• If You Are Having Trouble Logging In with Your Old Username and Password, Please use this Forgot Your Password link to get re-established.
  • Hey! Be sure to login or register!

PA18-150 Carb Heat for Landings

S

strand10

MEMBER
West MI
What’s the consensus from the PA18 community on use of Carb Heat for regular landings? I’m used to pulling it on abeam the numbers from other ac but the PA18 manual says to only use it if necessary (humid, cold, etc.).

What do you all do?
 
I always pull it when the power first comes significantly back, then push it back in on short final. I just feel like it's a habit that would reduce the chance of forgetting when it might matter. Just one opinion - -
 
Gordon Misch said:
I always pull it when the power first comes significantly back, then push it back in on short final. I just feel like it's a habit that would reduce the chance of forgetting when it might matter. Just one opinion - -
Click to expand...

This is what I practice, and what I teach. We have had enough carb ice develop at low (near idle) power that the engine quit at about touchdown (and once in power off stalls).

You always want to put it in on short final as the carb heat circumnavigates the air cleaner and if you are landing on anything other than pavement, you can suck some nasty stuff into your carb.

sj
 
Once you hear the silence you will use it. I got carb ice idling on the ground last week in Maine, it was 80F+

Glenn
 
And that’s the problem: Carburetor icing can be kinda sneaky. So, Piper says use carb heat when you suspect carb ice. Like others, my suggestion is to use carb heat when you’re in an inconvenient spot to have the engine quit.

I’ve only flown a little in AZ, but I flew Cubs a lot in Kodiak. There, I applied heat frequently, like when over water. I can’t tell you how many times I applied heat and the engine coughed, sputtered, then gained a hundred rpm or two.

abeam the numbers, then carb heat cold on short short final.

Lycomings aren’t very susceptible to carb ice, but if conditions are right.

Now Continental O-470s…..

MTV
 
And don't wait until the power is reduced to apply heat...exhausts cool quickly after power reduction (the cooling airflow over them continues) and there goes the source off some heat.

Gary
 
The intake tubes on Lycomings go through the sump and thus the air is preheated a little. Most of the early POH's for Lyc powered aircraft said "Carb heat- as required" Over the years the lawyers managed to effectively reduce the POH's to more of a legal CYA document than a users manual.

Continental engine intake tubes do not go through the sump and because of that the continental engines are much more prone to ice. Most POH's for continental powered engines would state "Carb heat - on" for any power reduction.

I have experienced far more carb ice in benign conditions with continental engines than Lycoming. But that said, I have experienced carb ice in my Lycoming in SE Alaska, but usually in conditions that were prime for ice, i.e. rain, temp 50 degrees, etc.



Bill
 
Add a manifold pressure gauge. It's an early falling canary for carb ice in level flight and constant power.

The Lyc heated sump is primarily there for fuel vaporization and is downstream of the carb's venturi. I'd not trust it to maintain carb heat or manufacturers would have eliminated the separate carb heater.

Gary
 
Lots of old pilots posting so far. Trivia question for the newer pilots. Previous posters have to wait two days to answer. Why was it common in the old days for instructors to keep carb heat on until the plane was on the ground (still common today with some that do not understand how carbs work and just do things because someone told them to do it)? DENNY
 
I've never owned a plane that made ice. My 180 has had two 470s and one 520. No ice. Old -12, no ice. The others were FI so not applicable. Learn YOUR plane. Other guys’ planes aren’t important.
 
Bill Rusk said:
The intake tubes on Lycomings go through the sump and thus the air is preheated a little. Most of the early POH's for Lyc powered aircraft said "Carb heat- as required" Over the years the lawyers managed to effectively reduce the POH's to more of a legal CYA document than a users manual.

Continental engine intake tubes do not go through the sump and because of that the continental engines are much more prone to ice. Most POH's for continental powered engines would state "Carb heat - on" for any power reduction.

I have experienced far more carb ice in benign conditions with continental engines than Lycoming. But that said, I have experienced carb ice in my Lycoming in SE Alaska, but usually in conditions that were prime for ice, i.e. rain, temp 50 degrees, etc.



Bill
Click to expand...

Does carb ice occur in induction tubes? It occurs in the venturi, upstream of the induction tubes. Some Lycomings are ice makers, some aren’t. The same is true for Continentals.
 
