Use of Carb Heat

[bobbysamd]

Carb heat

Pull it on during any time you operate at reduced power. Such asbeginning your decent from downwind to base. Typically, in a 172 youreduce power from 2000 rpm for your downwind to 1500 rpm; at that time,pull on the carb heat. Pull on carb heat without fail when practicingsimulated emergency landings, steep spirals, etc., anytime you are inflight and you reduce power to idle.

You really don't want to use carb heat for the hell of it during normalcruising because the hot air enrichens the mixture unnecessarily.

Of course, one can get carb ice at high power settings. I'll neverremember the time I was flying a 172 on a nice spring afternoon inOklahoma. The throttle was forward with power set at 2400 rpm but I waslosing power. Couldn't figure out why - but I pulled on the carb heatand shortly thereafter, all was well. Classic carb ice conditions thatday - temperature between 32 and 70 and humidity over 50%.

Finally, I found this FAA article on carb ice. Enjoy!

 

[Tinstaafl]

Carby ice in the Islanders I used to fly over the North Sea was a common occurrence. After a while it became automatic to apply carby heat every 10 or 15 mins or so, and on for all reduced power settings.

Sometimes I'd have to have carby heat hot for most of the flight.

 

[avbug]

Application of carburetor heat prior to power reduction is important, both to ensure that no ice exists, and to prepare the carburetor for that initial reduction when landing. Ice is most likely to form, and to form agressively at greater throttle settings, for reasons already mentioned. At idle, the throttle plate is closed, and the only place for ice to form is directly adjacent or after the throttle plate where the airflow is serviced by the idle jet.

If this is the case and idle icing as formed adjacent to the throttle plate, the remedy is to open the throttle; the little bit occluded by icing is now a big bit and not readily affected by the icing. Stumbling at this point indicates formation of ice (or a rich or lean mixture), and the engine should be cleared as required using ice.

If the engine is stumbling, I would strongly discourage trying to lean out the mixture. Especially on departure when close to the ground (such as on a go-around). This isn't the time to troubleshoot, but to take the fewest and most effective steps to handling all possible problems at once. This includes going rich on the mixture, rather than leaning it out. Unless the carburetor is grossly misadjusted, going rich isn't going to put your engine out...and unlike a turbine engine, you have spark plugs to keep it firing anyway. Go rich in a rouch engine situation prior to applying carburetor heat. After you ensure you do have a continuing power source, you can lean as required.

Another very common misapplication of carburetor heat occurs during ground operations. Often pilots are taught to apply it for only a moment during the runup. They are told this is to ensure an RPM drop (in fixed pitch normally aspirated installations)...then to push it back in and forget it. Carburetor heat should be left on for fifteen seconds to ensure that it has indeed removed any built up ice. One should also ensure upon shutting off the carburetor heat that the engine does return to the same level of operation that it had before the carb heat was applied. Application of carb heat is best done immediately prior to entering the runway for departure, or on the runway prior to brake release (if doing a braked departure).

 

[Peanut gallery]

Now we know the Continental anwer

POH POH POH and did I mention the POH

 

[SiuDude]

The carburetor on a Lycoming engine is attached to the oil pan, whereitabsorbs a lot of heat from the engine. I have never used carb heatinthe air in a Piper or the aircraft that I fly now (Lycomingengine).Cessnas are a different story. The carb is mounted farther fromtheengine, and thus absorbs less heat. You will not be able to getawaywith not using carb heat for very long.

The green arc is there for a reason.

 

[minitour]

That really doesn't make sense to me. All of the cessnas I'veflown have had Lycoming O-235 or O-320 (plus an IO-360 but thatwouldn't apply here) in them. How would that differ from thePipers?

-mini

 

[BD King]

Blah, Blah. Listen to AvBug.

.Now here is the question. You have carb ice and cannot get rid of it. What do you do? AvBug, you are not allowed to reply.

