Question on proper use of carb heat

How to keep the Cessna 170 flying and airworthy.

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Triplepac
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Joined: Sun Apr 08, 2012 3:50 pm

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
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flyboy122
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Re: Question on proper use of carb heat

Post by flyboy122 »

ghostflyer wrote: 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.
I don't use it much in my O-360 Lycoming converted 170 either. The only time it ever iced up was in long, low power decents like when shooting a VOR approach or getting vectored around by ATC flying at min power to avoid running to far out. Even then it only happened a couple times, and the engine responded instantaneously to application of heat (usually before I even get the control all the way out). I keep an eye out for it, but don't use it proactively as it adds more work to go arounds and makes the engine run unnervingly slow at idle. I figure the odds of an issue there are higher than the incidence of carb ice.

I have a carb temp gauge and I look at it regularly, but in reality it is kind of useless. Where I live (Wisconsin) it's in the yellow "ice range" at least 50% of the time.

DEM
Triplepac
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Re: Question on proper use of carb heat

Post by Triplepac »

gahorn,
Thanks so much for the reference. It's weird. I can log in but I get the "you are not authorized to view this post" message. Probably user error somehow...
Triplepac
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cessna170bdriver
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Re: Question on proper use of carb heat

Post by cessna170bdriver »

Triplepac wrote:gahorn,
Thanks so much for the reference. It's weird. I can log in but I get the "you are not authorized to view this post" message. Probably user error somehow...
Triplepac
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flyguy
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Re: Question on proper use of carb heat

Post by flyguy »

Just another goofy OT - well it is about carb ice - from Ole Gar. Over the years had lots of fun with hopped up VW engines on various running gear. We lived on a 1000 acre Oxbow lake in northwest Missouri. In the winter, after the like ice would support 1500 - 2000 pounds, we would race our dirt bikes, our dune buggies and various other toys on the frozen surface. On one of my Dune Buggies I had a pair of Weber 44 IDF carbs on an 2180CC air cooled VW engine. With studded tires and doing a lot of digging and sliding, - there was lots of powdered ice as we plowed around our race course. About every 15 minutes we would have to pull that buggy off the course and de-ice those big bore carbs. We learned not to wait too long or when the ice would melt we would get too much water in the intakes.

As for my '52 170B, owned since 1972, I've had my share of carb ice. Never got too concerned as the technique was hammered into my head by those who had scared themselves silly by waiting too long. Just like the Cessna explanation John posted and George's post, stated very clearly watch everything with eagle eyes and be pro active.
OLE GAR SEZ - 4 Boats, 4 Planes, 4 houses. I've got to quit collecting!
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flyguy
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Re: Question on proper use of carb heat

Post by flyguy »

I have been a member on and off for several times, but not currently a member. Back in April I got carb icing on the lyc 0360 in my 53 170B and had to put it down in some small trees. Long story short there was enough damage, we decided to part it out.
One post asked about carb ice in Lycoming Conversions. This excerpt came from Jon Blocker's email to Bruce
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flyguy
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Re: Question on proper use of carb heat

Post by flyguy »

Aryana wrote:I had 44 IDF Webers on my '67 Porsche 912. Those were great carbs, but a son of a gun to get the jetting dialed in properly.


We have had "Herman", our '67 912, with those 44s since 1987. And yes they are touchy to tune. They also, on rare occasions get a little ice in just the right conditions. Do you still have your 912?
OLE GAR SEZ - 4 Boats, 4 Planes, 4 houses. I've got to quit collecting!
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