Question on proper use of carb heat

How to keep the Cessna 170 flying and airworthy.

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voorheesh
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Re: Question on proper use of carb heat

Post by voorheesh »

Not to beat a dead horse here, but if one of you guys have a minute, could you explain how a carb temp guage works? Does it indicate a temp in the venturi where carb ice will not happen? What is involved with putting it in our carbs on C145/O300? Thanks.
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GAHorn
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Re: Question on proper use of carb heat

Post by GAHorn »

N9149A wrote:... I typed that without thought having just read your post which included the following:
gahorn wrote:I have experienced carb ice only ONE TIME in my 170 with the C-145/O-300 engine.
I do remember thinking how strange that you had only experienced carb ice once. But then you do live in Texas. Of course I should have thought that through a bit more and realized with your experiance you would have had to have more carb ice than once, even in Texas.
Ah-ha! That clarifies me for myself! :roll:

What I meant by that comment is, ....that in only one instance (of the many many times I've checked for carb ice by pulling the carb heat knob).... have I ever discovered a noticeable amount of carb ice actually being present in my own 170. It was evidenced by the usual result of a drop in RPM due to the application of heat...followed by a noticeable slight roughness and increase in RPM as the ice melted away. (I've noticed that many airplanes seem to have their own personalities with regard to their propensity to accumulate carb ice. My own 170 has only done it in significant amounts that one time, but i've experienced it more frequently in other airplanes, particularly with O-200 engines and other smaller Continentals.)

Most of the times I've pulled the carb heat is due to a perceived loss of RPM ...which resulted in NO ice being indicated. This is probably because I, check it/actuate it, from time to time during a flight...but also anytime I detect a loss of RPM (such as due to a slight increase in pitch/climb, etc.) ... and like yourself, ANYTIME I plan to make a reduction in power I FIRST apply carb heat to confirm no ice exists as well as to warm the carb before power reduction.

In the traffic pattern, as I enter downwind, I pull FULL carb heat for about 15-30 seconds to confirm the carb is clear and to warm the carb, then I remove it for the remainder of the approach. (That's a personal habit/technique because I hate the inefficiency of running around with carb heat applied.) It's not what is taught to most pilots during their training, because so many instructors prefer to instill an overly-cautious approach in their clients.
In my own view and experience, after the carb is cleared/warmed, then no ice is likely (and I've never experienced it) for the next couple of minutes of the approach and landing.... and no chance exists for me to forget to remove it in case of a go-around.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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GAHorn
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Re: Question on proper use of carb heat

Post by GAHorn »

voorheesh wrote:Not to beat a dead horse here, but if one of you guys have a minute, could you explain how a carb temp guage works? Does it indicate a temp in the venturi where carb ice will not happen? What is involved with putting it in our carbs on C145/O300? Thanks.
The probes mount in your carb at a carb-mfr'r provided position. The majority of Marvel-Schebler carbs have provision for the probe.
Image

"...the B-5 is the only probe that installs at the throttle valve - the critical icing point in fuel induction systems..."

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

(and there are other selections also available): http://www.aircraftspruce.com/menus/in/ ... es_ei.html
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
voorheesh
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Re: Question on proper use of carb heat

Post by voorheesh »

Thanks, That sounds like a good guage to have.
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mit
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Re: Question on proper use of carb heat

Post by mit »

1000 hours in 170's since early 80's have had carb ice a few times. I don't use it unless the temps are in the range. Flown through a cloud or two.
Tim
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Paul-WI
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Re: Question on proper use of carb heat

Post by Paul-WI »

Thanks for all the great replies. A wealth of different opinions as well as information. I guess I should have clarified that I do have a Carb Temp Gauge in the plane. Also, I am very aware of the cause and effects of carb ice in carburetors having been working as an auto mechanic for the past 30 years (anyone ever driven a Ford Tempo in cold damp weather and have the heat door in the air cleaner fail will knows what this will do). I guess that maybe I am being over cautious during cruise flight. I do apply carb heat when taxing in cold weather as well as apply full carb heat on the downwind. The only exception is in the summer. I take the carb heat off on final as I find that during hot weather if I apply throttle with carb heat, it wants to hesitate as it is running to rich with carb heat on.

Paul
Paul
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mongo2
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Re: Question on proper use of carb heat

Post by mongo2 »

Has anyone used the Westach 2A3-1 guage and the 399W probe?
It looks like drilling out the lead plug and tapping to 1/4-28 could get a little dicey if things aren't perfect, let alone the mfg warranty...

RC
Rick Champagne
C-170A N5475C
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ghostflyer
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Re: Question on proper use of carb heat

Post by ghostflyer »

Yes when my 170A had the Continental engine carby icing often occurred just on flare and the engine stopped . I used Carby on base leg and the start of finals but turned it off just before mid finals in case of a go round . It was a attention getting situation . But with the Lycoming clone there has never been a carby ice situation. I have done hundreds of hours with the Lycoming clone now and don't bother using carby at all. During our winter I was flying in near clear air and then experienced diamond dust icing on the wings . My thoughts went immediately to carby icing . The engine never missed a beat . I dropped to a lower altitude into warmer air as the wings were now white and not silver . There wasn't any performance loose at all .
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mongo2
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Re: Question on proper use of carb heat

Post by mongo2 »

On the 170A you mentioned, was it previously installed, or did you do the install?

