Fuel and APU study notes
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Fuel and APU study notes
fuel system apu turbine overhaul broten
Study notes for fuel and APU section of turbine overhaul
What factor is not used in the operation of an aircraft gas turbine engine fuel control unit?
Mixture control position
In order to stabilize cams, springs, and linkages within the fuel control, manufacturers generally recommend that all final turbine engine trim adjustments be made in the
When trimming a turbine engine, the fuel control is adjusted to
set idle RPM and maximum speed or EPR.
A supervisory electronic engine control (EEC) is a system that receives engine operating information and
adjusts a standard hydromechanical fuel control unit to obtain the most effective engine operation.
A full-authority electronic engine control (EEC) is a system that receives all the necessary data for engine operation and
develops the commands to various actuators to control engine parameters.
In a supervisory EEC system, any fault in the EEC that adversely affects engine operation
causes an immediate reversion to control by the hydromechanical fuel control unit.
The active clearance control (ACC) portion of an EEC system aids turbine engine efficiency by
ensuring turbine blade to engine case clearances are kept to a minimum by controlling case temperatures.
What should be checked/changed to ensure the validity of a turbine engine performance check if an alternate fuel is to be used?
Fuel specific gravity setting.
The generally acceptable way to obtain accurate on-site temperature prior to performing engine trimming is to
hang a thermometer in the shade of the nose wheel-well until the temperature reading stabilizes.
An aircraft should be facing into the wind when trimming an engine. However, if the velocity of the wind blowing into the intake is excessive, it is likely to cause a
false high compression and turbine discharge pressure, and a subsequent low trim.
Generally, the practice when trimming an engine is to
turn all accessory bleed air off.
What method is ordinarily used to make idle speed adjustments on a float-type carburetor?
An adjustable throttle stop or linkage.
For what primary purpose is a turbine engine fuel control unit trimmed?
To obtain maximum thrust output when desired.
Which type of fuel control is used on most of today's turbine engines?
Hydromechanical or electronic.
In turbine engines that utilize a pressurization and dump valve, the dump portion of the valve
drains the engine manifold lines to prevent fuel boiling and subsequent deposits in the lines as a result of residual engine heat (at engine shutdown).
What effect does high atmospheric humidity have on the operation of a jet engine?
Has little or no effect.
What are the positions of the pressurization valve and the dump valve in a jet engine fuel system when the engine is shut down?
Pressurization valve closed, dump valve open.
Which of the following is NOT an input parameter for a turbine engine fuel control unit?
Which of the following statements concerning a centrifugal-type fuel boost pump located in a fuel supply tank is NOT true?
The centrifugal-type pump is classified as a positive displacement pump.
Where is the engine fuel shutoff valve usually located?
Aft of the firewall.
Boost pumps in a fuel system
provide a positive flow of fuel to the engine pump.
What is the purpose of the fuel transfer ejectors?
To assist in the transfer of fuel from the main tank to the boost pump sump.
The fuel pump relief valve directs excess fuel to the
inlet side of the fuel pump.
The primary condition(s) that allow(s) microorganisms to grow in the fuel in aircraft fuel tanks is (are)
the presence of water.
It is desirable that fuel lines have a gentle slope upward or downward and not have sharp curves or sharp rises and/or falls in order to
prevent vapor lock.
Where should the main fuel strainer be located in the aircraft fuel system?
At the lowest point in the fuel system.
Where physical separation of the fuel lines from electrical wiring or conduit is impracticable, locate the fuel line
below the wiring and clamp the line securely to the airframe structure.
What is a characteristic of a centrifugal-type fuel boost pump?
It separates air and vapor from the fuel.
A pilot reports that the fuel pressure fluctuates and exceeds the upper limits whenever the throttle is advanced. The most likely cause of the trouble is
a sticking fuel pump relief valve.
Fuel pump relief valves designed to compensate for atmospheric pressure variations are known as
balanced-type relief valves.
Fuel lines are kept away from sources of heat, and sharp bends and steep rises are avoided to reduce the possibility of
Fuel crossfeed systems are used in aircraft to
maintain aircraft stability.
Kerosene is used as turbine engine fuel because
kerosene has more heat energy per gallon and lubricates fuel system components.
What are the principal advantages of the duplex fuel nozzle used in many turbine engines?
Provides better atomization and uniform flow pattern.
It is necessary to control acceleration and deceleration rates in turbine engines in order to
prevent blowout or die-out.
Which of the following turbine fuel filters has the greatest filtering action?
What is the purpose of the flow divider in a turbine engine duplex fuel nozzle?
Creates the primary and secondary fuel supplies.
What causes the fuel divider valve to open in a turbine engine duplex fuel nozzle?
Frequently, an aircraft's auxiliary power unit (APU) generator
is identical to the engine-driven generators.
Fuel is normally supplied to an APU from
the airplane's main fuel supply.
An APU is usually rotated during start by
an electric starter.
The function of an APU air inlet plenum is to
stabilize the pressure of the air before it enters the compressor.
When in operation, the speed of an APU
remains at or near rated speed regardless of the load condition.
Generally, when maximum APU shaft output power is being used in conjunction with pneumatic power
pneumatic loading will be automatically modulated to maintain a safe EGT.
When necessary, APU engine cooling before shutdown may be accomplished by
closing the bleed air valve.
Usually, most of the load placed on an APU occurs when
the bleed air valve is opened.
Fuel scheduling during APU start and under varying pneumatic bleed and electrical loads is maintained
automatically by the APU fuel control system.
On APU's equipped with a free turbine and load compressor, the primary function of the load compressor is to
provide bleed air for aircraft pneumatic systems.