[FAA] FAA题库之Powerplant

001. The function of an APU air inlet plenum is to

        stabilizes the pressure of the air before it enters the compressor
The APU air inlet plenum is a compartment, or chamber, into which the air flows before it enters the APU compressor. The plenum stabilizes the air pressure.

002. Fuel is normally supplied to an APU from


        the airplane's main fuel supply
The fuel used by an APU is normally taken from the airplane's main fuel supply.

003. Usually, most of the load placed on an APU occurs when

        the bleed air valve is opened
The majority of the load on an APU is the pneumatic load, and opening the bleed air valve places this load on the APU.

004. 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
APUs can normally supply all of the required electrical and pneumatic power. When the maximum shaft output power is being used, the pneumatic load is modulated, or varied, to keep the EGT within the safe range.

005. When in operation, the speed of an APU


        Remains at or near rated speed regardless of the load condition
The fuel control system used on an APU automatically controls the fuel for starting and then brings the engine up smoothly to its rated RPM. It automatically maintains this RPM as the air or electrical load conditions change.

006. Frequently, an aircraft's auxiliary power unit (APU) generator

        is identical to the engine-driven generators
The power produced by an APU must be the same as that produced by the engine-driven generators, and APU generators are often identical to those driven by the engines.

007. When necessary, APU engine cooling before shutdown may be accomplished by


         Closing the bleed air valve
The APU control contains a time delay that closes the bleed air valve to remove the largest part of the APU load and allows the APU to cool down before it is shut down.

008. 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
APUs that have a free turbine and load compressor are actually turboshaft engines in which a free turbine drives a compressor that is totally independent of the APU gas-generator compressor. The bleed air from the load compressor supplies pneumatic power for starting the main engines and other airplane functions.

009. Fuel scheduling during APU start and under varying pneumatic bleed and
        electrical loads is maintained


        automatically by the APU fuel control system
The fuel control system used on an APU automatically controls the fuel for starting and then brings the engine up smoothly to its rated RPM. It automatically maintains this RPM as the air or electrical load conditions change.

010. An APU is usually rotated during start by

       An electric starter
The small gas turbine engine that provides electrical power and compressed air is started by a DC electric starter.