Why should carburetor heat be limited when operating an engine on the ground?

Why should carburetor heat be limited when operating an engine on the ground?

• A. It can cause a rich fuel mixture.
• B. It reduces air density.
• C. The air entering the engine when carburetor heat is applied is not filtered.
• D. It increases engine RPM.

Answer: (B)

Carburetor heat adds heat to the air going into the engine, which makes the air less dense. Since engine power depends on the mass of air available for combustion, heating the air reduces the amount of oxygen per unit volume and thus lowers horsepower. On the ground you want maximum power for taxi and takeoff, so you limit carburetor heat to only what’s needed to prevent or clear icing, then switch back to unheated air as soon as possible. The other choices describe effects that aren’t the primary reason for limiting carb heat on the ground: heating air doesn’t inherently guarantee a richer mixture in a fixed metering system, it’s not a matter of filtration in this context, and it doesn’t increase engine RPM.

Carburetor heat adds heat to the air going into the engine, which makes the air less dense. Since engine power depends on the mass of air available for combustion, heating the air reduces the amount of oxygen per unit volume and thus lowers horsepower. On the ground you want maximum power for taxi and takeoff, so you limit carburetor heat to only what’s needed to prevent or clear icing, then switch back to unheated air as soon as possible. The other choices describe effects that aren’t the primary reason for limiting carb heat on the ground: heating air doesn’t inherently guarantee a richer mixture in a fixed metering system, it’s not a matter of filtration in this context, and it doesn’t increase engine RPM.