Patent GB-1472033-A (GB)
Title: Device for boosting and bleeding a gas turbine engine
IPC: F04D27/02
Filed: 1975-01-31
Abstract: 1472033 Gas turbine engines - compressor regulation SOC NATIONALE D'ETUDE ET DE CONSTRUCTION DE MOTEURS D'AVIATION 31 Jan 1975 [11 Feb 1974] 4274/75 Headings F1C F1G and F1J The invention relates to a gas turbine engine of the kind having a low-pressure rotor assembly 2, 3 and a high-pressure rotor assembly 5, 6, there being means for allowing air to pass into the flow duct between the LP and HP compressors 2, 5 for example during starting, and for allowing air to discharge from the flow duct between the compressors for example during acceleration to prevent surge. The engine shown is a by-pass type engine having a fan 11 driven by the LP rotor assembly, air from the fan discharging in part to the main flow duct 7 as indicated by arrow F1 and in part to the by-pass duct 9 as indicated by arrow F2. The casing 10 between the main flow duct 7 and the by-pass duct 9 between the LP and HP compressors 2 and 5 is shown in Fig. 2 and comprises a passage 20 between the two ducts which is normally closed by flap members. The flap members comprises a pair of main flap members 21a, 21b pivotally mounted at 22a, 22b and inter-connected by gear quadrants 24a, 24b for simultaneous movement. The flap members are controlled by an actuator 40 being shown in the closed position in Fig. 2 and in the open position in Fig. 5, the  latter position being selected for example at starting whereby air may flow directly into the HP compressor 5, the HP rotor assembly being that driven by the starter motor 12; this position is also adopted when the blades of the fan 11 are moved to the reverse thrust position when air-flow through the by-pass duct 9 is as indicated by arrow F<SP>1</SP> 2  so as to ensure continuing flow of air to the HP compressor 5. Each flap member 21a, 21b is formed with an opening 25a, 25b with which is associated an auxiliary flap member 26a, 26b pivotally mounted at 27a, 27b, the auxiliary flap members being normally urged to the closed position Fig. 2 by springs 30a, 30b, but movable to the open position as shown in Fig. 6 so as to provide an auxiliary passage through which air discharging from the LP compressor 2 may be bled off so as to prevent surge. The auxiliary flap members 26a, 26b are also inter-connected for simultaneous movement by means of links and gear quadrants 29a, 29b. The actuator 40 is normally supplied with fluid under pressure P4 so that the piston 42 is held to the left and the flap members 21a, 21b are held in the closed position; when the actuator is connected to a low-pressure Po the piston 42 moves to the right and the flap members 21a, 21b are moved by the linkage to the open position. The space 20 between the flap members is connected to the pressure in the by-pass passage 9 through an opening 31 so that the auxiliary flap members 26a, 26b open automatically when  pressure surge occurs in the flow duct 7. The  main flap members 21a, 21b also move automatically to the open position when the actuator is connected to low-pressure Po, by reason of the differential pressure acting on the member 21a.