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Topic Options
#35914 - 05/09/11 08:52 PM Carb Temperature Gauge?
Cessna Dude Offline
Diamond Pilot

Registered: 10/21/09
Posts: 6628
Loc: San Antonio, TX
How many of you have a carburetor temperature gauge installed installed in your plane? If so, how helpful and do you recommend?
_________________________
Due to certain economic uncertainty, the light at the end of the tunnel has been turned off until further notice.
Cessna 172, C172, C-172, Cessna Skyhawk fan.
www.cessna172club.com



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#35916 - 05/09/11 09:06 PM Re: Carb Temperature Gauge? [Re: Cessna Dude]
wrecksum Offline
SVP Public Relations
Platinum Pilot

Registered: 09/26/10
Posts: 2704
Loc: Dominican Republic
We have one. I always check it but over here in the tropics it's unlikely that we would need carb heat anyway.
In a temperate climate I think it would be a useful thing to have as it takes away the "shall I or shan't I ? factor of carb heat use.
_________________________
A person without a sense of humour is like a wagon without springs.It's jolted by every pebble in the road.

Cessna 172, C172, C-172, Cessna Skyhawk fan.
www.cessna172club.com

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#35918 - 05/09/11 09:18 PM Re: Carb Temperature Gauge? [Re: wrecksum]
Rusty Rudder Offline
Diamond Pilot

Registered: 02/26/10
Posts: 5143
Loc: NorthEast
I have one, but, I consistently use carb heat out of the RPM green arc and on decents of substantial altitude changes. I use the temperature monitoring that displays the carb temp and fix it on cyl head temp only. So for me, carb temp doesnt get used, carb heat does.
_________________________
Take-off's are optional, landings are manditory



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#35930 - 05/09/11 10:49 PM Re: Carb Temperature Gauge? [Re: Rusty Rudder]
bushpilot Offline
Second in Command

Registered: 01/30/11
Posts: 135
Loc: north eastern Ontario, Canada
The way we were taught on the 150s and 172s was to always put the carb heat on as part of the pre landing procedure and leave it on till landed. That is the way I have done it for 37 years and it works well. The advantage of having the carb heat on when on descent is not only to prevent carb icing but it enrichens the carb mixture and if you suddenly have to abort the landing and go around it makes sure the engine does not stall or stumble when you open the throttle quickly.

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#35938 - 05/10/11 12:18 AM Re: Carb Temperature Gauge? [Re: bushpilot]
EdW Offline
Club Sponsor
Gold Pilot

Registered: 11/21/10
Posts: 1218
Loc: Just east of Graceland
Originally Posted By: bushpilot
The way we were taught on the 150s and 172s was to always put the carb heat on as part of the pre landing procedure and leave it on till landed. That is the way I have done it for 37 years and it works well. The advantage of having the carb heat on when on descent is not only to prevent carb icing but it enrichens the carb mixture and if you suddenly have to abort the landing and go around it makes sure the engine does not stall or stumble when you open the throttle quickly.
Check your POH or AFM. Some aircraft show carb heat as "check", then "as required". With the wet sump engines we have on our airplanes the intake tubes run right through that place where the warm oil is kept (sump), so it is always heated to a degree [no pun intended, I think]. In some instances it might be detrimental due to higher carb air temps and overly rich mixtures.


Edited by EdW (05/10/11 12:19 AM)

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#35946 - 05/10/11 12:51 AM Re: Carb Temperature Gauge? [Re: EdW]
Nightowl Offline
Club Sponsor/Speed Demon
Gold Pilot

Registered: 02/14/10
Posts: 1826
Loc: Northwest lower Michigan
Carb temp is reported by our JPI 700 engine analyzer, but haven't paid much attention to it. The Lyc O-360 has not shown any tendency for making ice. Rarely use carb heat unless descending/landing in cold precip.

John
_________________________
CP-ASEL-IA
'77 C172N, AirPlains 180 hp conversion

Our sigmap has been flown entirely using aircraft with capabilities at or below those of the C-172.


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#35953 - 05/10/11 05:20 AM Re: Carb Temperature Gauge? [Re: Nightowl]
Willie Offline
Platinum Pilot

Registered: 12/28/10
Posts: 2797
Loc: Ft McMurray Alberta Canada
Food for thought
During a training flight last winter,the company owner told us not to use carb heat
We went up at -18C in a 172
Theory being that carb heat would raise the carb temp to icing temperature
Worked OK on that flight
_________________________
Flying is the 2nd greatest thrill known to man
Landing is 1st

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#35960 - 05/10/11 08:21 AM Re: Carb Temperature Gauge? [Re: Willie]
wrecksum Offline
SVP Public Relations
Platinum Pilot

Registered: 09/26/10
Posts: 2704
Loc: Dominican Republic
There seems to be a lot of mythology attached to carb heat, its function and use so let's see if we can make it clearer.

