Re: Cherokee Carb Heat.

[Greg Esres]

<<Is this just a technique or proper procedure?>>

All the Piper POH's I've seen say only use carb heat if you suspect
carb icing.

[Paul Tomblin]

In a previous article, (Hobbes1157) said:
>Hi there. I've got a question about the carb heat in a Cherokee. I was told
>that you only need to apply it for a short while (5 seconds) while on downwind

I'd make it 10 seconds myself. I once got a big power loss taking off
because I'd only done the carb heat check for 5 seconds in the run-up.
I was a solo student at the time, and having what I considered an
"inflight emergency" (even if it was solved by the second item on the
power loss checklist) was enough to give me the shakes for a while.

>to make sure the carb is clear of ice. She (CFI) said that Pipers don't need it
>all the time as Cessnas do. Is this just a technique or proper procedure?
>Comments appreciated.

The POH recommends occassional checks - I try and do it every 15-20
minutes in conditions conducive to icing. The difference in the
procedures between Piper and Cessna are that the carbs in the Pipers are
placed so that they get warmed by the engine better, so it's not as big a
problem.


--
Paul Tomblin >, not speaking for anybody
"The thing you don't check is the thing that will kill you."
-- Rick Grant (quoting RCAF pilot training)

[Jay Honeck]

> Plus: Hey Jay is this a family event at Oshkosh you're planning? I've got
my
> non-flying family driving with me up to OSH and would like to meet some
other
> local and non-local friendly folks!

As a matter of procedure we don't use carb heat in the pattern at all in
Pipers. In fact, in nine years of flying 140s thru 235s, I've only used
carb heat "for real" once. (Of course, I don't fly IFR...)

As for the Oshkosh get together being a "family event", well, my two
children (ages 9 and 12) will be there, so I guess we'd better keep our
clothes on for the most part! :)

If you're gonna stop by, it would be good to sign the roster (see the post
"Oshkosh Get Together Roster -- Sign in, please!") so we all have some idea
of who's who... (By the way, did you see the invite at Green Castle?)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Teacherjh]

Actually, I got in a situation in a cherokee (a 1980 Dakota) where the engine
was icing up and quitting just on the taxiway. By the time I got to the runup,
the engine just died. Happened a few times, had the thing looked at, the
conclusion was carb ice. On the ground, no less.

Jose

(for Email, make the obvious changes in my address)

[Marty Ross]

I just scanned my Warrior II POH for this. It says to use carb heat if you
suspect icing (anywhere, but particularly in descents with low throttle
settings), and advises on how to check for the presence if icing. There's
also an optional carb ice detection system available for my model. Unlike
the Grumman AA1-C I fly, however, the descent checklist in the Piper says
"CARB HEAT ON (if needed)" instead of an unqualified "CARB HEAT ON".

I seem to remember hearing something about the location of the carburator
intake under the hood in the Cherokee -- it gets pre-warmed air or something
like that, and that's why it's not as likely to happen.

There's a decent article out there about this, if you're interested:
http://www.avweb.com/news/columns/182189-1.html.

Happy Landings!


"Hobbes1157" > wrote in message
...
> Hi there. I've got a question about the carb heat in a Cherokee. I was
told
> that you only need to apply it for a short while (5 seconds) while on
downwind
> to make sure the carb is clear of ice. She (CFI) said that Pipers don't
need it
> all the time as Cessnas do. Is this just a technique or proper procedure?
> Comments appreciated.
> Plus: Hey Jay is this a family event at Oshkosh you're planning? I've got
my
> non-flying family driving with me up to OSH and would like to meet some
other
> local and non-local friendly folks!
>
> Thanks,
> Nolan
>
> PPSEL, INST, commerial student
> IA24 (green castle)

[G.R. Patterson III]

Teacherjh wrote:
>
> Actually, I got in a situation in a cherokee (a 1980 Dakota) where the engine
> was icing up and quitting just on the taxiway. By the time I got to the runup,
> the engine just died. Happened a few times, had the thing looked at, the
> conclusion was carb ice. On the ground, no less.

The main reason you don't need to habitually use carb heat with a Lycoming
is the fact that they run the induction tubes through the oil sump. When
the engine is warm, the hot oil tends to keep the carb warm. The situation
you describe (cold engine, near-closed throttle plate) would be perfect for
formation of carb ice if the humidity were high.

