# Tag Info

33

You should always pull the carb heat when throttling back no matter the conditions for 3 reasons: Ice forms from moisture (duh!), and there's much more moisture in hot tropical air than cold arctic air, so being in a tropical location does not lower the icing potential. The temperature drop is caused by the Venturi Effect which aerates the fuel in the ...

19

Carb heat use is not related to OAT, it's related to moisture and how it can turn to ice in the carb, causing the engine to stop. Carb ice can form at any outside air temperature, which is why you will not find any checklist or POH item for an aircraft with normally aspirated engines telling you to check OAT before activating carb heat. You just do it. I ...

19

I can think of two reasons: The efficiency of heat machines depends on the difference between lowest and highest temperature in the cycle, relative to the highest temperature, as formulated first by Sadi Carnot. Simply put, the efficiency cannot be larger than $$\eta_{max}≤\frac{T_{max}-T_{min}}{T_{max}}$$ where all temperatures are expressed relative to ...

11

You have mentioned OAT, but remember there are 2 variables for potential icing - the other being Dew Point. You (roughly) 85F OAT could easily fall into Serious Icing at glide power for a wide range of dew points.

8

Heating the air causes the air to be less dense. We all know that as you climb, the air becomes less dense and you have to lean the mixture for better performance and fuel economy. This also applies to Carb Heat. If you don't lean the mixture after applying Carb heat, the mixture will be richer and fuel economy will be reduced.

6

Thou shalt use Carb Heat. You said you fly in tropical area where the temperature is 30°C. Warm tropical air has a lot of moisture as others have mentioned. The venturi effect can drop the air temperature in your carburetor's venturi by as much as 38.89°C (or 70°F) according to this wikipedia article on Carburetor icing. Thus if you're flying around in ...

5

Because, in engaging the carburetor heat, you are decreasing the density of the air entering the engine with the same fuel flow, thereby richening the mixture. At idle power, if the throttle idle set screw is not properly adjusted, there is a risk of an engine failure from too rich a mixture entering the engine. The idle power carb heat check is a good way ...

4

Most of the temperature drop is from fuel evaporation downstream of the venturi, causing ice from ambient humidity to form on the throttle plate (injected engines also have venturis and throttle plates for fuel and air metering, but because no fuel is being introduced there, so there is no evaporative cooling, there is no need for carb heat and they just use ...

2

Carlo Felicione has given a great explanation of why carb heat at idle would need to be checked. The incoming air heated by the exhaust manifold would be less dense than the incoming air without carb heat. If the fuel mixture is too rich, it may cause the engine to quit. Some may call it flooding the engine. The most common time for this to be an issue is on ...

2

Carb heat is not specifically required by regulation. What is required by the following rule is a means to prevent ice accretion: 14 CFR 33.35 Fuel and induction system. (b) The intake passages of the engine through which air or fuel in combination with air passes for combustion purposes must be designed and constructed to minimize the danger of ...

1

It's because the spider duct that connects the carb to the intake runners going to the cylinders is cast into the oil sump and the carb mounts directly to that. So the carb gets a lot of engine heat that warms the carb body by conduction. Also, it's getting radiant heat from the sump directly above. On Continentals the carb is insulated from the engine by ...

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