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 Post subject: Carb heat and Cabin heat
PostPosted: Sat Sep 09, 2017 6:57 am 
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Just out of curiosity: I noticed that it makes a difference how far out you pull the Cabin heat knob. In my search for things to do 8) I now also want to keep the Comanche cockpit 'nice and steady' all the time. :wink: I noticed however that the Carb heat seems to be an on or off knob, unlike the Cabin heat knob: whenever I need the Carb heat just a little pull will do the trick, it makes no matter how far you pull it out.

I suppose this is as it is in real life? That it doesn't matter how far the pull the Carb heat knob?

As I said, just curious. :wink: I want to learn everything there is to know about the A2A Comanche which I'd like to officially declare my most favorite and best GA ever.

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PostPosted: Sat Sep 09, 2017 8:13 am 
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J van E wrote:
[...] whenever I need the Carb heat just a little pull will do the trick, it makes no matter how far you pull it out.

I suppose this is as it is in real life? That it doesn't matter how far the pull the Carb heat knob?
In real life GA's which don't benefit from a carb air temperature gauge, I understand the usual advice is "all or nothing" with the carb heat selector. I believe this is to guard against the risk of increasing the temperature of the venturi under cold conditions just enough that ice crystals in the air are melted to form vapour which can then re-freeze inside the carb.

If we have got a carb air temperature gauge, then the general idea is to keep the temp in a safe range which will protect against ice formation but also minimise the power loss caused by the engine sucking-up warmer, less dense air.

Remember - in the real aircraft that lever/plunger operates a diverter door which allows hot air (i.e. air heated by the exhaust) into the carb. It's not some kind of electronic "on/off switch" for a heater. :)

Cheers,
Nick


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PostPosted: Sat Sep 09, 2017 9:08 am 
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And thanks again, Nick! I think I am out of questions for now... :wink:

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PostPosted: Sat Oct 14, 2017 7:02 pm 
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J van E,

The fluid physics of these things, is sort of like placing your thumb over a hose. If you just move your thumb a little, a lot of water flows. Removing it completely adds more, but it's not linear, it's exponential. So, yes, when you crack the carb heat, a good but of heat comes in. Maybe 1/4 out will give you 2/3's everything it has to give.

Scott.

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PostPosted: Wed Oct 18, 2017 1:23 pm 
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Scott - A2A wrote:
J van E,

The fluid physics of these things, is sort of like placing your thumb over a hose. If you just move your thumb a little, a lot of water flows. Removing it completely adds more, but it's not linear, it's exponential. So, yes, when you crack the carb heat, a good but of heat comes in. Maybe 1/4 out will give you 2/3's everything it has to give.

Scott.

Thanks, that's a good example with that hose. Got it now!

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