Van's Air Force
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van's carb heat
- Thread starter dmeloche
- Start date
A couple have reported less than a 20F rise in carb induction temps with the small cuff setup full on. There have been a couple of incidents reported as well with this setup. A full muff may be a better choice here. Watch the temp gauge if you have one. If not, be careful. Most production carb heat setups will deliver a 75-100F change in induction temps when full on.
robertahegy
Moderator/Tech Counselor
I, too, have noticed little or no change in RPM when testing the carb heat on runup. Van's basically says that the Lycoming engines are generally not subject to venturi icing and the real purpose of the carb heat door is for keep ice from forming on the filter in the first place. Read their bulletin in the Van's website for more details. They also recommend the filter by-pass air source in the event the filter should get iced up. This system is not intended for venturi icing like the OEM Piper and Cessna carb heat system and will not function like them since the hot air is not directly input into the carb and by-passing the filter.
Hope this helps,
Roberta
Hope this helps,
Roberta
gmcjetpilot
Well Known Member
good news and bad news
Bottom line it is worth putting in the carb heat door in and think it would be negligent and dangerous not to install it. I also suggest using a much more substantial control cable to activate the door. The wire type fails with in 100-300 hours, and will continue to do so. The cable I refer to has a solid rod end like the mixture or throttle with a threaded tip, but it has a simple small knob. They cost more and weigh more but worth it.
The good news is Lycoming carbs are less subject (but not immune) to carb ice like other engines, such as continental. Also the good part is the flapper door does work. It does provide warmer temps and an alternate path for air.
The bad news is does the flapper door work well enough, i.e., enough temp rise. My guess is you could not certify it:
FAR part 23.1093 - Induction system icing protection.
(a) Reciprocating engines. Each reciprocating engine air induction system must have means to prevent and eliminate icing.
Unless this is done by other means, it must be shown that, in air free of visible moisture at a temperature of 30 ?F. --
(1) Each airplane with sea level engines using conventional venturi carburetors has a preheater that can provide a heat rise
of 90 ?F. with the engines at 75 percent of maximum continuous power;
There are 6 parts to this section, the above is the prime one for a sea level (non-turbo) engine with a carb and carb heat.
I doubt the little stove pipe device Van has on the cross over will raise the heat up 90F, but may help a little.
Again INSTALL carb heat if you have a Carb. If you were going to fly IFR in visible moisture in near freezing temps as part of your routine missions, I would use a dedicated heat muff for carb heat. Of course a carb air temp gage would be handy.
Put the carb heat door in, use it, check it (don't rush it) and be aware of the dew point spread. I don't have a rule of thumb except for the standard induction ice chart, showing probability against temp vs. dew point temp. Google: "carb ice" or "induction ice" airplane, to get a chart.
To compensate for Van's weak carb heat, use it sooner than later, more often and keep it on longer. Once the engine starts to choke from ice you may be screwed. BTW those fancy EGT gages may give you the first indication of ice in cruise. Again like the run-up, if in doubt pull it on. Watch RPM or MAP as appropriate for a change. Obviously you will get an initial MAP or RPM change from using alternate air, but watch it after that initial drop. As ice melts the RPM or MAP may increase. After the carb heat has beenon for a short period, turn heat off and note the RPM or MAP again for overall change from the start point. If you watch you will see you often will see small amount increase of RPM or MAP, indicating carb ice from time to time you may have not been aware of before.
You have to look to see it.
How to live with carb ice (read if bored and at own risk of involuntary drowsiness )
Here is the deal even with a weak carb heat system it is way better than none at all. Second you need to get carb heat on and early if it is likely or suspected. Consider this a limitation to respect and observe. Here is a tip you may or may not know about. As a former practicing CFI I have seen pilots do run-up checks of carb heat that do no good at all. You need pull the carb heat and leave it in for a reasonable period of time, while observing RPM or MAP if you have a constant speed prop. Note any increase in RPM or MAP. Here is the part some miss. Once you turn the carb heat back off note RPM or MAP again. If it has changed, higher than when you started, you likely had melted some ice off you got during taxi. Obviously if you are in Phoenix during the summer, carb ice is not an issue. A carb check can be just a quick functional check in this case. Remember you can have carb ice conditions with ambient temps as high as 23c to 30c with high humidity. Carb icing is most likely at 50%+ humidity from 20 to 90 degrees F. (Some texts give 80% humidity between 40 and 70 degrees.) This applies to RV's and Lycoming engines as well.
Detection: There is no direct way to detect ice except for a LED optical ice detector device like the "Iceman", which uses a LED and photo cel to "see" ice. However many report it is too sensitive, reporting the slightest ice or frost on the sensor. However consider an old fashion Carb Air Temp (CAT) probe and gage. If for any reason to see how effective you carb heat is. My GRT EIS4000 engine monitor uses a (CAT) probe and will give a visual alarm in the critical range. With the CAT you can keep track of actual venturi temp, but it still will not tell you if you have ice. You still need RPM, MAP, EGT and a careful eye. The critical CAT range is +15c to -10c. Some analog CAT gages show caution range as +/-20c and others show a +/-10c range. Again it is just an indirect indicator or possible ice, which is a little more useful than OAT.
