Fuel Metering Systems

Question 1

What factor is not used in the operation of an aircraft turbine engine fuel control unit?

Answer 1

Mixture control position.

Question 2

In order to stabilize cams, springs, and linkages within the fuel control, manufacturers generally recommend that all final turbine trim adjustments be made in the what?

Answer 2

increase direction.

Question 3

When trimming a turbine engine, the fuel control is adjusted to what?

Answer 3

set idle RPM and maximum speed or EPR.

Question 4

An electronic engine control (EEC) is a system that receives engine operating information and what?

Answer 4

adjusts a standard hydromechanical fuel control unit to obtain the most effective engine operation.

Question 5

A full-authority electronic engine control (EEC) is a system that receives all the necessary data for engine operation and what?

Answer 5

develops the commands to various actuators to control engine parameters.

Question 6

In a supervisory EEC system, any fault in the EEC that adversely affects engine operation…

Answer 6

causes an immediate reversion to control by the hydromechanical fuel control unit.

Question 7

The active clearance control (ACC) portion of an EEC system aids turbine engine efficiency by what?

Answer 7

ensuring turbine blade to engine case clearances are kept to a minimum by controlling case temperatures.

Question 8

What should be checked/changed to ensure the validity of a turbine engine performance check if an alternate fuel is to be used?

Answer 8

Fuel specific gravity setting.

Question 9

Prior to performing engine trimming, you should what?

Answer 9

obtain a true temperature reading comparable to that of the air that enters the engine.

Question 10

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 what?

Answer 10

false high compression and turbine discharge pressure, and a subsequent low trim.

Question 11

Generally, the practice when trimming an engine is to what?

Answer 11

turn all accessory bleed air off.

Question 12

Which of the following best describes the function of an automatic mixture control (AMC)?

Answer 12

It compensates for change in the air density due to temperature and altitude.

Question 13

On a float-type carburetor, the purpose of the economizer valve is to what?

Answer 13

provide a richer mixture and cooling at maximum power output.

Question 14

The fuel metering force of a conventional float-type carburetor in its normal operating range is the difference between the pressure acting on the discharge nozzle located within the venturi and the pressure…

Answer 14

acting on the fuel in the float chamber.

Question 15

If the main air bleed of a float-type carburetor becomes clogged, the engine will run…

Answer 15

rich at rated power.

Question 16

Which method is commonly used to adjust the level of a float in a float-type carburetor?

Answer 16

Add or remove shims under the needle-valve seat.

Question 17

What is the possible cause of an engine running rich at full throttle if it equipped with a float-type carburetor?

Answer 17

Clogged main air bleed.

Question 18

One of the things a metering orifice in a main air bleed helps to accomplish (at given altitude) in a carburetor is what?

Answer 18

better fuel vaporization and control of fuel discharge, especially at lower engine speeds.

Question 19

A punctured float in a float-type carburetor will cause the fuel level to what?

Answer 19

rise, and enrich the mixture.

Question 20

The back-suction mixture control system operates by what?

Answer 20

varying the pressure acting on the fuel in the float chamber.

Question 21

If an aircraft engine is equipped with a carburetor that is not compensated for altitude and temperature variations, the fuel/air mixture will become what?

Answer 21

richer as either the altitude or temperature increases.

Question 22

Float-type carburetors which are equipped with economizers are normally set for what?

Answer 22

their leanest practical mixture mixture delivery at cruising speeds and enriched by means of the economizer system at higher power settings.

Question 23

If a float type carburetor becomes flooded, the condition is most likely caused by what?

Answer 23

a leaking needle valve and seat assembly.

Question 24

If an engine is equipped with a float-type carburetor and the engine runs excessively rich at full throttle, a possible cause of the trouble is a clogged what?

Answer 24

main air bleed.

Question 25

What occurs when a back-suction type mixture control is placed in IDLE CUTOFF?

Answer 25

The float chamber will be vented to a negative pressure area.

Question 26

Which of the following best describes the function of an altitude mixture control?

Answer 26

Regulates the richness of the fuel/air charge entering the engine.

Question 27

Select the correct statement concerning the idle system of a conventional float-type carburetor.

Answer 27

The low pressure between the edges of the throttle valve and the throttle body pulls the fuel from the idle passage.

Question 28

On an engine equipped with a pressure-type carburetor, fuel supply in the idling range is ensured by the inclusion in the carburetor of what?

Answer 28

A spring in the unmetered fuel chamber to supplement the action of normal metering forces.

Question 29

The economizer system of a float-type carburetor performs which of the following functions?

Answer 29

It supplies and regulates the additional fuel required for all engine speeds above cruising.

Question 30

How will the mixture of an engine be affected if the bellows of the automatic mixture control (AMC) in a pressure carburetor ruptures while the engine is operating at altitude?

Answer 30

It will becomes richer.

