fuel meter
Expl- An automatic mixture control in a pressure carburetor or fuel injection system responds to changes in air density that are caused by changes in both altitude and temperature. As either altitude or temperature increases, the air becomes less dense, and the AMC decreases the amount of fuel metered to the engine to keep the fuel-air mixture ratio constant.
12- A reciprocating engine automatic mixture control responds to changes in air density caused by changes in A- altitude or humidity. B- altitude only. C- altitude or temperature.
Expl- The back-suction mixture control changes the fuel-air mixture ratio by varying the pressure on the top of the fuel in the float bowl. Lowering the pressure on this fuel leans the mixture.
20- The back-suction mixture control system operates by A- varying the pressure within the venturi section. B- varying the pressure acting on the fuel in the float chamber. C- changing the effective cross-sectional area of the main metering orifice (jet).
Expl- The throttle valve in a float-type carburetor is located after (downstream of) the main discharge nozzle and the venturi. The discharge nozzle is located in the venturi.
35- Where is the throttle valve located on a float-type carburetor? A- Between the venturi and the discharge nozzle. B- After the main discharge nozzle and venturi. C- After the venturi and just before the main discharge nozzle
xpl- An aircraft carburetor is equipped with a mixture control to prevent the fuel-air mixture from becoming too rich as the aircraft goes up in altitude and the air becomes less dense.
36- An aircraft carburetor is equipped with a mixture control in order to prevent the mixture from becoming too A- lean at high altitudes. B- rich at high altitudes. C- rich at high speeds.
Expl- The throttle valve in a float-type carburetor is a butterfly-type valve located between the venturi and the engine
41- The throttle valve of float-type aircraft carburetors is located A- ahead of the venturi and main discharge nozzle. B- after the main discharge nozzle and ahead of the venturi. C- between the venturi and the engine.
Expl- The pressure drop in the venturi of a carburetor is a function of the velocity of the air flowing into the engine. The relationship between pressure and velocity in a stream of moving fluid is explained by Bernoulli's principle.
46- During the operation of an aircraft engine, the pressure drop in the carburetor venturi depends primarily upon the A- air temperature. B- barometric pressure. C- air velocity.
xpl- The correct idling mixture adjustments are determined by watching the changes in the RPM and the manifold pressure as the mixture control is slowly moved into the IDLE CUTOFF position.
62- During idle mixture adjustments, which of the following is normally observed to determine when the correct mixture has been achieved? A- Changes in fuel/air pressure ratio. B- Fuel flowmeter. C- Changes in RPM or manifold pressure.
Expl- A float-type carburetor with a clogged idling jet will not provide fuel to the engine when the throttle is closed to the idle position. The engine will not run at idle speeds.
69- If the idling jet becomes clogged in a float-type carburetor, the A- engine operation will not be affected at any RPM. B- engine will not idle. C- idle mixture becomes richer.
Expl- A clogged main air bleed will cause an engine to run too rich at full throttle. This principle of restricting the main air bleed at full throttle operation is used in some carburetors as a power-enrichment system.
What is the possible cause of an engine running rich at full throttle if it is equipped with a float-type carburetor? A- Float level too low. B- Clogged main air bleed. C- Clogged atmospheric vent.
Expl- Low-lead 100-octane aviation gasoline is dyed blue. Turbine fuel is normally colorless or straw colored. Grade 80 aviation gasoline is dyed red.
1- The color of 100LL fuel is A- blue. B- colorless or straw. C- red.
Expl- Tetraethyl lead is added to aviation gasoline to increase its critical pressure and temperature. The higher critical pressure and temperature allow the engine to operate with higher cylinder pressures without the fuel-air mixture detonating.
10- Tetraethyl lead is added to aviation gasoline to A- retard the formation of corrosives. B- improve the gasoline's performance in the engine. C- dissolve the moisture in the gasoline.
Expl- An ideal fuel for an aircraft reciprocating engine must vaporize (change from a liquid into a vapor) easily, yet it must not vaporize so easily that it will form vapor locks in the fuel system. Liquid fuel will not burn, so for it to burn, it must be changed into a fuel vapor. If the fuel does not vaporize readily enough, it will cause the engine to be hard to start.
11- A fuel that does not vaporize readily enough can cause A- vapor lock. B- detonation. C- hard starting.
Expl- An economizer system, also called a power enrichment system, provides additional fuel at full power operation to remove some of the excess heat from the cylinders. This system is called an economizer system because it allows an economical operation at conditions other than full power.
