Simviation Forum - Temperature / pitot heat

Reply #15 - Sep 12^th, 2009 at 5:29pm

DaveSims Offline
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Capt.Propwash wrote on Sep 12^th, 2009 at 3:39pm:

carb heat. = on BEFORE Idle, off BEFORE bat out of hell. -- gotcha.

pitot heat = (ugh i hate metric scale being i live in Farenheight land) -- (reported ground temp) - 3.5º F / +1000' MSL) = Temp aloft ???

90º summer day at KCHS .. will be flying at FL200 to KMIA VFR.... KCHS @ +46 ft MSL,

so..... may as well get use to turning it on anyways? even though ground temp is 90º.

just flip the switch when atc says "you are cleared for take off"

Temperature has no bearing on pitot heat. Most GA planes turn it on before entering visible moisture (clouds), regardless of temperature. Turbine aircraft turn it on before takeoff and leave it on until landed. Pretty simple.

Dave

www.flymcw.com

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Reply #16 - Sep 12^th, 2009 at 5:53pm

Hagar Offline
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Fozzer wrote on Sep 12^th, 2009 at 4:41pm:

P.S. ..I must ignore the fact that my Firefox Dictionary keeps telling me that there are NOT two "T"'s in Carburettor... Cry

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I've told you many times before. Install the British English dictionary. https://addons.mozilla.org/en-US/firefox/addon/3366

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Reply #17 - Sep 14^th, 2009 at 5:43am

flaminghotsauce Offline
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Good thread.

Just for clarification, carb heat doesn't take power from the engine. There is a cowl surrounding the exhaust which air is allowed to blow through, absorbing heat. This air is diverted into the carburetor. The hot air will change the fuel mixture, causing a slight loss of power. It's like a sudden density altitude change for the mixture. Less oxygen to burn, so the mix gets richer.

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Reply #18 - Sep 14^th, 2009 at 5:55am

Layne. Offline
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In the A2A Piper Cub you get a bigger amount of power loss (not enough to stall) Is that usual in the Cubs??? or is it something i am doing wrong? Huh

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Reply #19 - Sep 14^th, 2009 at 6:00am

beaky Offline
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flaminghotsauce wrote on Sep 14^th, 2009 at 5:43am:

Good thread.

Just for clarification, carb heat doesn't take power from the engine. There is a cowl surrounding the exhaust which air is allowed to blow through, absorbing heat. This air is diverted into the carburetor. The hot air will change the fuel mixture, causing a slight loss of power. It's like a sudden density altitude change for the mixture. Less oxygen to burn, so the mix gets richer.

Yes, but effectively, it takes power away... maybe 1-200 rpm, but it's very noticeable when you're already losing rpm because of ice in the carb inlet... those few seconds (if you're lucky) when the carb heat is on and the ice hasn't melted can be a little disconcerting. Shocked

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Reply #20 - Sep 14^th, 2009 at 6:02am

beaky Offline
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Layne. wrote on Sep 14^th, 2009 at 5:55am:

In the A2A Piper Cub you get a bigger amount of power loss (not enough to stall) Is that usual in the Cubs??? or is it something i am doing wrong? Huh

No, that's pretty normal for that little engine.

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Reply #21 - Sep 14^th, 2009 at 6:16am

Fozzer Offline
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Many unexplainable Aircraft crashes can be put down to Carburettor icing, but the ice has already melted in the Carburettor by the time the investigation is carried out, so there is no firm conclusion... Sad

...!

As a ground check before take off, apply full engine revs with the brakes applied, and select Carb Heat. The engine revs should drop by approximately 150 RPM to ensure the system is working correctly.

The dangers of Carburettor Icing during flight, frightens me!...(even in the Sim!)...so I regularly apply it!....!

Paul...G-BPLF...FS 2004... Cool

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Reply #22 - Sep 14^th, 2009 at 9:30am

DaveSims Offline
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beaky wrote on Sep 14^th, 2009 at 6:00am:

flaminghotsauce wrote on Sep 14^th, 2009 at 5:43am:

Good thread.

Just for clarification, carb heat doesn't take power from the engine. There is a cowl surrounding the exhaust which air is allowed to blow through, absorbing heat. This air is diverted into the carburetor. The hot air will change the fuel mixture, causing a slight loss of power. It's like a sudden density altitude change for the mixture. Less oxygen to burn, so the mix gets richer.

Yes, but effectively, it takes power away... maybe 1-200 rpm, but it's very noticeable when you're already losing rpm because of ice in the carb inlet... those few seconds (if you're lucky) when the carb heat is on and the ice hasn't melted can be a little disconcerting. Shocked

Think that is bad, try using the mixture knob instead of the carb heat knob. Lesson there, always verify the handle, especially in an unfamilar aircraft.

Dave

www.flymcw.com

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Reply #23 - Sep 16^th, 2009 at 6:40pm

flaminghotsauce Offline
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DaveSims wrote on Sep 14^th, 2009 at 9:30am:

beaky wrote on Sep 14^th, 2009 at 6:00am:

flaminghotsauce wrote on Sep 14^th, 2009 at 5:43am:

Good thread.

Just for clarification, carb heat doesn't take power from the engine. There is a cowl surrounding the exhaust which air is allowed to blow through, absorbing heat. This air is diverted into the carburetor. The hot air will change the fuel mixture, causing a slight loss of power. It's like a sudden density altitude change for the mixture. Less oxygen to burn, so the mix gets richer.

