A&P - Powerplant Oral (Jeppesen)
What are the engine variables detected by the fuel control unit?
Power lever position, engine r.p.m., compressor inlet temperature, compressor inlet pressure, compressor discharge pressure,
burner pressure.
What are the two major components of a supervisory electronics engine control?
The electronic control unit (computer), and the hydromechanical fuel control.
What are some of the advantages of a full-authority digital engine control (FADEC) over a hydromechanical fuel control?
Better fuel economy, improved starts, requires no engine trimming, provides engine limit protection, provides constant idle speeds
regardless of atmospheric conditions or bleed air requirements, fully modulates the active clearance control, and allows more
repeatable engine transients.
What do turbine engine fuel spray nozzles do?
They inject fuel into the combustion area.
What are the different engine indications used for trimming a turbine engine?
Either EPR or r.p.m. is used depending on the particular engine
What maintenance adjustments are normally allowed on an installed hydromechanical fuel control?
Specific gravity for fuel, idle r.p.m., and a maximum r.p.m. (or maximum EPR).
What type of pump can vary the amount of fuel discharged regardless of speed?
A variable displacement pump.
What is used to keep water, sediment, and foreign matter out of the carburetor?
The main fuel strainer.
What is the purpose of a pressure relief valve in a constant displacement pump?
It returns excess fuel that is not required by the engine to the inlet side of the pump.
What type of engine-driven fuel pump is widely used other than gear or piston pumps?
A rotary vane type.
What function do fuel boost pumps perform?
They supply pressurized fuel to the fuel pump, which helps prevent vapor lock and cavitation.
What is a commonly used type of fuel boost pump?
The centrifugal type.
What causes vapor lock and why is it of concern?
Vapor lock is caused by insufficient fuel pressure, high fuel temperatures and excessive fuel turbulence, which may completely
block any fuel flow resulting in engine failure.
What function does the engine-driven pump on a turbine engine perform?
It provides a continuous supply of fuel at the proper pressure while the engine is running.
Name the two categories of turbine engine pumps.
Constant and variable displacement.
What category is a gear-type pump classified in?
Constant displacement.
When performing an external inspection of an engine-driven fuel pump, what should you look for?
Leaks and security of mounting.
What is the purpose of a shear section of the driveshaft in a dual element constant displacement pump?
If one element seizes, a portion of the driveshaft seizes, allowing the other element to continue to operate.
,Where in a turbine engine fuel system is ice formation likely to occur and how is it prevented?
The fuel filter is most susceptible to ice formation, so a fuel heater is used that consists of a heat exchanger using either engine oil
or bleed air to warm the fuel.
What is the purpose of a bypass valve in an engine fuel system micron filter?
It is a safety feature that allows fuel to flow to the engine if the filter becomes blocked.
What is the purpose of a duplex fuel nozzle?
A duplex fuel nozzle discharges two different spray patterns. The spray pattern is wider during start up and acceleration and
narrows when engine speed increases above idle.
What are the functions of the pressurizing and dump portions of a pressurizing and dump valve?
The pressurizing portion provides primary and secondary fuel flow to dual-line duplex fuel nozzles, and the dump portion allows fuel
to drain from the manifolds after engine shutdown.
What purpose do fuel selector valves serve?
They allow tank and engine selection, and provide a means for shutting off fuel flow.
How can the remaining service life of starter-generator brushes be determined?
By visually inspecting the amount of wear groove remaining on the brushes.
What components of the starter-generator require periodic inspection?
Both commutators and brushes should be inspected for wear beyond operational limits.
Between field and armature windings in starter-generators, which ordinarily receive current for operation in the start mode?
Generally, both field and armature receive current for operation in the start mode.
What are possible sources of low pressure compressed air used for starting jet transport aircraft equipped with air turbine starters?
A ground power unit, (GPU), an on-board auxiliary power unit (APU), compressed bleed air form an already running engine.
When should ignition ideally occur?
A specific number of degrees (as determined by the manufacturer) before the piston reaches top dead center on the compression
stroke.
Why are dual magnetos used in the engine ignition system?
To improve combustion efficiency, and provide redundancy for safety.
Why is magneto timing so important?
For an engine to run properly, the spark plug in a cylinder has to fire at a specific time. To produce the required energy for the spark
at the required time, the magneto must be in the E-gap position, the breaker points must start to open, and the distributor must be
electrically aligned with the particular cylinder. If any of these requirements are not correctly adjusted, the engine will run rough or
may not run at all. When preparing a magneto for installation, first the internal timing must be correctly adjusted, then the magneto-
to-engine timing is adjusted.
What function does a magneto perform?
It produces a high voltage that forces a spark to arc across a spark plug gap.
Name the components of a high tension magneto system.
A permanent multipole rotating magnet, soft iron core, and pole shoes.
Name the three main circuits of a high tension magneto system.
Magnetic, primary and secondary.
What is an E-gap angle?
