---------------------------------------------------------- Yak-List Digest Archive --- Total Messages Posted Tue 01/07/03: 6 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 05:11 AM - pressure carbs and carb ice (Brian Lloyd) 2. 07:42 AM - Re: pressure carbs and carb ice (Walt Lannon) 3. 08:31 AM - Re: pressure carbs and carb ice tests=QUOTED_EMAIL_TEXT,REFERENCES,SPAM_PHRASE_00_01, SUBJECT_IS_LIST,USER_AGENT_OE,USER_IN_WHITELIST version=2.43 (A. Dennis Savarese) 4. 09:00 AM - Re: pressure carbs and carb ice (Brian Lloyd) 5. 11:00 AM - Re: Re: Yak 52 Close Call (Yakjock) 6. 12:44 PM - Re: Re: Yak 52 Close Call (Brian Lloyd) ________________________________ Message 1 _____________________________________ Time: 05:11:03 AM PST US From: Brian Lloyd Subject: Yak-List: pressure carbs and carb ice --> Yak-List message posted by: Brian Lloyd At 09:17 PM 1/6/2003, you wrote: >--> Yak-List message posted by: "Frank Haertlein" >Also, the day this happened there were many clouds in the sky and it had >rained earlier that morning (not usual around here). But then I thought, >as with some others here, that a pressure carb wasn't subject to icing. >Is it or isn't it? I did come down very fast from up high. I am sure that this will spark an argument but I am going to go out on a limb here and say that the pressure carb is far less prone to icing than is a standard carb. In a standard carb the pressure drop in the venturi sucks the fuel from the float bowl and the fuel is injected at or just beyond the narrowest point of the venturi and upstream from the throttle valve. As the fuel vaporizes, the temperature drops and can get the air and throttle valve below freezing so ice can form. Looking at the plan view of the CJ6A pressure carb in the engine docs: (http://cj6.com/cj6_docs/Vol%204%20HS-6A%20Engine/16%20Engine%20Accessories.tif) you can see that the fuel spraybar is downstream from the throttle plate and there is no real venturi per se. ("Downstream" means "above" since this is an updraft carburetor.) There is a ram-air tube that functions as a mass airflow sensor to provide input to the metering diaphragm to control the fuel flow depending on the mass of air flowing through the carb instead of the volume. (That is why we can more-or-less ignore the mixture control since there is some mixture correction with altitude inherent in the mass airflow measurement.) The diaphragm meters the flow of fuel to the spraybar and there is nothing downstream from the spraybar until you hit the supercharger so there is nothing on which to form ice caused by fuel vaporization. The supercharger impeller is warm enough and massive enough that it never freezes. So the only way that a pressure carb is going to have ice is if the inlet air is below freezing and the moisture coming in is supercooled. At that point it may freeze upon encountering the throttle plate before it gets to the fuel spraybar. I suspect this is why the Russians and Chinese chose to measure inlet air temp rather than carburetor air temp. OK, you may throw rocks now. Brian Lloyd 6501 Red Hook Plaza, Ste 201 brian@lloyd.com St. Thomas, VI 00802 +1.340.998.9447 +1.360.838.9669 ________________________________ Message 2 _____________________________________ Time: 07:42:18 AM PST US From: "Walt Lannon" Subject: Re: Yak-List: pressure carbs and carb ice tests=QUOTED_EMAIL_TEXT,REFERENCES,SPAM_PHRASE_00_01, SUBJECT_IS_LIST,USER_AGENT_OE,USER_IN_WHITELIST version=2.43 --> Yak-List message posted by: "Walt Lannon" Hi Brian; Sorry; couldn't find any rocks. One comment though; The Chinese do measure carb. air inlet temp. exactly the same as the Harvard (British system) as opposed to the T6 (US System) which measures mixture temp. in the supercharger plenum. Cheers ----- Original Message ----- From: "Brian Lloyd" Subject: Yak-List: pressure carbs and carb ice > --> Yak-List message posted by: Brian Lloyd > > At 09:17 PM 1/6/2003, you wrote: > >--> Yak-List message posted by: "Frank Haertlein" > >Also, the day this happened there were many clouds in