Question 31

The fuel level within the float chamber of a properly adjusted float-type carburetor will be what?

Answer 31

slightly lower than the discharge nozzle outlet.

Question 32

The metered fuel pressure (chamber C) in an injection-type carburetor...

Answer 32

is held constant throughout the entire engine operating range.

Question 33

Select the statement which is correct relating to a fuel level check of a float-type carburetor.

Answer 33

Do not measure the level at the edge of the float chamber.

Question 34

What carburetor component measures the amount of air delivered to the engine?

Answer 34

Venturi.

Question 35

If fuel is found running from the carburetor with the engine not running, the likely cause is that the what?

Answer 35

float needle valve is not seated properly.

Question 36

Fuel is discharged for idling speeds on a float-type carburetor...

Answer 36

From the idle discharge nozzle.

Question 37

When air passes through the venturi of a carburetor, what three changes occur?

Answer 37

Velocity increases, temperature decreases, and pressure decreases.

Question 38

Where is the throttle valve located on a float-type carburetor?

Answer 38

After the main discharge nozzle and venturi.

Question 39

An aircraft carburetor is equipped with a mixture control in order to prevent the mixture from becoming too what?

Answer 39

rich at high altitudes.

Question 40

Which of the following is NOT a function of the carburetor venturi?

Answer 40

Regulates the idle system.

Question 41

Idle CUTOFF is accomplished on a carburetor equipped with a back-suction mixture control by what?

Answer 41

introducing low pressure (intake manifold) air into the float chamber.

Question 42

One purpose of an air bleed in a float-type carburetor is to what?

Answer 42

decrease fuel density and destroy surface tension.

Question 43

To determine the float level in a float-type carburetor, a measurement is usually made from the top of the fuel in the float chamber to the what?

Answer 43

parting surface of the carburetor.

Question 44

The throttle valve of float-type aircraft carburetors is located...

Answer 44

between the venturi and the engine.

Question 45

Why must a float-type carburetor supply a rich mixture during idle?

Answer 45

Because at idling speeds the engine may not have enough airflow around the cylinders to provide proper cooling.

Question 46

What component is used to ensure fuel delivery during periods of rapid engine acceleration?

Answer 46

acceleration pump.

Question 47

The device that controls the ratio of the fuel/air mixture to the cylinders is called a what?

Answer 47

mixture control.

Question 48

The device that controls the volume of the fuel/air mixture to the cylinders is called a what?

Answer 48

throttle valve.

Question 49

Which statement is correct regarding a continuous-flow fuel injection system used on many reciprocating engines?

Answer 49

Fuel is injected at each cylinder intake port.

Question 50

During the operation of an aircraft engine, the pressure drop in the carburetor venturi depends primarily upon the what?

Answer 50

air velocity.

Question 51

Which of the following causes a single diaphragm accelerator pump to discharge fuel?

Answer 51

An increase in manifold pressure that occurs when the throttle valve is opened.

Question 52

At what engine speed does the main metering jet actually function as a metering jet in a float-type carburetor?

Answer 52

All RPM's above idle range.

Question 53

An aircraft engine continuous cylinder fuel injection system normally discharges fuel during which strokes(s)?

Answer 53

All (continuously)

Question 54

What is the purpose of the carburetor accelerating system?

Answer 54

Temporarily enrich the mixture when the throttle is suddenly opened.

Question 55

When troubleshooting an engine that will not idle, what would be a probable cause?

Answer 55

Economizer valve not operating correctly.

Question 56

What is the relationship between the accelerating pump and the enrichment valve in a pressure injection carburetor?

Answer 56

No relationship since they operate independently.

Question 57

What is the relationship between the pressure existing within the throat of a venturi and the velocity of the air passing through the venturi?

Answer 57

The pressure is inversely proportional to the velocity.

Question 58

Which of the following is least likely to occur during operation of an engine equipped with a direct cylinder fuel injection systemm?

Answer 58

Backfiring.

Question 59

What carburetor component limits the maximum airflow into the engine at full throttle?

Answer 59

Venturi.

Question 60

On a carburetor without an automatic mixture control as you ascend to altitude, the mixture will what?

Answer 60

be enriched.

Question 61

During engine operation, if carburetor heat is applied, it will what?

Answer 61

decrease the air density to the carburetor.

Question 62

The desired engine idle speed and mixture setting...

Answer 62

is adjusted with engine warmed up and operating.

Question 63

A nine-cylinder radial engine, using a multiple-point priming system with a central spider, will prime which cylinders?

Answer 63

1, 2, 3, 8, and 9.

Question 64

What is a function of the idling air bleed in a float-type carburetor?

Answer 64

It aids in emulsifying/vaporizing the fuel at idle speeds.

Question 65

If the volume of air passing through a carburetor venturi is reduced, the pressure at the venturi throat will what?

Answer 65

increase.