It is a point a few degrees beyond the neutral position of a rotating magnet where maximum magnetic field stress exists.
What reduces arcing in the points and also aids the collapsing of the magnetic field in a magneto?
A capacitor.
, How does a magneto produce the high voltage required to fire a spark plug?
In the rotation cycle, when the magnetic rotor is in the E-gap position, the primary points open, which interrupts the current flow in
the primary circuit causing a high rate of flux change in the core, and inducing a pulse of high voltage in the secondary coil.
What is the P-lead and how does it function?
The P-lead connects the ignition switch to the primary circuit of the magneto. When the ignition switch is turned off, the P-leads on
both magnetos are grounded. When the ignition switch is turned to the "LEFT" position, the right magneto is grounded, so that only
the left magneto operates, and vice versa.
What is a magneto timing light used for, and what does it indicate?
It is used for both internal magneto timing and magneto-to-engine timing, and indicates the exact instant the magneto points open.
Why are turbine engine igniters generally not susceptible to carbon fouling?
Because the high energy sparks they produce clean off any deposits on the firing end.
What is the function of a duty cycle in relation to a turbine engine ignition system?
A duty cycle allows the operation of the ignition system for a given amount of time, and is then followed by a minimum specified
cooling down period.
What are the three main components of a turbine engine ignition system?
Ignition exciters, high tension leads, igniters.
When the engine is operating, what does an ammeter/loadmeter indicate when connected to:
1.Battery positive lead?
2.Generator output lead?
When connected to the battery positive lead, the ammeter indicates whether the battery is charging or discharging. When connected
to the generator output lead, it indicates the current produced by the generator or electrical system load.
What is the purpose of dynamic dampers on crankshafts?
They reduce engine vibration.
What types of bearings are generally found in reciprocating engines?
Plain, ball and roller bearings.
Are the connecting rods used in each cylinder of a radial engine the same? Explain.
No. Radial engines use master and articulating rod assemblies.
Name the different types of piston rings.
Oil control, compression, and oil scraper.
Where should piston ring gaps be installed relative to each other, and why?
Compression ring gaps should be staggered so that they do not align. This prevents excessive blow-by.
What could result from incorrectly installed piston rings?
Excessive oil consumption.
What purpose do oil control rings serve?
They regulate the thickness of the oil film on the cylinder walls.
What is used to help prevent valve surge or floating in an aircraft engine?
Two or more springs are used on each valve.
On engines equipped with hydraulic valve lifters, what should the running valve clearance be?
Zero.
What is the purpose of valve overlap?
What are the engine variables detected by the fuel control unit?
Power lever position, engine r.p.m., compressor inlet temperature, compressor inlet pressure, compressor discharge pressure,
burner pressure.
What are the two major components of a supervisory electronics engine control?
The electronic control unit (computer), and the hydromechanical fuel control.
What are some of the advantages of a full-authority digital engine control (FADEC) over a hydromechanical fuel control?
Better fuel economy, improved starts, requires no engine trimming, provides engine limit protection, provides constant idle speeds
regardless of atmospheric conditions or bleed air requirements, fully modulates the active clearance control, and allows more
repeatable engine transients.
What do turbine engine fuel spray nozzles do?
They inject fuel into the combustion area.
What are the different engine indications used for trimming a turbine engine?
Either EPR or r.p.m. is used depending on the particular engine
What maintenance adjustments are normally allowed on an installed hydromechanical fuel control?
Specific gravity for fuel, idle r.p.m., and a maximum r.p.m. (or maximum EPR).
What type of pump can vary the amount of fuel discharged regardless of speed?
A variable displacement pump.
What is used to keep water, sediment, and foreign matter out of the carburetor?
The main fuel strainer.
What is the purpose of a pressure relief valve in a constant displacement pump?
It returns excess fuel that is not required by the engine to the inlet side of the pump.
What type of engine-driven fuel pump is widely used other than gear or piston pumps?
A rotary vane type.
What function do fuel boost pumps perform?
They supply pressurized fuel to the fuel pump, which helps prevent vapor lock and cavitation.
What is a commonly used type of fuel boost pump?
The centrifugal type.
What causes vapor lock and why is it of concern?
Vapor lock is caused by insufficient fuel pressure, high fuel temperatures and excessive fuel turbulence, which may completely
block any fuel flow resulting in engine failure.
What function does the engine-driven pump on a turbine engine perform?
It provides a continuous supply of fuel at the proper pressure while the engine is running.
Name the two categories of turbine engine pumps.
Constant and variable displacement.
What category is a gear-type pump classified in?
Constant displacement.
When performing an external inspection of an engine-driven fuel pump, what should you look for?
Leaks and security of mounting.
What is the purpose of a shear section of the driveshaft in a dual element constant displacement pump?
If one element seizes, a portion of the driveshaft seizes, allowing the other element to continue to operate.
,Where in a turbine engine fuel system is ice formation likely to occur and how is it prevented?
