Lycoming Carb Heat

This is what Lycoming says in its "Key Reprints from the Lycoming Flyer"....
Note the sentence "It is also appropriate....in the traffic pattern."

Bob

"In conditions where carburetor ice is likely to form, the pilot may use
heat during cruise to prevent the formation of ice in the carburetor. It is
also appropriate to use full carburetor heat, if needed, to prevent icing
when operating at low power for instrument approaches, or for flight in the
traffic pattern. Unless the aircraft is equipped with a carburetor air
temperature (CAT) gage, and very few general aviation aircraft are, use of
full carburetor heat is recommended. An unknown amount of partial heat can
actually cause induction ice in the float type carburetor. This may occur
when moisture in crystal form in the incoming air that would ordinarily pass
through the induction system without any problem is melted by the partial
heat. This moisture then freezes when it comes in contact with the cold
metal of the throttle plate."

wrote in message
...
Bob Gardner wrote:
: I once read a report about carb heat use published by the NTSB (which,
of
: course, I can't lay hands on now). In it, they pointed out the hazard of
: having disparate methods of carb heat use depending on engine and
airframe,
: and suggested that full carb heat be applied any time the power was
reduced
: below cruise power...no matter who made the engine or airframe. They
felt
: that this standardization would have a positive effect on accident
rates.

Perhaps, but I don't like to apply the carb heat unless I know it's
needed.
In particular, there are situations where ice crystals would harmlessly
flow through
the induction system. If carb heat (especially *partial* carb heat) is
added, they
can melt enough to stick. Then you'd be stuck with an iced engine, below
freezing,
and not enough heat to melt it.

Maybe I'm overly paranoid about it. I have had carb ice twice in
Cherokees...
one with an O-320 in a long descent, and one in cruise (relatively low
power in misty
weather at low altitude). Application was a non-issue once I saw the MP
2" below what
I set it. I'll agree that on an IMC missed or legitamate go-around the
pucker factor
(and timing constraints) would be more of an issue.

I think that the Cessna left it in the POH from the O-300 Continental days
as
a CYA when the switched to Lycoming. Never a good reason to change it, so
left it was
it was required before.

-Cory


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* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
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