Carb Heat
Elsewhere, I posed some questions about carb heat, to offer a new poster some research points. I'm not sure if the poster has taken up the challenge, but it's been a few days, so I owe some thoughts to the points I raised. Everyone is eagerly encouraged to offer their thoughts/experiences/exceptions to these points:
Some GA planes have a carb heat some don't - which are which and why?
Airplanes with fuel injected engines do not have venturi carburettors, so are naturally immune to carb ice formation.
What is the relationship to carb heat and alternate air?
Alternate induction air is a design requirement for certified planes. The carb heat doubles as the alternate air control. Alternate air is not filtered (by design requirement), and usually drawn from within the cowling.
Do planes which do not have carb heat still have alternate air?
Yes, it's still a design requirement.
Do planes have an alternate air control if not a carb heat control?
Some planes have an alternate air control, others have a spring loaded door, which pops open if the manifold pressure demands airflow and the main induction is blocked
What information is necessary for you to apply partial carb heat?
If you have a carb air temperature indicator, you can use it to apply partial carh heat, to just melt ice. Otherwise it is recommended to apply full carb heat, if you need to use it.
If you apply carb heat for a rough running engine, and the engine then runs worse, what should you do? Why? For how long?
When you apply carb heat, you're melting any ice which may have accumulated in the carburettor. As it melts, the water will enter the engine, and the engine may run worse. Keep the carb heat applied at least until the engine continues to run smoothly, though you may want to leave it applied for the rest of the flight in those conditions.
If you apply carb heat, and it's not enough, what two engine controls can you adjust to get a little more carb heat? Adjust how?
Leaning the mixture may increase the exhaust gas temperature - so hotter carb heat air, and closing the throttle a little will reduce the amount to [moisture containing] air entering the carb, so reduce the demand for heating.
When might you need to urgently apply carb heat, but have not encountered carb icing conditions?
If something else blocks your main induction air filter
Why should you never use carb heat while taxiing?
Carb heat is unfiltered air, so any dust, grit, etc. will be ingested by the engine.
If your plane is equipped with an indicator associated with carb heat, what is that indicator?
A carb air temperature indicator will show you the temperature at the venturi.
What does the yellow arc on that indicator mean? Where will the yellow arc be on the scale? Will there be any green or red lines on that indicator?
The yellow arc on the carb air temperature indicator is the icing range, so avoid continued operation of the engine in that range. Applying carb heat will heat out of the range (in most cases).
Will a piston engined airplane which does not have a carb heat control always have an electric fuel pump? Why?
If a piston engine does not have a carburettor, it is fuel injected. Fuel injection systems always require pumped fuel pressure.
Could an airplane which does have an electric fuel pump also have a carb heat control?
Yes, you can have fuel pumped carburettor equipped planes, so understand your systems!
Where does the heat resulting from the application of carb heat come from?
The heated air comes from a muff around the exhaust system/muffler
If you have had an engine failure, will applying carb heat help you get it started again? Why?
If your engine has stopped as a result of carb ice, you will no longer have exhaust heat to heat carb heat air, so getting it running by normal means is unlikely - start looking for a forced landing place!
What would be a practical warm outside air temperature where you would be unconcerned about carb icing?
I've seen charts up into the 20+ C temperature range, it's not just a cold day thing...
What other atmospheric factors will affect carb icing?
The moisture content of the air
Can you get carb icing on the ground?
Yes, so if in doubt, a brief application of carb heat prior to takeoff, and then assure expected full power is available before committing to take off.
If you're flying in very well below freezing air, is carb heat a risk?
Much less so, as moisture in very cold air will pass through the carburettor venturi frozen, so not accumulate there.