Carb ice contributes to many accidents every year across the GA fleet, including several RV's. The problem is the evidence rapidly melts and disappears. The main thing is awareness. Use the darn thing EARLY and be real suspicious and discerning of what the gages are telling you, before, during and after carb heat applications. Also if you fly with Carb heat on below 75% power don't forget to re-lean. As far as taking off with carb heat ON, I would not recommend it. If you get carb ice taking off with full power, assuming it was cleaned out to start with, I would not be flying at all (in a SE recip airplane). The conditions would be severe and you likely could have airframe ice as well (100% humidity and OAT with in +10C of freezing).
Cheers George
Bottom line it is worth putting in the carb heat door in and think it would be negligent and dangerous not to install it. I also suggest using a much more substantial control cable to activate the door. The wire type fails with in 100-300 hours, and will continue to do so. The cable I refer to has a solid rod end like the mixture or throttle with a threaded tip, but it has a simple small knob. They cost more and weigh more but worth it.
The good news is Lycoming carbs are less subject (but not immune) to carb ice like other engines, such as continental. Also the good part is the flapper door does work. It does provide warmer temps and an alternate path for air.
The bad news is does the flapper door work well enough, i.e., enough temp rise. My guess is you could not certify it:
FAR part 23.1093 - Induction system icing protection.
(a) Reciprocating engines. Each reciprocating engine air induction system must have means to prevent and eliminate icing.
Unless this is done by other means, it must be shown that, in air free of visible moisture at a temperature of 30 ?F. --
(1) Each airplane with sea level engines using conventional venturi carburetors has a preheater that can provide a heat rise
of 90 ?F. with the engines at 75 percent of maximum continuous power;
There are 6 parts to this section, the above is the prime one for a sea level (non-turbo) engine with a carb and carb heat.
I doubt the little stove pipe device Van has on the cross over will raise the heat up 90F, but may help a little.
Again INSTALL carb heat if you have a Carb. If you were going to fly IFR in visible moisture in near freezing temps as part of your routine missions, I would use a dedicated heat muff for carb heat. Of course a carb air temp gage would be handy.
Put the carb heat door in, use it, check it (don't rush it) and be aware of the dew point spread. I don't have a rule of thumb except for the standard induction ice chart, showing probability against temp vs. dew point temp. Google: "carb ice" or "induction ice" airplane, to get a chart.
To compensate for Van's weak carb heat, use it sooner than later, more often and keep it on longer. Once the engine starts to choke from ice you may be screwed. BTW those fancy EGT gages may give you the first indication of ice in cruise. Again like the run-up, if in doubt pull it on. Watch RPM or MAP as appropriate for a change. Obviously you will get an initial MAP or RPM change from using alternate air, but watch it after that initial drop. As ice melts the RPM or MAP may increase. After the carb heat has beenon for a short period, turn heat off and note the RPM or MAP again for overall change from the start point. If you watch you will see you often will see small amount increase of RPM or MAP, indicating carb ice from time to time you may have not been aware of before.
You have to look to see it.How to live with carb ice (read if bored and at own risk of involuntary drowsiness
)Here is the deal even with a weak carb heat system it is way better than none at all. Second you need to get carb heat on and early if it is likely or suspected. Consider this a limitation to respect and observe. Here is a tip you may or may not know about. As a former practicing CFI I have seen pilots do run-up checks of carb heat that do no good at all. You need pull the carb heat and leave it in for a reasonable period of time, while observing RPM or MAP if you have a constant speed prop. Note any increase in RPM or MAP. Here is the part some miss. Once you turn the carb heat back off note RPM or MAP again. If it has changed, higher than when you started, you likely had melted some ice off you got during taxi. Obviously if you are in Phoenix during the summer, carb ice is not an issue. A carb check can be just a quick functional check in this case. Remember you can have carb ice conditions with ambient temps as high as 23c to 30c with high humidity. Carb icing is most likely at 50%+ humidity from 20 to 90 degrees F. (Some texts give 80% humidity between 40 and 70 degrees.) This applies to RV's and Lycoming engines as well.
Detection: There is no direct way to detect ice except for a LED optical ice detector device like the "Iceman", which uses a LED and photo cel to "see" ice. However many report it is too sensitive, reporting the slightest ice or frost on the sensor. However consider an old fashion Carb Air Temp (CAT) probe and gage. If for any reason to see how effective you carb heat is. My GRT EIS4000 engine monitor uses a (CAT) probe and will give a visual alarm in the critical range. With the CAT you can keep track of actual venturi temp, but it still will not tell you if you have ice. You still need RPM, MAP, EGT and a careful eye. The critical CAT range is +15c to -10c. Some analog CAT gages show caution range as +/-20c and others show a +/-10c range. Again it is just an indirect indicator or possible ice, which is a little more useful than OAT.
