Carb Ice on 180 hp

[Hottshot]

Have you experenced and what were the conditions?

[donknee]

I find that the O-540 can make ice pretty easy. I asked around about carb ice detectors and one that had good regard was the "iceman"

http://www.aircraftspruce.com/catalog/i ... etect2.php

All I have to do is fly by a cloud and it starts to pick up ice. Scouting for elk hunting sites last fall up by Randle and Packwood, up close to the ceiling it would start running rough...not where you want to experience power loss. It would be good to know if it is ice and not some other problem. Pulling the carb heat is easy.

Anyone else out there with suggestions?

[a64pilot]

If you already have a UBG-16, then the carb thermistor is cheap. I'm sure you could program the alarm to go off at a preset temp? I'm injected, so I haven't done it.

[donknee]

The iceman is different. It has a fibreoptic "eye" that senses the coating of ice rather than just a temperature. Some engines are subject to icing and for whatever reason others are not. Knowing that there is actually carb icing which inhibits performance vs. a temperature range in which ice can form, is the difference. I don't have one, just curious to hear from those who do.

[Hottshot]

I have yet to have the problem, I know the guys with the Carbed 540's fight it all the time but with the 180 it don't seam to be an issue as much??

[TomD]

Ditto O-540's icing.

Had a very tense night flying from Eastern WA across Snoqualmie pass one winter. Spent about as much time w/ carb heat on as off.

180's may be a whole different situation.

TD

[flyer]

WUP

The Continental engines may have more of an issue with carb icing than the Lycomings. The Carb and intake manifolds, I think, are in some way different.

I do fly in a fairly dry climate. I have not yet had any carb icing problem with my previous 0-320 or my present 0-360.

flyer

[mike davis]

In my plane when I had a 160 never had a problem same plane with 180 I have it happen 3 times in 60 hrs always on high humid days I am running 2400 rpm 20-21 in man. pressure. Maybe running it to easy as both engines have same induction and HA-6 carb.

[a64pilot]

You have a point Mike, the lower the manifold pressure, the more drop in pressure there is and therefore the higher drop in temp in the carb venturi.

[Flyin'Dutch']

Only a few hours in a M7-180 but dont recall it to be a problem.

The O-540 on the other hand, very prone in most conditions. Suspect that comes with the engine being derated.

[maules.com]

Flyindutch, nice to see you here.

Carb ice.... I would agree with donknee re the magic eye detactor which shows actual ice developement rather than temp and guesswork.

[montana maule]

My O 540 B4B5 is very susceptible to carb ice. I've notice it most at the low power settings I use for patrol work. The carb temp probe will be showing as high as 42 F and I will be losing m.p. due to carb ice. Maybe it's building up on the throttle body and not at the top of the venture where the probe is located.

[Walter Atkinson]

There are four operational regimes in which carb ice can be a problem—in order of frequency of occurrence, they are:

A) Startup
B) Take-off and climb
C) Cruise
D) Power reduction for landing

Yes, the *least likely* time to encounter carb ice is on the power reduction to land! Let's examine each of these scenarios and discuss why.

A) On the initial startup of the day: You are dealing with a cold engine and cold carburetor body and all of a sudden it's sucking air through the venturi. When the OAT and humidity are right--BINGO, carb ice. As a result, it is important to check that the carb heat is working BEFORE take-off (during the run up). The purpose of this carb heat application is two-fold... First to be sure the mechanism is working and second, to be
certain there is no ice present in the carburetor. If there is no ice present, there will be a drop in power as noted in rpm drop as the heated air enters the carburetor, thereby reducing the number of air molecules available for combustion. If there is ice present from the startup, there will be an increase in rpm as the ice is cleared from the carburetor and proper power is restored.

B) During high power application during take-off, there is a maximum flow of air through the carburetor which creates the greatest temperature drop across the venturi. Carb Ice can develop as a result.

C) During cruise, as the aircraft changes climates, OATs change, humidity changes, etc. and the engine is often WOT, the venturi again is having it's maximum temperature drop for the given situation.

D) During the power reduction to land, there is the least chance of developing carb ice! There is the lowest power being applied and, therefore, the lowest temperature drop across the venturi!

Now, that understood, why do we apply Carb heat as a matter of routine during the least-likely phase of flight?

The answer is simple. Before take-off we have checked the carb heat and know the condition of the carburetor before applying power. During take-off and climb we will know if ice begins to develop as we will see a power loss as the ice builds up. In cruise, we will also see a power loss as ice forms in the carburetor.

It is during the low power condition of preparing to land, that if ice builds up, we will have no way of knowing it. The power is already low and in some cases the engine is not producing any thrust at all. If the carburetor ices up and we need to go around, we will be unpleasantly surprised as we push the throttle forward and we continue to descend!

Soooooo, in the event of an urgent need for power, add throttle, the engine will come to your aid since there is Carb heat ON and no ice present, THEN push the carb heat in (off) to let the engine attain maximum power. It is common to see pilots push the carb heat in, then add power. I think this is not optimal. If the atmospheric condition is conducive to the formation of carb ice, turning the carb heat off, then adding power is a suboptimal idea... remember, the second most frequent time to encounter carb ice is during a high power application!

My recommendation is to add power, then carb heat OFF. That way, if you encounter carb ice as you need to go around, at least you'll already be developing power and know it. That likely scenario is power IN, carb heat off, power loss as ice then develops, then carb heat back ON--you'll make the go-around. If you push the carb heat in first and the conditions are right for ice formation, the likely scenario is Carb heat OFF, power in,
CARB ICE, power loss before you even get any....... and just when you don't need that headache! There is a reasonable argument for doing it either way.

MANY are now using Carb heat in cruise to improve fuel vaporization and improve F:A balance in carbed engines. MANY are able to run smoothly LOP as a result. The side benefit is that those who are doing this end up with a carb temp above freezing where it is not possible to have carb ice at all. Something to ponder......

[Walter Atkinson]

**My O 540 B4B5 is very susceptible to carb ice. I've notice it most at the low power settings I use for patrol work. The carb temp probe will be showing as high as 42 F and I will be losing m.p. due to carb ice. Maybe it's building up on the throttle body and not at the top of the venture where the probe is located**


THAT is a very good observation. That's INDUCTION icing--commonly on the air filter.

[a64pilot]

MANY are now using Carb heat in cruise to improve fuel vaporization and improve F:A balance in carbed engines. MANY are able to run smoothly LOP as a result. The side benefit is that those who are doing this end up with a carb temp above freezing where it is not possible to have carb ice at all. Something to ponder......

Something else to ponder is that whenever you are using carb heat, you are bypassing the airfilter.