Robbing carb heat for cabin heat.

[SkwentnaMan]

I have an exp. pa-14 with the pa-14/12 muffler. The muffler has a shroud around it and a bulk head in the middle of the shroud. On one side is the fresh air intake and and supply for the cabin heat, on the other side is the same for the carb heat.

I want to have more cabin heat for winter flying in Alaska.

Here is what I'm thinking - Hook up some 2inch scat to the bottom of the heat box and pipe into the cabin, since all that warm air is being wasted when the carb heat isn't on why not use it. When I pull carb heat it will work as normal but when not in use that heat will go to the cabin.

I know that unless I rig up some other kind of air dump I will always have heat going into the cabin. I'm sure it wouldnt be to hard to put a in-line tee that dumps the air after the carb box if I dont want heat into the cabin, or even simpler would be to tee over into my main cabin heat line.

So I guess my main question is - Has anyone ever done this or what problems would arise from taking heat from the bottom of the carb air box.

Thanks

 

[Little_Cub]

Did it with a 90 horse and C-150 muffs.. seemed to help.. so many air leaks in that ol cub it was warm breath at best.

good luck

 

[mike mcs repair]

http://fadodge.com/index.php?option=com_djcatalog2&view=item&id=4:rear-seat-heater-kit&cid=2:cockpit

 

[mvivion]

Another option that's easy to do and provides better more consistent heat: Take both sides of the muffler shroud into the cabin, as you've suggested. But, instead of making your secondary cabin heat either/or carb heat, get a carb heat shroud from a Scout or a mid year Lycoming equipped Cessna 172. These attach to one exhaust pipe, just below the flange, and provide carb heat. It's a certified system on the Scout, the C-172 M (I think), the Piper Warrior, and several other planes. I was able to get my system like this field approved on a Cessna 170 with an O-360. Makes PLENTY of cabin heat now, and still plenty of carb heat. The Inspector who signed it off liked the idea of having completely separate systems like this, even though there are a million Super Cubs running around with either/or systems. This system gives good cabin heat ALL the time, and it's pretty easy to do.

MTV

 

[TrentF]

Or maybe try wrapping a Sceen door spring around your muffler under the shroud (if you have room). It might help you get more heat out of the muffler.Kinda like a heat sink.

 

[nanook]

What mike's repair said... You need to remember to close rear seat heat when you use carb heat. In the summer you may have to block the valve at the firewall off for rear seat heat....There is always a little hot air leakage into the cabin. My cub stays relatively warm down to -15 to-20F, after that it is a losing battle... The Dodge defroster and rear seat heat are essential equipment in the cold North....

 

[gpepperd]

Israel, Give me a call and come over to see how I set mine up. It works like a charm and a call for carb heat automatically over rides it. 441-9205 Greg

 

[Senior]

I know that unless I rig up some other kind of air dump I will always have heat going into the cabin. I'm sure it wouldnt be to hard to put a in-line tee that dumps the air after the carb box if I dont want heat into the cabin, or even simpler would be to tee over into my main cabin heat line.

Thanks

My regular cabin heat box just dumps heated air out the bottom when it's closed to the cabin.
I would assume your regular cabin heat box does the same, just use another one.

 

[skywagon8a]

Or maybe try wrapping a Sceen door spring around your muffler under the shroud (if you have room). It might help you get more heat out of the muffler.Kinda like a heat sink.

I have tried this trick and was unable to notice any change.

 

[SkwentnaMan]

I ordered a carb only heat muff from these guys- www.robbinswings.com

Prices are good and products look nice. If this works, now I can install a second cabin heat box and have twice the heat.

 

[knucles]

You could also add heated seat pads into your upholstery , or put on top of seat. They work , they are cheap , come with a off , low and high switch. Can be wired in or plug into a 12 volt adapter /cigarette lighter adapter .
They come with a seat pad and back pad .

 

[Darrel Starr]

The Atlee Dodge rear seat heater shares heat originally intended for the carb from the right half of the muffler on a PA-18. A placard warns the pilot to shut off rear seat heat when using carb heat.

 

[SkwentnaMan]

The Atlee Dodge rear seat heater shares heat originally intended for the carb from the right half of the muffler on a PA-18. A placard warns the pilot to shut off rear seat heat when using carb heat.

Well that is the nice thing about being experimental I dont have to buy a 500.00 Atlee dodge part to get more heat.

 

[Darrel Starr]

I brought up the Atlee Dodge placard because the idea of NOT dividing carb heat at a critical moment seems like a good thought -- one that is worth considering rather certified or experimental, I'm thinking.

 

[mvivion]

And, that's precisely why I completely separated my airplane's source of carb heat from it's cabin heat. Was flying the other day at -15 and couldn't use full cabin heat.........Simple, and completely separate systems.

MTV

 

[nanook]

The Dodge rear seat heat comes off the tail pipe of the exhaust. There is no change to the cabin heat system when you put the rear seat heat system on. The cabin heat comes off the muffler shroud. The tail pipe heat is separate. It uses the ram air of the carb heat system. That is why you must shut the rear seat heat off, so you can keep all that ram air for carb heat. You are not taking any heat away from the carb heat system.

 

[mvivion]

If you reduce flow, you reduce the amount of heat available. With rear heat "on" and carb heat "on" at same time, the amount of carb heat available doesn't met certification standards.

You can make all kinds of heat, but without flow, it's useless.

MTV

 

[Senior]

If you reduce flow, you reduce the amount of heat available. With rear heat "on" and carb heat "on" at same time, the amount of carb heat available doesn't met certification standards.

You can make all kinds of heat, but without flow, it's useless.

MTV

That's why I plan on recovering the dumped air.
Your Carb heat box just dumps heated air out the bottom if the carb heat valve is not pulled.

If you take the heated air that's just dumped from the carb heat & run it into another cabin heat box then your not interrupting or dividing the flow to the carb when selected, the only downfall is when carb heat is selected there is none going to the 2nd cabin heat box.

 

[mvivion]

That's why I plan on recovering the dumped air.
Your Carb heat box just dumps heated air out the bottom if the carb heat valve is not pulled.

If you take the heated air that's just dumped from the carb heat & run it into another cabin heat box then your not interrupting or dividing the flow to the carb when selected, the only downfall is when carb heat is selected there is none going to the 2nd cabin heat box.

Not sure if I understand what you're describing. If I understand you correctly, you plan on taking the air that is bypassed over the side when carb heat is NOT selected and routing it into the cabin? If so, how do you plan to ensure that the muffler and shroud are cooled when NEITHER carb heat OR cabin heat are selected? I believe (and this may be incorrect) that it is a certification requirement to have air moving through the heat shroud/muffler at all times. Normally, when carb heat is selected, that air is directed to the carb air box, when carb heat is off, it's dumped over the side.

So, a question for the experts: If you were to take that "dumped" hot air, and route it into the cabin, but then turn that heat off, would this induce excessive heat to the muffler/heat shroud? Otherwise, why did Atlee design an "either-or" setup?

MTV

 

[Senior]

So, a question for the experts: If you were to take that "dumped" hot air, and route it into the cabin, but then turn that heat off, would this induce excessive heat to the muffler/heat shroud? Otherwise, why did Atlee design an "either-or" setup?

No because your cabin heat box also just dumps the air when not selected.

So if neither carb nor cabin is selected then the air is also just dumped.