Carb ice contributes to many accidents every year across the GA fleet, including several RV's. The problem is the evidence rapidly melts and disappears. The main thing is awareness. Use the darn thing EARLY and be real suspicious and discerning of what the gages are telling you, before, during and after carb heat applications. Also if you fly with Carb heat on below 75% power don't forget to re-lean. As far as taking off with carb heat ON, I would not recommend it. If you get carb ice taking off with full power, assuming it was cleaned out to start with, I would not be flying at all (in a SE recip airplane). The conditions would be severe and you likely could have airframe ice as well (100% humidity and OAT with in +10C of freezing).
Cheers George
Last edited:
robertahegy
Moderator/Tech Counselor
Excellent advice, George. Thanks for adding that.
Roberta
Roberta
Rick6a
Well Known Member
gmcjetpilot said:
Interesting. That Van's supplied cable failed a few inches aft of the flapper door linkage within the first three flight hours on "Darla". That was the first real "squawk" that required repair. I attributed the failure to a lack of adequate support and vibration issues. I did a minor reroute and added more substantial clamping. If it fails again, I will get the better quality cable.
Rick Galati RV-6A "Darla" 48 hours
garnt.piper
Well Known Member
Carb Heat
Hi, some practical experience on my carb heat set-up for you all to digest. I installed the FAB-360 airbox and carb heat flapper door as per Van's instructions. I built my own exhaust pipe muff that fitted over both exhaust pipes that pass in front of the sump. On the ground, and in flight, I get a noticeable RPM drop when selecting carb heat on. I installed an airbox temperature probe, one of those cheap Radio Shack indoor/outdoor dual sensor thermometers. During initial flight testing I had no trouble getting 50-70?C temp rises at 75% power. The max temp I saw in testing was 89?C in the airbox. I thought this was good enough, the cheap thermometer has since failed, but I know my system works.
'If it's stupid but it works, it ain't stupid'
Hi, some practical experience on my carb heat set-up for you all to digest. I installed the FAB-360 airbox and carb heat flapper door as per Van's instructions. I built my own exhaust pipe muff that fitted over both exhaust pipes that pass in front of the sump. On the ground, and in flight, I get a noticeable RPM drop when selecting carb heat on. I installed an airbox temperature probe, one of those cheap Radio Shack indoor/outdoor dual sensor thermometers. During initial flight testing I had no trouble getting 50-70?C temp rises at 75% power. The max temp I saw in testing was 89?C in the airbox. I thought this was good enough, the cheap thermometer has since failed, but I know my system works.
'If it's stupid but it works, it ain't stupid'
robertahegy
Moderator/Tech Counselor
Great info, Grant. Maybe I will install a larger heat muff at next annual.
Thanks,
Roberta
Thanks,
Roberta
How Tight Is the Plumbing?
When I installed carb heat on a FAB-equipped 7, I used the beer can Van's sells for the pick-off, knowing full well that sucking air across only 2" of exhaust isn't going to warm all that air all that much. No high math involved here; it doesn't pass the smell test. Yet I persisted. What I did do different was NOT use the Van's Carb Heat Connector because it is perched up on Z-brackets above the FAB hot air opening. This leaves a huge gap that will allow unheated air into the engine. I installed a spun aluminum 2" pick-off that Spruce sells to achieve a no-leak path from beer can (the plane's, not mine) to the intake (the plane's, not mine). It, incidently is rugged compared to the Van's offering. I removed the Z-brackets from the Van's connector to use it as the cabin air pick-off. The wimpy tack welds snapped within 20 hours; I remember others have posted similar failures. It's a piece of crap no matter the application.
I think I'll have a beer.
John Siebold
When I installed carb heat on a FAB-equipped 7, I used the beer can Van's sells for the pick-off, knowing full well that sucking air across only 2" of exhaust isn't going to warm all that air all that much. No high math involved here; it doesn't pass the smell test. Yet I persisted. What I did do different was NOT use the Van's Carb Heat Connector because it is perched up on Z-brackets above the FAB hot air opening. This leaves a huge gap that will allow unheated air into the engine. I installed a spun aluminum 2" pick-off that Spruce sells to achieve a no-leak path from beer can (the plane's, not mine) to the intake (the plane's, not mine). It, incidently is rugged compared to the Van's offering. I removed the Z-brackets from the Van's connector to use it as the cabin air pick-off. The wimpy tack welds snapped within 20 hours; I remember others have posted similar failures. It's a piece of crap no matter the application.
I think I'll have a beer.