DENNY said:
... Why was it common in the old days for instructors to keep carb heat on until the plane was on the ground (still common today with some that do not understand how carbs work and just do things because someone told them to do it)? DENNY
Click to expand...
Because they also taught throttle closed for approach and landing. Close the throttle opposite the proposed touchdown location and fly the wing to the ground. The only reason to keep the engine running was to have it available "just in case". Open the throttle briefly on base and final to ensure the carburetor is clear. Ice can form with the small Continentals at idle because there is very little heat being produced in the exhaust and the carburetor is mounted separate from a heat source. So even with carb heat on, there is very little heat. If a burst of power is needed on short final, there is a better chance of it being there if the carb heat is on. In "the old days" all the trainers had small Continentals. A PA-12 was not a trainer, it was a step up from a primary trainer.

With the carburetor being mounted directly to the warm oil sump of the Lycomings, there is less chance of ice forming due to the proximity of the ice producing portion of the carb being in close contact with the hot oil sump.

150 hp Cub pilots have become too used to the minimal icing characteristics of their engines. Well this is true of any pilot who learned to fly behind a Lycoming, this includes their instructors.

I think the "power on" throughout the entire approach technique began when the airport traffic increased and the airport became bigger and busier making it necessary to "extend" the size of the traffic pattern. Thus pilots today depend on the engine to get them to the runway never closing the throttle until touchdown. They just don't understand how to "fly the wing".

The Ranger engine's carburetor was mounted separately from the engine as it is on the Continentals. The manifold had a small chamber through which some of the exhaust was routed. This was called a "hot spot" heater. These were later disconnected.
 
Does anyone here use a carb temp gauge on a Cub? Does the carb temp always remain above freezing?

I’ve had a carb temp gauge on my 180 since I bought it. The original was a pointer with a green-yellow-red bezel. My temps ran in the yellow zone 100% of the time. It never made ice. In the early years of owning that plane I used carb heat on downwind. I never had any indication of ice. When I added an EDM monitor I added carb temp so I could try to improve fuel distribution in my o-520. It didn’t work. I haven’t looked at card temp since. Subsequently my fuel flow was increased and all my temps leveled out. And still no ice. I know guys with similar planes that do make ice. No explanation of why the difference.
 
stewartb said:
Does anyone here use a carb temp gauge on a Cub? Does the carb temp always remain above freezing?

I’ve had a carb temp gauge on my 180 since I bought it. The original was a pointer with a green-yellow-red bezel. My temps ran in the yellow zone 100% of the time. It never made ice. In the early years of owning that plane I used carb heat on downwind. I never had any indication of ice. When I added an EDM monitor I added carb temp so I could try to improve fuel distribution in my o-520. It didn’t work. I haven’t looked at card temp since. Subsequently my fuel flow was increased and all my temps leveled out. And still no ice. I know guys with similar planes that do make ice. No explanation of why the difference.
Click to expand...

I would like to have a carb temp in my cub just to see what is going on. I do have a digital carb temp in the 180 (O520 basically also) and it makes a bunch of ice in the right conditions - no matter the OAT. I have flown another PPonked 180 that had carb temps in the 60's without carb heat. In the same conditions, mine would be in the low 30's.

sj
 
stewartb said:
Does carb ice occur in induction tubes? It occurs in the venturi, upstream of the induction tubes. Some Lycomings are ice makers, some aren’t. The same is true for Continentals.
Click to expand...

More to the point, in small Lycomings, the carburetor is mounted directly to the sump, thus somewhat heated.

MTV
 
I can’t believe that the carb would be warm enough to continuously heat the venturi with a constant flow of cool air blasted through it. I could be wrong but that never has made sense to me. If that’s the case why do some Cubs make ice? I really am curious about carb temps in Cubs, or any other Lycoming installation. I’ve read that 0-320s in 172s are ice makers. Is that true?

FWIW, I believe application of carb heat on downwind is a good habit to have. After almost crashing into trees during a go-around with heat on? I believe pushing the heat knobby in on short final is an equally good habit.

https://www.lycoming.com/sites/default/files/Use of Carburetor Heat Control.pdf

https://www.ntsb.gov/Advocacy/safety-alerts/Documents/SA-029.pdf
 
Last edited:
Remember dew point is also part of the equation, not just temperature.

carb-icing-probability-chart-l.jpg

iu
 
Probably not a good post for student/low time cub pilots and when I was instructing I taught carb heat each approach to landing with the caveat of non-use in dirty/dusty conditions.
However.........I've been flying cubs ( mostly O-320's) since the early '70's and can't remember one instance of carb ice. I don't use carb heat.....maybe lucky or maybe the locations I usually fly. I do when temps are
extremely low only for a possible go around as I've had the engine stumble a bit without it. Could be icing more probably at idle......but I never idle my cub 'til touchdown. :peeper
 
Thank you all for contributing to this discussion. I don't have much to add, but I'm definitely learning. I fly a PA-18-150 and have gotten out of the habit of using any carb heat except on rare occasion. I really appreciate the discussion - has given me a lot to think on (and to incorporate into my practice).
 
