Carb heat: my new policy. Any comments

On Sat, 6 Sep 2008 20:54:22 -0700 (PDT), "Robert M. Gary"
wrote:

On Sep 6, 9:58*am, Tman x@x wrote:

I think I'm going to follow a new SOP. *Turn the carb heat off on
mid-final. *Reasoning: no carb, esp a warm one is going to ice up in 30
seconds, sets me up better for a go-around, and will prevent this
stumble business (I did test it out at altitude, and it prevents or at
least seriously mitigates the stumble).

Don't put any money on that bet. I've had carbs freeze up on me during
stop-n-goes from the time it takes to kick off the heat to the time it
takes to pour on the coals. The carb can freeze in seconds.

-Robert, CFII

I'm with you Bob.
I once thought I'd throttle back and poke under some mist and pop out
the other side and resume. when the power came off the revs started
dropping and dropping and dropping. I bunged on full carb heat and
then full throttle and still the revs kept dropping. out the corner of
the eye I noticed a shaft of sunlight and turned toward the hole in
the mist. about 2 seconds into the sunlight and I had full power back
again. when it happens it happens quickly.

now back to the op's description of a rev drop on opening the
throttle.
my bet is that the carb has been in service for quite a while and the
leather bucket seal on the accelerator pump is knackered. it isnt
giving the full squirt of fuel on acceleration. the other possibility
is that the little jet pipe has moved out of the centre venturi
position and the squirt isnt making it up into the inlet tubing.
far better me thinks that he doesnt wank on creating new procedures
and gets the a&p's to check the carby functioning.

Stealth Pilot

"Stealth Pilot" wrote in message
...

I'm with you Bob.
I once thought I'd throttle back and poke under some mist and pop out
the other side and resume. when the power came off the revs started
dropping and dropping and dropping. I bunged on full carb heat and
then full throttle and still the revs kept dropping. out the corner of
the eye I noticed a shaft of sunlight and turned toward the hole in
the mist. about 2 seconds into the sunlight and I had full power back
again. when it happens it happens quickly.

now back to the op's description of a rev drop on opening the
throttle.
my bet is that the carb has been in service for quite a while and the
leather bucket seal on the accelerator pump is knackered. it isnt
giving the full squirt of fuel on acceleration. the other possibility
is that the little jet pipe has moved out of the centre venturi
position and the squirt isnt making it up into the inlet tubing.
far better me thinks that he doesnt wank on creating new procedures
and gets the a&p's to check the carby functioning.

Stealth Pilot

Very interesting points, which I plan to keep in mind when I return to
flying.

The only thing that I can add is that the results might be more reliable if
the A&P is experienced in servicing carburetors--and possibly magnetoes as
well.

Peter
(Having seen some poor work from folks who should have known better)

"Bertie the Bunyip" wrote in message
...

Lycomings, no problem with your plan at all. Continentals ice a bit more
easily, and on a clear dry day, there won't be a problem either, though
I'd be inclined to leave it on just a bit longer. I'd also get in the
habit of pushing the carb heat in with the throttle if you go around..

Bertie

Your a dumb ass. What next, practicing emergency landings by turning off the
fuel?

If you don't like an engines throttle response with carb heat on, turning
off the carb heat is NOT the solution. There are far too many safe ways to
deal with the issue, other than deviation from the POH.

On Sep 7, 5:53*am, Stealth Pilot
wrote:

I'm with you Bob.
I once thought I'd throttle back and poke under some mist and pop out
the other side and resume. when the power came off the revs started
dropping and dropping and dropping. I bunged on full carb heat and
then full throttle and still the revs kept dropping. out the corner of
the eye I noticed a shaft of sunlight and turned toward the hole in
the mist. about 2 seconds into the sunlight and I had full power back
again. *when it happens it happens quickly.

I lost the engine in the J-3 once during climb out. I had done a stop-
n-go and even though I was under full power I had picked up some carb
ice after turning off the carb heat in order to go. I got down to
about 200 feet before the power came back. Since then I've always done
stop-n-gos will carb heat on until I get a positive climb. I've not
had that problem since using that procedure. That procedure is in
conflict with the OPs. Now, it is true that a J-3 is going to freeze
up much faster than a Cherokee and somewhat faster than C-172 but it
just shows that it can happen very, very fast.

-Robert

On Sep 6, 2:35*pm, Bertie the Bunyip wrote:

Lycomings, no problem with your plan at all. Continentals ice a bit more
easily, and on a clear dry day, there won't be a problem either,

That observation is in conflict with my experience. Everytime I've
gotten carb ice in the pattern has been on a clear day.