George Patterson
The optimist feels that we live in the best of all possible worlds. The
pessimist is afraid that he's correct.
James Branch Cavel

[John Galban]

(Paul Tomblin) wrote in message >...
> The difference in the
> procedures between Piper and Cessna are that the carbs in the Pipers are
> placed so that they get warmed by the engine better, so it's not as big a
> problem.

And it really only applies to early models of Cessna 172s.
Beginning in the '68 model year, the 172 used the same Lycoming
engines as Piper, with the carb mounted on the oil pan. For some
reason (probably liability), Cessna chose to keep their "always use
carb heat" instructions, even though the Lycoming engine is far less
susceptable to carb ice.

Looking at the big picture, it really doesn't matter much which
procedure you use. If you use carb heat for landing, you just have to
remember to shut it off if you go around or after you land.

John Galban=====>N4BQ (PA28-180)

[Rocky]

(Hobbes1157) wrote in message >...
> Hi there. I've got a question about the carb heat in a Cherokee. I was told
> that you only need to apply it for a short while (5 seconds) while on downwind
> to make sure the carb is clear of ice. She (CFI) said that Pipers don't need it
> all the time as Cessnas do. Is this just a technique or proper procedure?
> Comments appreciated.
> Plus: Hey Jay is this a family event at Oshkosh you're planning? I've got my
> non-flying family driving with me up to OSH and would like to meet some other
> local and non-local friendly folks!
>
> Thanks,
> Nolan
>
> PPSEL, INST, commerial student
> IA24 (green castle)

Nolan
For the lesser experienced pilots in particular, the use of carb heat
can save you some anxious moments without unduly affecting the engine
performance in the pattern. Of course you'll notice the loss of
performance if you forget to turn carb heat OFF if you elect to make a
take-off or go-around. Even then it isn't life threatening unless
really adverse conditions exist.
A little trick that I learned back in the early 50's, and pass on to
all who don't know of it, is using the PRIMER to keep the engine
running if it shuts down for carb ice. The primer injects fuel
directly into the intake manifold bypassing the carburetor and can
keep the engine running intermittently and in many cases generate
enough heat for the carb heat to become effective again. I've used
this technique a few times in aircraft to get home. In Pipers (PA25
Pawnee while crop dusting) and Cessnas (C-172 and 177).
Ol Shy & Bashful

[David Megginson]

(Rocky) writes:

> A little trick that I learned back in the early 50's, and pass on to
> all who don't know of it, is using the PRIMER to keep the engine
> running if it shuts down for carb ice. The primer injects fuel
> directly into the intake manifold bypassing the carburetor and can
> keep the engine running intermittently and in many cases generate
> enough heat for the carb heat to become effective again. I've used
> this technique a few times in aircraft to get home. In Pipers (PA25
> Pawnee while crop dusting) and Cessnas (C-172 and 177).
> Ol Shy & Bashful

That's a brilliant suggestion -- I'm assuming that you leave carb heat
on, so that there's still an air supply into the cylinders.


All the best,


David

--
David Megginson, , http://www.megginson.com/

[John Galban]

(Rocky) wrote in message >...
<snip>
> A little trick that I learned back in the early 50's, and pass on to
> all who don't know of it, is using the PRIMER to keep the engine
> running if it shuts down for carb ice. The primer injects fuel
> directly into the intake manifold bypassing the carburetor and can
> keep the engine running intermittently and in many cases generate
> enough heat for the carb heat to become effective again. I've used
> this technique a few times in aircraft to get home. In Pipers (PA25
> Pawnee while crop dusting) and Cessnas (C-172 and 177).
> Ol Shy & Bashful

I've heard this before, but haven't yet found anyone who can explain
how that would work. The development of carb ice causes the engine
to run rough/die because the ice is blocking air from entering the
carb. This generally results in a very rich mixture. How does adding
even more fuel via the primer help the engine to run??

John Galban=====>N4BQ (PA28-180)

[Rocky]

David Megginson > wrote in message >...
> (Rocky) writes:
>
> > A little trick that I learned back in the early 50's, and pass on to
> > all who don't know of it, is using the PRIMER to keep the engine
> > running if it shuts down for carb ice. The primer injects fuel
> > directly into the intake manifold bypassing the carburetor and can
> > keep the engine running intermittently and in many cases generate
> > enough heat for the carb heat to become effective again. I've used
> > this technique a few times in aircraft to get home. In Pipers (PA25
> > Pawnee while crop dusting) and Cessnas (C-172 and 177).
> > Ol Shy & Bashful
>
> That's a brilliant suggestion -- I'm assuming that you leave carb heat
> on, so that there's still an air supply into the cylinders.
>
>
> All the best,
>
>
> David
Carb heat is left on in the event that the generated engine heat
becomes effective again to change the intake air temp.