the sky and it had > >rained earlier that morning (not usual around here). But then I thought, > >as with some others here, that a pressure carb wasn't subject to icing. > >Is it or isn't it? I did come down very fast from up high. > > I am sure that this will spark an argument but I am going to go out on a > limb here and say that the pressure carb is far less prone to icing than is > a standard carb. > > In a standard carb the pressure drop in the venturi sucks the fuel from the > float bowl and the fuel is injected at or just beyond the narrowest point > of the venturi and upstream from the throttle valve. As the fuel > vaporizes, the temperature drops and can get the air and throttle valve > below freezing so ice can form. > > Looking at the plan view of the CJ6A pressure carb in the engine docs: > > (http://cj6.com/cj6_docs/Vol%204%20HS-6A%20Engine/16%20Engine%20Accessories. tif) > > you can see that the fuel spraybar is downstream from the throttle plate > and there is no real venturi per se. ("Downstream" means "above" since > this is an updraft carburetor.) There is a ram-air tube that functions as > a mass airflow sensor to provide input to the metering diaphragm to control > the fuel flow depending on the mass of air flowing through the carb instead > of the volume. (That is why we can more-or-less ignore the mixture control > since there is some mixture correction with altitude inherent in the mass > airflow measurement.) The diaphragm meters the flow of fuel to the > spraybar and there is nothing downstream from the spraybar until you hit > the supercharger so there is nothing on which to form ice caused by fuel > vaporization. The supercharger impeller is warm enough and massive enough > that it never freezes. > > So the only way that a pressure carb is going to have ice is if the inlet > air is below freezing and the moisture coming in is supercooled. At that > point it may freeze upon encountering the throttle plate before it gets to > the fuel spraybar. I suspect this is why the Russians and Chinese chose to > measure inlet air temp rather than carburetor air temp. > > OK, you may throw rocks now. > > Brian Lloyd 6501 Red Hook Plaza, Ste 201 > brian@lloyd.com St. Thomas, VI 00802 > +1.340.998.9447 +1.360.838.9669 > > ________________________________ Message 3 _____________________________________ Time: 08:31:34 AM PST US From: "A. Dennis Savarese" Subject: Re: Yak-List: pressure carbs and carb ice tests=QUOTED_EMAIL_TEXT,REFERENCES,SPAM_PHRASE_00_01, SUBJECT_IS_LIST,USER_AGENT_OE,USER_IN_WHITELIST version=2.43 --> Yak-List message posted by: "A. Dennis Savarese" Carb inlet temp. on the YAK 52 as well. Dennis Savarese ----- Original Message ----- From: "Walt Lannon" Subject: Re: Yak-List: pressure carbs and carb ice tests=QUOTED_EMAIL_TEXT,REFERENCES,SPAM_PHRASE_00_01, SUBJECT_IS_LIST,USER_AGENT_OE,USER_IN_WHITELIST version=2.43 > --> Yak-List message posted by: "Walt Lannon" > > Hi Brian; > Sorry; couldn't find any rocks. One comment though; The Chinese do measure > carb. air inlet temp. exactly the same as the Harvard (British system) as > opposed to the T6 (US System) which measures mixture temp. in the > supercharger plenum. > Cheers > ----- Original Message ----- > From: "Brian Lloyd" > To: > Subject: Yak-List: pressure carbs and carb ice > > > > --> Yak-List message posted by: Brian Lloyd > > > > At 09:17 PM 1/6/2003, you wrote: > > >--> Yak-List message posted by: "Frank Haertlein" > > > >Also, the day this happened there were many clouds in the sky and it had > > >rained earlier that morning (not usual around here). But then I thought, > > >as with some others here, that a pressure carb wasn't subject to icing. > > >Is it or isn't it? I did come down very fast from up high. > > > > I am sure that this will spark an argument but I am going to go out on a > > limb here and say that the pressure carb is far less prone to icing than > is > > a standard carb. > > > > In a standard carb the pressure drop in the venturi sucks the fuel from > the > > float bowl and the