But my other instructor said...

S

shdw

Well-Known Member
we have to put on the carb heat anytime we fly slowly. <Me> What about for descent? No, only if your flying slowly while descending!!!

Keep it going, I am sure every instructor has at least 1 "but my other instructor said..." that they have heard. I would love to hear some of the interesting things that other instructors have, according to their students, taught them.
 
I find that about 80% of the time the student either misunderstood the other instructor, or took what the other instructor said and blew it WAY out of proportion.
 
Roger said:
I find that about 80% of the time the student either misunderstood the other instructor, or took what the other instructor said and blew it WAY out of proportion.
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Of course, it is more about what kind of interesting things students have come up with. I am just looking for some good stories :)
 
We can't go up, it's overcast. (I had 25 hour simulated instrument time training for my IRA. It was well above minimums, and I found out a week later who took his other students up IMC during their training. Other than instrument conditions, there were no airmets or sigmets to speak of)
 
shdw said:
we have to put on the carb heat anytime we fly slowly. <Me> What about for descent? No, only if your flying slowly while descending!!!

Keep it going, I am sure every instructor has at least 1 "but my other instructor said..." that they have heard. I would love to hear some of the interesting things that other instructors have, according to their students, taught them.
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I prefer to have the carb heat on in slow flight if I'll be out of the green arc while I'm flying around, but I usually don't pull power to descend, only to slow down.
 
I hate to hear,
"Instructor XYZ never taught me that!"

Leaves me to think what instructor down the line will have him say that about me.
 
Roger said:
I find that about 80% of the time the student either misunderstood the other instructor, or took what the other instructor said and blew it WAY out of proportion.
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That is so "on target" that it should be carved in gold.

Many unchecked stories have that same feature.
 
Ask for references:

http://www.aero-news.net/news/genav...097BF-A647-4181-8408-6E24C8D2AB38&Dynamic=1#d

FAA-Carb-Ice-Chart-0609a.jpg
 
GlenA said:
"But the King video said we HAVE to suck on the stall warning horn!"
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Screw those videos I had a student watching them and all he learned was how to call things like "abeam the numbers" the "key point." I mean common do you really have to change nearly 100 year old language to teach someone how to fly?

There were 4 or 5 other things like this, he ran out of cash though so I didn't get to see the XC side of it. I don't think they are bad in what they accomplish, but it makes teaching very annoying when you don't know the "king" terminology and your student starts busting it out.
 
Codyjp said:
care to elaborate?
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The only effect that airspeed has on carb ice is the same as typical wind chill. The faster you go the colder the air will feel when it hits you, relative of course to the airs temperature. These changes are fairly minimal on the effect of carb ice, in 0 degree temperature a change from 0 knots to 50 knots will only introduce a 9 degree colder air temperature.

The greater cause of carb ice lies in the position of the butterfly valve, this is that thing that if you see a drag racer rev up you see the red valves open and close sticking out of the hood. We know Bernoulli's principle says that if we speed air up conversely we will lower its temperature and its pressure. Take a volume of air traveling into a 2-3 inch opening (approximate guess for intake size) and then shoving it through a quarter inch hole.

I don't have the information to show some numbers here for you, but the change in temperature from this effect is much greater than that of typical wind speed effect. Not only that the opening being much smaller introduces less surface area which can be cooled more quickly. Ice almost always forms on small areas first, that is why we check our temp probe in icing situations as it is typically of a small surface area.

So to sum up: smaller surface area plus a decrease in temperature from the venturi effect caused by lower throttle settings plays the majority of the role in a carb ice situation. Sure there are other factors, such as airspeed, but their roll is fairly negligible.
 
shdw said:
The only effect that airspeed has on carb ice is the same as typical wind chill. The faster you go the colder the air will feel when it hits you, relative of course to the airs temperature. These changes are fairly minimal on the effect of carb ice, in 0 degree temperature a change from 0 knots to 50 knots will only introduce a 9 degree colder air temperature.
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Um...isn't wind chill just how it FEELS to the human skin? That would not effect the formation of carb ice-only actual temperature and humidity would do that.
 
Roger said:
Um...isn't wind chill just how it FEELS to the human skin? That would not effect the formation of carb ice-only actual temperature and humidity would do that.
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If it feels that way to human skin why wouldn't it feel that way to a metal carburetor? As air impacts a surface at a given speed it causes that surface to get colder than the actual air, touch your car after you drive down the road on a cloudy day. The metal on the car is colder than the outside air temperature because of wind chill.

Edit: For a little more in depth, as air passes over a surface energy is transferred, in this case in the form of heat. Air moving 10 knots at over any given surface at any temperature will have a certain volume of air go over that surface for a given period of time. At 20 knots for the same given amount of time a larger volume of air will pass over the surface allowing more heat/energy to be transferred.
 
Because the carburetor doesn't have nerves.
shdw said:
The metal on the car is colder than the outside air temperature because of wind chill.
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Um..No. It just feels that way because metal at a given temperature is more efficient at taking heat away from your hand than air at the same temperature is. The car feels colder than the air even if it has been sitting still.

That would be physically impossible. If the car were cooler than the air around it, it would be transferring its heat to the surrounding air. You cannot use 32° air to cool your car to, say, 10°.
 
Roger said:
Because the carburetor doesn't have nerves.

Um..No. It just feels that way because metal at a given temperature is more efficient at taking heat away from your hand than air at the same temperature is. The car feels colder than the air even if it has been sitting still.

That would be physically impossible. If the car were cooler than the air around it, it would be transferring its heat to the surrounding air. You cannot use 32° air to cool your car to, say, 10°.
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Ok let's make this simple I can figure out thermal transfer later without babbling on here. So are you saying wind speed/airspeed has no effect on carb ice or it does but not for this reason?

I think I see what you mean that the wind chill formula is heat transfer off of a human not off of a metal surface, is that what your getting at?

I don't know what I was thinking saying cooler than the outside air, I meant cooler than surfaces not exposed to the wind.
 
Roger said:
You cannot use 32° air to cool your car to, say, 10°.
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Yes, that would violate the Second Law of Thermodynamics.

Edit: One of the amusing things I have read a number of times is that marble is always 11 degrees (or 14, 12, etc) below the ambient temperature of the room. Ah, no.
 
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