Emergency

"John Theune" wrote in message
news:8obWf.14186$ES3.7989@trnddc02...
I may be perpetuating a OWT but I seem to recall something about carb heat
putting unfiltered air into the carb and that was why it was not always on
in addition to the issue of the hotter air decreasing performance.

I can't speak for all airplanes -- maybe there's one out there that uses a
filter with carb heat -- but yes, generally speaking carb heat means the air
is not filtered.

However, that is primarily a concern while on the ground, where all sorts of
dust and dirt can get blown up and into the air intake. Once you get aloft,
it's unusual for the air to contain enough stuff to cause harm to the
engine. Not impossible, but unusual.

A better argument against constant use of carb heat is that doing so can
take a non-icing situation and turn it into an icing one. I think this
would be very rare, but I don't believe you can rule it out. Of course,
carb heat also reduces performance, since it lowers the density of the air
coming into the engine. Better to wait for signs of carb ice and use the
carb heat as needed, rather than as a general prophylactic.

Pete

"Peter Duniho" wrote:

Of course, carb heat also reduces performance, since it lowers the density
of the air coming into the engine. Better to wait for signs of carb ice
and use the carb heat as needed, rather than as a general prophylactic.

In future I will be using carb heat as a matter of course when ambient
conditions are in the "severe" area of the chart. I definitely will not be
waiting for symptoms in such cases.

--
Dan
C-172RG at BFM

In future I will be using carb heat as a matter of course when ambient
conditions are in the "severe" area of the chart. I definitely will not be
waiting for symptoms in such cases.

Dan, I have a couple hundred hours behind the normally aspirated 0-470
Continental in C182's.
Anytime there is significant moisture in the air, the carb will ice up.
The trick is to constantly monitor the manifold pressure. As soon as you
see a one-inch drop, you apply carb heat. When the pressure comes back
up, turn the carb heat off. Repeat as necessary.
I will not fly with carb heat on constantly.
I read somewhere in the past (years ago, don't recall where) that flying
with constant carb heat moves the ice farther down the throat where no
heat will be available to melt it.
SPORT AVIATION had an excellent article on carb ice back in the early
90's. The author had all the math and discussed latent heat of
vaporization and all the other technical stuff, but he made it
understandable by anyone with an eighth grade education.

"john smith" wrote:

In future I will be using carb heat as a matter of course when ambient
conditions are in the "severe" area of the chart. I definitely will not
be
waiting for symptoms in such cases.

Dan, I have a couple hundred hours behind the normally aspirated 0-470
Continental in C182's.
Anytime there is significant moisture in the air, the carb will ice up.

As I understand it, the carburetor arrangement on the TCM O-470 does not
provide for conduction of as much engine heat to the carburetor as the LYC
O-360s and O-540s, thus the O-470's notorious reputation for carb icing.

The trick is to constantly monitor the manifold pressure. As soon as you
see a one-inch drop, you apply carb heat. When the pressure comes back
up, turn the carb heat off. Repeat as necessary.

That's pretty much what my buddy Filipo told me about his 182. Carb ice is
a regular fact of life for him; it's a rare event for me (twice in six
years with this airplane).

--
Dan
C172RG at BFM

john smith wrote:



Dan, I have a couple hundred hours behind the normally aspirated 0-470
Continental in C182's.
Anytime there is significant moisture in the air, the carb will ice up.

Not true. I recently sold my 182 after having put 1000 hours on it.
Never had it ice up, even after trying. I would go out on those rare
days here when we had fog and fly just as it lifts, still 90 somethun'
percent humidity. Couldn't make it happen.


I will not fly with carb heat on constantly.
I read somewhere in the past (years ago, don't recall where) that flying
with constant carb heat moves the ice farther down the throat where no
heat will be available to melt it.

Old wives tale. Cessna Pilots Assoc reccomends whatever amount of carb
heat is necessary to keep the carb at about 45 degrees in cruise. Also
has the effect of evening out the fuel mixture so the engine ran smoother.

In article ,
Newps wrote:

john smith wrote:



Dan, I have a couple hundred hours behind the normally aspirated 0-470
Continental in C182's.
Anytime there is significant moisture in the air, the carb will ice up.

Not true. I recently sold my 182 after having put 1000 hours on it.
Never had it ice up, even after trying. I would go out on those rare
days here when we had fog and fly just as it lifts, still 90 somethun'
percent humidity. Couldn't make it happen.

Okay, I will rephrase my statement, temperature and humidity have to be
in the proper range. It can be too warm or too cold, but with
significant moisture in the proper range, the O-470 Continental in a
Cessna 182 will likely form carb ice.