15.11 Flashcards
Two sections of aircraft fuel system?
Airframe (primary) stores the fuel
Engine (secondary)
What is the purpose of the secondary fuel system?
Supply fuel to combustion chamber
Also controls quantity of fuel necessary for all operating conditions
Two subsystems of fuel systems?
Fuel distribution subsystem
Fuel control subsystem
The low pressure pump ensure the high pressure pump doesn’t do what?
Draw fuel from fuel tanks by suction and also prevents cavitation
The high pressure pump produces what pressure?
900 Psi
Overpressure relief valve operates at what pressure?
1250 psi
Bypassed fuel can be used to do what?
Cool the Integrated drive generator oil cooler
In low engine power conditions the hot bypass return fuel does what?
Heats up the fuel from the low pressure pump too much
Results in engine oil not cooling sufficiently
The fuel control unit of an engine is usually mounted to what?
Engine fuel pump on accessory gearbox
Two types of fuel control systems? Which is old and which is new?
Speed governed fuel control units-Old
Constant thrust fuel control units-Modern
The pipes and push pull cables in fuel control units are needed to transmit what signals?
Throttle demand signal
Temperature signal
Pressure signal
Speed feedback signal
The N2 speed feedback signal is usually transmitted how?
Via a mechanical drive shaft from main fuel pump
The N1 speed feedback signal is what type of signal and where does it come from?
Fuel pressure signal
Comes from hydro mechanical N1 sensor
How do hydromechanical temperature sensors work?
Convert air temperature to fuel pressure signals
Two major sections of fuel control unit? What are they further split into?
Fuel metering section
Computing section
Further split into:
Governing section
Limiting section
What are the sections that represent main tasks of fuel control units?
Fuel metering
Power control
Engine protection
What is FADEC?
Fuel authority digital engine control
What is the heart of a FADEC system?
The digital computer
What is the second main component of FADEC?
Fuel metering system (FMU)
The terms FMU and HMU do not have the letter C, what does this indicate?
They cannot control
Only receives orders from ECU and move them to the Fuel metering valve
Where is the electronic control unit located?
On fan stator case of engine
What is the power supply for FADEC?
Can come from aircraft or magnet alternator in gear box
The ECU needs a feedback signal about what?
The opening condition of fuel metering valve
In general terms what is the FADEC system?
It’s a centralised computer with all the necessary sensors, which control the engine and all it’s important sub systems