The fuel filter is most susceptible to ice formation, so a fuel heater is used that consists of a heat exchanger using either engine oil
or bleed air to warm the fuel.
What is the purpose of a bypass valve in an engine fuel system micron filter?
It is a safety feature that allows fuel to flow to the engine if the filter becomes blocked.
What is the purpose of a duplex fuel nozzle?
A duplex fuel nozzle discharges two different spray patterns. The spray pattern is wider during start up and acceleration and
narrows when engine speed increases above idle.
What are the functions of the pressurizing and dump portions of a pressurizing and dump valve?
The pressurizing portion provides primary and secondary fuel flow to dual-line duplex fuel nozzles, and the dump portion allows fuel
to drain from the manifolds after engine shutdown.
What purpose do fuel selector valves serve?
They allow tank and engine selection, and provide a means for shutting off fuel flow.
How can the remaining service life of starter-generator brushes be determined?
By visually inspecting the amount of wear groove remaining on the brushes.
What components of the starter-generator require periodic inspection?
Both commutators and brushes should be inspected for wear beyond operational limits.
Between field and armature windings in starter-generators, which ordinarily receive current for operation in the start mode?
Generally, both field and armature receive current for operation in the start mode.
What are possible sources of low pressure compressed air used for starting jet transport aircraft equipped with air turbine starters?
A ground power unit, (GPU), an on-board auxiliary power unit (APU), compressed bleed air form an already running engine.
When should ignition ideally occur?
A specific number of degrees (as determined by the manufacturer) before the piston reaches top dead center on the compression
stroke.
Why are dual magnetos used in the engine ignition system?
To improve combustion efficiency, and provide redundancy for safety.
Why is magneto timing so important?
For an engine to run properly, the spark plug in a cylinder has to fire at a specific time. To produce the required energy for the spark
at the required time, the magneto must be in the E-gap position, the breaker points must start to open, and the distributor must be
electrically aligned with the particular cylinder. If any of these requirements are not correctly adjusted, the engine will run rough or
may not run at all. When preparing a magneto for installation, first the internal timing must be correctly adjusted, then the magneto-
to-engine timing is adjusted.
What function does a magneto perform?
It produces a high voltage that forces a spark to arc across a spark plug gap.
Name the components of a high tension magneto system.
A permanent multipole rotating magnet, soft iron core, and pole shoes.
Name the three main circuits of a high tension magneto system.
Magnetic, primary and secondary.
What is an E-gap angle?
It is a point a few degrees beyond the neutral position of a rotating magnet where maximum magnetic field stress exists.
What reduces arcing in the points and also aids the collapsing of the magnetic field in a magneto?
A capacitor.
, How does a magneto produce the high voltage required to fire a spark plug?
In the rotation cycle, when the magnetic rotor is in the E-gap position, the primary points open, which interrupts the current flow in
the primary circuit causing a high rate of flux change in the core, and inducing a pulse of high voltage in the secondary coil.
What is the P-lead and how does it function?
The P-lead connects the ignition switch to the primary circuit of the magneto. When the ignition switch is turned off, the P-leads on
both magnetos are grounded. When the ignition switch is turned to the "LEFT" position, the right magneto is grounded, so that only
the left magneto operates, and vice versa.
What is a magneto timing light used for, and what does it indicate?
It is used for both internal magneto timing and magneto-to-engine timing, and indicates the exact instant the magneto points open.
Why are turbine engine igniters generally not susceptible to carbon fouling?
Because the high energy sparks they produce clean off any deposits on the firing end.
What is the function of a duty cycle in relation to a turbine engine ignition system?
A duty cycle allows the operation of the ignition system for a given amount of time, and is then followed by a minimum specified
cooling down period.
What are the three main components of a turbine engine ignition system?
Ignition exciters, high tension leads, igniters.
When the engine is operating, what does an ammeter/loadmeter indicate when connected to:
1.Battery positive lead?
2.Generator output lead?
When connected to the battery positive lead, the ammeter indicates whether the battery is charging or discharging. When connected
to the generator output lead, it indicates the current produced by the generator or electrical system load.
What is the purpose of dynamic dampers on crankshafts?
They reduce engine vibration.
What types of bearings are generally found in reciprocating engines?
Plain, ball and roller bearings.
Are the connecting rods used in each cylinder of a radial engine the same? Explain.
No. Radial engines use master and articulating rod assemblies.
Name the different types of piston rings.
Oil control, compression, and oil scraper.
Where should piston ring gaps be installed relative to each other, and why?
Compression ring gaps should be staggered so that they do not align. This prevents excessive blow-by.
What could result from incorrectly installed piston rings?
Excessive oil consumption.
What purpose do oil control rings serve?
They regulate the thickness of the oil film on the cylinder walls.
What is used to help prevent valve surge or floating in an aircraft engine?
Two or more springs are used on each valve.
On engines equipped with hydraulic valve lifters, what should the running valve clearance be?
Zero.
What is the purpose of valve overlap?