13- On a float-type carburetor, the purpose of the economizer valve is to A- provide extra fuel for sudden acceleration of the engine. B- maintain the leanest mixture possible during cruising best power. C- provide a richer mixture and cooling at maximum power output.
Expl- The fuel-metering force in a float-type carburetor is the pressure difference between the pressure in the float bowl and the pressure at the discharge nozzle which is located in the venturi. The low pressure at the discharge nozzle is determined by the amount of air flowing into the engine through the venturi.
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 A- acting on the fuel in the float chamber. B- of the fuel as it enters the carburetor. C- of the air as it enters the venturi (impact pressure
Expl- A clogged main air bleed will cause the mixture to be too rich at the rated power of the engine. It will have no effect on the mixture at idling because the idling system does not use the main air bleed.
15- If the main air bleed of a float-type carburetor becomes clogged, the engine will run A- lean at rated power. B- rich at rated power. C- rich at idling
Expl- A widely used method of adjusting the float level on a float-type carburetor is by adding or removing shims under the needle-valve seat.
16- Which method is commonly used to adjust the level of a float in a float-type carburetor? A- Lengthening or shortening the float shaft. B- Add or remove shims under the needle-valve seat. C- Change the angle of the float arm pivot.
Expl- A metering orifice in the main air bleed of a float-type carburetor meters the correct amount of air into the fuel just before it reaches the main discharge nozzle. This air emulsifies the fuel to decrease its density and make it easier to vaporize, especially at the lower engine speeds.
18- One of the things a metering orifice in a main air bleed helps to accomplish (at a given altitude) in a carburetor is A- pressure in the float chamber to increase as airflow through the carburetor increases. B- a progressively richer mixture as airflow through the carburetor increases. C- better fuel vaporization and control of fuel discharge, especially at lower engine speeds.
Expl- A punctured float, in a float-type carburetor, will allow fuel to enter the float, making it less buoyant. The fuel will have to rise to a higher level in the float bowl to shut the fuel off. This higher level of fuel in the float bowl will enrich the mixture.
19- A punctured float in a float-type carburetor will cause the fuel level to A- lower, and enrich the mixture. B- rise, and enrich the mixture. C- rise, and lean the mixture.
Expl- A noncompensated carburetor (a carburetor that cannot be adjusted for mixture changes with altitude) will produce a richer mixture as the air density decreases because of an increase in either altitude or temperature. The reason for this enrichment is that the carburetor meters the fuel according to the volume of air, but the engine burns it according to its weight. The weight of a given volume of air decreases as both altitude and temperature increase, so the mixture becomes richer.
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 A- leaner as either the altitude or temperature increases. B- richer as the altitude increases and leaner as the temperature increases. C- richer as either the altitude or temperature increases
Expl- A carburetor equipped with an economizer system is adjusted so the mixture will be sufficiently lean for economical operation under all conditions other than full power. Under full power conditions, the economizer system adds fuel to enrich the mixture enough that detonation will not occur.
22- Float-type carburetors which are equipped with economizers are normally set for A- their richest mixture delivery and leaned by means of the economizer system. B- the economizer system to supplement the main system supply at all engine speeds above idling. C- their leanest practical mixture delivery at cruising speeds and enriched by means of the economizer system at higher power settings.
Expl- If a needle valve and seat assembly in a float-type carburetor leaks, the fuel level will rise above the discharge level of the main discharge nozzle and the carburetor will become flooded.
23- If a float-type carburetor becomes flooded, the condition is most likely caused by A- a leaking needle valve and seat assembly. B- the accelerating pump shaft being stuck. C- a clogged back-suction line.
Expl- Under full-throttle operation, the main air bleed must introduce enough air into the fuel to prevent the mixture becoming excessively rich. If this air bleed becomes restricted, or clogged, the engine will run excessively rich at wide-open throttle. The power enrichment system used on some float-type carburetors enriches the mixture at full power by restricting the main air bleed.
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 A- main air bleed. B- back-suction line. C- atmospheric vent line.
Expl- The back-suction mixture control regulates the fuel-air mixture by varying the pressure above the fuel in the float chamber. When this type of carburetor is placed in the IDLE CUTOFF position, the float chamber is vented to a negative pressure.
25- What occurs when a back-suction type mixture control is placed in IDLE CUTOFF? A- The fuel passages to the main and idle jets will be closed by a valve. B- The float chamber will be vented to a negative pressure area. C- The fuel passage to the idle jet will be closed by a valve.