Question 66

(Refer to Figure 6.) Which curve most nearly represents an aircraft engine's fuel/air ratio throughout its operating range?

Answer 66

2

Question 67

What will occur if the vapor vent float in a pressure carburetor loses its buoyancy?

Answer 67

The amount of fuel returning to the fuel tank from the carburetor will be increased.

Question 68

What method is ordinarily used to make idle speed adjustments on a float-type carburetor?

Answer 68

An adjustable throttle stop or linkage.

Question 69

For what primary purpose is a turbine engine fuel control unit trimmed?

Answer 69

To obtain maximum thrust output when desired.

Question 70

Which type of fuel control is used on most of today's turbine engines?

Answer 70

Hydromechanical or electronic.

Question 71

Under which of the following conditions will the trimming of a turbine engine be most accurate?

Answer 71

No wind and low moisture.

Question 72

(1) The mixture used at rated power in air cooled reciprocating engines is richer than the mixture used through the normal cruising range. (2) The mixture used at idle in air cooled reciprocating engines is richer than the mixture used at rated power.

Answer 72

Both 1 and 2 are true.

Question 73

Under which of the following conditions would an engine run lean even though there is a normal amount of fuel present?

Answer 73

Incomplete fuel vaporization.

Question 74

During idle mixture adjustments, which of the following is normally observed to determine when the correct mixture has been achieved?

Answer 74

Changes in RPM or manifold pressure.

Question 75

An indication that the optimum idle mixture has been obtained occurs when the mixture control is moved to IDLE CUTOFF and manifold pressure...

Answer 75

decreases and RPM increases momentarily before the engine ceases to fire.

Question 76

The use of less than normal throttle opening during starting will cause what?

Answer 76

a rich mixture.

Question 77

When checking the idle mixture on a carburetor, the engine should be idling normally, then pull the mixture control toward the IDLE CUTOFF position. A correct idling mixture will be indicated by what?

Answer 77

an increase of 10 to 50 RPM before decreasing.

Question 78

When a new carburetor is installed on an engine, ...

Answer 78

and the engine is warmed up to normal temperatures, adjust the idle mixture, then the idle speed.

Question 79

The purpose of the back-suction mixture control in a float-type carburetor is to adjust the mixture by what?

Answer 79

regulating the pressure on the fuel in the float chamber.

Question 80

Reciprocating engine power will be decreased at all altitudes if the what?

Answer 80

humidity is increased.

Question 81

If the idling jet becomes clogged in a float-type carburetor, the what?

Answer 81

engine will not idle.

Question 82

An aircraft engine equipped with a pressure-type carburetor is started with the what?

Answer 82

primer while the mixture control is positioned at IDLE CUTOFF.

Question 83

One of the best ways to increase engine power and control detonation and preignition is to what?

Answer 83

use water injection.

Question 84

An excessively lean fuel/air mixture may cause what?

Answer 84

an increase in cylinder head temperature.

Question 85

The density of air is very important when mixing fuel and air to obtain a correct fuel-to-air ratio. Which of the following weighs the most?

Answer 85

100 parts of dry air.

Question 86

A mixture ratio of 11:1 normally refers to what?

Answer 86

1 part fuel to 11 parts air.

Question 87

The economizer system in a float-type carburetor...

Answer 87

increases the fuel/air ratio at high power settings.

Question 88

A carburetor is prevented from leaning out during quick acceleration by the what?

Answer 88

accelerating system.

Question 89

In turbine engines that utilize a pressurization and dump valve, the dump portion of the valve...

Answer 89

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)

Question 90

What effect does high atmospheric humidity have on the operation of a jet engine?

Answer 90

has little or not effect.

Question 91

What are the positions of the pressurization valve and the dump valve in a jet engine fuel system when the engine is shut down?

Answer 91

pressurization valve closed, dump valve open.

Question 92

What could cause a lean mixture and high cylinder head temperature at sea level or low altitudes?

Answer 92

automatic mixture control stuck in the extended position.

Question 93

Which of the following is NOT an input parameter for a turbine engine fuel control unit?

Answer 93

Ambient humidity.

Question 94

Detonation occurs when the fuel/air mixture...

Answer 94

burns too fast.

Question 95

What corrective action should be taken when a carburetor is found to be leaking fuel from the discharge nozzle?

Answer 95

Replace the needle valve and seat.

Question 96

A major difference between the Teledyne-Continental and RSA (Precision Airmotive or Bendix) continuous flow fuel injection systems in fuel metering is that the what?

Answer 96

Continental system uses fuel pressure only as a metering force.

Question 97

The function of the altitude compensating, or aneroid valve used with the Teledyne-Continental fuel injection system on many turbocharged engines is to what?

Answer 97

prevent an overly rich mixture during sudden acceleration.

Question 98

The primary purpose of the air bleed openings used with continuous flow fuel injector nozzles is to what?

Answer 98

aid in proper fuel vaporization.