Why Carb Heat?
As air passes through the carburetor into the engine it passes through a venturi, which is a reduced diameter part of the intake tube. This forces the air to speed up at this point and causes a pressure drop in the air.This pressure drop is proportional to the amount of air passing through and then this value can be used by the carb to determine the amount of gas to be sucked into the mixture. Assuming no change at this time in the mixture control, the air/fuel mixture ratio will remain constant at different throttle openings.

One phenomenon of reducing the pressure of the air is that the temperature of the air in the throttle body drops cooling the metal around it and encouraging water drops to condense and subsequently freeze causing an ice obstruction inside the carb and impeding the smooth flow of air to the engine.Unless something is done, this can cause blockage an engine stoppage.

We don't like engine stoppage do we?

(Notice now that this does not apply to injected engines which have a different system to dose the fuel and don't have a venturi as such.)

How does it work?

The manufacturer has provided us with a control which allows us to heat the air entering the carb in the hope that this will increase the temperature above freezing point.
This is done by passing the intake air over the engine exhaust pipe which is very hot thus heating the intake air and melting the ice and preventing further formations of ice.Different engines have different susceptibilities to icing at varying throttle settings so you have to be on the lookout for rough running in cool and damp conditions especially.

Why is it not always on then?

The drawback is that the mixture has been optimised for best operation by using 'Jets' which are little calibrated holes allowing the fuel to get into the mixture at the correct amount to maintain smooth running and max performance.

When you heat the intake air, the air density decreases, (Less molecules in the same volume) so this changes the air/fuel mixture and, as the jets have not changed passes a richer than normal mixture into the engine which can cause loss of power.Weakening the mixture manually could fix this but at the cost of further reducing power so it's not normally done except in continued cruise if needed.
Continued use of an over-rich mixture can lead to plug fouling, carbon build-up and increased bore wear.

The other aspect is that this system also provides us with an alternate source of air should the air filter or intake be blocked which is Good, But, the air is now unfiltered allowing potentially damaging particles into the engine so long term use could lead to increased engine wear.






Edited by wrecksum (05/10/11 08:24 AM)
_________________________
A person without a sense of humour is like a wagon without springs.It's jolted by every pebble in the road.

Cessna 172, C172, C-172, Cessna Skyhawk fan.
www.cessna172club.com

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#35965 - 05/10/11 08:48 AM Re: Carb Temperature Gauge? [Re: wrecksum]
wrecksum Offline
SVP Public Relations
Platinum Pilot

Registered: 09/26/10
Posts: 2704
Loc: Dominican Republic
Part Two

You all got bored reading that so I've split it up.

When and How to use it?

Short answer...Read the book!

I can only quote from my book which states as follows:

"Carburetor heat should not be used during take off unless it is absolutely necessary for obtaining smooth engine acceleration "

As your carb is fitted with an accelerator pump, and the mixture correct for the field, then carb heat will not prevent acceleration die-out or hesitation during a go-around.If this occurs the the carb settings are incorrect and must be fixed.
Italics my comment.

Cessna Again:
"Carburetor ice, as evidenced by an unexplained drop in RPM, can be removed by application of full carb heat.Upon regaining the original RPM, use the minimum amount of heat (by trial and error) to prevent ice from forming. Since the heated air causes a richer mixture, readjust the mixture setting when carb heat is to be used continuously in cruise flight."

Under Cold Weather Operations.
"Take off is normally made with carb heat off.
Carb heat may be used to overcome any occasional roughness due to ice.
When operating at temperature below -18C avoid using carb heat.Partial heat may increase carb air temp to the 0 to 21C range where icing is critical under certain atmospheric conditions."

Your POH may be different so please check it.

That's what Cessna say and who am I to disagree with them

Know your systems ,POH and read all the books you can get if you're still uncertain about it.

Sorry it's long, but brevity is overrated anyway.
_________________________
A person without a sense of humour is like a wagon without springs.It's jolted by every pebble in the road.

Cessna 172, C172, C-172, Cessna Skyhawk fan.
www.cessna172club.com

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#35980 - 05/10/11 11:52 AM Re: Carb Temperature Gauge? [Re: wrecksum]
bnt1983 Offline
Safety Pilot

Registered: 03/26/11
Posts: 93
Loc: USA
I wish to add my 2 cents to this bank.

