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Carby heat.

Python

Member
Hi, My engineer has looked at my Carby heat on my 2000 RV 6 & said that it’s no good ? He has suggested that I get a cabin heat shroud & convert it for Carby heat. My current system as seen in the photo doesn’t drop many revs when applied during run ups & to be honest I haven’t tried it in icing conditions. Has any one had issues with this type of Carby heater ? ( I realise this is a standard Vans RV 6 Carby heat system).

P.S I’ve looked at the cable & gate & they both work fine.701A80C5-0D3F-4215-B46C-A7668166E26D.jpg
 
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That’s the standard van’s setup.. and honestly very similar to Cessna 172s.. I would leave it and educate your mechanic.. besides, Lycoming engines Have their carbs mounted on the oil sump, they almost never ice up.. one NEVER gotten carb ice on a Lycoming, it’s just not that common. If you had a Continental, then perhaps a heat muff setup would be more appropriate.
 
Agree with Tom.

Same install on mine (though slightly cleaner ;)) with the the Vans FAB. RPM drop during the run-up in only 20 RPM, so the heating action is say, minute.
I've now flown >1'200 hours with my bird, some in dire weather, icing, freezing rain, snow, etc, and never had any indication of carb ice. I finally even ditched the carb temp indicator, which again, despite dancing in the yellow warning sector on the instrument, never gave any hint of icing.

Think of your carb heat system as an alternate air system. Will be more likely used in the case of FOD (bird, etc) or ram inlet complete icing.
 
Carby set up

I have the same set up in my -3. When I was taking my training 40 years ago in Ohio, the instructor always said, "every 15 minutes or so pull the carb heat for 10 seconds to prevent the carb from icing up", which I did until we moved to Florida. I figured that it was just too warm to worry about carb icing, until one day when I was flying back from North Florida, and I got to about Zephyrhills and the rpms started to drop. Slowly at first, I adjusted the mixture, no help, still dropped more. Then I changed tanks, no good. Now I looked at the gps for the closest field because the engine is running rough, as I turned towards the airport, I pulled the carb heat, and low and behold I could hear the ice breaking loose and going thru the engine, and then all things smoothed out. The rest of the trip was uneventful. I did call Lakeland and ask for the advisory, and the dew point spread was only 5 degrees. First time in over 40 years of flying that I have had carb ice. Short point is this, the carb heat worked when it was needed.

Just my $.02
 
Agree with Tom.

Same install on mine (though slightly cleaner ;)) with the the Vans FAB. RPM drop during the run-up in only 20 RPM, so the heating action is say, minute.
I've now flown >1'200 hours with my bird, some in dire weather, icing, freezing rain, snow, etc, and never had any indication of carb ice. I finally even ditched the carb temp indicator, which again, despite dancing in the yellow warning sector on the instrument, never gave any hint of icing.

Think of your carb heat system as an alternate air system. Will be more likely used in the case of FOD (bird, etc) or ram inlet complete icing.


Dan, the dire weather you described is not conducive to carb ice. There’s a huge temperature drop from the Venturi pressure drop in the carb, along with evaporative cooling.. if you are flying in already cold air, there’s not enough moisture in the cold air, plus any moisture is already (or close) to freezing to be an issue. You are more likely to experience carb ice on a warmer, more humid day like Taz explains.. 60 to 70 degrees out, then the temperature drop in the throat of the carb, especially at reduced throttle settings, puts the temp and humidity right at the optimum ice zone. Still, I haven’t experienced carb ice in a Lycoming.. however, I once got extreme carb ice in a Continental O200 while full throttle climbing out on a warm spring evening in NY..
 
There used to be a company called Robin Wing (or wings) that sold a nice carb heat muff that fit on the crossover tube. I think you may still be able to source it through Vettermans. I have one on my O-360 RV6A, it works great.

FP17032013A0004W.jpg
 
Dan, the dire weather you described

Tom, I did not describe the dire weather… there is dire weather, and the stuff I described.
 
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My RV6 exhaust kit came with this type heat exchanger. Supplies carb heat and cabin heat both, but captures heat from two pipes in the cross over system. The carb heat check is more noticeable with this heat exchanger.

2EB30DE7-6CF5-42DE-8EDD-1EE160F399B4.jpg
 
Rpm drop?

There used to be a company called Robin Wing (or wings) that sold a nice carb heat muff that fit on the crossover tube. I think you may still be able to source it through Vettermans. I have one on my O-360 RV6A, it works great.

FP17032013A0004W.jpg

Do you remember what rpm drop you typically see with that system?
 
carb heat rpm drop

Do you remember what rpm drop you typically see with that system?

