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Carb heat: my new policy. Any comments



 
 
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  #21  
Old September 8th 08, 02:57 PM posted to rec.aviation.piloting
Shirl
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Posts: 190
Default Carb heat: my new policy. Any comments

a wrote:
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!


How fast does carb ice form? If you've had carb heat on from abeam the
numbers in the downwind, is ice going to form from short final to flare?
I usually leave mine on to touchdown, but a CFI-friend shuts off carb
heat when on short short-final in anticipation of a possible go-round.

Keep in mind this is written by someone who flies in Arizona!
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  #22  
Old September 8th 08, 03:05 PM posted to rec.aviation.piloting
[email protected]
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Posts: 1,130
Default Carb heat: my new policy. Any comments

On Sep 8, 7:07*am, Tman [email protected] 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


If the POH says to lean for smooth operation on downwind,
then do it if the carb heat makes it stumble. These carbs are designed
to provide a rich mixture at sea level, and when the DA is higher than
that the fuel:air mix can become too rich to run properly. WE operate
at a 3000' airstrip and the DA is at 5000' or more almost all summer.
You learn something about mixture, and you learn about carb ice on
clear days, too.
Lycoming's service manuals call for an idle setting of 650-750
RPM. I think they know a little bit about lubrication and so on, a lot
more than that CFI knows about engines. 1000 RPM is way too high and
just burns out brakes. The only place 1000 RPM should be used is when
the engine has been started from a cold-soaked state, and the oil is
still thick enough that it doesn't throw onto the cylinder walls too
well. Once it's warmed up some it's OK. If the oil pressure is falling
off badly at 650 RPM, the engine's bearings or oil pump or both are
shot and it shouldn't be flying. While we're on the subject of
dragging the brakes to control speed, if you go on to get a Commercial
ticket and do that to expensive airplanes, you might find yourself
looking for another job. Overheated brakes have been known to set fire
to tires and the whole airplane goes up in smoke.
As far as approaches go, we use the "plan-for-abort-unless-
everything's-good" training. Most landing accidents are a result of a
refusal to go around when things aren't lining up properly. Airspeed,
altitude, track---everything must be within reason or we just don't
land. SO, the carb heat is left on until we accelerate to get out of
there, and we don't slam the throttle open, either. Besides risking
stumble or outright failure, it's hard on the engine when cylinder
pressures rise so high at low RPM. Take two seconds to open the
throttle unless things are really urgent.

Dan
  #23  
Old September 8th 08, 05:11 PM posted to rec.aviation.piloting
Gig 601Xl Builder
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Posts: 683
Default Carb heat: my new policy. Any comments

Tman 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).

thoughts?
T


Well that will make it easier on the crash investigators. They will see
the carb heat in the off position and mark it down to carb ice caused by
pilot error. Think of the money you will save the tax payers.
  #24  
Old September 8th 08, 05:55 PM posted to rec.aviation.piloting
RandyL[_2_]
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Posts: 16
Default Carb heat: my new policy. Any comments



"Tman" [email protected] wrote in message
. ..
Flying a lot of 152s and 172s with carb heat lately. When inbound, I've 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).

thoughts?
T


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 knob 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.


  #25  
Old September 8th 08, 06:20 PM posted to rec.aviation.piloting
Stella Starr
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Posts: 92
Default Carb heat: my new policy. Any comments

Tman wrote:
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


Sounds pretty reasonable; you can't blame every engine stumble on carb
icing (or carb heat), and I remember watching a fellow student do
go-arounds and hearing the hiccup as he jammed in full power in the "go"
part of each touch-and-go.
  #26  
Old September 8th 08, 06:51 PM posted to rec.aviation.piloting
Dudley Henriques[_2_]
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Posts: 2,546
Default Carb heat: my new policy. Any comments

Stella Starr wrote:
Tman wrote:
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


Sounds pretty reasonable; you can't blame every engine stumble on carb
icing (or carb heat), and I remember watching a fellow student do
go-arounds and hearing the hiccup as he jammed in full power in the "go"
part of each touch-and-go.


I'd say a vast amount of engine "hiccups" on a go around are caused not
by carb heat but rather by over aggressive use of throttle. SMOOTH is
the key word for throttle use on a go around. Aggressive throttle use
might get you a "hiccup" in a 150 Cessna. It might even cause an engine
failure. It can kill you in a high performance prop airplane.

--
Dudley Henriques
  #27  
Old September 8th 08, 08:49 PM posted to rec.aviation.piloting,alt.usenet.kooks
Bertie the Bunyip[_25_]
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Posts: 3,735
Default Carb heat: my new policy. Any comments

"Lonnie" @_#~#@.^net wrote in :


"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.



Didn't say it was, fjukkktard.


Bertie
  #29  
Old September 8th 08, 11:46 PM posted to rec.aviation.piloting
[email protected]
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Posts: 1,130
Default Carb heat: my new policy. Any comments

On Sep 8, 11:51 am, Dudley Henriques wrote:

I'd say a vast amount of engine "hiccups" on a go around are caused not
by carb heat but rather by over aggressive use of throttle. SMOOTH is
the key word for throttle use on a go around. Aggressive throttle use
might get you a "hiccup" in a 150 Cessna. It might even cause an engine
failure. It can kill you in a high performance prop airplane.



The hiccup is only one part of the risk when shoving the
throttle in too fast, too. When high manifold pressures are applied at
low RPM, the cylinder pressures get much too high and detonation
becomes a danger. Broken pistons and rings and other cylinder parts
can all result from this, as can overloaded bearings. The propeller is
a very heavy flywheel and we can't expect the same acceleration we get
in our cars. Further, even old cars had variable ignition timing that
would drop the spark advance to 10 or 6 degrees BTDC during
acceleration to avoid detonation, but our LyConts don't have that and
are stuck at 20 or 25 or 28 or whatever degrees. The pilot will never
hear the pinging because of all the other racket, but it's there if
they get too rough with the throttle.

Dan
  #30  
Old September 9th 08, 12:08 AM posted to rec.aviation.piloting
Dudley Henriques[_2_]
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Posts: 2,546
Default Carb heat: my new policy. Any comments

wrote:
On Sep 8, 11:51 am, Dudley Henriques wrote:

I'd say a vast amount of engine "hiccups" on a go around are caused not
by carb heat but rather by over aggressive use of throttle. SMOOTH is
the key word for throttle use on a go around. Aggressive throttle use
might get you a "hiccup" in a 150 Cessna. It might even cause an engine
failure. It can kill you in a high performance prop airplane.



The hiccup is only one part of the risk when shoving the
throttle in too fast, too. When high manifold pressures are applied at
low RPM, the cylinder pressures get much too high and detonation
becomes a danger. Broken pistons and rings and other cylinder parts
can all result from this, as can overloaded bearings. The propeller is
a very heavy flywheel and we can't expect the same acceleration we get
in our cars. Further, even old cars had variable ignition timing that
would drop the spark advance to 10 or 6 degrees BTDC during
acceleration to avoid detonation, but our LyConts don't have that and
are stuck at 20 or 25 or 28 or whatever degrees. The pilot will never
hear the pinging because of all the other racket, but it's there if
they get too rough with the throttle.

Dan


As a pilot of Warbirds through the years I've run into the problem
consistently when advising new pilots on how to handle these airplanes.
Some SE warbirds will actually torque roll if high MP is applied on a go
around with the prop in full increase (Low pitch/high RPM), if the power
is ham handed in with the airplane under about 120 with high AOA
involved in the power up equation.


--
Dudley Henriques
 




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