Expl- An altitude mixture control allows the pilot to maintain a fuel-air mixture ratio entering the engine that will produce the desired engine operation. This is the same as regulating the richness of the fuel-air charge entering the engine.
26- Which of the following best describes the function of an altitude mixture control? A- Regulates the richness of the fuel/air charge entering the engine. B- Regulates the air pressure above the fuel in the float chamber. C- Regulates the air pressure in the venturi.
Expl- In a conventional float-type carburetor at idle, there is not enough air flowing through the venturi to pull fuel from the main discharge nozzle. The idle discharge nozzle is located in the throttle body at the edge of the throttle valve, and all of the air flowing into the engine for idling must pass between the edges of the throttle valve and the throttle body. It produces a low pressure that pulls the fuel-air emulsion from the idle passage.
27- Select the correct statement concerning the idle system of a conventional float-type carburetor. A- The low-pressure area created in the throat of the venturi pulls the fuel from the idle passage. B- Climatic conditions have very little effect on idle mixture requirements. C- The low pressure between the edges of the throttle valve and the throttle body pulls the fuel from the idle passage.
Expl- The economizer system on a float-type carburetor adds additional fuel to that which is metered through the main metering jet at all conditions above cruise. It is for this reason that economizer systems are often called power enrichment systems.
28- The economizer system of a float-type carburetor performs which of the following functions? A- It supplies and regulates the fuel required for all engine speeds. B- It supplies and regulates the additional fuel required for all engine speeds above cruising. C- It regulates the fuel required for all engine speeds and all altitudes.
Expl- The fuel level of a properly adjusted float-type carburetor will be slightly lower than the discharge nozzle outlet. This prevents fuel flowing out of the discharge nozzle when the aircraft is sitting in a level-ground attitude.
29- The fuel level within the float chamber of a properly adjusted float-type carburetor will be A- slightly higher than the discharge nozzle outlet. B- slightly lower than the discharge nozzle outlet. C- at the same level as the discharge nozzle outlet.
Expl- Tetraethyl lead is added to aviation gasoline to improve its antidetonation characteristics (to raise its critical pressure and temperature), but deposits left inside the cylinders from the tetraethyl lead foul spark plugs and cause corrosion. In order to get rid of the residue from the tetraethyl lead, ethylene dibromide is mixed with the gasoline. When the gasoline burns, the ethylene dibromide combines with the lead and forms volatile lead bromides that go out the exhaust and do not form solid contaminants inside the cylinder.
3- Why is ethylene dibromide added to aviation gasoline? A- To remove zinc silicate deposits from the spark plugs. B- To scavenge lead oxide from the cylinder combustion chambers. C- To increase the antiknock rating of the fuel.
Expl- The fuel level must not be measured at the edge of the float chamber because of the tendency of the fuel to wet the walls of the chamber. At the wall, the fuel will be slightly higher than it is in the center. A straightedge should be placed across the parting surface of the float bowl and the level measured away from the edge and away from the float.
30- Select the statement which is correct relating to a fuel level check of a float-type carburetor. A- Use 5 pounds fuel pressure for the test if the carburetor is to be used in a gravity fuel feed system. B- Block off the main and idle jets to prevent a continuous flow of fuel through the jets. C- Do not measure the level at the edge of the float chamber.
Expl- A venturi is used to measure the amount of the air pulled into the cylinders of an engine. The pressure drop in the throat of a venturi is directly proportional to the velocity of the air flowing through it.
31- What carburetor component measures the amount of air delivered to the engine? A- Economizer valve. B- Automatic mixture control. C- Venturi
xpl- A float-type carburetor leaking when the engine is stopped is caused by fuel rising in the float bowl to a level higher than the tip of the fuel discharge nozzle. A leaking needle valve is the most likely cause of the fuel level rising when the engine is not running.
32- If a float-type carburetor leaks fuel when the engine is stopped, a likely cause is that the A- float needle valve is worn or otherwise not seated properly. B- float level is adjusted too low. C- main air bleed is clogged.
Expl- In a float-type carburetor at idle speed, fuel is discharged from the idle discharge nozzle which is located opposite the throttle valve in the carburetor throat.
33- Fuel is discharged for idling speeds on a float-type carburetor A- from the idle discharge nozzle. B- in the venturi. C- through the idle discharge air bleed.
xpl- When air passes through a venturi, its velocity increases, and both its temperature and pressure decrease.