fuel is injected at or just beyond the narrowest point > > of the venturi and upstream from the throttle valve. As the fuel > > vaporizes, the temperature drops and can get the air and throttle valve > > below freezing so ice can form. > > > > Looking at the plan view of the CJ6A pressure carb in the engine docs: > > > > > (http://cj6.com/cj6_docs/Vol%204%20HS-6A%20Engine/16%20Engine%20Accessories. > tif) > > > > you can see that the fuel spraybar is downstream from the throttle plate > > and there is no real venturi per se. ("Downstream" means "above" since > > this is an updraft carburetor.) There is a ram-air tube that functions as > > a mass airflow sensor to provide input to the metering diaphragm to > control > > the fuel flow depending on the mass of air flowing through the carb > instead > > of the volume. (That is why we can more-or-less ignore the mixture > control > > since there is some mixture correction with altitude inherent in the mass > > airflow measurement.) The diaphragm meters the flow of fuel to the > > spraybar and there is nothing downstream from the spraybar until you hit > > the supercharger so there is nothing on which to form ice caused by fuel > > vaporization. The supercharger impeller is warm enough and massive enough > > that it never freezes. > > > > So the only way that a pressure carb is going to have ice is if the inlet > > air is below freezing and the moisture coming in is supercooled. At that > > point it may freeze upon encountering the throttle plate before it gets to > > the fuel spraybar. I suspect this is why the Russians and Chinese chose > to > > measure inlet air temp rather than carburetor air temp. > > > > OK, you may throw rocks now. > > > > Brian Lloyd 6501 Red Hook Plaza, Ste 201 > > brian@lloyd.com St. Thomas, VI 00802 > > +1.340.998.9447 +1.360.838.9669 > > > > > > ________________________________ Message 4 _____________________________________ Time: 09:00:15 AM PST US From: Brian Lloyd Subject: Re: Yak-List: pressure carbs and carb ice --> Yak-List message posted by: Brian Lloyd At 11:38 AM 1/7/2003, you wrote: >--> Yak-List message posted by: "Walt Lannon" > >Hi Brian; >Sorry; couldn't find any rocks. One comment though; The Chinese do measure >carb. air inlet temp. exactly the same as the Harvard (British system) as >opposed to the T6 (US System) which measures mixture temp. in the >supercharger plenum. Intake charge temp (in the plenum) has an effect on detonation margin so I can see why they would measure the temp there for larger engines that support higher intake MAP boost and may vary operating parameters depending on available fuel types. Brian Lloyd 6501 Red Hook Plaza, Ste 201 brian@lloyd.com St. Thomas, VI 00802 +1.340.998.9447 +1.360.838.9669 ________________________________ Message 5 _____________________________________ Time: 11:00:53 AM PST US From: "Yakjock" Subject: Re: Yak-List: Re: Yak 52 Close Call --> Yak-List message posted by: "Yakjock" I was told that there are a number of things that are useless to a pilot: Runway behind you, Fuel back at the airport, altitude above you, speed you don't have. Could probably add: too many drinks the night before, an attitude that you didn't leave behind. Happy New Year to all! The Society and Tuamotu Islands were a blast! Evelyn and I did remember our toasts to y'all on Christmas and New Years. Somehow SCUBA diving and "White Christmas" seem worlds apart. It's a glorious day here in the NW and "8" has been sitting idle way to long, so.................... Hal Morley ________________________________ Message 6 _____________________________________ Time: 12:44:36 PM PST US From: Brian Lloyd Subject: Re: Yak-List: Re: Yak 52 Close Call --> Yak-List message posted by: Brian Lloyd At 02:59 PM 1/7/2003, you wrote: >--> Yak-List message posted by: "Yakjock" > >I was told that there are a number of things that are useless to a pilot: Does this mean you are back from paradise? Brian Lloyd 6501 Red Hook Plaza, Ste 201 brian@lloyd.com St. Thomas, VI 00802 +1.340.998.9447 +1.360.838.9669