AirTalk.org Aviation discussions newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Carb Heat          AirTalk.org Forum Index -> Helicopters and rotary wing aircrafts View previous topic :: View next topic   Author Message Guest Posted: Thu Apr 19, 2007 10:03 pm    Post subject: Carb Heat I heard, somewhere, that if you apply full carb heat and then immediately lower the collective (on R22s and 44s)this can cause the engine to run rough and in extreme cases can even cause engine failure.I s there any evidence for this or is it just a silly rumour? I have, up until now, always pulled on full carb heat just before descending now I wait a few seconds before lowering the collective. Back to top Guest Posted: Sat Apr 21, 2007 3:22 am    Post subject: Re: Carb Heat On 19 Apr 2007 10:03:06 -0700, alastair_smith (AT) hotmail (DOT) com wrote: Quote: I heard, somewhere, that if you apply full carb heat and then immediately lower the collective (on R22s and 44s)this can cause the engine to run rough and in extreme cases can even cause engine failure.I s there any evidence for this or is it just a silly rumour? I have, up until now, always pulled on full carb heat just before descending now I wait a few seconds before lowering the collective. You should always wait to give the heat time to melt any ice that might be present. If you lower the collective immediately, you might not have given the ice any time to melt which might lead to a stalled engine. Regards. Jan Back to top Guest Posted: Sat Apr 21, 2007 4:04 pm    Post subject: Re: Carb Heat On 20 Apr, 23:22, NoSpam@my-home_NoSpam.demon_ZeroSpam.co.uk wrote: Quote: On 19 Apr 2007 10:03:06 -0700, alastair_sm...@hotmail.com wrote: I heard, somewhere, that if you apply full carb heat and then immediately lower the collective (on R22s and 44s)this can cause the engine to run rough and in extreme cases can even cause engine failure.I s there any evidence for this or is it just a silly rumour? I have, up until now, always pulled on full carb heat just before descending now I wait a few seconds before lowering the collective. You should always wait to give the heat time to melt any ice that might be present. If you lower the collective immediately, you might not have given the ice any time to melt which might lead to a stalled engine. Regards. Jan Thanks Jan, that makes sense. So what you are saying that the carburettor is more prone to icing when using less power? Back to top B4RT Guest Posted: Sun Apr 22, 2007 2:14 am    Post subject: Re: Carb Heat Carb heat lowers the amount of O2 available thereby making a richer mixture. This is on your Written exam. Rapid power changes can freak out any engine. The two thing together probably cause the effect, but I would wager that a well maintained engine would not quit on you. But what do I know? I fly a turbine machine because I hate those finicky suck-bang-blows so much. <grin> Bart <alastair_smith (AT) hotmail (DOT) com> wrote in message Quote: Thanks Jan, that makes sense. So what you are saying that the carburettor is more prone to icing when using less power? Back to top Guest Posted: Sun Apr 22, 2007 3:57 am    Post subject: Re: Carb Heat On 21 Apr 2007 04:04:00 -0700, alastair_smith (AT) hotmail (DOT) com wrote: Quote: On 20 Apr, 23:22, NoSpam@my-home_NoSpam.demon_ZeroSpam.co.uk wrote: On 19 Apr 2007 10:03:06 -0700, alastair_sm...@hotmail.com wrote: I heard, somewhere, that if you apply full carb heat and then immediately lower the collective (on R22s and 44s)this can cause the engine to run rough and in extreme cases can even cause engine failure.I s there any evidence for this or is it just a silly rumour? I have, up until now, always pulled on full carb heat just before descending now I wait a few seconds before lowering the collective. You should always wait to give the heat time to melt any ice that might be present. If you lower the collective immediately, you might not have given the ice any time to melt which might lead to a stalled engine. Regards. Jan Thanks Jan, that makes sense. So what you are saying that the carburettor is more prone to icing when using less power? Not really - the engine is more prone to the effects of icing when using less power. I haven't flown a piston aircraft in over 7 years but it's no big deal having to look after carburetor heat. You know when you've suffered a fair amount of icing if the engine runs rough while it clears the ice as it sucks the water through the system. However, it shouldn't get to this because you should be looking after the intake temperature throughout the flight. Pulling full carb heat before the descent is "to leave no chance" of ice being present. You get into the habit of following procedure whatever you fly - hopefully! Jan Back to top Guest Posted: Sun Apr 22, 2007 7:30 pm    Post subject: Re: Carb Heat On 21 Apr, 22:14, "B4RT" <noahb...