-Robert

On Sep 6, 2:40*pm, a wrote:
Best practice without a lot of experimentation is to follow the POH,

I hope I never let my rookie ass become so confident I consider
deviating from the POH based on my own anecdotal experience. Next
thing you know, you're an example of someone who made reasonable
conclusions except for a heretofore unknown exception.

There's a certain risk factor, also, I think, in deviating from one's
training and, I assume in this case, longtime practice.

The OP doesn't mention their typical strip, but I think they would be
best served by adhering to the POH and just aiming a little further
down the runway.
-----

- gpsman

gpsman wrote:
On Sep 6, 2:40 pm, a wrote:
Best practice without a lot of experimentation is to follow the POH,

I hope I never let my rookie ass become so confident I consider
deviating from the POH based on my own anecdotal experience. Next
thing you know, you're an example of someone who made reasonable
conclusions except for a heretofore unknown exception.

There's a certain risk factor, also, I think, in deviating from one's
training and, I assume in this case, longtime practice.

The OP doesn't mention their typical strip, but I think they would be
best served by adhering to the POH and just aiming a little further
down the runway.
-----

- gpsman

This is excellent advice and I add my voice to what you have said.
General aviation engines particularly Lycoming and Continental, handle
carb ice just differently enough that every aircraft POH should be
checked to see what the engine manufacturer recommends pertaining to the
use of carb heat, especially the exact circumstances where it is
recommended and the suggested procedure for it's use.
Pilots who alter the manufacturer's recommendations on the use of carb
heat anticipating a go around situation are potentially creating a
problem where no problem should exist.
There is no reason at all why a go around should necessitate an action
with carb heat that deviates from recommended procedure.
If you have to go around, simply follow recommended procedure.


--
Dudley Henriques

"John Smith" wrote in message
...
Tman wrote:


There will come the day when you need full power for the go-around. Too
silly if you then have the carb heat on.

Then again, how hard is it to shove in the carb heat knob while you advance
the throttle in a Cessna? They are right next to each other. I have always
just pushed in the carb heat handle at the same time as I advance the
throttle, not that difficult to do, even using the same hand.

Randy L.
--
Remember: Any landing that you can walk away from,
is a landing that you can be fined, sued, or prosecuted for.

Couple things I want to add to some of the (kind of) opinionated but
helpful replies in this thread.

My C152 POH, and this is a late -70s model, does not give a clear cut
protocol for use of carb heat. It basically says use it when icing is
possible or suspected. I think it's standard practice to pull it on
power reduction for approach, but as you can see from the replies here
there are a variety of standard practices. If I read the POH literally,
I'd say turning the heat off when on short final is not contrary to what
it says, and is not really more in line with its suggestions than
leaving it full on till clear of the runway or go-around power is
needed. Does one suspect carb ice in the last 30 seconds of approach?
Well there are some anecdotes in this thread that raise the possibility
of that, so maybe I won't do this practice anyways, but either way there
isn't a sentence in the POH that says to leave that carb heat on till
the wheels are on the ground.

By the way, the topic of leaning on downwind for approach under high
density altitude conditions was brought up in this thread. The C152 POH
is almost silent on that also. It talks about leaning in cruise,
leaning for max rpm in a full power static runup when over 3000 DA, and
to place the mixture rich or "for smooth operation" on approach. I've
been taught the former, but another very experienced CFI told me to lean
it out "an inch" and push it in only if you need to go around. Both
pieces of advice I'd say consistent with the POH text, and both different.

FYI, the engine stumble in the original post happens at about 2000 DA days.

Just to go off on this tangent, one CFI I has says absolutely avoid
operating your Cessna Lycoming less than 1,000 RPM -- not enough oil
pressure to lube up the beast, and in fact there is an examiner that
will demerit you if you taxi at less than 1000 RPM on your checkride.
Now another CFI is adamant about taxiing at minimum possible power -- to
save the brakes. Both very respectable experienced CFI's, both with
reasons for their suggestion. And both suggestions are "not contrary"
to the POH guideline. So sometimes you gotta use your brain to
determine a good SOP, and solicit info on the pros / cons / risks to
make your own decision. But I'm not bending any of the guidelines in
the thin POH.

And as far as taking it to the A&P... We've talked about this. He says,
well grasshopper, you go the mixture full rich, it's hot, and you punch
in the throttle -- this is a carb engine, they sometimes stumble. It's
also pretty accepted performance around here by some of the other more
experienced pilots -- there recommendation is in line with a few of the
posts here -- some combination of: don't pull the throttle to cutoff,
lean it out on downwind, push in the carb heat on short final, push the
throttle in more slowly, and/or don't worry about the momentary
hesitation / stumble , it'll get ya used to the power delay when you get
flying turbofans. That last one a little tongue in cheek....
T



Dudley Henriques wrote:
gpsman wrote:
On Sep 6, 2:40 pm, a wrote:
Best practice without a lot of experimentation is to follow the POH,

I hope I never let my rookie ass become so confident I consider
deviating from the POH based on my own anecdotal experience. Next
thing you know, you're an example of someone who made reasonable
conclusions except for a heretofore unknown exception.

