Carb Heat

[flyingriki]

I've been flying my plane for going on 7 years and 700 hours now, all over the country in all weather and have never used carb heat in any conditions. Does any one use it or had issues with not using it?
It'a a 320 with standard MS 4 carb.

[Sugar Dunkerton]

I've had to pull carb heat once while on a shallow climb out of KMYF in San Diego. This was in a 160hp Cherokee Warrior. OAT was probably low 60s with high relative humidity. Engine sputtered a bit, so I pulled heat and momentarily turned back towards the field until it cleared up. It will definitely get your attention!

[ArVeeNiner]

I have heard that with the way the Lycomings run the intake air through the hot oil pan that carb ice is rare with them. Having said that, a friend of mine who flies a biplane equipped with an O-290 went down a few years ago (not a scratch on him) due to carb ice.

I ALWAYS use carb heat just like I was trained. You have to look at the trade offs. What is gained by not using it vs. what is the risk if the conditions are right for carb ice and it develops? The answers as I see them are 1) not much and 2) going down when you didn't want to and hitting something hard.

[Yen]

I havn't had carbie ice in an RV, but a C150 I used to fly would have ice if there was a cloud in the sky. it was lost in the ocean, but the pilot survived. I have also had ice in a Rotax 503 2 stroke engine, which a lot of experts say will not happen.

[Neal@F14]

I experienced carb ice in a lycoming O-320 equipped Cessna 172 one day right after takeoff, while in a full power climb when I'd just reached about 1500 AGL. Got my attention quick. When I pulled the carb heat, the engine almost died when it melted and swallowed the slug of water. I was a freshly minted PP-ASEL with about 70 hours under my belt then. OAT was in the upper 40's and humidity was really high. Then I owned and flew a Cherokee 140 with an O-320 for about 10 years and never had a hint of carb ice in that plane.

In my RV-6, knowing that its carb heat pickup off the front exhaust crossover pipe is very wimpy at best, I religiously run carb heat whenever I suspect conditions might favor the formation of carb ice. The reduction of power is miniscule in this plane with carb heat full on, and I'd rather be safe than sorry.

[terrykohler]

If you haven't experienced carb ice, it's likely that you haven't flown in visible moisture (clouds, rain, or snow) near the freezing temp. There's a reason that Vans put carb heat on these aircraft and a reason there was a service bulletin to add a bypass. I agree that the location of the carb on the O320 lessens the need for heat, particularly on the descent/when power is reduced. In moisture (at lower temps) is another matter.
Here in the mid-west, most icing occurs near the cloud tops. Climbing up, as the air gets thinner, we end up pulling heat and starving the engine even more. So just when you could use more power, you have less available. On the other hand, it beats having ice choke off the engine completely.
The important thing to remember with the RV setup is that the heat is for anti-ice and not de-ice. Pull it too late and it won't do any good. If I'm in visible moisture anywhere near the freezing temperature, the carb heat is already on.
Terry, CFI
RV9A N323TP

[RV10inOz]

Originally Posted by Neal@F14

I experienced carb ice in a lycoming O-320 equipped Cessna 172 one day right after takeoff, while in a full power climb when I'd just reached about 1500 AGL. Got my attention quick. When I pulled the carb heat, the engine almost died when it melted and swallowed the slug of water. I was a freshly minted PP-ASEL with about 70 hours under my belt then. OAT was in the upper 40's and humidity was really high. Then I owned and flew a Cherokee 140 with an O-320 for about 10 years and never had a hint of carb ice in that plane.

In my RV-6, knowing that its carb heat pickup off the front exhaust crossover pipe is very wimpy at best, I religiously run carb heat whenever I suspect conditions might favor the formation of carb ice. The reduction of power is miniscule in this plane with carb heat full on, and I'd rather be safe than sorry.

Correct Neal.

Most folk seem to think the likely time for ice is when the throttle is pulled on descent or in the pattern

Not So!

They are in order of likeliness and severity;
A) Startup/Taxi
B) Take-off and climb
C) Cruise
D) Power reduction for landing

And going full rich on descent makes that phase worse than leaving it in a nice LOP state from the cruise.

[flyingriki]

Great stuff guys, thank you! Sure didn't realize climb was a place to worry. Will pay attention when humid or visible or potential moisture and low temps.
Thanks again!

[N941WR]

With both the O-290 I had and my current O-360 I found that in MY RV, the carb temperature rises as the planes slow down. I believe this is due to the decreased air flow in the engine compartment. That coupled with the carb being bolted to a heat source (the sump), makes MY RV experience limited susceptibility to carb ice.

Yes, I have flown in snow, rain, very high humidity, etc. and never once have had to pull on the carb heat, although I have tested it to see if I would see any MP or RPM increase and never have.

Every airplane is different and your experience may be different than mine. Use caution and if you think you might get or have carb ice, put on the heat.

[rhill]

In a Cherokee you have a larger cowl,housing a large muffler and plumbing,its easy to forget the carb heat and get away with it.RVs run straight pipes,Vetterman's muffler system will help keep heat up around the carb.Anytime Dew point and temperature are close,run the carb heat.Once the ice has formed and you lose power and heat,its too late.The whole issue gos away with ported Fuel injection,throttle body injection responds the same as a carb and needs heat also.
RHill