Patent GB-1133242-A (GB)
Title: Improvements in or relating to aircraft gas turbine jet propulsion engines having reheat devices and variable area propulsion nozzles
Inventor: AUBERT JACQUES
IPC: F02K1/17
Filed: 1966-03-09
Abstract: 1,133,242. Gas turbine jet engines - reheat control. SOCIETE NATIONALE d'ETUDE ET DE CONSTRUCTION DE MOTEURS D'AVIATION. March 9, 1966 [March 10, 1965], No. 10393/66. Heading F1J. [Also in Divisions G1 and G3] The invention relates to a method of regulating a gas turbine jet engine having exhaust reheat and a variable area propulsion nozzle, the nozzle area being controlled in dependence on at least one engine characteristic (for example turbine inlet temperature) and the reheat fuel being varied in the sense to increase the flow when the nozzle area is less than a preselected value, and in the sense to decrease the flow when the nozzle area is greater than the preselected value. In Fig. 1 the engine jet pipe is indicated at 1 and the variable area propulsion nozzle by flaps 2 which are pivotally mounted at 3. The flaps 2 are adjusted by means of an actuator 4 which is controlled by means for example responsive to the turbine inlet temperature. Movement of the flaps in an opening direction causes the linkage 10, 11, 12 to move so that the member 12 rotates about its pivot point 13 in an anti-clockwise direction, the end 12b of the member thus moving the rod 14 and the servopilot piston 5a to the right, so that servofluid passes to the right-hand side of control piston 6a which moves to the left moving the piston 8 to the left to the position shown in full lines so that the supply of reheat fuel through the reheat fuel control valve 9 is reduced. The temperature at the turbine inlet becomes reduced so that the nozzle flaps tend to move inwardly whereupon the reheat fuel control valve moves to open thus increasing the supply of reheat fuel. When reheat is set in operation, the propulsion nozzle is initially in a position suitable for non-reheat so that the reheat combustion tends to block the flow through the engine, the expansion ratio across the turbine decreases, the power transmitted to the compressor is reduced and the turbine speed is reduced. The main control unit tends to restore the turbine speed by increasing the fuel-flow, therefore the turbine inlet temperature increases and the propulsion nozzle which is dependent on turbine inlet temperature acts to increase the nozzle area by moving the flaps 2. In Fig. 2, the position of the nozzle flaps 2 is sensed by a pneumatic device which comprises a cam member 16 which moves with the rod 4c of the nozzle actuator 4, the cam controlling the outlet of nozzle 17 and thus the pressure p of air or gas acting on the servopiston 19a which controls the opening movement of the reheat fuel control valve 9. The valve 9 thus has a predetermined position for each position of the nozzle flap 2. In Fig. 3, the postion of the flaps 2 is sensed by a hydraulic device, the postion of the actuator 4 acting to control the position of a valve 24 with respect to a bleed orifice 25 thus controlling the pressure of the hydraulic fluid which acts at the right-hand side of the piston 20a which in turn controls the postion of the reheat fuel valve 8. In Fig. 4 an electrically controlled servo device is provided. When the propulsion nozzle flaps 2 reach their selected position the contacts 27 are closed and the electro-valve 29 opens thus allowing servofluid to pass into the chamber 32a at the right-hand side of the pilot valve 34; the pilot valve moves to the left against the action of spring 35 and now servofluid passes to the left-hand side of the servopiston 6a which moves to the right and causes the reheat fuel control valve 8 to move to reduce the supply of reheat fuel. The temperature sensitive device then acts to move the nozzle flap 2 towards the closed position, the contacts 27 open, the valve 29 closes and the pressure in the chamber 32a falls by leakage through orifice 33, and the spring 35 returns the pilot valve 34 to the right and the servofluid acts to return the servopiston 6a to the left thus reopening the reheat fuel control valve 8. In Figs. 5 and 5a (not shown), the position of the propulsion nozzle flaps is determined by a linear inductive device which comprises a rod 36 movable axially by the nozzle flaps and carrying a helically grooved shank 37 which varies the reluctances of four coils 38, 38a, 38b, 38c which form a Wheatstone bridge. Current leaving the bridge passes to the winding 42 of a motor 43 which is adapted to control the position of a reheat fuel control valve 46. A generator 44 mounted on the same shaft as the motor 43 and the control valve rotary member 46a acts to impose a time-delay on movement of the member 46a. The position of the pivot point 13 Fig. 1 of the lever 12 may be controllable so that the "specific" value of the nozzle area may be adjusted as desired, a suitable means for effecting this being described with reference to Fig. 6 (not shown).