carb heat and power reduction

[MidlifeFlyer]

Probably. But he's going to face the same issue when he gets to a CS prop.

Maybe. I put my prop to the low pitch/high rpm setting on final so it's not an issue in the quasi-emergency of an unanticipated go-around (yeah, I know, you're supposed to assume the go-around on every landing)

But even so, there are plenty examples of what you say. Different airplanes, for example, have different procedures on whether you retract flaps or gear first on a go-around. There are things that are there because it's a function of the system. Doesn't mean that things that can be kept simple should not be.

 

[ppragman]

Maybe. I put my prop to the low pitch/high rpm setting on final so it's not an issue in the quasi-emergency of an unanticipated go-around (yeah, I know, you're supposed to assume the go-around on every landing)

But even so, there are plenty examples of what you say. Different airplanes, for example, have different procedures on whether you retract flaps or gear first on a go-around. There are things that are there because it's a function of the system. Doesn't mean that things that can be kept simple should not be.

Constant speed wise, I wait until the prop is off of the governor before I move the lever forward. It freaks out the pax if you move the lever forward to early, plus, when I'm by myself, I don't like the noise. If I need to go around, prop and power go in simultaneously, if the airplane has carb heat that goes in after prop and power are in.

 

[nosehair]

An added reason is that during cruise, you may have already iced up the idle ports inside the throttle plate; closing the throttle could result in instant engine failure. I add carb heat for 10-15 seconds before reducing power in order to melt any pre-existing ice.

This is the reason the carb heat should be applied a few seconds prior to an anticipated power reduction in a school training environment - to establish a habit pattern that always works, and makes the student aware of what he is doing; applying the heat and listening for any change other than the one he got on run-up.

Pulling the throttle first when the icing conditions are just right will cause an instantaneous icing coat to form in the carburator like the frost from your breath on a mirror.

It is fool-hardy to teach carb heat after power reduction.

Sure, when you have learned a safe habit, and gained some experience, you can modify your actions to apply to the situation in the moment, but this is not a safe training habit.

 

[BrewMaster]

Carb icing is prevalant(sp?) in both high and low power settings, the REASON the low power setting is emphasized to students is that it is more crucial during that low power setting when a quick addition of power might be needed. Not because you are going to have that much more carb ice.

You are slowing down anyways, so by pulling that carb heat prior to that power reduction you aren't gonna miss the few extra RPM's that the carb takes away. You are reducing your power setting by more than what the carb takes away.

By pulling carb heat prior to a power reduction, you can't really hurt anything (already slowing down) but by doing it afterwards, you could be affected by the carb ice(how much I'm not sure)

You are going to be ok by pulling it prior, but you are taking a little more risk by pulling it after. Just make you sure you actually turn it on and you have a standardized procedure to ensure you do it!

 

[CoffeeIcePapers]

Carb icing is prevalant(sp?) in both high and low power settings, the REASON the low power setting is emphasized to students is that it is more crucial during that low power setting when a quick addition of power might be needed. Not because you are going to have that much more carb ice.

That is partially true, but I believe there is a higher chance for blockage at lower power settings. If you look at the throttle valve, at lower power settings, it is almost perpendicular to the flow (obviously), so there is more surface area for the ice to stick as it accumulates. The nearly closed throttle valve also lowers the pressure, making the temperature drop more.

http://www.faa.gov/ats/afss/newyork/ENROUTE.htm
http://www.flycorvair.com/carbice.html

Carb ice forms at the pressure drop point, which occurs at the
restriction to flow. At a reduced power setting, the throttle plate is the
restriction, not the venturi. At 2,200rpm and 12"map, the throttle plate is barely cracked open. Right at this crack is the idle fuel port, a tiny hole. A minute film of ice could cover it in an instant.

 

[BrewMaster]

Good point. The lower power setting will have a greater build up, but both have the potential. I guess that just reinforces why pulling carb heat before is a better idea.

 

[matt152]

I talked it over with the chief CFI. Basically, they standardized power first then carb heat to get students into the idea of always making the change in power first, primarily for go-arounds, touch and go's and missed approaches. So if that's the way he wants it, that's the way I'll teach it.

Thanks for all the excellent input.