34- When air passes through the venturi of a carburetor, what three changes occur? A- Velocity increases, temperature increases, and pressure decreases. B- Velocity decreases, temperature increases, and pressure increases. C- Velocity increases, temperature decreases, and pressure decreases.
Expl- The carburetor venturi has nothing to do with regulating the idle system of the carburetor. The venturi does proportion the fuel/air mixture and limits the airflow at full throttle.
37- Which of the following is NOT a function of the carburetor venturi? A- Proportions the fuel/air mixture. B- Regulates the idle system. C- Limits the airflow at full throttle.
Expl- Idle cutoff in a carburetor equipped with a back-suction mixture control is accomplished by introducing low-pressure air (suction) into the float chamber. This low pressure lowers the level of fuel in the discharge nozzle so much that the low pressure caused by air flowing through the venturi cannot pull fuel from it.
38- Idle cutoff is accomplished on a carburetor equipped with a back-suction mixture control by A- introducing low pressure (intake manifold) air into the float chamber. B- turning the fuel selector valve to OFF. C- the positive closing of a needle and seat.
Expl- Gasoline has a higher heat energy per pound than kerosine (nominally 20,000 Btu per pound for gasoline versus about 18,500 Btu per pound for kerosine). Kerosine, however, weighs more than gasoline (about 6.7 pounds per gallon for kerosine compared with about 6.0 pounds per gallon for gasoline). Because there are more pounds of kerosine per gallon, there are more Btu's in a gallon of kerosine than in a gallon of gasoline. Note: ASA prefers to adopt the scientific/technical spelling of 'kerosine.'
4- Both gasoline and kerosene have certain advantages for use as turbine fuel. Which statement is true in reference to the advantages of each? A- Kerosene has a higher heat energy/value per unit weight than gasoline. B- Gasoline has a higher heat energy/value per unit volume than kerosene. C- Kerosene has a higher heat energy/value per unit volume than gasoline.
Expl- The fuel level in the float bowl of a float-type carburetor is measured between the parting surface of the carburetor float bowl and the surface of the fuel in the bowl measured at a point away from both the float chamber wall and the float
40- 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 A- parting surface of the carburetor. B- top of the float. C- centerline of the main discharge nozzle.
Expl- The idle mixture is considerably richer than a normal mixture because at idling speeds the mixture distribution is sometimes uneven, and the engine may not have enough airflow around the cylinders to provide proper cooling.
42- Why must a float-type carburetor supply a rich mixture during idle? A- Engine operation at idle results in higher than normal volumetric efficiency. B- Because at idling speeds the engine may not have enough airflow around the cylinders to provide proper cooling.
Expl- An accelerator system usually contains an accelerator pump to provide a momentarily rich mixture during periods of rapid engine acceleration. Under these conditions, the normal metering system is unable to provide an adequately rich mixture.
43- What component is used to ensure fuel delivery during periods of rapid engine acceleration? A- Acceleration pump. B- Water injection pump. C- Power enrichment unit.
Expl- Most aircraft reciprocating engines are equipped with a mixture control that allows the pilot to control the fuel-air mixture ratio as it enters the cylinders of the engine.
44- The device that controls the ratio of the fuel/air mixture to the cylinders is called a A- throttle valve. B- mixture control. C- metering jet.
Expl- The main metering jet in a float-type carburetor functions as a metering jet at all RPMs above the idling range. In the idling range, the idling metering jet meters the fuel.
47- At what engine speed does the main metering jet actually function as a metering jet in a float-type carburetor? A- All RPM's. B- Cruising RPM only. C- All RPM's above idle range
Expl- There is normally a temporary lag between the time the throttle is opened and the time the engine builds up its speed. This lag is due to the time required to transition between the idle system and the main metering system. To prevent this lag, most carburetors are equipped with an accelerating system that provides a momentarily rich mixture during this transition time.
48- What is the purpose of the carburetor accelerating system? A- Supply and regulate the fuel required for engine speeds above idle. B- Temporarily enrich the mixture when the throttle is suddenly opened. C- Supply and regulate additional fuel required for engine speeds above cruising.
Expl- If the engine will not idle because the mixture is too rich, and the idle mixture adjustment on the carburetor will not lean it sufficiently, there is a possibility that the economizer valve is not operating correctly and feeding fuel into the engine.
