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Icing at different throttle settings..?

I tend to do a lot of PFLs… in fact most of my landings are pfls.

Another group member has argued that it’s a bad idea not to come in with power, because keeping some power trickling through means you’re less likely to ice up.

My own reasoning is that icing is a distinct possibility either when you’re at idle or a low power setting, but that it’s probably less likely when you are at idle because the pressure drop and hence temperature change at the venturi is likely to be less. On the other hand, I suppose you could be running slightly richer at idle which might nullify this.

Any ideas as to which is actually the case?

Carb or fuel injection?

Administrator
Shoreham EGKA, United Kingdom

Carb

It’s not the pressure drop that causes using, it is the evaporation of fuel. Carb heat is the only solution, or FI of course.

The elephant is the circulation
ENVA ENOP ENMO, Norway

Carb icing has three sources – pressure drop, fuel evap and humidity %. They all work in conjunction.

Pressure drop causes a temperature drop of 3C at idle. Fuel evaporation causes a temperature drop of 25-30C. If the conditions are favourable for carb ice, the throttle setting is only of academic interest.

This is why FI engines are not susceptible to carb ice.

The elephant is the circulation
ENVA ENOP ENMO, Norway

Hmmm.

Pressure drop causes a temperature drop of 3C at idle. Fuel evaporation causes a temperature drop of 25-30C. If the conditions are favourable for carb ice, the throttle setting is only of academic interest.

That doesn’t make any sense.

The throttle setting affects the airflow velocity in the venturi which affects the temperature drop!

Administrator
Shoreham EGKA, United Kingdom
Why doesn’t it make sense? Heard about refugiration principles? Evaporating fuel is a very good refugirator. Anything evaporating is.
The elephant is the circulation
ENVA ENOP ENMO, Norway

This video shows the formation of carb ice on a motorcycle engine. Although this engine has a fuel jet with a moveable needle (unlike a fixed jet aircraft carb) it is apparent that the ice forms due to fuel evaporation, which blocks the fuel jet. There is only a small amount of ice, and the air intake path is not plugged.



Last Edited by Silvaire at 29 Apr 13:52
25 Posts
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