Engines 3: Compressor Stalls Flashcards
Compressor Blade AOA
The angle between the relative wind and the rotor blade’s chord line
What elements make up the compressor’s relative wind?
The compressor rotation and inlet airflow
Compressor Stall
When an increase in compressor AOA results in a decrease in lift
What are some indications of a compressor stall?
Mild pulsations
Engine vibrations
Loud bangs
A drop in engine RPMs
Rise in turbine temperatures
What are the two main causes of compressor stalls?
Airflow distortion
Mechanical failures
What are the four mechanical malfunctions that can cause a compressor stall?
Variable inlet guide vane and stator vane
Fuel control unit (FCU)
Foreign object damage (FOD)
Variable exhaust nozzle
How can a failure of the variable inlet guide vanes cause a compressor stall?
If the AOA is not automatically changed, then not enough (or too much) airflow will enter the compressor at low engine speeds
How can a failure of the fuel control unit cause a compressor stall?
It would lead to improper fuel mixture in the combustion chamber creating an over-rich or too-lean mixture
Over-rich: causes a backflow of air into the compressor
Too lean: engine can flame out
How can foreign object damage cause a compressor stall?
Any deformation to the compressor blades will change its aerodynamic properties
How can failure of the variable exhaust nozzle cause a compressor stall?
If the nozzle does not open when afterburner is in use, then the excessive back pressure would lead to a compressor stall
What systems can manufacturers install to prevent compressor stalls?
Variable inlet guide and stator vanes
Dual/Twin/Split-spool compressors
Bleed valves
Variable exhaust nozzles
How can pilots avoid compressor stalls
Avoid abrupt PCL changes
Maintain the minimum prescribed airspeed
Avoid flying in severe weather and turbulence
How should a pilot recover from a compressor stall?
Reduce aircraft AOA to reduce inlet AOA
Reduce PCL to just below stall threshold
What might be necessary if you cannot recover from a compressor stall?
Shutting down the engine