49- When troubleshooting an engine for too rich a mixture to allow the engine to idle, what would be a possible cause? A- Economizer valve not operating correctly. B- Mixture setting too rich. C- Air leak in the intake manifold
Expl- When fuel changes from a liquid into a vapor, it absorbs heat from the surrounding air. This absorption of heat drops the temperature of the air enough that moisture can condense out and freeze. This is the main cause of carburetor ice.
5- What must accompany fuel vaporization? A- An absorption of heat. B- A decrease in vapor pressure. C- A reduction in volume.
Expl- The pressure in the throat of a venturi is inversely proportional to the velocity of the air flowing through it. This is in accordance with Bernoulli's principle.
50- What is the relationship between the pressure existing within the throat of a venturi and the velocity of the air passing through the venturi? A- There is no direct relationship between the pressure and the velocity. B- The pressure is directly proportional to the velocity. C- The pressure is inversely proportional to the velocity.
Expl- The venturi limits the maximum airflow into the engine at full throttle operation. At conditions other than full throttle, the position of the butterfly-type throttle valve limits the amount of air
51- What carburetor component actually limits the desired maximum airflow to the engine at full throttle? A- Throttle valve. B- Venturi. C- Manifold intake.
Expl- If the carburetor does not have an automatic mixture control, the mixture ratio will become richer as the aircraft goes up in altitude and the air density becomes less
52- On a carburetor without an automatic mixture control as you ascend to altitude, the mixture will A- be enriched. B- be leaned. C- not be affected.
Expl- When carburetor heat is applied, the temperature of the air entering the engine is increased. Increasing its temperature decreases the density of the intake air.
53- During engine operation, if carburetor heat is applied, it will A- increase fuel/air ratio. B- increase engine RPM. C- decrease the air density to the carburetor.
Expl- Engine idle speed and mixture setting can be adjusted only when the engine is warmed up and operating properly
54- The desired engine idle speed and mixture setting A- is adjusted with engine warmed up and operating. B- should give minimum RPM with maximum manifold pressure. C- is usually adjusted in the following sequence; speed first, then mixture.
Expl- A radial engine, using multiple-point priming, primes all of the cylinders above the center line of the engine. In a nine-cylinder engine, these are cylinders 1, 2, 3, 8, and 9.
55- A nine-cylinder radial engine, using a multiple-point priming system with a central spider, will prime which cylinders? A- One, two, three, eight, and nine. B- All cylinders. C- One, three, five, and seven
Expl- Curve 1 is not correct, because the mixture does not get progressively richer as the RPM increases. Curve 2 is correct, because a richer mixture is provided for idling when scavenging is poor and also for full power operation when extra fuel is needed for cooling. Curve 3 is not correct, because the actual mixture ratio needs are exactly opposite to that shown in this curve. Curve 4 is not correct, because the mixture does not get progressively richer as the RPM increases.
558- (Refer to Figure 6.) Which curve most nearly represents an aircraft engine's fuel/air ratio throughout its operating range? A- 1 B- 3 C- 2
Expl- The idle air bleed on a float-type carburetor aids in emulsifying the fuel drawn from the idle system during idle-speed operation
56- What is a function of the idling air bleed in a float-type carburetor? A- It provides a means for adjusting the mixture at idle speeds. B- It vaporizes the fuel at idling speeds. C- It aids in emulsifying/vaporizing the fuel at idle speeds.
Expl- Idle speed adjustment on a float-type carburetor is made by adjusting the amount the throttle valve remains away from the throttle body wall when the throttle control is against its stop. This adjustment is normally made with an adjustable throttle stop screw.
59- What method is ordinarily used to make idle speed adjustments on a float-type carburetor? A- An adjustable throttle stop or linkage. B- An orifice and adjustable tapered needle. C- An adjustable needle in the drilled passageway which connects the airspace of the float chamber and the carburetor venturi.
Expl- Detonation is an uncontrolled burning, or explosion, of the fuel-air mixture within the cylinder of a reciprocating engine. The fuel-air mixture ignites and burns normally. But as it burns, it compresses and heats the mixture ahead of the flame front. When the heated and compressed mixture reaches its critical pressure and temperature, it releases its energy almost instantaneously (it explodes). It is the explosions inside the cylinder that cause the cylinder-head temperature to go up, the cylinder pressure to go up, and the engine power to decrease.
