Winter Flying PSA: Don't Use This Carb Ice Chart

Pasting the "do not use" chart here for quick reference. It doesn't have a legend, but the regions look identical to the "use this" chart.

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Tbe chart is not an intended to be demonstrative. It’s just an illustration.
 
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Sierra_Hotel said:
The regions are identical, but the axes are totally wrong...
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Yes. 100% humidity is found where the temp and dewpoint are the same. In the "do not use" chart they are ten degrees apart, a physical impossibility. And probably a typo.
 
There was a still-earlier version of this chart showing an artistically obvious and impossible strip of near max icing where the chances of the icing were suddenly less likely. The world doesn't work this way. This version persisted in various publications for years.
 
Mikey52 said:
What is an average temperature drop in the Venturi?
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I found this explanation on wikipedia

"Carburetor icing is caused by the temperature drop in the carburetor, as an effect of fuel vaporization, and the temperature drop associated with the pressure drop in the venturi. If the temperature drops below freezing, water vapor will freeze onto the throttle valve, and other internal surfaces of the carburetor. The venturi effect can reduce the air temperature by 39 °C (70 °F). In other words, air at an outside temperature of 38 °C (100 °F), can drop to −1 °C (30 °F) in the carburetor. Carburetor icing most often occurs when the outside air temperature is below 21 °C (70 °F) and the relative humidity is above 80 percent. The risk of carburettor icing is significantly increased at partial power settings (such as when power is reduced during descent), due to the cooling effect of the partly-closed throttle."
 
Clip4 said:
Tbe chart is not an intended to be demonstrative. It’s just an illustration.
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There have been a couple studies of carb ice by bench testing engines at different power levels resulting in charts very similar to the one I posted (but nothing like the erroneous one). One by the Canadian DOT which I can't seem to locate and another by the FAA / DOT where they use a continental O-200A.
 
Here is a question. Relative humidity in a cloud is 100%. So is carb heat normal procedure for flying in the clouds?
 
Who is making these charts? The “corrected” chart has two “serious” categories?
 
AA5Bman said:
Who is making these charts? The “corrected” chart has two “serious” categories?
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Read the whole label…they’re substantially different power settings. (And if you read the whole label, you’ll note that there are actually three “serious” colors. Maybe we can take that to mean carb icing can be serious.)
 
Yeah, I get that, call me a booger-picker but most scales I’m familiar with don’t go Light > Serious > Moderate > Serious
 
AA5Bman said:
Who is making these charts? The “corrected” chart has two “serious” categories?
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The chart is copy/pasted so many times it's hard to say but there is at least one version from the FAA in 1982 (see my previous post) and another version from the Canucks in 1970 (see this aviation stack post for some details on that one).

If you want the full deets on the categories I think it's in that PDF in my last post - I've only skimmed it for a few details. I assume it corresponds to power settings / RPM ranges used in testing.
 
AA5Bman said:
Yeah, I get that, call me a booger-picker but most scales I’m familiar with don’t go Light > Serious > Moderate > Serious
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Oh I see your point - I think that's because the lower two categories are for cruise / glide power and the upper two are for climb... well... actually that is more confusing now that I look at it.....
 
AA5Bman said:
Yeah, I get that, call me a booger-picker but most scales I’m familiar with don’t go Light > Serious > Moderate > Serious
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It doesn’t…it goes light>moderate>serious (blue>orange>red), light>serious>serious (blue>yellow>orange), and serious (red)
 
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