5-3 Compressor Stalls

  1. DESCRIBE the angle of attack of compressor blades
    • The relative wind is formed by combining the compressor rotation (RPM) and the inlet airflow.
    • The angle between the relative wind and the rotor blade's chordline make up the AOA.
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  2. DESCRIBE a compressor stall
    • Too high of an AOA yields a possible stall.
    • Changing the rotation speed of the rotors (RPM) during engine operation and/or the velocity of the inlet airflow will cause the compressor AOA to change.
    • Can be caused by airflow distortions or mechanical malfunctions.
    • Results in a decrease of thrust
  3. DESCRIBE four mechanical malfunctions that can lead to a compressor stall
    • Variable inlet guide vanes (IVG) and stator vanes
    • Failure to change the AOA will cause too much or too little airflow at low engine speed.

    • Fuel Control Unit (FCU)
    • If the FCU fails, too much or too little fuel is added.
    • Too much fuel causes excessive burner pressure and a back-flow of air into the compressor.
    • Too little fuel may cause the engine to flame out.

    • Foreign object damage (FOD)
    • An object damages the compressor.

    • Variable Exhaust Nozzles
    • Used for afterburner operations for supersonic airflow.
    • If it fails to open, it will create excessive back pressure to lead to a stall.
  4. DESCRIBE appropriate actions a pilot can take regarding compressor stalls
    • Avoidance
    • Avoid erratic or abrupt Power Control Lever (PCL) movements, especially at high AOA and low airspeeds.
    • Maintain at least the prescribed minimum airspeed.
    • Avoid abrupt changes in attitude.
    • Avoid severe weather and turbulence.

    • Remedy and Recovery
    • Reduce attitude to reduce inlet's AOA.
    • PCL retarded to just below stall threshold to allow engine to "catch up" with inlet airflow.
    • Many aircraft will have automatic bleed valves or a procedure to open a valve to allow airflow through the compressor.
    • Once engine indications return to normal, slowly advance the PLC
  5. DESCRIBE four engine design features that can be incorporated into a gas turbine engine design to minimize the potential for a compressor stall
    • Variable inlet guide vane and stator vane
    • Installed so the AOA is changed at low engine speed.
    • Automatically positioned by the stator vane actuator (SVA) using fuel pressure via the FCU.

    • Dual/twin/split-spool compressor
    • This design allows the front rotor to turn at a slower RPM than the rear rotor.

    • Bleed Valves
    • "Bleed" air (vent to the atmosphere) and increase airflow in the front of the compressor at low engine RPMs.

    • Variable Exhaust Nozzle
    • Used to unload the pressure during afterburner operation.
Card Set
5-3 Compressor Stalls
Enabling Objectives