RC
Rick Champagne
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BeeMan
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Re: Question on proper use of carb heat

Post by BeeMan »

Two thoughts about use of carb heat:
1. A bunch of years ago I owned a C180 (O-470) that showed signs of a serious carb ice problem after major overhaul. Symptoms included rough running but didn't show up as a change in manifold pressure. The cause was eventually diagnosed as an intake leak and poor mixture distribution that could be overcome somewhat by application of carb heat.
2. I often fly when it is very cold and very dry (Alaska Arctic high conditions) and have had my O-300D stumble badly on application of throttle after descent to check out a possible landing site on skis. As I recall the carb heat was not on when this happened because of course it was too cold and dry to experience carb ice. The engine responded immediately upon application of carb heat, which I take to mean that the carb was too cold to properly atomize the fuel. Anyone have this experience or a different take on my understanding of the cause?
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pdb
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Re: Question on proper use of carb heat

Post by pdb »

BeeMan wrote:Two thoughts about use of carb heat:
1. A bunch of years ago I owned a C180 (O-470) that showed signs of a serious carb ice problem after major overhaul....

2. I often fly when it is very cold and very dry (Alaska Arctic high conditions) and have had my O-300D stumble badly on application of throttle after descent to check out a possible landing site on skis. As I recall the carb heat was not on when this happened because of course it was too cold and dry to experience carb ice. The engine responded immediately upon application of carb heat, which I take to mean that the carb was too cold to properly atomize the fuel. Anyone have this experience or a different take on my understanding of the cause?
It might be that the very low temp hinders fuel vaporization but it could also be that when the air is very cold, and hence very dense, the mixture is too lean if the mixture was previously adjusted at warmer temperatures. Adding carb heat then enrichens the mixture. It's the opposite of leaning at high density altitudes for peak power and smooth operation. Have your mechanic take a look at it.
Pete Brown
Anchorage, Alaska
N4563C 1953 170B
http://farm3.staticflickr.com/2366/2527 ... 4e43_b.jpg
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blueldr
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Re: Question on proper use of carb heat

Post by blueldr »

I used to have passengers that became concerned if I didn't apply preventive carburetor heat on the downwind leg, but I do not remember EVER atually getting any carburetor ice on my particular C-170B in any meteorological condition.
My old Stinson L-5G with the Lycoming O-435-11 engine was more prone to carburetor icing, particularly in high humidity conditions.
BL
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ghostflyer
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Re: Question on proper use of carb heat

Post by ghostflyer »

In answer to mongo 2 about the 170A . I fitted the STC myself .used Harry delicker STC . Very good STC.
Triplepac
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Re: Question on proper use of carb heat

Post by Triplepac »

Just a rude discovery this past winter to pass along. My plane lives in the Pacific Northwest and unfortunately, it lives in the rainy environment, outdoors. I've lived with the ice prone O-200, C-85 and my O-300. For some reason, my O-300 seemed to be especially prone. It got so bad, I was getting really concerned. Over the summer, we looked at the carb heat box, the controls, and even the carb itself for we weren't 100% sure it was carb ice. To regress, I have a 1956 172 with what was the original Bolen conversion to a Taildragger. Anyway, I flew my plane out for my annual and a couple of days later, I got a text message with a picture of an alarming amount of water that was trapped in the Scat tubing leading to the Carb Heat Muff. The Front Baffles were acting like a big rain barrel. Pulling the Carb Heat Control was actually ADDING Carb Icing! I promptly added Cowl Inlet Covers and a Carb Temp Gauge. I'm happy to report that I can get another 3 months of utility out of my plane without fretting...

As for the proper use of Carb Heat... In the airlines, you have two concepts; Anti-Ice and De-Ice. Two completely different ideas and Jets generally don't even have De-Ice. I use Carb Heat as an Anti-Ice. Turn on, leave on... unless you're fretting... :roll:
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GAHorn
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Re: Question on proper use of carb heat

Post by GAHorn »

Triplepac wrote:Just a rude discovery this past winter to pass along. My plane lives in the Pacific Northwest and unfortunately, it lives in the rainy environment, outdoors. I've lived with the ice prone O-200, C-85 and my O-300. For some reason, my O-300 seemed to be especially prone. It got so bad, I was getting really concerned. Over the summer, we looked at the carb heat box, the controls, and even the carb itself for we weren't 100% sure it was carb ice. To regress, I have a 1956 172 with what was the original Bolen conversion to a Taildragger. Anyway, I flew my plane out for my annual and a couple of days later, I got a text message with a picture of an alarming amount of water that was trapped in the Scat tubing leading to the Carb Heat Muff. The Front Baffles were acting like a big rain barrel. Pulling the Carb Heat Control was actually ADDING Carb Icing! I promptly added Cowl Inlet Covers and a Carb Temp Gauge. I'm happy to report that I can get another 3 months of utility out of my plane without fretting...

As for the proper use of Carb Heat... In the airlines, you have two concepts; Anti-Ice and De-Ice. Two completely different ideas and Jets generally don't even have De-Ice. I use Carb Heat as an Anti-Ice. Turn on, leave on... unless you're fretting... :roll:
Triplepac, there was a discussion many years ago in these forums (sorry, I don't recall which) ...in which I referred to a Cessna Service letter recommending that flexible hoses (SCAT/SCEET) used for Carb Heat, etc be pierced at their lowest points to drain water from rain or washing, in order to prevent that puddled water from being ingested by the carburetor. You (and everyone else) might wish to consider that.

Addendum: OK I found the discussion: http://cessna170.org/forums/viewtopic.php?f=32&t=6548
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
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