Cherokee Carb Heat.

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.

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

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

"Rocky" wrote in message
om...
pamaway (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

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

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