John Siebold
Last edited:
jthocker
Well Known Member
carb heat
To All
I too was having trouble getting any rpm drop with Van's small muff. I started flying last July and had my time flown off in Sept. I had all the bugs worked out except for the carb heat problem. Winter was around the corner and I wanted to fly IFR but the carb heat kept nawing at me. First I sealed up the flange that Van supplies with the muff, no help. So I purchased a stainless muff from Wicks and installed it on the front crossover tube above the carb heat door. I did not route air to the muff, I just let it draw air from inside the cowl. This helped alot. Since I'm starting my annual(condition) inspection I decided to get some good baseline numbers after 1 year and 100 hrs. Usually when I do a runup I check for a drop with carb heat but never really look to see how much I get. After reading the replies about the carb heat I decided to wait a while and take note. So with the engine warmed up (325cht), 30 deg.C OAT, RPM at 1800 (Digital EIS), full carb heat, after 30 seconds RPM was down to 1740, carb heat full off Rpm recovered to 1800. Maybe I'll get a carb temp probe or the Grand Rapids EIS but for now I'm much happier with the full muff.
Jon
To All
I too was having trouble getting any rpm drop with Van's small muff. I started flying last July and had my time flown off in Sept. I had all the bugs worked out except for the carb heat problem. Winter was around the corner and I wanted to fly IFR but the carb heat kept nawing at me. First I sealed up the flange that Van supplies with the muff, no help. So I purchased a stainless muff from Wicks and installed it on the front crossover tube above the carb heat door. I did not route air to the muff, I just let it draw air from inside the cowl. This helped alot. Since I'm starting my annual(condition) inspection I decided to get some good baseline numbers after 1 year and 100 hrs. Usually when I do a runup I check for a drop with carb heat but never really look to see how much I get. After reading the replies about the carb heat I decided to wait a while and take note. So with the engine warmed up (325cht), 30 deg.C OAT, RPM at 1800 (Digital EIS), full carb heat, after 30 seconds RPM was down to 1740, carb heat full off Rpm recovered to 1800. Maybe I'll get a carb temp probe or the Grand Rapids EIS but for now I'm much happier with the full muff.
Jon
wicks carb heat muff
I finally bought and installed the wicks stainless steel muff. It is part number EC100-020. It clamps to the crossover tube and just fits between the 2 pipes. I did a runup and got a 60 rpm drop with this. much better than the vans setup. If you're concerned about the vans muff try this. I tried uploading a picture of the setup but gave up after a number of error messages. hope you can visualize it.
regards
doug
I finally bought and installed the wicks stainless steel muff. It is part number EC100-020. It clamps to the crossover tube and just fits between the 2 pipes. I did a runup and got a 60 rpm drop with this. much better than the vans setup. If you're concerned about the vans muff try this. I tried uploading a picture of the setup but gave up after a number of error messages. hope you can visualize it.
regards
doug
jonbakerok
Well Known Member
ghost stories around a campfire
These discussions about carb ice always strike me like ghost stories around a campfire. I'm not trying to diminish the threat, but carb ice has been a problem since the Wright Brothers days. Why can't we ever get any REAL information? Has no one ever studied it scientifically?
Think of what's been said so far:
1. Carb ice can happen anytime the humidity is above 50% the temperature is below 30 degrees celsius. 30 degrees celsius is 86 in real degrees! If that's all it takes then carburated flight in Houston would be impossible more than 9 months out of the year!
2. Carb ice can happen anytime the humidity is above 50% and the carb temp guage is between -10 and +10 degrees celsius. Has anyone ever seen water freeze at 50 degrees farenheight?
These numbers are so broad they're useless. It's like saying carb ice can happen on on Wednesdays.
Common sense tells me that there must be some other reason that once in a few hundred thousand flights someone's carburator freezes up. What are the other factors? What about air density? Should we be especially alert when the air pressure is significantly below 29.92? How much below? Are there other factors? Has anyone really gone down with carb ice on a clear humid June day in Atlanta buzzing around at 3000 feet? Or is the typical scenario a guy loafing along at half power at 10000 feet in the clouds in January? And how come the other few hundred guys doing the same thing that day didn't get carb ice? Was it the clouds, the air density, the sub-freezing weather? Or could it have been a dirty airfilter?
Sorry to be so bitchy, but when the topic turns to safety, I get really tired of the same old wives tales and a warning to "be careful". You'd think that with a subject as technical as aviation, we'd occasionally get some real science.
These discussions about carb ice always strike me like ghost stories around a campfire. I'm not trying to diminish the threat, but carb ice has been a problem since the Wright Brothers days. Why can't we ever get any REAL information? Has no one ever studied it scientifically?
Think of what's been said so far:
1. Carb ice can happen anytime the humidity is above 50% the temperature is below 30 degrees celsius. 30 degrees celsius is 86 in real degrees! If that's all it takes then carburated flight in Houston would be impossible more than 9 months out of the year!
2. Carb ice can happen anytime the humidity is above 50% and the carb temp guage is between -10 and +10 degrees celsius. Has anyone ever seen water freeze at 50 degrees farenheight?
These numbers are so broad they're useless. It's like saying carb ice can happen on on Wednesdays.