[G.R. Patterson III]

Rocky wrote:
>
> A little trick that I learned back in the early 50's, and pass on to
> all who don't know of it, is using the PRIMER to keep the engine
> running if it shuts down for carb ice. The primer injects fuel
> directly into the intake manifold bypassing the carburetor and can
> keep the engine running intermittently and in many cases generate
> enough heat for the carb heat to become effective again.

Since carb ice blocks the induction air, this is unlikely to work well.

George Patterson
The optimist feels that we live in the best of all possible worlds. The
pessimist is afraid that he's correct.
James Branch Cavel

[G.R. Patterson III]

David Megginson wrote:
>
> That's a brilliant suggestion -- I'm assuming that you leave carb heat
> on, so that there's still an air supply into the cylinders.

Carb heat does not provide an alternate air supply to the cylinders. It
bypasses the air filter, but the air still has to pass through the carb
and the (blocked) butterfly valve.

George Patterson
The optimist feels that we live in the best of all possible worlds. The
pessimist is afraid that he's correct.
James Branch Cavel

[Andy R]

"Rocky" > wrote in message
om...
> (Hobbes1157) wrote in message
>...
> > Hi there. I've got a question about the carb heat in a Cherokee. I was
told
> > that you only need to apply it for a short while (5 seconds) while on
downwind
> > to make sure the carb is clear of ice. She (CFI) said that Pipers don't
need it
> > all the time as Cessnas do. Is this just a technique or proper
procedure?
> > Comments appreciated.
> > Plus: Hey Jay is this a family event at Oshkosh you're planning? I've
got my
> > non-flying family driving with me up to OSH and would like to meet some
other
> > local and non-local friendly folks!
> >
> > Thanks,
> > Nolan
> >
> > PPSEL, INST, commerial student
> > IA24 (green castle)
>
> Nolan
> For the lesser experienced pilots in particular, the use of carb heat
> can save you some anxious moments without unduly affecting the engine
> performance in the pattern. Of course you'll notice the loss of
> performance if you forget to turn carb heat OFF if you elect to make a
> take-off or go-around. Even then it isn't life threatening unless
> really adverse conditions exist.
> A little trick that I learned back in the early 50's, and pass on to
> all who don't know of it, is using the PRIMER to keep the engine
> running if it shuts down for carb ice. The primer injects fuel
> directly into the intake manifold bypassing the carburetor and can
> keep the engine running intermittently and in many cases generate
> enough heat for the carb heat to become effective again. I've used
> this technique a few times in aircraft to get home. In Pipers (PA25
> Pawnee while crop dusting) and Cessnas (C-172 and 177).

So you ignored the needs of the engine and gave so little consideration to
the atmospheric conditions you let it quit through carb ice. Forgiveable
once, we all make mistakes but you say you've done it a few times. I
suggest you take up gliding (oops, sorry, you already have, in Cessnas,
Pipers...)

Rgds

Andy R

[Snowbird]

David Megginson > wrote in message >...

> That's a brilliant suggestion -- I'm assuming that you leave carb heat
> on, so that there's still an air supply into the cylinders.

Carb heat does not, in the engine installations I'm familiar
with, provide an alternate supply of air to the engine cylinders.

It provides an alternate supply which must still go through the
carb venturi.

If the carb venturi is sufficently blocked so as not to supply
air/fuel in the proper ratio for combustion, it's not clear to
me how injecting more fuel into the cylinders is likely to help.

OTOH, the primer is worth trying because if the problem is really
with the fuel supply, the primer is an independent fuel supply
system and this might help. Might also help suck out a little
more fuel from nearly-dry tanks -- have heard so anyway.

A lot of times IMO people really don't know what the problem
is, unless they have a "carb temp" probe. It's just assumed
that carb ice is a likely cause of engine failure when the
atmospheric conditions are right and there isn't anything
found to be wrong w/ the engine at a later time.

My $0.02
Sydney

[G.R. Patterson III]

Angus Davis wrote:
>
> The type of engine does not affect whether or not it will be susceptible
> to carb ice.

Yes, it does. Lycoming routes the induction through the oil sump in many
of their engines. Once the engine reaches operating temperature, that
keeps the induction tubes at about 180 degrees. That keeps the carburetor
much warmer than Continental engines do.

George Patterson
The optimist feels that we live in the best of all possible worlds. The
pessimist is afraid that he's correct.
James Branch Cavel