Sure. Even down here in the balmy south, at -20C
in Jan or Feb I have had little Continentals run much
better with carb heat, than without. I'm sure it helps
the atomization of the 100LL. Probably not as much
of an issue if you are running (winter) mogas which
evaporates much better in the cold.
CF-CFR 1947 Cessna 140 down en route Smith Falls pilot ok
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Re: CF-CFR 1947 Cessna 140 down en route Smith Falls pilot o
Pelmet,
The Cessna 180/182 ran into problems with the front cylinders running too lean below about -20*c or so, so I commonly ran Carb Heat continuously below that temperature. Once at about -40 I turned off the Carb heat in curiousity
, and it felt like the thing had quit before I had the control knob all the way in!
There are a few other aircraft - the Luscombes are placarded to run full carb heat to reduce the fuel flow during TO and landing.
The RAF set up the Chipmunk to have full Carb Heat at all times, and the English Tiger Moth have a valve allowing cold air into the carb at full throttle, switching over to warm air from incside the cowling once the power is reduced a bit.
The Cessna 180/182 ran into problems with the front cylinders running too lean below about -20*c or so, so I commonly ran Carb Heat continuously below that temperature. Once at about -40 I turned off the Carb heat in curiousity
, and it felt like the thing had quit before I had the control knob all the way in!There are a few other aircraft - the Luscombes are placarded to run full carb heat to reduce the fuel flow during TO and landing.
The RAF set up the Chipmunk to have full Carb Heat at all times, and the English Tiger Moth have a valve allowing cold air into the carb at full throttle, switching over to warm air from incside the cowling once the power is reduced a bit.
Re: CF-CFR 1947 Cessna 140 down en route Smith Falls pilot o
Thanks,jamesel wrote:Pelmet,
The Cessna 180/182 ran into problems with the front cylinders running too lean below about -20*c or so, so I commonly ran Carb Heat continuously below that temperature. Once at about -40 I turned off the Carb heat in curiousity
There are a few other aircraft - the Luscombes are placarded to run full carb heat to reduce the fuel flow during TO and landing.
The RAF set up the Chipmunk to have full Carb Heat at all times, and the English Tiger Moth have a valve allowing cold air into the carb at full throttle, switching over to warm air from incside the cowling once the power is reduced a bit.
I have never used carb heat myself in colder temperatures but nice to hear some actual experience in it. Strange about the Luscombe. Why would you want to reduce the fuel flow for takeoff and landing. Overly rich mixture and concern about high power settings.
Heard about the Chipmunk stuff by the RAF. Of course, they operate in a maritime environment.
Apparently the Gipsy Major engine can be susceptable to carb ice. I think you'll find Canadian Tiger Moths also have carb heat automatically on all the time as well except at full power. Doesn't use hot exhaust heat but engine block heat with an intake for warm air very close to the engine.
Last edited by pelmet on Wed Nov 28, 2012 5:48 pm, edited 2 times in total.
Re: CF-CFR 1947 Cessna 140 down en route Smith Falls pilot o
The Carb Heat use is an easy way to reduce the power/fuel flow without leaning the mixture!
Here is the wording from the type certificate:
"Full carburetor air heat required for takeoff and
landing." The reason for this placard is that during takeoff acceleration and initial high angle-
of-attack climb, the fuel flow may not be adequate for proper operation.
Application of full carburetor heat in this case helps overcome the possible deficiency of
fuel flow during takeoff. Carburetor ice is not a basic consideration in requiring this
placard.
It was applicable to the 65 hp Continental ONLY. It doesn't appear to be related to using a fuselage tank or wing tanks. There is some evidence the use of wing tanks would increase the fuel level/head pressure enough to remove the problem, but.... I've been told by an old AME that it was due to using the same fuel lines as the original 50 hp engines & they are just too small in diameter to keep up with the flow of the larger engine AND the steeper attitude the "big" engine can produce. According to him, the later (75 hp + up) aircraft had larger diameter fuel lines.
Here is the wording from the type certificate:
"Full carburetor air heat required for takeoff and
landing." The reason for this placard is that during takeoff acceleration and initial high angle-
of-attack climb, the fuel flow may not be adequate for proper operation.
Application of full carburetor heat in this case helps overcome the possible deficiency of
fuel flow during takeoff. Carburetor ice is not a basic consideration in requiring this
placard.
It was applicable to the 65 hp Continental ONLY. It doesn't appear to be related to using a fuselage tank or wing tanks. There is some evidence the use of wing tanks would increase the fuel level/head pressure enough to remove the problem, but.... I've been told by an old AME that it was due to using the same fuel lines as the original 50 hp engines & they are just too small in diameter to keep up with the flow of the larger engine AND the steeper attitude the "big" engine can produce. According to him, the later (75 hp + up) aircraft had larger diameter fuel lines.
Re: CF-CFR 1947 Cessna 140 down en route Smith Falls pilot o
I don't quite understand. You initially said that carb heat reduces power. That I understand. You also said it reduces fuel flow which if true would reduce power.jamesel wrote:The Carb Heat use is an easy way to reduce the power/fuel flow without leaning the mixture!
Here is the wording from the type certificate:
"Full carburetor air heat required for takeoff and
landing." The reason for this placard is that during takeoff acceleration and initial high angle-
of-attack climb, the fuel flow may not be adequate for proper operation.
Application of full carburetor heat in this case helps overcome the possible deficiency of
fuel flow during takeoff. Carburetor ice is not a basic consideration in requiring this
placard.