Common sense tells me that there must be some other reason that once in a few hundred thousand flights someone's carburator freezes up. What are the other factors? What about air density? Should we be especially alert when the air pressure is significantly below 29.92? How much below? Are there other factors? Has anyone really gone down with carb ice on a clear humid June day in Atlanta buzzing around at 3000 feet? Or is the typical scenario a guy loafing along at half power at 10000 feet in the clouds in January? And how come the other few hundred guys doing the same thing that day didn't get carb ice? Was it the clouds, the air density, the sub-freezing weather? Or could it have been a dirty airfilter?
Sorry to be so bitchy, but when the topic turns to safety, I get really tired of the same old wives tales and a warning to "be careful". You'd think that with a subject as technical as aviation, we'd occasionally get some real science.
Jon,
You probably already know this but a few comments ...
The temperature that REALLY matters is the temperature inside the carb. The low pressure (higher velocity?) inside causes the temp to drop quite a bit inside.
I installed a carb ice detector on my Piper some years ago (light gets blocked by ice buildup) and I was AMAZED!!! At startup you set the initial threshold for the system (no ice) and even on taxi out there would be **some** buildup.
There were indications so often of **some** buildup that I now don't bother to turn it on. The point here is that there is more ice in there (on hot days with some humidity even) than you might think.
I only recall a couple of times where I felt performance was beginning to be affected by card ice. Once throttled back to fly with some friends who were in a 172 and the outside was VERY humid (and cool). The other on base over some water on a hot day. On the flying along case, I added carb heat and full power (told my friends I would wait for them at next stop) and on base I just added carb heat I think (in Piper handbook, you add it only if indicated) and landed no problem.
James
You probably already know this but a few comments ...
The temperature that REALLY matters is the temperature inside the carb. The low pressure (higher velocity?) inside causes the temp to drop quite a bit inside.
I installed a carb ice detector on my Piper some years ago (light gets blocked by ice buildup) and I was AMAZED!!! At startup you set the initial threshold for the system (no ice) and even on taxi out there would be **some** buildup.
There were indications so often of **some** buildup that I now don't bother to turn it on. The point here is that there is more ice in there (on hot days with some humidity even) than you might think.
I only recall a couple of times where I felt performance was beginning to be affected by card ice. Once throttled back to fly with some friends who were in a 172 and the outside was VERY humid (and cool). The other on base over some water on a hot day. On the flying along case, I added carb heat and full power (told my friends I would wait for them at next stop) and on base I just added carb heat I think (in Piper handbook, you add it only if indicated) and landed no problem.
James
jonbakerok said:
There is a substantial drop in temperature through the venturi of the carb plus just downstream of the fuel nozzle, the temperature can drop even further due to the vaporization of the fuel. Best to fit a carb temp sensor and gauge to find out what is happening.
I've seen statements here that RV Lycoming engine installations rarely suffer carb icing. The fact that a Lycoming is installed in an RV has nothing to do with anything. If the temperature in the venturi is below freezing and there is enough humidity, you may form carb ice. I've had it at +23C one day and -18C another day, neither of which days were very humid.
Regs require an adequate system to prevent carb ice. Van's supplied 90 degree pipe muff will not. What will you do if you get carb ice? Good chance you are going down if you can't get out of the conditions. I think many unexplained power loss accidents are caused by carb ice. Accident investigators find nothing an hour after the crash as the ice melts from the latent engine heat. Traces gone.
I just don't understand people's reluctance to fit a proper system. It's not rocket science and it is important.
I've seen statements here that RV Lycoming engine installations rarely suffer carb icing. The fact that a Lycoming is installed in an RV has nothing to do with anything. If the temperature in the venturi is below freezing and there is enough humidity, you may form carb ice. I've had it at +23C one day and -18C another day, neither of which days were very humid.
Regs require an adequate system to prevent carb ice. Van's supplied 90 degree pipe muff will not. What will you do if you get carb ice? Good chance you are going down if you can't get out of the conditions. I think many unexplained power loss accidents are caused by carb ice. Accident investigators find nothing an hour after the crash as the ice melts from the latent engine heat. Traces gone.
I just don't understand people's reluctance to fit a proper system. It's not rocket science and it is important.
osxuser
Well Known Member
As to Lycomings being less prone to carb ice, I don't know. In my relatively meager 370Hr's flight time, I've encountered carb ice 4 times. Twice it was one the ground while still in RUNUP. Once was in a 172 and once was in our o-360 powered 177. This is in Los Angeles and both of the ground incidences were with the temperatures between 60 and 80 degrees, and the relative humidity high. The time in the 172, I had to leave carb heat on or it would just keep coming back. I think that much of the time when a pilot encounters carb ice they don't even know it.