One more piece of data - I have experienced significant carb ice twice with my -12's O-320 in the 46 years I've been flying it. Once in climb in CAVU conditions, and once in cruise just under some low cloud. By "significant ice" I mean significant power loss that was recovered with carb heat. Even insignificant ice has been rare, but - - - - -
 
My Cub has an O360 and it is an ice maker, so much so the previous owner installed a carb ice detector. Just yesterday and again this morning it was making ice quite often. This morning I expected it, but yesterday it was very warm and when the light came on, I was not expecting it.

An old timer taught me to keep carb heat on until short final, then push it in and give the throttle a blast to clear any ice, always nice to have full power of you need to go around, and often when a dog or moose runs out on the runway, pushing in carb heat might forget to happen.
 
I have had very little evidence of carb icing in my 150 hp Pa-18. I did have one event on the 4th of July a couple years ago. I departed a pond I fished and camped at overnight.
It was very humid and after 30 minutes the engine began to run a little rough. I added carb heat and it went away after a couple minutes.
I checked the dew point and there was only a few degrees between the air temp and the dew point. I believe the weather station reported that they met at 4500 ft. I was at 3000 ft and there were clouds at 2000 ft. I changed my route to avoid the clouds and dropped to 1500 ft and used carb heat once in a while the rest of the trip.
I do regularly use carb heat on downwind but close on final.


Sent from my iPhone using Tapatalk
 
This belongs in the oops thread, but as it relates specifically to carb ice I’m pasting it here.
This is a bad deal on many fronts, but the cause was carb ice.

- NTSB Issues the final report into the fatal accident involving a Cessna 177B Cardinal, N34633, that occurred on November 11, 2020, at Whidbey Airpark (W10), Whidbey Island, Washington:

On November 11, 2020, at 1144 Pacific standard time, a Cessna 177B airplane, N34633, was substantially damaged when it was involved in an accident near Whidbey Air Park (W10), Langley, Washington. The private pilot and flight instructor were fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

About 16 minutes after takeoff, at 6,500 ft above mean sea level , the airplane’s groundspeed decreased and the airplane started to descend. Shortly thereafter, the flight instructor reported to air traffic control that they were declaring an emergency because they were at full power and rpm setting, and about to lose the engine. They were also unable to maintain altitude. The airplane continued southeast for about 2 miles when it made a left turn east and then back to the southeast. The flight instructor reported they had a little power but were still descending. He further stated that the engine would not stay on for very long and they were at idle power. The controller asked if he had carburetor heat on and he replied “affirmative.”

Shortly thereafter, the flight instructor reported that they did not have engine power and they were going directly to nearby Whidbey Air Park, Langley, Washington. The airplane crossed and flew over a highway before turning north to the airport. Shortly thereafter, the flight instructor stated they were diverting off-airport and the airplane track turned right away from the airport. However, about 15 seconds later he reported the airport insight and the airplane’s track changed back toward the airport. There was no further communication from the accident airplane. The last radar point was over the runway at an altitude of about 300 ft.

A witness reported who was at the airport observed the accident airplane about pattern altitude passing from west to east. The accident airplane continued slightly east of the airport before it made a left turn to a northwest heading. It appeared as if the airplane was “porpoising,” continuously nosing up and down. He noted that the propeller was not turning and there were no audible engine sounds. As the airplane passed over the runway the left wing dropped, and the airplane spun out of sight behind the trees and hangars. Shortly thereafter, the witness heard the impact. The airplane came to rest about 153 ft west of the runway surface against trees that were about 65 ft tall. The witness account and the condition of the wreckage were indicative of the flight instructor’s failure to maintain airspeed, which resulted in an aerodynamic stall and subsequent spin.

