ATA 75 - ENGINE AIR

• LPTACC, HPTACC, RACC are controlled by ECU moved by HMU using fuel servo

• The RACC system modulates the 5 th stage high pressure (HP) compressor bleed air into the compressor rotor bore to vary and control the clearances.

• The CFM56 engine high pressure turbine (HPT) clearance control system uses high pressure compressor (HPC) bleed air from stages 5 and 9 to obtain maxim um-steady-state HPT performance and to minimize exhaust gas temperature (EGT) transient overshoot during throttle bursts.

• The 2 T-case sensors measure the temperatures in the HP Case and send this signal to the ECU. ECU then decides which air supply (5th or 9th stage) must be used (cooling or heating).

• The low pressure turbine casing is cooled by fan discharge air sprayed through an array of piping and small air jets that impinge on the outside surface of the casing.

• The bleed valves open during low and transient operations to increase the booster mass flow and to improve booster and HPC matching.

• VBV,1 master bleed with gear rotor valve and 11 bleed valve with ball screw actuator. VBV are 12 in total.

• The variable stator vane (VSV) actuation system consists of 2 VSV hydraulic actuators with dual independent transducers (LVDT) for position feedback, and 2 actuation mechanisms and linkages.

• The VSV system positions the compressor variable stator vanes (IGV through stage 3) to the angles necessary to provide optimum compressor efficiency at steady state and provide adequate stall margin for transient engine operation.

• A nacelle temperature probe measures core compartment temperature. It will indicate over temperature resulting from loose or broken air ducts or from loose flanges, worn VSV bushings.

• When the value reaches 240°C the indication flashes (green advisory).

• The gap between the blade and tips and the casing is actively controlled in order to optimize engine performance:

cool air to shrink the LP and HP turbine casings, hot air into the HP compressor cavity in order to expand it.

• RACSB uses 5th stage HP compressor air to heat the rotor cavity during cruise, during starts and transients, it unloads the HP compressor by discharging 9th stage air.

• The High Pressure Turbine Active Clearance Control system uses stage 4 HP and stage 9 HP air to heat or cool the High Pressure Turbine shroud support structure.(5B)

• The CFM56-SB DAC ll PIP introduces a nacelle cooling system. This system utilizes 5th stage HPC air routed to a TRF dual counterflow manifold system which directs the cool engine air towards the TRF outer skin and the nacelle components.

• Anti-ice inlet cowl (5th HPC stage)(5B)

• HPTACC (5B): One butterfly valve controls the air flow from the 4th stage compressor bleed while the other butterfly valve controls the air flow from the 9 th stage. (fail safe closed) (2 feedback from LVDT and 2 T case thermocouple)

• The purpose of the Low Pressure Turbine Active Clearance Control system is: To prevent LP Turbine Case over temperature and to optimize the LP Turbine clearance above 10000 ft.

• The Rotor Active Clearance Control (RACC) and Start Bleed system (SB) improves compressor efficiency during cruise by heating the High Pressure Rotor cavity with compressor 5th stage air.

• At steady speeds, above idle and low altitude, the RACSB valves are in the no air position. (5B)

• At high altitude the RACSB valve bleeds 5th stage air to heat the HP compressor bore, which reduces compressor clearances and improves compressor efficiency. (fail safe closed)

• Engine air flows:

- Primary flow: inside engine’s core

- Secondary flow: Bypass and around engine casing

• Fan Booster Engine Front Cone is made of composite materials, Rear Cone includes 36 balance screws, one for each fan blades.

• FAN DISK: Ident marks are provided on each side of blade recesses, on positions 1 and 5.

• Engine air sum-up:

- LPTACC (Low Pressure Turbine Active Clearance Control): Prevents LPT overheating and optimize LPT clearances, LPTACC control valve opens as engine speeds up.

- HPTACC (High Pressure Turbine Active Clearance Control): Uses 4 th and 9th HPC stages bleed air to optimize HPT clearances and minimize EGT peaks.

- RACSB (Rotor Active Clearance and Start Bleed): During engine starting it uses 9 th HPC stage bleed to unload HPT in order to ease engine acceleration process, and, during cruise, it uses 5th HPC stage bleed to improve stall margins and fuel efficiency (CFM56-5A doesn’t have RACSB)-

- NAC/TB (Nacelle Cooling and Transient Bleed) Offloads the HPC during engine acceleration and deceleration, also cools TRF (Turbine Rear Frame).

- VBV, VSV, RACSB, HPTACC are moved by servos. These servos are controlled by: ECU → HMU → SERVOS