I know a flight instructor who encountered some severe carb ice in a 152, and didn't understand why when he pushed the carb heat off after it cleared up, it came back within a minute. So his solution was to dramaically lean the mixture to get smooth combustion. He really didn't think he had carb ice, he thought something else was wrong. I think the best was to avoid the whole issue is fuel injection, but lacking that option, I want to see at least 100rpm drop at runup if I'm gonna take off. The 177 had a pretty weak heat system coming off the muffler. But we installed a pickup off the #3 riser to fix that problem.
I know a flight instructor who encountered some severe carb ice in a 152, and didn't understand why when he pushed the carb heat off after it cleared up, it came back within a minute. So his solution was to dramaically lean the mixture to get smooth combustion. He really didn't think he had carb ice, he thought something else was wrong. I think the best was to avoid the whole issue is fuel injection, but lacking that option, I want to see at least 100rpm drop at runup if I'm gonna take off. The 177 had a pretty weak heat system coming off the muffler. But we installed a pickup off the #3 riser to fix that problem.
vlittle
Well Known Member
carb heat issues
Interesting discussion on Van's beer-can carb heat muff.
The Van's set up is not truly carb heat, it's induction heat.
As posted earlier, it's supposed to minimize the build up of frozen precipitation on the air filter.
A true carb heat system would bypass the air filter and let hot air directly into the carburetor intake. Certified A/C do this, and hence the warning about applying carb heat in dusty conditions (unfiltered air into carb).
It may be hard to get a 90 degree rise with Van's set-up because the Air Filter has some thermal mass and acts as a bit of a heat sink.
If someone out there wants to experiment with a true carb heat system, it may be worth looking at the induction bypass system as a starting point, and routing hot air to it and controlling the magnetic flapper valve with a cable. This will take some effort because the cowling fit is tight under the FAB.
The worst case scenario is both induction ice and carb ice simultaneously. I doubt that any induction heat system would could melt a plug of filter ice and carb ice quickly. This would call for a large heat muff.
On a final note: the design of the Van's system lends itself to ground taxiing with carb heat 'hot'... the air is both filtered and drawn from inside the cowling, which can be cleaner in dusty conditions. Lean the engine for taxiing (good practice at all times to keep the plugs clean).
Vern Little
RV-9A
Interesting discussion on Van's beer-can carb heat muff.
The Van's set up is not truly carb heat, it's induction heat.
As posted earlier, it's supposed to minimize the build up of frozen precipitation on the air filter.
A true carb heat system would bypass the air filter and let hot air directly into the carburetor intake. Certified A/C do this, and hence the warning about applying carb heat in dusty conditions (unfiltered air into carb).
It may be hard to get a 90 degree rise with Van's set-up because the Air Filter has some thermal mass and acts as a bit of a heat sink.
If someone out there wants to experiment with a true carb heat system, it may be worth looking at the induction bypass system as a starting point, and routing hot air to it and controlling the magnetic flapper valve with a cable. This will take some effort because the cowling fit is tight under the FAB.
The worst case scenario is both induction ice and carb ice simultaneously. I doubt that any induction heat system would could melt a plug of filter ice and carb ice quickly. This would call for a large heat muff.
On a final note: the design of the Van's system lends itself to ground taxiing with carb heat 'hot'... the air is both filtered and drawn from inside the cowling, which can be cleaner in dusty conditions. Lean the engine for taxiing (good practice at all times to keep the plugs clean).
Vern Little
RV-9A
Carb Ice Experience
To Jon Baker, jclark, and others.
Carb ice can and does happen with very high ambient temperatures and at low altitudes!!
I am a retired Air Force pilot who flew the Cessna O-1 Bird Dog (L19) in Viet Nam as a Forward Air Controller (FAC). I don't remember the engine designation, but it was a 213 HP Continental.
I experienced sudden engine failure due to carb ice on two occasions with the OAT in the mid 80's to low 90'sF and humidities near 100%. Once was at around 1500'AGL and again around 800-1000'AGL. On both occasions rapid application of carb heat resulted in restarts within 15-20 seconds.
My personal observation was that the key seemed to be the near juxtaposition of the OAT and the dew point. The supersaturated air racing through the venturi can freeze in a heartbeat. In the Mekong Delta region of South Viet Nam as the temperature rose each day you could almost count on the sudden formation of a very thin, but solid (maybe 200-300' thick) overcast deck. It usually formed at around 800' then slowly rose in altitude to around 2000' where it began breaking up into cumulus puffies that continued to rise and build throughout the day. The life span of the overcast deck was usually 30-45 minutes. This behavior clearly indicates overlapping temps and dew points.
I even had engine coughing and sputtering on the ground while taxiing a few times that was cured with application of carb heat. Maybe that particular Continental engine setup (not always the same airplane) was more prone to developing carb ice.
At any rate, I quickly became a believer in carb ice forming at unexpected times and in high OAT conditions.
Mike Clay
To Jon Baker, jclark, and others.
Carb ice can and does happen with very high ambient temperatures and at low altitudes!!