6- Characteristics of detonation are A- cylinder pressure remains the same, excessive cylinder head temperature, and a decrease in engine power. B- rapid rise in cylinder pressure, excessive cylinder head temperature, and a decrease in engine power. C- rapid rise in cylinder pressure, cylinder head temperature normal, and a decrease in engine power
Expl- Statement (1) is true. The mixture ratio used when an engine is developing its rated horsepower is richer than the ratio used throughout the normal cruising range. The additional fuel is used for cooling. Statement (2) is also true. The mixture used at idling is richer than the mixture used at rated power because incomplete scavenging and uneven mixture distribution during idle operation requires an excessively rich mixture.
60- (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. Regarding the above statements, A- only No. 1 is true. B- only No. 2 is true. C- both No. 1 and No. 2 are true.
Expl- Incomplete fuel vaporization causes an excess of air for the amount of vaporized fuel. Incomplete fuel vaporization causes an engine to operate lean even though a normal amount of fuel has been metered.
61- Under which of the following conditions would an engine run lean even though there is a normal amount of fuel present? A- The use of too high an octane rating fuel. B- Incomplete fuel vaporization. C- The carburetor air heater valve in the HOT position.
Expl- The optimum idle mixture setting causes a slight decrease in the manifold pressure and a slight rise in RPM as the mixture control is pulled back into the IDLE CUTOFF position. These changes occur just before the engine stops firing.
63- An indication that the optimum idle mixture has been obtained occurs when the mixture control is moved to IDLE CUTOFF and manifold pressure A- decreases momentarily and RPM drops slightly before the engine ceases to fire. B- increases momentarily and RPM drops slightly before the engine ceases to fire. C- decreases and RPM increases momentarily before the engine ceases to fire.
Expl- If the throttle is opened less than normal during the engine starting procedure, a rich mixture will be drawn into the cylinders.
64- The use of less than normal throttle opening during starting will cause A- a rich mixture. B- a lean mixture. C- backfire due to lean fuel/air ratio.
Expl- The correct idling fuel-air mixture is indicated when there is a slight rise in RPM before the engine stops running as the mixture control is slowly moved into the IDLE CUTOFF position.
65- 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 A- an immediate decrease in RPM. B- a decrease of 20 to 30 RPM before quitting. C- an increase of 10 to 50 RPM before decreasing.
Expl- After a new carburetor is installed on an aircraft engine, the engine must be warmed up to its normal operating temperature and the idle mixture and idle speed adjustments made.
66- When a new carburetor is installed on an engine, A- warm up the engine and adjust the float level. B- do not adjust the idle mixture setting; this was accomplished on the flow bench. C- and the engine is warmed up to normal temperatures, adjust the idle mixture, then the idle speed.
Expl- A back-suction mixture control in a float-type carburetor adjusts the fuel-air mixture ratio by regulating the air pressure on the fuel in the float bowl. This pressure determines the fuel level at the discharge nozzle.
67- The purpose of the back-suction mixture control in a float-type carburetor is to adjust the mixture by A- regulating the pressure drop at the venturi. B- regulating the pressure on the fuel in the float chamber. C- regulating the suction on the mixture from behind the throttle valve.
Expl- An increase in humidity decreases the power produced by an engine, because the amount of power released from the fuel is determined by the mass of air mixed with the fuel when it is burned. Water vapor is less dense than dry air, so humid air has less mass than an equal volume of dry air.
68- Reciprocating engine power will be decreased at all altitudes if the A- air density is increased. B- humidity is increased. C- manifold pressure is increased.
Expl- If a fuel vaporizes too readily, it has a high vapor pressure. It requires a high pressure to keep the vapors in the fuel. Vapors that form in a fuel line can prevent liquid fuel flowing through the line and can stop the engine because of fuel exhaustion. This is a vapor lock.
7- A fuel that vaporizes too readily may cause A- hard starting. B- detonation. C- vapor lock.
Expl- A water-injection system (ADI system) is used to allow a reciprocating engine to operate with maximum power without detonation or preignition.
70- One of the best ways to increase engine power and control detonation and preignition is to A- enrich the fuel/air mixture. B- use water injection. C- lean the fuel/air mixture.
Expl- An excessively lean fuel-air mixture ratio burns slowly. It is still burning when the gases are forced out past the exhaust valve. This slow burning will cause an increase in cylinder head temperature.
71- An excessively lean fuel/air mixture may cause A- an increase in cylinder head temperature. B- high oil pressure. C- backfiring through the exhaust.
