Excellent lesson. The instructor mentioned something I was waiting to hear and have not otherwise. That is, that upon passing through the Venturi the accelerated air then expands into the larger diameter portion of the flow passage / throat of the carb. Am I mistaken in thinking that it is this expansion of the air that causes the cooling - just as a compressor driven refrigeration system works? Much text in sources refer to the 'acceleration of the air' through the narrowed region that causes cooling...that doesn't seem to jibe with physics. TIA
Good question. While both expansion of the air (increase of volume) causes it to cool per "Boyle's Law", there is cooling due to the evaporation of the fuel. Due to a fuel leak in the cockpit, I once had the unfortune experience of having a 10 minute foot bath in 100LL, and I can tell that it is a very very cold experience - it was summertime in Illinois and I would not have been surprised to have seen frostbite on my toes. Maybe a little bit of hyperbole in my comment there, but it was a very cold experience. SC
Because as she said, ice can form anytime the air is below 70 with high humidity. It is not a function of power setting. My father managed to get himself killed back in 1967 while spotting salmon in Alaska. He had descended into cloud, got a restart, and flew into the side of a mountain upon climb out. With 3 heavy fishermen in a Cherokee 140, he was pushing his luck already!
OK, I’ve experienced carburetor icing in a 150 at night when the temperature was 63 degrees. It was the first time I ever experienced a carb Icing in 40 years of flying. I was doing pattern work and I was entering downwind when I reduced my power from max to 2300 which was still in the green arc, the engine immediately ran rough and the plane started to vibrate. As soon as I pulled carburetor heat within 30 seconds it’s smooth out. When the butterfly valve is closed, airflow is restricted so you’re air speed in the Venturi slows down. It must form ice because it allows the water molecules to freeze just as a lower turning propeller will gather ice near the root as opposed to a high rpm propeller, which virtually does not collect any ice on the blade tips that are almost near Mach speed.
Thanks for the clarity
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Excellent lesson. The instructor mentioned something I was waiting to hear and have not otherwise. That is, that upon passing through the Venturi the accelerated air then expands into the larger diameter portion of the flow passage / throat of the carb. Am I mistaken in thinking that it is this expansion of the air that causes the cooling - just as a compressor driven refrigeration system works? Much text in sources refer to the 'acceleration of the air' through the narrowed region that causes cooling...that doesn't seem to jibe with physics. TIA
Good question. While both expansion of the air (increase of volume) causes it to cool per "Boyle's Law", there is cooling due to the evaporation of the fuel. Due to a fuel leak in the cockpit, I once had the unfortune experience of having a 10 minute foot bath in 100LL, and I can tell that it is a very very cold experience - it was summertime in Illinois and I would not have been surprised to have seen frostbite on my toes. Maybe a little bit of hyperbole in my comment there, but it was a very cold experience. SC
SALUTE,Thankyou Mam🎉
Superb teaching👍🏼
From
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My pleasure 😊
So why does ice form at lower rpm when higher rpm has a much greater airspeed through the Venturi which results in even colder temperature?
Higher engine heat due to burning of a lot more fuel at high RPM?
because the butterfly valve is partially closed at lower rpm increasing the venturi effect
Because as she said, ice can form anytime the air is below 70 with high humidity. It is not a function of power setting. My father managed to get himself killed back in 1967 while spotting salmon in Alaska. He had descended into cloud, got a restart, and flew into the side of a mountain upon climb out. With 3 heavy fishermen in a Cherokee 140, he was pushing his luck already!
OK, I’ve experienced carburetor icing in a 150 at night when the temperature was 63 degrees. It was the first time I ever experienced a carb Icing in 40 years of flying. I was doing pattern work and I was entering downwind when I reduced my power from max to 2300 which was still in the green arc, the engine immediately ran rough and the plane started to vibrate. As soon as I pulled carburetor heat within 30 seconds it’s smooth out. When the butterfly valve is closed, airflow is restricted so you’re air speed in the Venturi slows down. It must form ice because it allows the water molecules to freeze just as a lower turning propeller will gather ice near the root as opposed to a high rpm propeller, which virtually does not collect any ice on the blade tips that are almost near Mach speed.
@@ConvairDart106 So why do people pull carb heat when we pull the rpm below the green arc but not before reducing power for stalls or when landing?