I felw in Seattle last week for about 10 hours in an O-300 powered 172. The weather in Seattle was somewhere around 45 - 50 degrees F and we were hitting the freezing level around 3,500 - 4,000 AGL in the soupy clouds. We were getting carb ice on every almost every flight. I am very hard of hearing and since the O-300 runs so smooth it can be hard to detect. It started to make me nervous that there was a possibily of not catching it in time and being able to remedy the icing. We were able to fly around with partial heat on (1/4-1/2) and had no more issues.

Take carb ice seriously please it may bite you someday.

On the other hand in my dad's C-177 (O-320) we have never had carb ice. But we do all of our flying in that airplane in South Dakota and Nebraska, typically a much drier climate.

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#35981 - 05/10/11 11:58 AM Re: Carb Temperature Gauge? [Re: bnt1983]
bnt1983 Offline
Safety Pilot

Registered: 03/26/11
Posts: 93
Loc: USA
Dad's C-177 had a carb temp gauge but we needed the real estate and elected to remove it. I'm not sure the cost of installing one is worth the pain, but just be aware of how the airplane is breathing as she is keeping you alive.

If your airplane has a constant speed prop maybe it would be worth while to install a carb temp.

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#36013 - 05/10/11 05:47 PM Re: Carb Temperature Gauge? [Re: bnt1983]
Lee T. Hargic Offline
Gold Pilot

Registered: 08/13/10
Posts: 1631
Loc: Louisville, KY
Wrecksum... Very nice. thanks.
_________________________
"A smart man learns from his mistakes. A wise man learns from the mistakes of others" -Anonymous

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#36065 - 05/11/11 05:58 AM Re: Carb Temperature Gauge? [Re: Lee T. Hargic]
Rusty Rudder Offline
Diamond Pilot

Registered: 02/26/10
Posts: 5143
Loc: NorthEast
They say carb icing can occure up to 80 F with high humidity during certain terms and conditions. Great info WS, POH is the ultiimate authority. One other point, I've been taught it's all or nothing, some condtions with partial will promote carb icing... the other to remember is, some POH reccomend carb heat during extreme precip flying, heavy rain, apply carb heat, excessive rain can overwhelm the carb intake filter, carb heat is as others have indicated, not filtered air from within the cowl.
_________________________
Take-off's are optional, landings are manditory



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#36100 - 05/12/11 12:17 AM Re: Carb Temperature Gauge? [Re: bnt1983]
Nightowl Offline
Club Sponsor/Speed Demon
Gold Pilot

Registered: 02/14/10
Posts: 1826
Loc: Northwest lower Michigan
Originally Posted By: bnt1983
I wish to add my 2 cents to this bank.

I felw in Seattle last week for about 10 hours in an O-300 powered 172. The weather in Seattle was somewhere around 45 - 50 degrees F and we were hitting the freezing level around 3,500 - 4,000 AGL in the soupy clouds. We were getting carb ice on every almost every flight. I am very hard of hearing and since the O-300 runs so smooth it can be hard to detect. It started to make me nervous that there was a possibily of not catching it in time and being able to remedy the icing. We were able to fly around with partial heat on (1/4-1/2) and had no more issues.

Take carb ice seriously please it may bite you someday.

On the other hand in my dad's C-177 (O-320) we have never had carb ice. But we do all of our flying in that airplane in South Dakota and Nebraska, typically a much drier climate.

We've owned two Continental-powered airplanes (O-200 in a C-150D, and O-300 in a C-172H), and I can attest to the fact that both of these engines would make ice if you didn't stay on top of it. Almost had an engine shut down in flight in the 150 due to carb ice.

Our other two 172s have both been Lycoming-powered and showed little or no tendency to make ice. I'm told it has something to do with the way air is routed around the engine - the Lycomings just naturally keep the carb warmer. Works for me.

John
_________________________
CP-ASEL-IA
'77 C172N, AirPlains 180 hp conversion

Our sigmap has been flown entirely using aircraft with capabilities at or below those of the C-172.


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#36123 - 05/12/11 10:18 AM Re: Carb Temperature Gauge? [Re: Nightowl]
Don Tedrow Offline
Gold Pilot

Registered: 07/16/10
Posts: 2084
Loc: Bastrop, TX
I was going to install carb temp function when I installed my UBG-16 last fall, then discovered that my carb wasn't drilled for one. (It's a lycoming O-320) I decided I was NOT going to dismount the carb to have it drilled and tapped.

I would probably have some type of monitor if I flew a Continental, but Lycomings just don't make much ice in the southwest. If I flew where icing, (airframe and induction) coditions were more common, I'd probably think differently. I can't ever recall getting carb ice on a Lycoming. Plug fouling much more common.

FWIW, the C182 owners I know say that carb ice is at least as likely, if not more so, during TO and climb as descent. The real reason for carb heat during approach is because it's almost impossible to detect at low power settings; until you need the power...
_________________________
1972 C172L



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