4 - Compressors Flashcards
What do the centrifugal fan blade forces depend on
Rotor speed
Blade mass
Distance of C.O.G from rotational axis
What can the moment weight be given in
- Gram inches
- Cm.g
- Ounce inches
Where can the moment weight be found
Blade root
When are balance screws used
When a fan blade replacement’s moment weight is too dissimilar
Where are fan balance weights placed
fan disc or spinner cone
What are compressors sensitive too
Changes in airflow
What is a stall throughout the whole compressor called
Compressor stall
What causes compressor stall
High A.O.A on rotors/stators
What results from compressor stall
Airflow slows, stops or reverses
Explain the process of compressor surge
Rapid decrease of airflow causes stall
Stall causes blockage in airflow which causes stronger stall in subsequent stages.
Causes low-pressure zones and airflow comes to a stop/reverses
What can trigger a compressor stall
- Engine speed is too low
- A/C accelerates or decelerates too much
What methods are used to prevent stall/surge
Compressor bleed valves
Dual or triple-spool rotors
Variable compressor stator vanes
When are bleed valves open
During low engine speeds so that excessive airflow can be vented
What does N1 and N2 refer to
N1 = Low pressure
N2 = High pressure
Where are variable stator vanes located
Forward stages of HP compressor
What is meant by compressor ratio
The amount the air is compressed by each stage
What are the primary and secondary functions of the compressor
Supply sufficient quantity of air for combustion (primary)
Supply air to systems needing bleed air
What are the main components of the compressor
Rotor
Stator
What forms a compressor stage
A set of stators and rotors
What are the two compressors used
Centrifugal
Axial flow
Do centrifugal compressors have a high or low compressor ratio
High (around 8:1)
What are centrifugal compressors limited to
Two stages
What is meant by the term axial and centrifugal
Axial - Air continues in its original direction
Centrifugal - Air is expelled outwards
