turbine engine and its arrangement, the system comprising a blade, an actuator, a pressurised fluid system and a control system that regulates pressurised fluid to the actuator to control its position and thereby the blade's pitch; the blade pitch change system operates in a forward thrust mode and a reverse thrust mode, the control system comprises a main pitch control valve and a first reverse blade control valve through which the pressurised fluid passes. The method comprises the steps of a) continuously varying the main control valve to change the blade's pitch within the forward thrust mode at a first rotational rate, b) switching the first reverse blade control valve on to change the blades' pitch between the forward thrust mode and the reverse thrust mode at a second rotational rate that is greater than the first rotational rate.

1 . A blade pitch change system comprising a blade, an actuator, a pressurised fluid system and a control system that regulates pressurised fluid to the actuator to control its position and thereby the blade's pitch; the blade pitch change system operates in a forward thrust mode and a reverse thrust mode,
 the control system comprises a main pitch control valve and a first reverse blade control valve through which the pressurised fluid passes,   the main control valve is continuously variable to change the blade's pitch within the forward thrust mode at a first rotational rate,   the first reverse blade control valve is on/off switchable to change the blades' pitch between the forward thrust mode and the reverse thrust mode at a second rotational rate that is greater than the first rotational rate.   
   
   
       2 . A blade pitch change system as claimed in  claim 1  wherein the main pitch control valve and the first reverse blade control valve are configured in parallel with each other. 
   
   
       3 . A blade pitch change system as claimed in  claim 1  wherein a second reverse blade control valve is configured in series with the first reverse blade control valve. 
   
   
       4 . A blade pitch change system as claimed in  claim 1  wherein an EEC is provided to control the valves. 
   
   
       5 . A blade pitch change system as claimed in  claim 1  wherein the actuator comprises a cylinder and piston, the piston connects to a linkage that rotates the blade, the main pitch control valve and the first reverse blade control valve are both connected to both sides of the piston to control its position and therefore the pitch of the blade. 
   
   
       6 . A blade pitch change system as claimed in  claim 1  wherein the main pitch control valve is operable for blade rotation rates of up to 5 deg/sec. 
   
   
       7 . A blade pitch change system as claimed in  claim 1  wherein the main pitch control valve is operable for blade rotation rates between 2 and 3 deg/sec. 
   
   
       8 . A blade pitch change system as claimed in  claim 1  wherein the reverse blade control valve(s) is operable for blade rotation rates greater that 20 deg/sec. 
   
   
       9 . A method of operating a blade pitch change system comprising a blade, an actuator, a pressurised fluid system and a control system that regulates pressurised fluid to the actuator to control its position and thereby the blade's pitch; the blade pitch change system operates in a forward thrust mode and a reverse thrust mode, the control system comprises a main pitch control valve and a first reverse blade control valve through which the pressurised fluid passes, the method comprises the steps of
 a) continuously varying the main control valve to change the blade's pitch within the forward thrust mode at a first rotational rate,   b) switching the first reverse blade control valve on to change the blades' pitch between the forward thrust mode and the reverse thrust mode at a second rotational rate that is greater than the first rotational rate.   
   
   
       10 . A method of operating a blade pitch change system as claimed in  claim 9  wherein the main pitch control valve and the first reverse blade control valve are configured in parallel with each other. 
   
   
       11 . A method of operating a blade pitch change system as claimed in  claim 9  wherein a second reverse blade control valve is configured in series with the first reverse blade control valve, the method comprising the step of switching the second reverse blade control valve on simultaneously with switching the first reverse blade control valve on. 
   
   
       12 . A method of operating a blade pitch change system as claimed in  claim 9  wherein the main pitch control valve is operated to rotate the blade at rates of up to 5 deg/sec. 
   
   
       13 . A method of operating a blade pitch change system as claimed in  claim 9  wherein the main pitch control valve is operated to rotate the blade at rates between 2 and 3 deg/sec. 
   
   
       14 . A method of operating a blade pitch change system as claimed in  claim 1  wherein the reverse blade control valve(s) is operable for blade rotation rates greater that 20 deg/sec.