Answers - Induction and Engine Airflow Systems

1. a
Induction system ice forms in float and pressure carburetors when water condenses out of the air in a carburetor's venturi and freezes. Therefore, the easiest way to prevent icing is to heat the intake air to the point where ice cannot form.

2. a
Normally aspirated engines using float-type carburetors are most susceptible to icing when operated in temperatures between 30 and 40 degrees Fahrenheit. The reason for this is that any time the air being brought into the carburetor is near freezing, the additional temperature drop created by the carburetor venture can readily cause water vapor to condense and freeze. However, it is important to note that carburetor icing can occur when the outside temperature is as high as 70 degrees Fahrenheit.

3. b
In addition to a carburetor heat system, some large reciprocating engines utilize an alcohol deicing system. This system allows the pilot to spray alcohol into the inlet of the carburetor to remove ice and assist the warm air in keeping the carburetor free of ice.

4. c
On engines equipped with constant speed propellers, the engine's power output is indicated on the manifold pressure gauge. Therefore, induction system icing is readily detected by a reduction in manifold pressure and no change in rpm.

5. c
When the air temperature is above freezing and there is no visible moisture, a carburetor will be the first part of an aircraft to accumulate ice. The reason for this is that as fuel vaporizes and the air pressure drops in the venturi, the air temperature typically drops enough to cause water vapor to condense and freeze.

6. c
Heating the air in the inlet duct and spraying alcohol in the carburetor inlet are the two primary methods of eliminating carburetor ice.

7. b
Because fuel injection systems inject fuel directly into an engine's intake manifold, there is no need for a carburetor. Therefore, no carburetor air heater is required.

8. a
On engines equipped with constant speed propellers, engine power output is indicated on the manifold pressure gauge. Therefore, the onset of induction system icing is indicated by a reduction in manifold pressure. Another indication of the presence of carburetor ice is when manifold pressure increases after carburetor heat is applied.

9. c
In the induction system of an unsupercharged engine, the air pressure from the venturi to the intake valve is always less than atmospheric pressure when the engine is running. Therefore, of the options given, the highest pressure exists in the carburetor air scoop where ram air enters the induction system.

10. c
When carburetor heat is used, warm air is routed into the carburetor. Since warm air is not as dense as cool air, the application of carburetor heat when it is not needed results in a slight decrease in power and an increase in cylinder head temperature which could lead to detonation.

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