@nospam.org> wrote: Quote: Carb heat lowers the amount of O2 available thereby making a richer mixture. This is on your Written exam. Rapid power changes can freak out any engine. The two thing together probably cause the effect, but I would wager that a well maintained engine would not quit on you. But what do I know? I fly a turbine machine because I hate those finicky suck-bang-blows so much. <grin Bart alastair_sm...@hotmail.com> wrote in message Thanks Jan, that makes sense. So what you are saying that the carburettor is more prone to icing when using less power?- Hide quoted text - - Show quoted text - Unfortunately I've forgotten most of what I learnt for the exams! I am only a PPL with about 100 hours and have to pay for my flying so cost wise I can't aford a turbine... but I dream. It seems to me that if they can't find a cause for an accident they blame it on good old "carb icing". Back to top Guest Posted: Sun Apr 22, 2007 7:35 pm    Post subject: Re: Carb Heat On 21 Apr, 23:57, NoSpam@my-home_NoSpam.demon_ZeroSpam.co.uk wrote: Quote: On 21 Apr 2007 04:04:00 -0700, alastair_sm...@hotmail.com wrote: On 20 Apr, 23:22, NoSpam@my-home_NoSpam.demon_ZeroSpam.co.uk wrote: On 19 Apr 2007 10:03:06 -0700, alastair_sm...@hotmail.com wrote: I heard, somewhere, that if you apply full carb heat and then immediately lower the collective (on R22s and 44s)this can cause the engine to run rough and in extreme cases can even cause engine failure.I s there any evidence for this or is it just a silly rumour? I have, up until now, always pulled on full carb heat just before descending now I wait a few seconds before lowering the collective. You should always wait to give the heat time to melt any ice that might be present. If you lower the collective immediately, you might not have given the ice any time to melt which might lead to a stalled engine. Regards. Jan Thanks Jan, that makes sense. So what you are saying that the carburettor is more prone to icing when using less power? Not really - the engine is more prone to the effects of icing when using less power. I haven't flown a piston aircraft in over 7 years but it's no big deal having to look after carburetor heat. You know when you've suffered a fair amount of icing if the engine runs rough while it clears the ice as it sucks the water through the system. However, it shouldn't get to this because you should be looking after the intake temperature throughout the flight. Pulling full carb heat before the descent is "to leave no chance" of ice being present. You get into the habit of following procedure whatever you fly - hopefully! Jan- Hide quoted text - - Show quoted text - I do pay a lot of attention to carb heat whilst flying. I keep the needle out of the yellow, but is it the case that the more carb heat you use the less efficient the engine runs? I always (well nearly always) push in the carb heat at 300ft when on finals. Back to top Guest Posted: Sun Apr 22, 2007 7:57 pm    Post subject: Re: Carb Heat On 22 Apr 2007 07:35:30 -0700, alastair_smith (AT) hotmail (DOT) com wrote: Quote: On 21 Apr, 23:57, NoSpam@my-home_NoSpam.demon_ZeroSpam.co.uk wrote: On 21 Apr 2007 04:04:00 -0700, alastair_sm...@hotmail.com wrote: On 20 Apr, 23:22, NoSpam@my-home_NoSpam.demon_ZeroSpam.co.uk wrote: On 19 Apr 2007 10:03:06 -0700, alastair_sm...@hotmail.com wrote: I heard, somewhere, that if you apply full carb heat and then immediately lower the collective (on R22s and 44s)this can cause the engine to run rough and in extreme cases can even cause engine failure.I s there any evidence for this or is it just a silly rumour? I have, up until now, always pulled on full carb heat just before descending now I wait a few seconds before lowering the collective. You should always wait to give the heat time to melt any ice that might be present. If you lower the collective immediately, you might not have given the ice any time to melt which might lead to a stalled engine. Regards. Jan Thanks Jan, that makes sense. So what you are saying that the carburettor is more prone to icing when using less power? Not really - the engine is more prone to the effects of icing when using less power. I haven't flown a piston aircraft in over 7 years but it's no big deal having to look after carburetor heat. You know when you've suffered a fair amount of icing if the engine runs rough while it clears the ice as it sucks the water through the system. However, it shouldn't get to this because you should be looking after the intake temperature throughout the flight. Pulling full carb heat before the descent is "to leave no chance" of ice being present. You get into the habit of following procedure whatever you fly - hopefully! Jan- Hide quoted text - - Show quoted text - I do pay a lot of attention to carb heat whilst flying. I keep the needle out of the yellow, but is it the case that the more carb heat you use the less efficient the engine runs? I always (well nearly always) push in the carb heat at 300ft when on finals. You are correct, the more heat the less efficient the engine because of the mixture. But less efficient is better than no power any day of the week! Remember, you usually only have an issue when you loose translational lift - around 20 knots. If this happens after a flight, depending on altitude you've used fuel in the flight (which you had to take off with) so life can be easier because of less weight. Back to top Guest Posted: Mon Apr 23, 2007 12:41 pm    Post subject: Re: Carb Heat On 22 Apr, 15:57, NoSpam@my-home_NoSpam.demon_ZeroSpam.co.uk wrote: Quote: On 22 Apr 2007 07:35:30 -0700, alastair_sm...