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.

On 20 Apr, 23:22, wrote:
On 19 Apr 2007 10:03:06 -0700, 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?

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

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?

On 21 Apr, 22:14, "B4RT" wrote:
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



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".

wrote in message
oups.com...
On 20 Apr, 23:22, wrote:
On 19 Apr 2007 10:03:06 -0700, 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

On 23 Apr, 17:29, "Andrew Crane" wrote:
wrote in message

oups.com...





On 20 Apr, 23:22, wrote:
On 19 Apr 2007 10:03:06 -0700, 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.

On 21 Apr, 23:57, wrote:
On 21 Apr 2007 04:04:00 -0700, wrote:





On 20 Apr, 23:22, wrote:
On 19 Apr 2007 10:03:06 -0700, 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.

On 22 Apr, 15:57, wrote:
On 22 Apr 2007 07:35:30 -0700, wrote:





On 21 Apr, 23:57, wrote:
On 21 Apr 2007 04:04:00 -0700, wrote:

On 20 Apr, 23:22, wrote:
On 19 Apr 2007 10:03:06 -0700, 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.

On 23 Apr, 08:41, wrote:
On 22 Apr, 15:57, wrote:





On 22 Apr 2007 07:35:30 -0700, wrote:

On 21 Apr, 23:57, wrote:
On 21 Apr 2007 04:04:00 -0700, wrote:

On 20 Apr, 23:22, wrote:
On 19 Apr 2007 10:03:06 -0700, 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.