 

[SiuDude]

That really doesn't make sense to me. All of thecessnas I'veflown have had Lycoming O-235 or O-320 (plus an IO-360 butthatwouldn't apply here) in them. How would that differ from thePipers?

-mini

It wouldn't. Lycoming equipped Cessnas are less succeptible to carbice. However, if the conditions are perfect, any carburetor willdevelop induction ice (I've seen it first hand). It just may come as abigger surprise in a Lycoming.

 

[SiuDude]

Blah, Blah. Listen to AvBug.

.Now here is the question. You have carb ice and cannot get rid of it.What do you do? AvBug, you are not allowed to reply.

Lean the engine to "best economy?" If that doesn't work, make lemonade?

 

[minitour]

It wouldn't. Lycoming equipped Cessnas are lesssucceptible to carbice. However, if the conditions are perfect, anycarburetor willdevelop induction ice (I've seen it first hand). It justmay come as abigger surprise in a Lycoming.

oh okay...now I get what you were saying...misunderstanding on my part...

my bad

-mini

 

[avbug]

.Now here is the question. You have carb ice and cannot get rid of it. What do you do? AvBug, you are not allowed to reply.

Must...not...answer. Trying...very...hard. Cannot...hold...out...any...

Pick something soft to land on. Use a rubber band to hold the control yokes together, crawl out on the cowl and use a squirter bottle in the induction intake to apply glycol. Think warm thoughts. Increase angle of attack until aircraft stalls, apply hard rudder (right or left), enter spin and hold it until impact. Everyone knows that when the engine quits a spin always results and always ends in a fatality. With a big fireball at the end. A really big one.

Or you could just shut it off and let the ice melt...stopping airflowthrough the carb removes the very thing that's causing the ice to form...

Of course, you're probably thinking about causing a backfire to clear the carb. Personally, I'm against that action for several reasons, but suffice it to say it's not a good idea. If you've no other choice, then one does what one must. But in general it's not a good idea, and certainly shouldn't be performed unless you have no other choice. If you're put in the position where a forced landing is going to result in damage anyway, and you're not going to recover that engine, and it's your only one (or your last one, as the case may be), the have at it. Open the throttle and lean her out until she bangs away, or lean her and throw the throttle open. Give her a shot or two of primer first and then open at the same time while running lean. A little like you probably used to do to scare folks while cruising mainstreet in dad's pickup truck.

You did do that, didn't you? Or is that too redkneck for most folks?

 

[nosehair]

like you probably used to do to scare folks while cruising mainstreet in dad's pickup truck.

You're talkin' when they had "clutches", arentcha?

 

[BD King]

AvBug is correct. When there is no choice, backfire through the carb. Flip the mags off and turn them back on. Does it work? Yeah. I had a load of carb ice in a C-140 and could not get rid of it (cable came off). It was stick it in a field. Back fire worked.

 

[minitour]

You're talkin' when they had "clutches", arentcha?

LOL

Funny story. From the student pilot days.

Told my Aunt "yeah I have to get more comfortable at doing stalls in the airplane."

She says, "It's easy, just pop the clutch and the engine will start right up"

I must have stared at her for 10 minutes with that "you're f*cking kidding me, right?" look on my face...

 

[A Squared]

AvBug is correct. When there is no choice, backfire through the carb. Flip the mags off and turn them back on. Does it work? Yeah. I had a load of carb ice in a C-140 and could not get rid of it (cable came off). It was stick it in a field. Back fire worked.

That's not a backfire, that's an afterfire. A backfire is an ignition of fuel air mixture in the induction system. What you get if you turn the mags off and back on is an explosive ignition of unburned fuel air mixture built up in the exhaust system. It is very unlikely to do anything to the carburator, Ice or no ice. It very likely may damage your exhaust system though. When I was a foolish kid, I thought it was pretty cool to do this with my dad's pickup truck, until I blew the muffler up. Looked like someone had lit off a cherry bomb inside it. My dad was not amused. Anyway, although this is sometimes incorrectly referred to as a backfire, it is in fact not.