Yes, but effectively, it takes power away... maybe 1-200 rpm, but it's very noticeable when you're already losing rpm because of ice in the carb inlet... those few seconds (if you're lucky) when the carb heat is on and the ice hasn't melted can be a little disconcerting. Shocked

Think that is bad, try using the mixture knob instead of the carb heat knob. Lesson there, always verify the handle, especially in an unfamilar aircraft.

Just to clarify my clarification: I probably wasn't clear when I said it doesn't take power from the engine. When I say "take power from the engine" that's more like turning on an air conditioner that actually takes power... from the engine. Carb heat doesn't "take" power, but it prevents the power from being produced by changing the mixture.

Semantics I know.

I've pulled the mixture instead of the carb heat. Once. Never did that again! Shocked

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Reply #24 - Sep 16^th, 2009 at 8:00pm

DaveSims Offline
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flaminghotsauce wrote on Sep 16^th, 2009 at 6:40pm:

DaveSims wrote on Sep 14^th, 2009 at 9:30am:

beaky wrote on Sep 14^th, 2009 at 6:00am:

flaminghotsauce wrote on Sep 14^th, 2009 at 5:43am:

Good thread.

Just for clarification, carb heat doesn't take power from the engine. There is a cowl surrounding the exhaust which air is allowed to blow through, absorbing heat. This air is diverted into the carburetor. The hot air will change the fuel mixture, causing a slight loss of power. It's like a sudden density altitude change for the mixture. Less oxygen to burn, so the mix gets richer.

Yes, but effectively, it takes power away... maybe 1-200 rpm, but it's very noticeable when you're already losing rpm because of ice in the carb inlet... those few seconds (if you're lucky) when the carb heat is on and the ice hasn't melted can be a little disconcerting. Shocked

Think that is bad, try using the mixture knob instead of the carb heat knob. Lesson there, always verify the handle, especially in an unfamilar aircraft.

Just to clarify my clarification: I probably wasn't clear when I said it doesn't take power from the engine. When I say "take power from the engine" that's more like turning on an air conditioner that actually takes power... from the engine. Carb heat doesn't "take" power, but it prevents the power from being produced by changing the mixture.

Semantics I know.

I've pulled the mixture instead of the carb heat. Once. Never did that again! Shocked

At least you only did it once, it took me twice to figure out what was going on. The first time I was puzzled why I had a 1000 rpm drop (2400-1400) pushed it in and tried it again. Fortunately both times it restarted, and at the position I was in, could have easily made the landing at the airport.

Dave

www.flymcw.com

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Reply #25 - Sep 16^th, 2009 at 10:36pm

Splinter562 Offline
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Fozzer wrote on Sep 14^th, 2009 at 6:16am:

The dangers of Carburettor Icing during flight, frightens me!...(even in the Sim!)...so I regularly apply it!....!

I've had carb ice form in cruise over mountainous terrain when flying through foggy conditions a little bit above freezing. I noticed the engine sound had changed from it's cruise setting, like the throttle had slipped back. I pushed to full throttle and got little RPM change. This immediately set of the carb ice flag in my head. I pulled the carb heat and within 15 seconds the RPMs were coming back up again. If it is caught early, it is not really a big deal. The warning signs are subtle but unmistakable.

The danger is having the ice form in a high-workload situation when the signs are harder to notice. This is why carb ice in the pattern is of particular concern. With the pilot's attention divided and constant power changes, it is easy to miss the warning signs. This is why it is always a good idea to pull carb heat with power reduction. Even if ice doesn't form 999 out of 1,000 times, the one time it does form you could easily not notice until the engine stops when turning base.

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Reply #26 - Sep 19^th, 2009 at 6:58am

Mtns2Skies Offline
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Capt.Propwash wrote on Sep 12^th, 2009 at 3:39pm:

90º summer day at KCHS .. will be flying at FL200 to KMIA VFR.... KCHS @ +46 ft MSL,

so..... may as well get use to turning it on anyways? even though ground temp is 90º.

just flip the switch when atc says "you are cleared for take off"

Well item #1, it is illegal to fly VFR at or above FL180, And as for Item #2 I'd say no because you do not produce as much power as normal, as stated before but on takeoff your exhaust temperature is MUCH higher causing the air going into the engine to be MUCH higher. You will lose roughly 400RPM's if you apply carb heat on takeoff and climb out in a Cessna. Rather than the standard 75-150 on run-up/ descent.

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Reply #27 - Sep 20^th, 2009 at 10:17am

Brett_Henderson Offline
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Mtns2Skies wrote on Sep 19^th, 2009 at 6:58am:

Capt.Propwash wrote on Sep 12^th, 2009 at 3:39pm:

90º summer day at KCHS .. will be flying at FL200 to KMIA VFR.... KCHS @ +46 ft MSL,

so..... may as well get use to turning it on anyways? even though ground temp is 90º.

just flip the switch when atc says "you are cleared for take off"

Well item #1, it is illegal to fly VFR at or above FL180, And as for Item #2 I'd say no because you do not produce as much power as normal, as stated before but on takeoff your exhaust temperature is MUCH higher causing the air going into the engine to be MUCH higher. You will lose roughly 400RPM's if you apply carb heat on takeoff and climb out in a Cessna. Rather than the standard 75-150 on run-up/ descent.

I'm sure he's talking about turning pitot heat on after takeoff Wink

And I'm sure he meant VFR conditions, as in not IMC, as it would apply to pitot heat.

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