Lycoming Carb Heat

Gents,

Though this is not strictly an IFR question, I am pretty sure that you have
opinions that I would like to get.

Subject is Lycoming O-360 engines. I have flown behind a number of them in
Pipers and the POH instruction on carb heat is always "as required."
Specifically there is no requirement for carb heat on the landing checklist.
This makes sense to me as the intake charge is routed through the oil pan cum
intake manifold and, with the throttle nearly closed hence low flow velocity,
should get adequately warmed up. At least that is my rationale for why the POH
does not call for heat.

I am about to get checked out in a Civil Air Patrol 172 that has an STC'd O-360
installed in place of the original Lycoming O-320. The 172 POH wants carb heat
on approach. This makes no sense to me. If I have to do a go around it is just
one more workload item/one more thing to forget and, from my Piper experience,
it does not appear to be necessary. My guess, without benefit of any actual
facts, is that this POH requirement comes from Cessna's Continental roots and
has no engineering justification. So it seems wise to ignore it.

Comments? (Please, let's not go to the FARS with this question. That is not my
interest.)

Mitty wrote:

I am about to get checked out in a Civil Air Patrol 172 that has an
STC'd O-360 installed in place of the original Lycoming O-320. The 172
POH wants carb heat on approach. This makes no sense to me. If I have
to do a go around it is just one more workload item/one more thing to
forget and, from my Piper experience, it does not appear to be
necessary. My guess, without benefit of any actual facts, is that this
POH requirement comes from Cessna's Continental roots and has no
engineering justification. So it seems wise to ignore it.

Your Piper experience differs from mine. Facing a long slow ILS through wet
clouds in a Piper, I'd set full carb heat, a minute or two before reducing
power. Ever taxi off the runway and have your engine quit?

In article 1126723296.783817@sj-nntpcache-3, Dave Butler wrote:
Mitty wrote:

I am about to get checked out in a Civil Air Patrol 172 that has an
STC'd O-360 installed in place of the original Lycoming O-320. The 172
POH wants carb heat on approach. This makes no sense to me. If I have
to do a go around it is just one more workload item/one more thing to
forget and, from my Piper experience, it does not appear to be
necessary. My guess, without benefit of any actual facts, is that this
POH requirement comes from Cessna's Continental roots and has no
engineering justification. So it seems wise to ignore it.

Your Piper experience differs from mine. Facing a long slow ILS through wet
clouds in a Piper, I'd set full carb heat, a minute or two before reducing
power. Ever taxi off the runway and have your engine quit?

I have had it quit on short final (in a PA-28-181). Almost exactly
the situation you described -- ILS on a cool day with very small
temp/dp spread, low vis, low scattered layer. Over the airport
boundary, I pulled the throttle back to idle to land and things got
quiet. I was on the ground almost before I had a chance to realize
what went wrong. Hung out for a while on the runway while the ice
melted then started up and taxied off. Had a mechanic look at it, he
found no problems, so we assumed carb ice.

From that day on, I used carb heat in Pipers on instrument approaches.

I've also gotten carb ice in an Archer at cruise power in clouds.

"Roy Smith" wrote:

Your Piper experience differs from mine. Facing a long slow ILS through wet
clouds in a Piper, I'd set full carb heat, a minute or two before reducing
power. Ever taxi off the runway and have your engine quit?

I have had it quit on short final (in a PA-28-181). Almost exactly
the situation you described -- ILS on a cool day with very small
temp/dp spread, low vis, low scattered layer.

My CFII always used carb heat on a C-172 O-320 at anything less than full
power in wet conditions, and I've continued the practice with my 172RG O-360.

I have had one carb ice incident in 700 hours of operating an O-360, and that
was after a long taxi out on a wet morning. The engine would not throttle up
for the mag check, and half minute of carb heat cleared it.

Has using carb heat during damp approaches really kept me out of trouble? I
don't know; maybe it was my lucky key chain.
--
Dan
C-172RG at BFM

I too have had carb ice in the clouds, cold OAT. Noticed low power (full to
maintain alt.) Carb heat solved it. Never had a problem on final but then
I didn't have that many IA's in the cold/clouds.

--

Thx, {|;-)

Victor J. (Jim) Osborne, Jr.

"Roy Smith" wrote in message
...

