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  #1  
Old 10-31-2018, 12:31 PM
rag rag is offline
 
Join Date: Feb 2012
Location: Holmen, WI
Posts: 57
Default Carb Temperature - How to use? - Useful?

I replaced the panel (and firewall forward) on my RV4. I'm learning all the neat things that the Skyview has to offer. One is carb temperature. I have not figured out how to use the info it is providing. It seems to be in the "red" most of the time (32 +- 10 degrees). OAT's in the low 40's. Older posts indicate the carb temperature is of limited value due to the inaccuracy. Wondering if others would have more current info as to if and how they use it to determine carb ice conditions? What is the typical temperature they see as compared to OAT - in cruise and on the ground. Thanks!
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  #2  
Old 11-01-2018, 05:12 PM
RV7 To Go's Avatar
RV7 To Go RV7 To Go is offline
 
Join Date: May 2011
Location: Ontario, Canada
Posts: 321
Default CAT

Carb air temp can be used to check if your carb heat is working. One of the guys on the field noticed with his 6A that the carb heat gave him about a 50 degree rise on the ground but in the air he had no rise in temp unless he pulled hard on the carb heat knob and held it. He had a ratcheting cable but not locking. I don't have CAT in my 7 yet but I did hook up the carb heat with a locking cable which does give an RPM drop both on the ground and in the air. There is a chart for probable carb ice condition which you could use to set your Dynon range. FWIW.

Al
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  #3  
Old 11-01-2018, 05:20 PM
David Paule David Paule is offline
 
Join Date: Dec 2009
Location: Boulder, CO
Posts: 5,054
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On my carbureted Cessna 180, I have an ARP carb ice detector. It has a light that comes on when there's ice - no interpretation needed: light=ice. When the light comes on, I pull carb heat, and things improve.

Actually, it senses ice before I can, so instead of things improving, they stay good. Even better.

It's been reliable over the last 600-700 hours.

I like it so much I bought one for my RV-3B project, too. Aircraft Spruce sells them.

Dave
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  #4  
Old 11-01-2018, 09:19 PM
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N941WR N941WR is offline
 
Join Date: Jan 2005
Location: SC
Posts: 12,887
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Each of our planes is slightly different, so this may or may not be helpful.

On my -9, with both the old O-290 and the current O-360, when I would slow down for landing, the carb temperature would rise without the use of carb heat.
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RV-9 (Yes, it's a dragon tail)
O-360 w/ dual P-mags
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SC86 - Easley, SC
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  #5  
Old 11-02-2018, 05:46 AM
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snopercod snopercod is offline
 
Join Date: Aug 2016
Location: Asheville, NC
Posts: 2,122
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I installed carb temp to troubleshoot a "vapor lock" problem I was having. It didn't turn out to be vapor lock, but rather, the carb was getting heat soaked from the oil sump on a hot day. It got hot enough to boil the fuel in the bowl and cause the engine to sputter and die from too rich a mixture. I fixed that by doing two things: 1. inserting a piece of 1/16" phenolic (with a gasket on either side) between the oil sump and the carb, and 2. Adding more air to the oil cooler. Problem solved.

These days I check the carb temp gauge when pulling power back on approach to see if I need carb heat. On my O-290-D2, I have never seen the temp get down into the danger zone. Like Bill said, the gauge also confirms that carb heat is working during runup.
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  #6  
Old 11-02-2018, 09:01 AM
Southern Pete Southern Pete is offline
 
Join Date: Jul 2015
Location: England
Posts: 125
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I would say its very useful - I've not (in 16 years) knowingly had carb ice on my O-320. I've had a carb temp gauge for 6 years after I fitted an EFIS as it almost came for free and the sensor was straight forward to fit. I can't remember it being below 40 deg once the engine has been running for a few minutes. I have no idea how accurate it is, but I have no reason to believe it to be inaccurate. Before start it shows the approximate OAT. On run up it shows the carb heat is functioning. I can't see any reason not to use it.
Pete
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  #7  
Old 11-02-2018, 11:44 AM
RVDan RVDan is offline
 
Join Date: Jun 2012
Location: Frederick, MD
Posts: 942
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The most useful part is that when you are in conditions where icing is likely you can see the actual carb throat temp, and if in the freezing range add a bit of carb heat to bring it up a bit. Otherwise you only option is off or full on for carb heat.
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PA28-140
Hph 304CZ
RV6 built and sold
N199EC RV6A flying
Retired Aerospace Engineer and A&P/IA
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