@hotmail.com wrote: On 21 Apr, 23:57, NoSpam@my-home_NoSpam.demon_ZeroSpam.co.uk wrote: On 21 Apr 2007 04:04:00 -0700, alastair_sm...@hotmail.com wrote: On 20 Apr, 23:22, NoSpam@my-home_NoSpam.demon_ZeroSpam.co.uk wrote: On 19 Apr 2007 10:03:06 -0700, alastair_sm...@hotmail.com wrote: I heard, somewhere, that if you apply full carb heat and then immediately lower the collective (on R22s and 44s)this can cause the engine to run rough and in extreme cases can even cause engine failure.I s there any evidence for this or is it just a silly rumour? I have, up until now, always pulled on full carb heat just before descending now I wait a few seconds before lowering the collective. You should always wait to give the heat time to melt any ice that might be present. If you lower the collective immediately, you might not have given the ice any time to melt which might lead to a stalled engine. Regards. Jan Thanks Jan, that makes sense. So what you are saying that the carburettor is more prone to icing when using less power? Not really - the engine is more prone to the effects of icing when using less power. I haven't flown a piston aircraft in over 7 years but it's no big deal having to look after carburetor heat. You know when you've suffered a fair amount of icing if the engine runs rough while it clears the ice as it sucks the water through the system. However, it shouldn't get to this because you should be looking after the intake temperature throughout the flight. Pulling full carb heat before the descent is "to leave no chance" of ice being present. You get into the habit of following procedure whatever you fly - hopefully! Jan- Hide quoted text - - Show quoted text - I do pay a lot of attention to carb heat whilst flying. I keep the needle out of the yellow, but is it the case that the more carb heat you use the less efficient the engine runs? I always (well nearly always) push in the carb heat at 300ft when on finals. You are correct, the more heat the less efficient the engine because of the mixture. But less efficient is better than no power any day of the week! Remember, you usually only have an issue when you loose translational lift - around 20 knots. If this happens after a flight, depending on altitude you've used fuel in the flight (which you had to take off with) so life can be easier because of less weight.- Hide quoted text - - Show quoted text - Sorry, not sure what you meant in the last "missive". I do not understand your last sentance. Back to top Guest Posted: Mon Apr 23, 2007 12:44 pm    Post subject: Re: Carb Heat On 23 Apr, 08:41, alastair_sm...@hotmail.com wrote: Quote: On 22 Apr, 15:57, NoSpam@my-home_NoSpam.demon_ZeroSpam.co.uk wrote: On 22 Apr 2007 07:35:30 -0700, alastair_sm...@hotmail.com wrote: On 21 Apr, 23:57, NoSpam@my-home_NoSpam.demon_ZeroSpam.co.uk wrote: On 21 Apr 2007 04:04:00 -0700, alastair_sm...@hotmail.com wrote: On 20 Apr, 23:22, NoSpam@my-home_NoSpam.demon_ZeroSpam.co.uk wrote: On 19 Apr 2007 10:03:06 -0700, alastair_sm...@hotmail.com wrote: I heard, somewhere, that if you apply full carb heat and then immediately lower the collective (on R22s and 44s)this can cause the engine to run rough and in extreme cases can even cause engine failure.I s there any evidence for this or is it just a silly rumour? I have, up until now, always pulled on full carb heat just before descending now I wait a few seconds before lowering the collective. You should always wait to give the heat time to melt any ice that might be present. If you lower the collective immediately, you might not have given the ice any time to melt which might lead to a stalled engine. Regards. Jan Thanks Jan, that makes sense. So what you are saying that the carburettor is more prone to icing when using less power? Not really - the engine is more prone to the effects of icing when using less power. I haven't flown a piston aircraft in over 7 years but it's no big deal having to look after carburetor heat. You know when you've suffered a fair amount of icing if the engine runs rough while it clears the ice as it sucks the water through the system. However, it shouldn't get to this because you should be looking after the intake temperature throughout the flight. Pulling full carb heat before the descent is "to leave no chance" of ice being present. You get into the habit of following procedure whatever you fly - hopefully! Jan- Hide quoted text - - Show quoted text - I do pay a lot of attention to carb heat whilst flying. I keep the needle out of the yellow, but is it the case that the more carb heat you use the less efficient the engine runs? I always (well nearly always) push in the carb heat at 300ft when on finals. You are correct, the more heat the less efficient the engine because of the mixture. But less efficient is better than no power any day of the week! Remember, you usually only have an issue when you loose translational lift - around 20 knots. If this happens after a flight, depending on altitude you've used fuel in the flight (which you had to take off with) so life can be easier because of less weight.