I am a retired Air Force pilot who flew the Cessna O-1 Bird Dog (L19) in Viet Nam as a Forward Air Controller (FAC). I don't remember the engine designation, but it was a 213 HP Continental.
I experienced sudden engine failure due to carb ice on two occasions with the OAT in the mid 80's to low 90'sF and humidities near 100%. Once was at around 1500'AGL and again around 800-1000'AGL. On both occasions rapid application of carb heat resulted in restarts within 15-20 seconds.
My personal observation was that the key seemed to be the near juxtaposition of the OAT and the dew point. The supersaturated air racing through the venturi can freeze in a heartbeat. In the Mekong Delta region of South Viet Nam as the temperature rose each day you could almost count on the sudden formation of a very thin, but solid (maybe 200-300' thick) overcast deck. It usually formed at around 800' then slowly rose in altitude to around 2000' where it began breaking up into cumulus puffies that continued to rise and build throughout the day. The life span of the overcast deck was usually 30-45 minutes. This behavior clearly indicates overlapping temps and dew points.
I even had engine coughing and sputtering on the ground while taxiing a few times that was cured with application of carb heat. Maybe that particular Continental engine setup (not always the same airplane) was more prone to developing carb ice.
At any rate, I quickly became a believer in carb ice forming at unexpected times and in high OAT conditions.
Mike Clay
jonbakerok
Well Known Member
Science
No argument there.. carb ice definately happens at unexpected times.
My point is that an anecdote telling me that you had carb ice once when it warm outside, or a "rule" that tells me to "watch" for carb ice when it's 86 degrees and 50% humidity, are basically worthless. You might as well just say "Be careful -- sometimes carberators ice up for no apparent reason". (Or for that matter -- "Be carefull, sometimes fuel injectors vapor lock for no apparent reason").
I just think it would be much more helpful if at sometime during the last 100 years, somebody had bothered to do some real science and figure out why hundreds of carburated planes are able to fly around Houston nearly every day of the year in the exact conditions you describe without a problem -- and what was different about the one in a thousand that had a problem.
If it was simply humidity plus temperature, then a given engine would always ice when the humidity and temperature reached a specific, predictable point.
Now THAT would be a useful scientific fact to know.
mtclay said:
No argument there.. carb ice definately happens at unexpected times.
My point is that an anecdote telling me that you had carb ice once when it warm outside, or a "rule" that tells me to "watch" for carb ice when it's 86 degrees and 50% humidity, are basically worthless. You might as well just say "Be careful -- sometimes carberators ice up for no apparent reason". (Or for that matter -- "Be carefull, sometimes fuel injectors vapor lock for no apparent reason").
I just think it would be much more helpful if at sometime during the last 100 years, somebody had bothered to do some real science and figure out why hundreds of carburated planes are able to fly around Houston nearly every day of the year in the exact conditions you describe without a problem -- and what was different about the one in a thousand that had a problem.
If it was simply humidity plus temperature, then a given engine would always ice when the humidity and temperature reached a specific, predictable point.
Now THAT would be a useful scientific fact to know.
Jeff Vaughan
Well Known Member
Carb Heat
My instructor taught me that carb ice was possible whenever there was moisture present. Dew, mist, clouds, humidity etc. This is the rule I was taught.
Jeff Vaughan
My instructor taught me that carb ice was possible whenever there was moisture present. Dew, mist, clouds, humidity etc. This is the rule I was taught.
Jeff Vaughan
Barry
Well Known Member
Carburettor Ice
I have often wondered about the possibility of carburettor ice with my RV. To the best of my knowledge I have never experienced carburettor ice with the RV and I have flown it in many different climatic conditions including IMC.
I have about 670 hours on it over the last 6 years. The plane has the Robbins (sp?) heat muff on the cross over tube which routes the air via a scat tube to the filtered air box with my LycO360A1A engine.
I also have a RMI engine monitor which has a carburetor temperature probe. The display shows carburettor temperatures up to +19 deg. C.
It is very rare that the carburettor temperature drops to +10 C, even with freezing OAT. With the Lycoming the carburettor is bolted directly to the sump, Continental engines are different and this may be why they are more prone to carburettor icing.
As the oil temperature in the sump is in the region of 90 C this heat is conducted directly to the carburettor and is probably the reason for seeing high carburettor temperatures.
For example today I was out flying today, the OAT was +19C and the carburettor temperature display was pegged at its maximum of +19 C.
Even during the engine run up prior to take off the carburettor temperature was pegged at its maximum of +19 C
I would be interested in hearing from anyone else you has a carburettor temperature probe so see what their reading are.
Some one talked about using an Ice Man carburettor ice detector. They mentioned that during ground operation they so often had ice warnings that they turned the system off. As this system works with an optical detector instead of providing a temperature output is it possible that condensation is forming in the carburettor and this is being erroneously detected as ice?
Barry RV6A
I have often wondered about the possibility of carburettor ice with my RV. To the best of my knowledge I have never experienced carburettor ice with the RV and I have flown it in many different climatic conditions including IMC.