It was applicable to the 65 hp Continental ONLY. It doesn't appear to be related to using a fuselage tank or wing tanks. There is some evidence the use of wing tanks would increase the fuel level/head pressure enough to remove the problem, but.... I've been told by an old AME that it was due to using the same fuel lines as the original 50 hp engines & they are just too small in diameter to keep up with the flow of the larger engine AND the steeper attitude the "big" engine can produce. According to him, the later (75 hp + up) aircraft had larger diameter fuel lines.
But later on you stated that not enough fuel is getting to the engine to provide enough power due to restricted fuel flow from small diameter lines. So why would you add carb heat if it lowers fuel flow even more?
Re: CF-CFR 1947 Cessna 140 down en route Smith Falls pilot o
Sorry. I wasn't clear enough on what was cause & what was effect here. As you stated, an engine requires fuel flow in proportion to the power generated. Usually, we will design the fuel system to allow more than enough fuel to provide this. If we are unable or unwilling to change the fuel system, we could go the other way & restrict the power generated to a level that the system can provide.
This system doesn't allow enough fuel to flow in, so the Carb. Heat is used to reduce the power & therefore the fuel flow required. Which is mechanically easier than screwing around with throttle lever restrictions.
Basically, to recap: the diameter of the fuel line and the head pressure (height of the fuel tank above the carburetor) determine the fuel flow from the tank. With the smaller diameter line, and at the highest power settings, not enough fuel would flow through to keep the engine from running too lean. There could also be an increased chance of vapour lock. Pulling on the Carb. Heat reduces the Engine Power & therefore the Fuel flow requirement. Apparently it's reduced to a level that the system can provide. For a current production aircraft the usual standard is that the fuel system must provide 150% of the max power requirement in the steepest sustained climbing attitude attainable. Obviously, not obtained here.
This use of carb. heat appears to be a placard/operational work-around of an engineering error, or might have been done this way 'cause a placard is way cheaper than modifying the production line and/or retrofitting the flood of Luscombes that left the factory in '46 by changing the fuel lines or fuel tank system...
This system doesn't allow enough fuel to flow in, so the Carb. Heat is used to reduce the power & therefore the fuel flow required. Which is mechanically easier than screwing around with throttle lever restrictions.
Basically, to recap: the diameter of the fuel line and the head pressure (height of the fuel tank above the carburetor) determine the fuel flow from the tank. With the smaller diameter line, and at the highest power settings, not enough fuel would flow through to keep the engine from running too lean. There could also be an increased chance of vapour lock. Pulling on the Carb. Heat reduces the Engine Power & therefore the Fuel flow requirement. Apparently it's reduced to a level that the system can provide. For a current production aircraft the usual standard is that the fuel system must provide 150% of the max power requirement in the steepest sustained climbing attitude attainable. Obviously, not obtained here.
This use of carb. heat appears to be a placard/operational work-around of an engineering error, or might have been done this way 'cause a placard is way cheaper than modifying the production line and/or retrofitting the flood of Luscombes that left the factory in '46 by changing the fuel lines or fuel tank system...
Re: CF-CFR 1947 Cessna 140 down en route Smith Falls pilot o
Well, to continue this thread drift.... Though the preceding post does contain some factual information, and the reference to the placard in the Luscombe is correct, I think that in the bigger picture, pilot of certified aircraft should not be considering the application of carb heat for the purpose of changing fuel flow - that's not what it's there for. Apparently the Luscombe is a certification aberration. All other certified aircraft have actually demonstrated compliance with the design requirement for fuel flow at 150% (or 125% for pumped systems) of what the engine requires at maximum power.
Pilots, fly your aircraft within the limitations of, and using the techniques specified in, the flight manual or placards. Unless you're flying a Luscombe, or are otherwise limited by another factor (turbo boost limits, for example) you can use full power in a climb without worrying about running out of fuel, and you can leave the carb heat cold while you do it.
Similarly, freedom from vapour lock has also been demonstrated with adequate margin for all certified airplanes, as long as you use the specified fuel, and follow any specified procedures.
The fact that the Luscombe was allowed to be certified with this odd procedure is a very isolated circumstance, and has probably never occurred since.
Pilots, fly your aircraft within the limitations of, and using the techniques specified in, the flight manual or placards. Unless you're flying a Luscombe, or are otherwise limited by another factor (turbo boost limits, for example) you can use full power in a climb without worrying about running out of fuel, and you can leave the carb heat cold while you do it.
Similarly, freedom from vapour lock has also been demonstrated with adequate margin for all certified airplanes, as long as you use the specified fuel, and follow any specified procedures.
The fact that the Luscombe was allowed to be certified with this odd procedure is a very isolated circumstance, and has probably never occurred since.
Re: CF-CFR 1947 Cessna 140 down en route Smith Falls pilot o
According to the website www.luscombesilvaire.info, the requirement for carb heat on takeoff has nothing to do with the mixture or fuel flow requirements:
Q29. What's this I hear about using carb heat on takeoff?
A29: Refer to ATC694 and service letter. It is required to reduce the power on an A-65 or -75 when using a fuselage tank. With low fuel, (1/2 tank or less) and a cool day, when the engine is making lots of power and you are in a steep(er) climb angle it is possible to get the engine fuel inlet ABOVE the fuel tank outlet, which causes fuel flow to cease (and the engine quits). Carb heat on was a simple and cheap fix to this as it reduced the power the engine could make and thus reduced the deck angle. It is also why wing tanks are required on higher HP engine conversions, and why wing tanks are strongly recommended for all Luscombes in general.
Re: CF-CFR 1947 Cessna 140 down en route Smith Falls pilot o
oops, guess I should've emphasized that particular use of carb. heat applied ONLY to the Luscombe powered by the A-65...
