To carb heat or to not carb heat.....

[Christopher Murphy]

Someday somewhere that carb heat will be needed. If you dont have it available it will become a very high pucker factor experience.

Ive had my 0320 ice up between the hangar and the runway and Ive had airborne battles with carb ice. I know from the previous posts there is a lack of understanding of carb ice and how you deal with it. Flying around with the carb heat on is a bad idea.

Cm

[Sam Buchanan]

Originally Posted by Christopher Murphy

Someday somewhere that carb heat will be needed. If you dont have it available it will become a very high pucker factor experience.

Ive had my 0320 ice up between the hangar and the runway and Ive had airborne battles with carb ice. I know from the previous posts there is a lack of understanding of carb ice and how you deal with it. Flying around with the carb heat on is a bad idea.

Cm

Yep, the two instances of carb ice I recall in the 21 years of flying my O-320 carbed RV-6 occurred during long taxi to the runway. The runup was a little rough and a few moments of heat cleared it up. Otherwise, carb heat has never been used inflight, but I only fly VFR.

The O-200 in the biplane is a first-class ice maker, however.

[David Paule]

Get rid of the carb temperature gauge. Install a carburetor ice detector instead.

I have one in my non-RV, and it's worked great for more than twenty years. It has a probe that senses ice and a panel light that comes on when there is ice. No light, no ice. Sometimes partial heat will cure it but occasionally it needs full carb heat.

The light will come on at low voltage, too, FYI. It's a purely analog system.

The only source I know of is Aircraft Spruce.

Since my RV-3B engine has a carburetor, I bought one of these for that plane.

Dave

[blaplante]

Got carb ice at 500' AGL while flying around Catalina Island California at relatively low power. Sunny 60 degree day. If you aren't familiar with the location, pull it up and estimate your pucker factor. Engine - o-320 Lycoming, updraft carb. Clearly near the water the humidity was up there.... [Wasn't in an RV]

Also one other time (same plane), again at a lower power setting.

For the advice given on not bothering with it until you've determined you have ice... keep in mind the amount of carb heat is proportional to the engine power. If you don't have much power (due to carb ice), you won't have much heat in the muff, and the carb heat is going to be pretty slow to work. Not a good thing if your carb heat is marginal as several have noted above.

[longranger]

With a carburetor, I’d rather have it and not need it than need it and not have it.

[Taltruda]

Originally Posted by longranger

With a carburetor, I’d rather have it and not need it than need it and not have it.

I don’t think he’s debating on not having carb heat available.. I think he meant when to use it or not based only on a temp gauge...

[Bicyclops]

Latent heat of vaporization of the fuel literally sucks heat out of the air and lowers the temperature in the venturi a bunch. This is one of the reasons you can get carb ice at relatively high temps.

The carb on a Lycoming mounts right to the hot oil sump and on a Continental, it mounts to a cold air plenum. That's why the Conties will ice up so easily. I've never seen carb ice with a Lyc at high throttle. Doesn't mean it can't happen if the air is moist enough though. As others have mentioned, it's a lot more likely at low power settings - eg. taxi or descent.

A poster said to never use partial carb heat. I agree, if we are using carb heat for ice removal. We can, however, use partial carb heat to aid fuel vaporization while trying to get lean of peak in non-icing conditions. That and just a little tiny bit of throttle reduction to add some turbulence to the fuel air mixture can make the difference. With a touch of carb heat, you can often lean much further without running rough.


Ed Holyoke

[Roadjunkie1]

Originally Posted by Sam Buchanan

Yep, the two instances of carb ice I recall in the 21 years of flying my O-320 carbed RV-6 occurred during long taxi to the runway. The runup was a little rough and a few moments of heat cleared it up. Otherwise, carb heat has never been used inflight, but I only fly VFR.

The O-200 in the biplane is a first-class ice maker, however.

Originally Posted by Christopher Murphy

Someday somewhere that carb heat will be needed. If you dont have it available it will become a very high pucker factor experience.

Flying around with the carb heat on is a bad idea.

Cm

For decades, my preflight check includes carb heat, and left on for a count of at least 5 (and my hand left on it to make sure I put it back in) and see if there is a rise in RPM. You leave it on as it may take a few seconds or longer for the ice that is there to be heated away. Pulling it on and shoving it right back in is not going to tell you anything except, perhaps, that it is working.

Ice may form at any time. As fuel goes from a liquid to an "aerosolized gas", that takes energy, which is heat from the environment and that evaporative loss of heat is the reason ice can form: decrease in temperature as the air is mixed with the fuel. As long as there is moisture in the air, ice can form. I've seen studies that show ambient temperature sometimes is not a factor. Don't ask me where; that was years ago. Evaporative cooling: works in my house coolers as well.

That said, I do not use it in flight unless I suspect ice: usually from a perceived drop in RMP. In all the hours I have in both O-320 (carburetor) SuzieQ and the C-90 Cub, I have had maybe one or two episodes of carburetor ice in the Cub and cannot remember what the circumstances were. Most of my perceived RPM drops seem to be attributed to "auto-rough".

As it is a habit born of decades of flying, I will pull it before my turn from downwind to base on both airplanes. Consistency. I would rather pull carb heat for no reason than to have the engine go quiet on base or short final

Warm air is less dense and cruise with heat on makes your engine less efficient: there is less air going into the cylinders. What in the world did we do before carb temperature probes? The Cub has......well, a carburetor. Throttle, mixture, carb heat. And has been flying since 1946.........

IMHO; your mileage may vary......... What is your usual routine? Stick with that..........

[Planecrazy232]

I use about 1/3 carb heat at altitude during cruise. I find it evens out my temps and allows me to lean past peak with my O-360 RV6.

[BobTurner]

For many years I flew a 182 with an O-470 which, as others have noted, seems more carb ice prone than many other aircraft. I got carb ice a few ‘typical’ times (taxiing in 50 F pouring rain, flying low over the bay at 59F, high humidity) and at least once atypical (IMC, 100% humidity but 40F, full power climb) time. A few thoughts:
1. The recommendation to pull carb heat for landing is for landing approaches made at idle power, because under such conditions carb ice can actually shutdown the engine without the pilot knowing.
2. As others noted, most of the cooling is due to the evaporation of fuel.
3. In some engines (like the O470) the mixture distribution is awful. Partial carb heat can increase fuel vaporization, which may help improve the distribution. In the 470 this effect resulted in more power from the engine, even though the most optimum cylinder produced less, most notable at altitude/full throttle.