I have the same carb heat muff on my -6A. Don’t have a digital tach to give exact rpm drop (using a Vans tach), but I can tell you I get something less than 50 rpm drop with carb heat on. Guessing around 30 rpm, based on the gauge needle movement .
 
I have the same carb heat muff on my -6A. Don’t have a digital tach to give exact rpm drop (using a Vans tach), but I can tell you I get something less than 50 rpm drop with carb heat on. Guessing around 30 rpm, based on the gauge needle movement .

there are two factors that will determine how effective the carb heat is. First is how good the muff is at capturing heat and the second is how effective the door is in sealing off the pressurized inlet air from the cowl. I feel the second is the bigger issue for most. Just about all that I have seen have very large gaps between the door and the filter housing. If this is not completely blocked off, the carb heat will be minimal, as the pressurized air fulfills a large part of the engines need and therefore doesn't PULL air through the muff. On mine, I kept it pretty tight and used RTV for sealing. I got consistent 50+ RPM drops during run up.

I recently build a new FAB for a guy and found a change in the FAB. They now have you sandwich a rubber pad in the door, making it much easier to get a good fitting door, as you can progressively trim it to fit with scissors and a tight door will not chafe away the F/G. However, most of the stuff out there could use some clean up. The original FAB we were replacing had gaps the size of Montana and the owner reported going from a 0-10 RPM drop to 50 after installation.

Also, the stock flange is installed with a very large gap at it's base. If this isn't also closed off, most of the air will be drawn in from that spot and not drawn through the muff.

Just like the fiberglass parts, it is not assembly here but building where the builder needs to think through the application and refine things to make them work well. I kind of feel for those building the newer highly refined kits, as they are not challenged enough to build these skills throughout the build process.

Larry
 
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there are two factors that will determine how effective the carb heat is. First is how good the muff is at capturing heat and the second is how effective the door is in sealing off the pressurized inlet air from the cowl. I feel the second is the bigger issue for most. Just about all that I have seen have very large gaps between the door and the filter housing. If this is not completely blocked off, the carb heat will be minimal, as the pressurized air fulfills a large part of the engines need and therefore doesn't PULL air through the muff. On mine, I kept it pretty tight and used RTV for sealing. I got consistent 50+ RPM drops during run up.

Also, the stock flange is installed with a very large gap at it's base. If this isn't also closed off, most of the air will be drawn in from that spot and not drawn through the muff.

Should have also mentioned two things about my FAB setup:
1. The door on my FAB closes off the opening almost completely.
2. I did not use the Vans stock (2 sided) flange. Mine is closed off on all 4 sides, minimizing leakage from inside the bottom cowl.

Also, about the 30 to 50- rpm drop I see…..done at 1800 rpm during mag check run-up. Most likely would see a larger carb heat rpm drop done at a higher run-up rpm.
 
Carb Ice.

Flying in the Pacific NW since 1970 I have experienced carburetor ice in Lycoming Engines.
There are a number of RV accidents that the “probable cause” was carb ice with Lycoming engines. More carb heat is always better.
 
I had one of the Vans setups, and I also had a carb temp probe. The best rise I could ever get out of the heat arrangement was about 3-4 C which may not keep the carb venturi out of the icing range when needed. I put on the Robbins muff and then got 10 degrees or more rise.

With the Vans setup, I got icing during taxi that shut the engine down with carb heat on. You have to do what you feel comfortable with, but the Robbins muff is relatively cheap solution. If you are IFR, a carb temp probe is really helpful.
 
The best way to measure the effectiveness of your carb heat is not RPM drop while doing your run-up. That test ignores the ram-air effect of the induction system overpowering your carb heat door.
The best test is to install a $35 carb heat temperature probe (assuming you already have a digital engine monitor)
https://www.aircraftspruce.com/catalog/inpages/grt-carb-01.php?clickkey=9876581

I put one on my RV6A with a Sam James cowl. I was seeing a 5 degree temperature rise in cruse when I applied carb heat. That did not make me feel too comfortable. I replaced the heat muff with a Rob’s Wings, and I re-worked the plenum door seal. Now I see a 40 degree temperature rise in flight.
I would install the temperature probe and see where you are before doing anything. Data and facts are way better than any opinion or antidotal information you will get on-line
 
There used to be a company called Robin Wing (or wings) that sold a nice carb heat muff that fit on the crossover tube. I think you may still be able to source it through Vettermans. I have one on my O-360 RV6A, it works great.

FP17032013A0004W.jpg

Hi, Can these be retro fitted to an existing exhaust system & if so without pulling the system off ?🐍
 
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