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Regional Gliding School

The Carburetor

measure the correct quantity of fuel and vaporize this fuel,

mix it with air in the proper proportion, and

deliver the mixture to the cylinders.

The carburetor has three important functions:


Components of a Carburetor

Venturi air is drawn into the venturi

and because of its shape, the air is accelerated while the pressure is reduced

Nozzle provides a passage for fuel

from the float chamber to the venturi

reduced pressure draws fuel into the venturi where it is vaporized



Throttle Valve regulates the volume of

fuel/air mixture

Intake Manifold distributes the fuel/air

mixture from the carburetor to the cylinders

Float Chamber contains a consistent level

of fuel in order to keep fuel supply steady

Throttle Valve To

Intake Manifold

Float Chamber



Needle Valve opens and closes the fuel line and

is controlled by the float

Vent allows the pressure to be equalized

with that of the changing outside air pressure

Idle Jet used to keep the engine going

when there is insufficient air flow to draw in fuel from the nozzle


Fuel/Air Mixture The ratio of fuel to air is regulated by the

pilot with the mixture control. The throttle valve regulates the flow of

air/fuel mixture into the engine. It also creates turbulence to assist in the mixing of fuel and air.

The proportion of fuel to air is governed by weight and not by volume.


Fuel/Air Mixture The chemically correct mixture is about 1:15,

where it is one part fuel to fifteen parts air. An engine will run hotter with a lean mixture

because the lean mixture is slower burning, exposing the cylinder walls to high temperatures for a longer period of time.

An engine will run cooler with a richer mixture because the rich mixture burns more quickly.


NOTE: You must use the buttons in the Confirmation Stage


Aero EnginesAero EnginesCarburetor and Exhaust SystemsCarburetor and Exhaust Systems

A

B

C

D

Weight

Mass

Area

Let's try a few review questions on Aero Engines:

Question #1 - How is the mixture of gasoline to air measured?

Volume

I’m afraid that answer is incorrect

Let's try again...

Flying Scholarship Program


That answer is correct.

Let's move on...


Fuel/Air Mixture The ratio of fuel to air is regulated by the

pilot with the mixture control.

The throttle valve regulates the flow of airinto the engine and creates turbulence at thebutterfly valve to assist in the mixing of fueland air.

The proportion of gasoline to air is governedby weight and not by volume.


Mixture ControlAs altitude increases, the density of air decreases. Carburetors are calibrated for sea level operation.Therefore, with altitude, the mixture would

become over-rich, causing a waste of fuel and a loss of power.

Mixture control is fitted to adjust the amount of fuel being drawn from the nozzle.

Mixture control can be used to produce a rich or lean fuel/air mixture.


Besides lowering the combustion temperature, too rich a mixture will result in unburned wasted fuel.

It contributes to fouled spark plugs and combustion chamber deposits.

Can also cause rough engine operation, appreciable loss of power or engine failure.

Used for high power settings.


May cause rough engine operation, sudden “cutting out”, “popping back” or back-firing, detonation, overheating or appreciable loss of power.

Continual operation at too lean a mixture has also been responsible for engine failure.

Used for cruise power settings.


When to Lean the Engine

At cruise power, below approximately 75% of the rated RPM of the engine.

At any altitude above 3000 feet. For take-off at high altitude airports. After climbing to a higher altitude.


Why Lean the EngineProper leaning of engine is both practical and

economical. It results in:

economy of fuel,a smoother running engine,a more efficient engine,extended range,less spark plug fouling,more desirable engine temperatures, andcleaner combustion chambers.

Confirmation Stage




A

B

C

D

Final approach

Climbing at high altitudes


Question #2 - When do you lean your engine?

Take off at low altitude

Climbing at low altitudes


Let's try again...




Let's move on...


When to Lean the Engine

At cruise power, below approximately 75% of the rated RPM of the engine.

At any altitude above 3000 feet.

For take-off at high altitude airports.

After climbing to a higher altitude.



A

B

C

D

Longer spark plug life

Cleaner engine

All the above


Question #3 - Why do you lean your engine?

Extended range


Let's try again...




Let's move on...


Why Lean the EngineProper leaning of engine is both practical and

economical. It results in:

economy of fuel, a smoother running engine, a more efficient engine, extended range, less spark plug fouling, more desirable enigne temperatures, and cleaner combustion chambers.


Forms under moist atmospheric conditions with air temperatures anywhere from approximately -5C to 30C.

Indicated by a loss of power (RPM drop).

Can cause complete engine failure.


Forms of Carburetor Ice

There are three forms of carburetor ice:

– fuel vaporization ice,

– impact ice, and

– throttle ice.


Prevention of Carb Icing Carb icing does not occur in

engines that have fuel injectors rather than a carburetor.

Carb heat uses air heated by the exhaust system which is pumped into the carburetor.

Results in initial drop in RPM. If ice is present, its melting will

give a short period of engine roughness.


Exhaust SystemBasically a scavenging system.Collects and disposes of the high temperature,

noxious gases discharged by the engine.Main function is to prevent the escape of these

potentially destructive gases into the airframe and cabin.

Two types: short stack system, and collector system.


Short Stack Exhaust System

Used on non-turbocharged engines and on low powered engines.

Relatively simple: a down stack from each

cylinder, an exhaust collector tube on

each side of the engine, and an exhaust ejector on each

side of the cowling.


Collector Exhaust System

Used on most large engines and on all turbocharged engines.

Individual exhaust headers empty into a collector ring that collects the exhaust from all the cylinders.

One outlet from this rings routes the hot exhaust gas to the turbocharger.

An exhaust tailpipe carries the gases away.



A

B

C

D

-30°C to -5°C

-30°C to 5°C

5°C to 30°C


Question #4 - At approximately what temperature range can carburetor ice form?

-5°C to 30°C


Let's try again...




Let's move on...


Forms under moistatmospheric conditionswith air temperaturesanywhere fromapproximately -5 C to30C.

Indicated by a loss ofpower (RPM drop).

Can cause complete enginefailure.



A

B

C

D

Collector

Venturi

Both B and C


Question #5 - Which is NOT a type of exhaust system?

Short Stack


Let's try again...




Let's move on...


Exhaust SystemBasically a scavenging system.Collects and disposes of the high temperature,

noxious gases discharged by the engine.

Main function is to prevent the escape of thesepotentially destructive gases into the airframe andcabin.

Two types:short stack system, and

collector system.


Congratulations!!

You have now completed the Carburetor and Exhaust Systems lesson of the Aero Engines Module. Of course, this lesson is always available to you for future reference if required.

You are now ready to move along to the next Aero Engines lesson you have not completed or to any other module you wish. You can advance to the Self Test Module if you feel ready to challenge the final exam.

Good Luck!