- Hide quoted text - - Show quoted text - Sorry, not sure what you meant in the last "missive". I do not understand your last sentance.- Hide quoted text - - Show quoted text - Appalling spelling there I meant sentence not sentance. Back to top Andrew Crane Guest Posted: Mon Apr 23, 2007 9:29 pm    Post subject: Re: Carb Heat <alastair_smith (AT) hotmail (DOT) com> wrote in message news:1177153440.796951.177940 (AT) b75g2000hsg (DOT) googlegroups.com... Quote: On 20 Apr, 23:22, NoSpam@my-home_NoSpam.demon_ZeroSpam.co.uk wrote: On 19 Apr 2007 10:03:06 -0700, alastair_sm...@hotmail.com wrote: I heard, somewhere, that if you apply full carb heat and then immediately lower the collective (on R22s and 44s)this can cause the engine to run rough and in extreme cases can even cause engine failure.I s there any evidence for this or is it just a silly rumour? I have, up until now, always pulled on full carb heat just before descending now I wait a few seconds before lowering the collective. You should always wait to give the heat time to melt any ice that might be present. If you lower the collective immediately, you might not have given the ice any time to melt which might lead to a stalled engine. Regards. Jan Thanks Jan, that makes sense. So what you are saying that the carburettor is more prone to icing when using less power? This is so basic that I am surprised that you are in the machine at all without this knowledge. There is a depression formed between the carb venturi and the inlet valve. If the butterfly valve of the carb is closed, the expansion of the air after the valve is greater than if the valve is completely open and therefore the temperature drop is greater. The depression is measured with the MAP gauge. ie, anything less than atmospheric pressure is depression. The carb air temperature is measured upstream of the butterfly in the R22. This is why it is unreliable under 18" MAP. It is measuring the air before it is subject to the cooling effect of being expanded after the butterfly. The carb air temperature in the R44 is measured after the butterfly. The only way you are going top conk by cutting the throttle after applying full carb heat is if you are already iced up and the melting ice is being ingested by the engine. Or alternatively, the ice has narrowed the venturi area and dropping the butterfly asphyxiates the engine completely. Regards Andrew Back to top Guest Posted: Mon Apr 30, 2007 10:34 pm    Post subject: Re: Carb Heat On 23 Apr, 17:29, "Andrew Crane" <n...@inweb.co.uk> wrote: Quote: alastair_sm...@hotmail.com> wrote in message news:1177153440.796951.177940 (AT) b75g2000hsg (DOT) googlegroups.com... On 20 Apr, 23:22, NoSpam@my-home_NoSpam.demon_ZeroSpam.co.uk wrote: On 19 Apr 2007 10:03:06 -0700, alastair_sm...@hotmail.com wrote: I heard, somewhere, that if you apply full carb heat and then immediately lower the collective (on R22s and 44s)this can cause the engine to run rough and in extreme cases can even cause engine failure.I s there any evidence for this or is it just a silly rumour? I have, up until now, always pulled on full carb heat just before descending now I wait a few seconds before lowering the collective. You should always wait to give the heat time to melt any ice that might be present. If you lower the collective immediately, you might not have given the ice any time to melt which might lead to a stalled engine. Regards. Jan Thanks Jan, that makes sense. So what you are saying that the carburettor is more prone to icing when using less power? This is so basic that I am surprised that you are in the machine at all without this knowledge. There is a depression formed between the carb venturi and the inlet valve. If the butterfly valve of the carb is closed, the expansion of the air after the valve is greater than if the valve is completely open and therefore the temperature drop is greater. The depression is measured with the MAP gauge. ie, anything less than atmospheric pressure is depression. The carb air temperature is measured upstream of the butterfly in the R22. This is why it is unreliable under 18" MAP. It is measuring the air before it is subject to the cooling effect of being expanded after the butterfly. The carb air temperature in the R44 is measured after the butterfly. The only way you are going top conk by cutting the throttle after applying full carb heat is if you are already iced up and the melting ice is being ingested by the engine. Or alternatively, the ice has narrowed the venturi area and dropping the butterfly asphyxiates the engine completely. Regards Andrew- Hide quoted text - - Show quoted text - Andrew, Good point. I feel really quite stupid. 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