Turbine engine fuel and metering systems

Question 1

What are the different types of jet fuel and which is the most common?

Answer 1

Jet A most common
Jet A1
Jet B

Question 2

Why does jet fuel cause more problems that avgas?

Answer 2

Jet fuel has a higher viscosity than avgas and holds contaminants better

Question 3

What is an FCU and what is its function?

Answer 3

Fuel Control Unit is to schedule the fuel flow to match the power required by the pilot

Question 4

What are basic types of fuel control units?

Answer 4

Hydromechanical
Hydromechanical/electronic
Full Authority Digital Engine (or Electronics) Control (FADEC)

Question 5

What are the two sections on a hydromechanical FCU?

Answer 5

Computing and metering

Question 6

What is the computing section of an FCU?

Answer 6

It determines the correct amount of fuel flow

Question 7

What is the metering section of a FCU?

Answer 7

Delivers the fuel to the engine fuel system through cams and servo valves

Question 8

How does a hydromechanical/electronic FCU work?

Answer 8

The system uses a remotely located EEC to adjust the fuel flow

Question 9

How does the FADEC FCU work?

Answer 9

A system of electronic sensors that feed engine parameter information into the EEC

Question 10

What type of adjustments are allowed on an FCU?

Answer 10

Only external commonly called trimming the engine

Question 11

What are the two trimming adjustments?

Answer 11

Idle RPM
Maximum RPM

Question 12

What FCU require trimming?

Answer 12

Hydromechanical or supervisory

Question 13

In which direction should the aircraft be facing while trimming the engines?

Answer 13

Into the wind for a specific target RPM or EPR

Question 14

How is target RPM or EPR determined?

Answer 14

Using charts based on temp and barometric pressure

Question 15

Where does the fuel pump receive fuel?

Answer 15

The fuel pump

Question 16

Which stage of the boost pump pressurized the fuel and sends it to the fuel/oil cooler?

Answer 16

The low pressure boost state.

Question 17

What happens in the high pressure main stage?

Answer 17

It increases the fuel pressure and sends it to the fuel metering unit

Question 18

What is the fuel filter located?

Answer 18

After every pump

Question 19

What is a Delta P?

Answer 19

Differential pressure switch that gives a warning to the crew if the fuel filter is blocked

Question 20

What are different types of fuel filters?

Answer 20

Wafer screens
Steel mesh
Cellulose fiber

Question 21

Why do turbine powered aircraft require fuel heaters?

Answer 21

They operate in cold ambient air that can cause ice crystals to form and clog the filter

Question 22

What are the two types of fuel heaters?

Answer 22

Air to fuel-air from the engines compressor
Oil to fuel-hot oil from the lubricating system

Question 23

What are the two distinct fuel system pump categories?

Answer 23

Constant displacement
Variable displacement

Question 24

What is a positive displacement pump?

Answer 24

The gear that supplies a fixed quantity of fuel to the engine for every revolution of the pump gears

Question 25

What is the function of fuel nozzles?

Answer 25

To inject fuel into the combustion area in a highly atomized, precisely patterned spray so that burning is completed evenly, in the shortest possible time

Question 26

What are the two types of fuel nozzles?

Answer 26

Simplex
Duplex

Question 27

What is the advantage of a duplex over a simplex fuel nozzle?

Answer 27

Provides better atomization at starting and idling speeds

Question 28

What is a flow divider?

Answer 28

Creates primary and secondary fuel supples