G650 - APU
After reaching at least 99% rpm for two seconds, the APU can support operation of the generator and after _____ bleed air is available.
The APU starter is electrically driven by the power source selected by the ECU. The starter is physically mounted on the accessory gearbox and spins up the APU through the gear interface. As the APU drive shaft rotates, the blades in the compressor section draw in ambient air through the open-air inlet and furnish pressurized air flow to the combustion chamber. Fuel and ignition are introduced in the chamber and the APU accelerates through the forces generated in the turbine section. The starter is disengaged when the APU reaches _____ rpm if the aircraft is on the ground or _____ if the aircraft is airborne.
Load control valve is prevented from opening in flight as a function of Weight-On-Wheels (WOW).
When does the 'READY' light illuminate?
The APU ECU performs a prestart Built-In Test (BIT), opens the air inlet door and opens the fuel shutoff valve at the left tank rear wing spar. Within 10 - 16 seconds when the BIT test is complete and the air inlet door and fuel shutoff valve configurations are correct, the ECU illuminates the READY light below the START switch.
During flight, the APU can be used as a backup electrical power supply if a malfunction renders one or both aircraft engine generators inoperative. If necessary, APU air may also be used to assist in air-starting an engine if the aircraft altitude is _____ and below.
The APU operating envelope extends up to 45,000 ft if the APU is started at a lower altitude. The APU is guaranteed to start at or below 30,000 feet.
After the APU has been started, operation of the APU is controlled by the Electronic Control Unit (ECU). The ECU functions autonomously to maintain APU temperature and rpm within limits during all load conditions.
The ECU also controls the operation of the air inlet and maintains oversight of the power quality of the AC generator by monitoring the Generator Control Unit (GCU). The ECU provides protective shutdowns of the APU if operational parameters are exceeded to prevent damage to the unit.
Fuel is supplied to the APU from the left wing tank using the left main fuel pump (the right main tank and pump may be used if the crossflow valve is opened).
Pressurized fuel is routed through the APU fuel shutoff valve on the left wing rear beam structure that is controlled by the APU MASTER switch and the Electronic Control Unit (ECU). A fuel line transits aft from the shutoff valve to supply the APU fuel control.
If the Outside Air Temperature (OAT) is _____ or below, the APU will start, but requires a longer interval to reach normal speed.
If the ECU senses oil temperature below -23.3 deg.C (-10 deg.F), the starter motor may remain engaged for up to 50 seconds.
Maximum Rotor Speed in all conditions is:
If the APU START switch is depressed during the cool down period, the APU will accelerate back to normal rpm.
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Two igniters in the combustion chamber supply an intermittent, high voltage spark to ignite fuel during the start sequence. Operation of the igniters is fully automatic and controlled by the ECU. During ground starting, ignition is terminated at 50% rpm. During an airstart, ignition is terminated at _____.
The ignition unit will also automatically energize through the auto-relight function of the ECU if the APU flames out during operation.
When the APU has reached an operating rpm of 56% for at least two seconds, the APU is capable of driving the generator.
When the APU has reached an operating rpm of 99% for at least two seconds, the APU is capable of driving the generator. If the APU was started under cold conditions, APU air loading will be delayed for 60 seconds, unless the bleed air is being used in attempting to start a main engine in flight.
Continuous operation of the APU starter, when powered by airplane batteries, is limited to a maximum of 3 consecutive start attempts. A 30-minute cool down period must be observed before the next full starter cycle is commenced.
A one-hour cool down period must be observed before the next full starter cycle is commenced. Successful consecutive starts are limited to 6 at ten 10 minute intervals per start.
What happens when the APU MASTER switch is selected to OFF?
If the APU MASTER switch is selected OFF with the APU running, the 60-second cool down is bypassed, and an immediate shutdown is commanded. The 60-second cool down bypass mode is not recommended by Gulfstream due to reduction in APU life.
In non-essential mode (i.e on ground), there are many conditions which would cause ECU to shutdown the APU (e.g., ECU failure, loss of speed, APU fire, overtemp, reverse flow, low oil pressure, etc.). If this were to occur, cool down mode is bypassed, APU’s fuel shutoff valve closes, and APU shuts down immediately. When in essential mode (WOW air), some protective shutdowns are disabled to allow continued operation.
When selecting APU BLEED AIR switch to ON during ground operations, what valve opens in addition to load control valve?
The APU is housed within a fireproof titanium container in the aft equipment bay. The air intake for the APU is on the top of the aircraft fuselage to the left of the dorsal fin forward of the vertical stabilizer. The APU exhaust is below the left engine pylon.
Spent exhaust gases from the APU turbine section are directed through a tailpipe exhaust assembly overboard, venting beneath the right engine nacelle. Because the APU exhaust is located beneath the right engine pylon, starting the APU on the ground is inhibited with the lower cowling open since the APU exhaust high temperature gases would seriously damage the cowling. An amber warning indicator on the APU control panel (located on the COP) illuminates whenever the lower cowling on the right engine is open for servicing or maintenance and indicates to the flight crew that the APU cannot be started until the cowling is closed.
A Surge Control Valve (SCV) is installed on the APU to promote uninterrupted smooth air flow through the compressor and turbine stages. The ECU opens the SCV when the APU is started above _____.
When the valve is open, some air is bled from the compressor section is ducted to discharge into the APU exhaust shroud through a separate port.
When should you check APU oil level?
Overfilling of oil tank may occur if APU oil level is not checked 15 - 30 minutes after APU shutdown. damage to APU may occur if oil system is overfilled.
Use of an external DC power source to start the APU is authorized under very restricted conditions.
Use of an external DC power source to start the APU is prohibited!
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EGT display is active when APU MASTER switch is selected ON, until _____ after APU MASTER switch is selected off.
A generator mounted on the APU gearbox provides a source of Alternating Current (AC) power for use on the ground or in flight if an engine-driven generator is not available. The APU generator produces three-phase 400 Hz 115 / 120 volt power and can deliver up to 40 kVA. The generator can provide a full 40 kVA output up to _____.
The APU generator can deliver 100% (40 kVA) electrical power on the ground or in flight from sea level to 45,000 ft.
The RE220 APU is a turbine engine composed of _____ with accessory mountings for a 40 KVA generator and a Load Control Valve that provides compressor pressurized air for the aircraft pneumatic system bleed air supply manifold.
The APU has a single-stage compressor section coupled on a common shaft to a two-stage turbine.
The ECU automatically initiates an immediate protective shutdown if a fire exists, bypassing the normal APU cool down period.
Automatic APU shutdown is inhibited during FIRE TEST checks.