Turbine Engines Flashcards
What is meant by trimming a turbine engine?
Adjusting the fuel control so the engine develops the correct idle and trim speed RPM
What type of equipment should be used to determine that a turbine engine is performing up to the standards specified by the engine manufacturer?
A JetCal analyzer/trimmer has all of the instrumentation and cables to determine the EGT, EPR, and other parameters specified by the engine manufacturer
What is meant by a hot-section inspection?
An inspection of the hot section of a turbine. The hot section includes the combustors, the turbine, and the exhaust system
An inspection of the combustors, turbine, and exhaust system
What is meant by on-condition maintenance of a turbine engine?
The monitoring of the engine performance at regular intervals and determining when maintenance is required based on certain operating parameters specified by the engine manufacture
What checks of a turbine engine are necessary to verify preflight condition?
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- Inspect the cowling and all air inlet areas and attachment of the engine to the airframe
- Inspect the inlet guide vanes and the first stage of the compressor or fan blades
- Check for unusual noise when the compressor is rotated
- Inspect the rear turbine and exhaust system
- Check the quantity of the lubricating oil for the engine and the constant-speed drive unit
- Check the ignition system for operation by listening for the sparks
Explain the main difference and advantage of turbofan over turbojet engines
A turbofan engine uses a fan to bypass some air around the engine core and to provide thrust. The advantage is that this provides additional thrust without increasing fuel flow
Name the major components in a gas turbine engine
- Air inlet
- Compressor section
- Combustion section
- Turbine section
- Exhaust section
- Gearbox
- Accessory section
What determines the amount of airflow through a turbine engine?
- Forward speed of the aircraft
- Compressor speed
- Air density
Name the two types of compressors commonly used in turbine engines
- Axial
- Centrifugal
Name two different methods for attaching turbine engine rotor blades to the rotor disks
- Dovetail
- Bulb
- Fir tree
What is a split compressor system?
(Also called dual or twin spool compressors) These are connected to the turbine section with two rotor shafts, one inside of the other
What are the different types of combustion chambers used in turbine engines?
- Can
- Annular
- Can-annular
- Reverse flow annular
What prevents the combustion chambers from burning?
Cooling air along the inside of the liner
What is the purpose of the interconnecting tubes attached between can-type combustion chambers?
For flame propagation during start
What functions do axial flow turbine nozzles perform?
They direct the mass airflow to drive the turbine rotor at a specific angle
How is thermal stress relieved on a turbine disc?
By directing bleed air onto the face of the disk, or by grooves cut into the disk
What are carbon seals used for in turbine engines?
They are used as oil seals for the rotor shaft bearings
What is shaft horsepower?
It is an indication of the torque developed by a turboprop or turboshaft engine
What is the purpose of an APU
They provide ground electrical and pneumatic power for aircraft systems when the engines are not running. Many APUs may also be used as an emergency source of inflight electrical power
Name the main components of a typical APU
- A small power turbine for power and bleed air
- An electrical generator
When is the greatest demand placed on an APU
When supplying bleeding air
How is an APU generally started?
With its own electrical starter and battery power
Where does the APU get its fuel supply?
From one of the aircraft’s main fuel tanks
At what speed does a gas turbine APU operate and how is this speed maintained?
At or near its rated speed regardless of electrical or pneumatic loads imposed. The APU fuel control automatically adjusts the fuel flow to maintain the rated speed
What is used to prevent a heavily loaded APU from exceeding its maximum EGT?
A load control valve modulates the pneumatic load to keep EGTs within limits
How is an APU shut down and why is this procedure used?
After the APU is unloaded by closing the bleed air valve, it’s typically run for three minutes to allow the EGT to cool and stabilize.
If a heavily loaded APU is abruptly shut down without any cooling down period, damage could occur as a result of thermal shock
What powers are the variable inlet guide vanes used on some APUs to regulate compressor intake airflow?
Fuel Pressure
What is fan blade shingling?
When the midspan shrouds overlap the fan blade
When a turbofan or turbojet engine is shut down, what should a mechanic listen for during coastdown?
Any rubbing sound or other unusual noises from the engine
Why are compressor washes performed and what methods are commonly used?
Fluid and abrasive grit wash are commonly used to remove contaminants from the compressor section and improve engine performance
How can you tell if a turbofan or turbojet engine is out of trim?
There will be a high EGT at the target EPR for takeoff power
Name the different types of compressor blade damage that may be found during inspection
- Dents
- Cracks
- Galling
- Pitting
- Scratches
- Burrs
- Burns
- Gouges
What kind of markers can be used to mark the parts in hot and cold sections during repair?
- Layout dye
- Felt tip marker
- Chalk
How does relative humidity affect turbine engines?
It has a negligible effect
What criteria determines replacement of life limited turbine engine components?
Cycles, hours and/or calendar time
If turbine blades are removed from a turbine disc, why should they be reinstalled in the same location?
To maintain the balance of the turbine wheel
How are gas turbine engine tachometers calibrated?
In percent RPM
On a turbine engine, what is the engine pressure ratio and what does it indicate?
It is the ratio between the inlet pressure and turbine exhaust pressure and is used to indicate the thrust developed by the engine
On a turbine engine, what does exhaust gas temperature (EGT) indicate and how is it obtained?
EGT is the average temperature of the turbine discharge gasses and is obtained by thermocouples placed near the turbine exit
Can the EGT system on a turbine engine be checked without running the engine?
Yes, by checking the resistance of the thermocouples and circuits