Expl- Water vapor weighs only about 5/8 as much as dry air. Therefore, 100 parts of dry air will weigh more than any of the other choices given with this question.
72- 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? A- 75 parts of dry air and 25 parts of water vapor. B- 100 parts of dry air. C- 50 parts of dry air and 50 parts of water vapor.
Expl- An air/fuel mixture ratio of 11:1 is a mixture of eleven parts of air and one part of fuel by weight. An air-fuel ratio of 11:1 is the same as a fuel-air ratio of 0.091.
73- A mixture ratio of 11:1 normally refers to A- a stoichiometric mixture. B- 1 part air to 11 parts fuel. C- 1 part fuel to 11 parts air.
Expl- The economizer system in a float-type carburetor increases the fuel-air mixture ratio at high power settings. By using the rich mixture only at the higher power settings, the engine can use an economically lean mixture during all other operations.
74- The economizer system in a float-type carburetor A- keeps the fuel/air ratio constant. B- functions only at cruise and idle speeds. C- increases the fuel/air ratio at high power settings.
Expl- The accelerating system provides a momentarily rich mixture during quick acceleration of the engine to prevent its 'leaning out.'
75- A carburetor is prevented from leaning out during quick acceleration by the A- power enrichment system. B- mixture control system. C- accelerating system.
Expl- If the needle valve in an automatic mixture control in a pressure-injection carburetor sticks while it is in its extended position, it can cause a lean mixture and a high cylinder head temperature.
76- What could cause a lean mixture and high cylinder head temperature at sea level or low altitudes? A- Mixture control valve fully closed. B- Defective accelerating system. C- Automatic mixture control stuck in the extended position.
Expl- Detonation causes high cylinder head temperatures because the fuel-air mixture burns too fast. In detonation, the fuel-air mixture actually explodes rather than burning evenly as it should.
77- Detonation occurs when the fuel/air mixture A- burns too fast. B- ignites before the time of normal ignition. C- is too rich.
Expl- If a float-type carburetor is leaking fuel from the discharge nozzle when the engine is not running, it is probably because the needle valve in the float bowl is leaking. The needle valve and the seat should be replaced.
78- What corrective action should be taken when a carburetor is found to be leaking fuel from the discharge nozzle? A- Replace the needle valve and seat. B- Raise the float level. C- Turn the fuel off each time the aircraft is parked.
Expl- The main difference between grades 100 and 100LL aviation gasoline is the content of tetraethyl lead and the color. Their antiknock characteristics are the same. Grade 100 is allowed to have a maximum of 3.0 milliliter of TEL per gallon, and it is dyed green. Grade 100LL is allowed to have a maximum of 2.0 milliliter of TEL per gallon, and it is dyed blue.
8- The main differences between grades 100 and 100LL fuel are A- volatility and lead content. B- volatility, lead content, and color. C- lead content and color.
Expl- Aviation gasoline is suitable as a fuel for reciprocating engines because it has a high heat value (nominally 20,000 Btu per pound) and a high volatility. It readily changes from a liquid into a vapor so that it can be burned.
9- Characteristics of aviation gasoline are A- high heat value, high volatility. B- high heat value, low volatility. C- low heat value, low volatility.
Expl- Aviation fuel whose antidetonation characteristics are better than those of the reference fuel (100-octane) are rated in performance numbers.
How are aviation fuels, which possess greater antiknock qualities than 100 octane, classified? A- According to the milliliters of lead. B- By reference to normal heptane. C- By performance numbers.
Expl- When the volume of air passing through the carburetor venturi is reduced by partially closing the throttle valve, the pressure at the venturi throat will increase.
If the volume of air passing through a carburetor venturi is reduced, the pressure at the venturi throat will A- decrease. B- be equal to the pressure at the venturi outlet. C- increase.
Expl- An air bleed in a float-type carburetor mixes air in the fuel between the metering jet and the discharge nozzle. This decreases the density of the fuel and destroys its surface tension, resulting in better vaporization and control of fuel discharge, especially at lower engine speeds.
One purpose of an air bleed in a float-type carburetor is to A- increase fuel flow at altitude. B- meter air to adjust the mixture. C- decrease fuel density and destroy surface tension.
Expl- The throttle valve in a carburetor determines the volume of fuel-air mixture allowed to enter the cylinders.
The device that controls the volume of the fuel/air mixture to the cylinders is called a A- mixture control. B- metering jet. C- throttle valve.