This is excellent advice and I add my voice to what you have said.
General aviation engines particularly Lycoming and Continental, handle
carb ice just differently enough that every aircraft POH should be
checked to see what the engine manufacturer recommends pertaining to the

On Sep 8, 9:07*am, Tman x@x wrote:
Couple things I want to add to some of the (kind of) opinionated but
helpful replies in this thread.

My C152 POH, and this is a late -70s model, does not give a clear cut
protocol for use of carb heat. *It basically says use it when icing is
possible or suspected. *I think it's standard practice to pull it on
power reduction for approach, but as you can see from the replies here
there are a variety of standard practices. *If I read the POH literally,
I'd say turning the heat off when on short final is not contrary to what
it says, and is not really more in line with its suggestions than
leaving it full on till clear of the runway or go-around power is
needed. *Does one suspect carb ice in the last 30 seconds of approach?
Well there are some anecdotes in this thread that raise the possibility
of that, so maybe I won't do this practice anyways, but either way there
isn't a sentence in the POH that says to leave that carb heat on till
the wheels are on the ground.

By the way, the topic of leaning on downwind for approach under high
density altitude conditions was brought up in this thread. *The C152 POH
is almost silent on that also. *It talks about leaning in cruise,
leaning for max rpm in a full power static runup when over 3000 DA, and
to place the mixture rich or "for smooth operation" on approach. *I've
been taught the former, but another very experienced CFI told me to lean
it out "an inch" and push it in only if you need to go around. *Both
pieces of advice I'd say consistent with the POH text, and both different..

FYI, the engine stumble in the original post happens at about 2000 DA days.

Just to go off on this tangent, one CFI I has says absolutely avoid
operating your Cessna Lycoming less than 1,000 RPM -- not enough oil
pressure to lube up the beast, and in fact there is an examiner that
will demerit you if you taxi at less than 1000 RPM on your checkride.
Now another CFI is adamant about taxiing at minimum possible power -- to
save the brakes. *Both very respectable experienced CFI's, both with
reasons for their suggestion. *And both suggestions are "not contrary"
to the POH guideline. *So sometimes you gotta use your brain to
determine a good SOP, and solicit info on the pros / cons / risks to
make your own decision. *But I'm not bending any of the guidelines in
the thin POH.

And as far as taking it to the A&P... We've talked about this. *He says,
well grasshopper, you go the mixture full rich, it's hot, and you punch
in the throttle -- this is a carb engine, they sometimes stumble. *It's
also pretty accepted performance around here by some of the other more
experienced pilots -- there recommendation is in line with a few of the
posts here -- some combination of: don't pull the throttle to cutoff,
lean it out on downwind, push in the carb heat on short final, push the
throttle in more slowly, and/or don't worry about the momentary
hesitation / stumble , it'll get ya used to the power delay when you get
flying turbofans. *That last one a little tongue in cheek....
T

Dudley Henriques wrote:
gpsman wrote:
On Sep 6, 2:40 pm, a wrote:
Best practice without a lot of experimentation is to follow the POH,

I hope I never let my rookie ass become so confident I consider
deviating from the POH based on my own anecdotal experience. *Next
thing you know, you're an example of someone who made reasonable
conclusions except for a heretofore unknown exception.
This is excellent advice and I add my voice to what you have said.
General aviation engines particularly Lycoming and Continental, handle
carb ice just differently enough that every aircraft POH should be
checked to see what the engine manufacturer recommends pertaining to the

Take a look at your oil pressure gauge as you change RPMs. If it stays
acceptable, the engine manufacturer says there's enough oil pressure.

If you are running at low manifold pressures you have set up a
condition for carb icing, haven't you? I'd suggest it would be prudent
when landing to keep the carb heat on until touchdown, or until you
decide to go around. As has been pointed out here, carb heat and
throttle can be operated with one hand when advancing the throttle.
Why take the chance of growing some ice just when a deer runs on the
runway 500 feet in front of you while you're in the flare? Or, more
likely, someone has finished their run up and is taxiing out when
you're on short final? You have the carb heat on as insurance you'll
get power when you need it, don't cancel the policy prematurely.

Keep in mind this is written by someone who flies an injected engine!