I have had it quit on short final (in a PA-28-181). Almost exactly
the situation you described -- ILS on a cool day with very small
temp/dp spread, low vis, low scattered layer. Over the airport
boundary, I pulled the throttle back to idle to land and things got
quiet. I was on the ground almost before I had a chance to realize
what went wrong. Hung out for a while on the runway while the ice
melted then started up and taxied off. Had a mechanic look at it, he
found no problems, so we assumed carb ice.

From that day on, I used carb heat in Pipers on instrument approaches.

I've also gotten carb ice in an Archer at cruise power in clouds.

The key is the "as required". That puts the monkey on your back.
Lycomings do incur carb ice, though perhaps less often.

paul kgyy wrote:
The key is the "as required". That puts the monkey on your back.
Lycomings do incur carb ice, though perhaps less often.

Tell me about it. I used to have a GO-435 lycoming. The engine
always ran hot and the conventional wisdom was that the PS-5C
pressure carb was near immune to carb ice. Well, we had it
happen. Margy flew back from the next field over at 20" of
MP (about ten minutes) and it wasn't that cold of a day even.
The thing iced up about the time we hit the pattern.

Of course, the replacment engien can't get carb ice (no carb).

Mitty wrote:

Gents,

Though this is not strictly an IFR question, I am pretty sure that you
have opinions that I would like to get.

Subject is Lycoming O-360 engines. I have flown behind a number of them
in Pipers and the POH instruction on carb heat is always "as required."
Specifically there is no requirement for carb heat on the landing
checklist. This makes sense to me as the intake charge is routed through
the oil pan cum intake manifold and, with the throttle nearly closed
hence low flow velocity, should get adequately warmed up. At least that
is my rationale for why the POH does not call for heat.

I am about to get checked out in a Civil Air Patrol 172 that has an
STC'd O-360 installed in place of the original Lycoming O-320. The 172
POH wants carb heat on approach. This makes no sense to me. If I have
to do a go around it is just one more workload item/one more thing to
forget and, from my Piper experience, it does not appear to be
necessary. My guess, without benefit of any actual facts, is that this
POH requirement comes from Cessna's Continental roots and has no
engineering justification. So it seems wise to ignore it.

Comments? (Please, let's not go to the FARS with this question. That
is not my interest.)

Bottom line, Pipers need carb heat a lot less than Cessnas because of a
different air induction system design.

Cessna 172's need carb heat pretty much all the time below a certain RPM
(it was 1800 in the last one I flew) because they don't route their
induction air as close to the manifold so it doesn't get heated as well.

On the runup with a Piper when you check carb heat you get a lot smaller
RPM drop than a Cessna does. This is because the Piper's air is already
pretty warm.

On 9/14/2005 2:15 PM, xyzzy wrote the following:
snip

Bottom line, Pipers need carb heat a lot less than Cessnas because of a
different air induction system design.

Cessna 172's need carb heat pretty much all the time below a certain RPM
(it was 1800 in the last one I flew) because they don't route their
induction air as close to the manifold so it doesn't get heated as well.

On the runup with a Piper when you check carb heat you get a lot smaller
RPM drop than a Cessna does. This is because the Piper's air is already
pretty warm.

I think you've just described the difference between Continental and Lycoming
engines, no? This is a Cessna with a Lycoming, where a single casting functions
both as the intake manifold and the oil sump.

Mitty wrote:



On 9/14/2005 2:15 PM, xyzzy wrote the following:
snip


Bottom line, Pipers need carb heat a lot less than Cessnas because of
a different air induction system design.

Cessna 172's need carb heat pretty much all the time below a certain
RPM (it was 1800 in the last one I flew) because they don't route
their induction air as close to the manifold so it doesn't get heated
as well.

On the runup with a Piper when you check carb heat you get a lot
smaller RPM drop than a Cessna does. This is because the Piper's air
is already pretty warm.

I think you've just described the difference between Continental and
Lycoming engines, no? This is a Cessna with a Lycoming, where a single
casting functions both as the intake manifold and the oil sump.

No I haven't. The Cessna I flew (a 1975 M) had a Lyc, and so does the
Piper Warrior I fly now.

Cessnas need more carb heat for the same engine. Not all of the
induction system is designed by the engine manufacturer.

--
"You can support the troops but not the president"
--Representative Tom Delay (R-TX), during the Kosovo war.