I have about 670 hours on it over the last 6 years. The plane has the Robbins (sp?) heat muff on the cross over tube which routes the air via a scat tube to the filtered air box with my LycO360A1A engine.
I also have a RMI engine monitor which has a carburetor temperature probe. The display shows carburettor temperatures up to +19 deg. C.
It is very rare that the carburettor temperature drops to +10 C, even with freezing OAT. With the Lycoming the carburettor is bolted directly to the sump, Continental engines are different and this may be why they are more prone to carburettor icing.
As the oil temperature in the sump is in the region of 90 C this heat is conducted directly to the carburettor and is probably the reason for seeing high carburettor temperatures.
For example today I was out flying today, the OAT was +19C and the carburettor temperature display was pegged at its maximum of +19 C.
Even during the engine run up prior to take off the carburettor temperature was pegged at its maximum of +19 C
I would be interested in hearing from anyone else you has a carburettor temperature probe so see what their reading are.
Some one talked about using an Ice Man carburettor ice detector. They mentioned that during ground operation they so often had ice warnings that they turned the system off. As this system works with an optical detector instead of providing a temperature output is it possible that condensation is forming in the carburettor and this is being erroneously detected as ice?
Barry RV6A
kentb
Well Known Member
IO engine heat?
I am building a RV9A with IO-320 engine. I will be installing the induction alt. air into the filter and the other door below the TB if the filter gets clogged. Both doors will be operated by pull cables.
Question: Should I try to route extra heat off the crossover to the induction alt. air door?
Kent
I am building a RV9A with IO-320 engine. I will be installing the induction alt. air into the filter and the other door below the TB if the filter gets clogged. Both doors will be operated by pull cables.
Question: Should I try to route extra heat off the crossover to the induction alt. air door?
Kent
gmcjetpilot
Well Known Member
FI = no heat
I agree Van's "carb heat" is marginal from a part 23 certification standard. The saving grace is the Lycoming is less likely (LESS NOT UNLIKELY) to get carb ice. The tight cowl may even enhance this characteristic.
I will be blunt. You are crazy to build your plane without carb heat, unless you plan on only flying in Southern Arizona in the summer VFR.
Yes carb ice happens and claims a dozen or more planes a year. Since the evidence melts there are many more cases no doubt not quite explained but due to carb ice.
Google carb ice. Lots of good info. George
No carb ice with fuel injection. Yes an alternate air is good but you don't need the heat. Georgekentb said:
I agree Van's "carb heat" is marginal from a part 23 certification standard. The saving grace is the Lycoming is less likely (LESS NOT UNLIKELY) to get carb ice. The tight cowl may even enhance this characteristic.
I will be blunt. You are crazy to build your plane without carb heat, unless you plan on only flying in Southern Arizona in the summer VFR.
Yes carb ice happens and claims a dozen or more planes a year. Since the evidence melts there are many more cases no doubt not quite explained but due to carb ice.
Google carb ice. Lots of good info. George
About a week ago, I started my RV-6 on a cold damp morning in Oregon. We had light rain showers and the temperature was below 40 degrees F. My run-up before departure revealed that I'd picked up carb ice while taxiing out. The Van's "beer can" heat muff provided enough heat to remove the ice in about a minute. I would say it appears to be effective, at least in this climate.
Bob Severns
Bob Severns
gmcjetpilot
Well Known Member
Bob I flew in the North West for 15 years and know what you mean. It is good to know you had enough heat on the ground. Taxi is a prime place for carb ice. I guess the real measure would be in-flight, which I would guess would be sufficient if caught early. I guess the watch word would be if at all suspect, carb heat on often and early. After the flame is blown out (carb chokes the engine) you may not have heat to melt the ice.hngrflyr said:
Putting my CFI cap on for one minute, my pet peeve:
(after a long wet taxi) During run-up check the carb ice by leaving it on for more than a fraction of second. Leave it on an note the RPM drop (fixed) or MAP drop and than wait to see of the RPM/MAP rise while the heat is still on. Than after the run up note any change. If idle RPM or MAP is higher after the run-up (and carb ice) you most likely burned ice off.
Hat off
If you are in mild conditions, HOT/DRY, than hightened caution may not be as warrennted, but the range of humidity and temps that are condusive to ice are pretty wide. George
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alpinelakespilot2000
Well Known Member
gmcjetpilot said:
George, or others...
I've heard on this forum (and elsewhere) that RVs don't show much (if any) RPM drop when testing the carb heat during run-up, for whatever reason.
1. If this is true, is that because the carb heat is less effective in an RV? Would this suggest using a feed off the heat muff, like some have suggested earlier in this thread, to be sure you're getting good heat to the carb?
2. If this is true, does having the carb heat on for more than one fraction of a second during run-up (which I agree is essential to usefully test carb heat) going to be of help in an RV?
Just curious. Maybe I've got different carb. issues confused.