A postaccident airframe and engine examination did not reveal any anomalies that would have precluded normal operations. The airplane’s engine monitoring system revealed the carburetor temperature had been steadily decreasing from 31°F during the accident flight. When the carburetor temperature reached 17°F there was an abrupt decrease in fuel flow and a corresponding reduction in exhaust gas temperatures. For the remainder of the flight, the exhaust and cylinder head temperatures slowly decreased, and the carburetor temperature slowly increased. The fuel flow spiked several times but immediately decreased.

The nearest weather reporting station reported the temperature as 6°C and dewpoint, 2°C. When plotted on the carburetor ice chart, this temperature dewpoint spread is consistent with serious icing at cruise power. Therefore, it is likely carburetor ice was building during the accident flight and it eventually starved the engine of fuel.

- Probable Cause: The flight instructor’s failure to maintain airspeed, which resulted in an aerodynamic stall and subsequent loss of control while attempting to conduct an emergency landing. Contributing to the accident was a total loss of engine power as a result of carburetor icing.

- Report: https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/102268/pdf

- Docket: https://data.ntsb.gov/Docket?ProjectID=102268

IMG_1305.JPG


Transmitted from my FlightPhone on fingers… [emoji849]
 

Attachments

  • IMG_1305.JPG
    IMG_1305.JPG
    195.6 KB · Views: 82
Farmboy said:
This belongs in the oops thread, but as it relates specifically to carb ice I’m pasting it here.
This is a bad deal on many fronts, but the cause was carb ice.
A postaccident airframe and engine examination did not reveal any anomalies that would have precluded normal operations. The airplane’s engine monitoring system revealed the carburetor temperature had been steadily decreasing from 31°F during the accident flight. When the carburetor temperature reached 17°F there was an abrupt decrease in fuel flow and a corresponding reduction in exhaust gas temperatures. For the remainder of the flight, the exhaust and cylinder head temperatures slowly decreased, and the carburetor temperature slowly increased. The fuel flow spiked several times but immediately decreased.

The nearest weather reporting station reported the temperature as 6°C and dewpoint, 2°C. When plotted on the carburetor ice chart, this temperature dewpoint spread is consistent with serious icing at cruise power. Therefore, it is likely carburetor ice was building during the accident flight and it eventually starved the engine of fuel.

- Probable Cause: The flight instructor’s failure to maintain airspeed, which resulted in an aerodynamic stall and subsequent loss of control while attempting to conduct an emergency landing. Contributing to the accident was a total loss of engine power as a result of carburetor icing.

- Report: https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/102268/pdf

- Docket: https://data.ntsb.gov/Docket?ProjectID=102268

View attachment 62103
Click to expand...
All the investigation says carb ice. One thing they didn't mention was the position of the carburetor heat control. Where was it? Hot or cold?
 
When I did my 180 make-over in 2010 my then mechanic, Brian Gillette, pitched the original Cessna exhaust riser heat robber and had Atlee’s weld a scat outlet on the new Acorn muffler shroud. My carb heat is freakin’ hot. Brian said when you need carb heat there isn’t enough heat in the heat robber to melt anything so he moved the heat source to one that’ll work at low power. Ice doesn’t stand a chance. I like it.
 
Last edited:
BC12D-4-85 said:
I read a couple of studies of carb ice in a test bed engine some time ago. The authors claimed fuel types influenced ice by some creating more cold during vaporization. The auto fuel they used was the worst offender. Also teflon coating of the throttle plate was recommended in the first one to reduce ice buildup.


Several years ago before changing to the 180 hp I used only auto fuel. I was caught off guard one day hauling some freight to my cabin when I noticed a power loss. Adding to or changing throttle positioning caused immediate backfire. Carb heat application made it nearly quit. Fortunately I was high enough and began a long straight in approach to our lake. (Good lesson about not cruising too low)
At shutdown I checked the carb and it was ice cold.

Over the next few flights I experienced lots of icing indications, and in different weather conditions.

I decided to go back to AV gas and all signs of icing disappeared.

I had consumed thousands of gallons of auto fuel over the years from the same source with no issues.
I no longer use auto fuel.
Click to expand...
 
You must log in or register to reply here.

Similar threads

S
Robbing carb heat for cabin heat.
Replies
19
Views
10K
Senior
S
mgberry
Carb Heat
Replies
6
Views
2K
skywagon8a
skywagon8a
Bearhawk Builder
Flying with carb heat
2
Replies
32
Views
14K
cubowner
C
B
Art of leaning and carb heat
Replies
9
Views
6K
cubdriver
C
G
carb. heat question
Replies
21
Views
6K
arcticflyr
A
Back
Top