Use Carb Heat or Not?

[uwochris]

Hey guys,

Like most people, I was taught to use carb heat in the downwind checks prior to landing and anytime I was operating at reduced power settings (below the green arc on the RPM gauge).

Currently I fly a 152 and am doing aerial photography. I am averaging 6 hours of flight time per day when I fly, and usually take a break somewhere in between.

While I am working, I am configured at approx. 2000 RPM, 20 degrees flaps, and 60-70 knots. I maintain this configuration while I am flying and taking pictures. When I enter the traffic pattern to land I have NOT been using carb heat in my pre-landing checks. I figure that by flying around at 2000 RPM and 60-70 knots for 3 hours or more at a time the engine will get pretty hot.

Now I am no engine expert so I hope some experienced people here can provide some insight. Do you think my decision NOT to use carb heat is warranted, or is it just ignorant? Would you be using it if you were in my situation?

Thanks in advance,

Chris.

 

[Mmmmmm Burritos]

Engine temp has nothing to do with it. It's inlet air temperature and the venturi effect in the carb that causes the air to cool down up to 70-80 degrees F. Use the carb heat when not making cruise power as a preventative measure.

 

[satpak77]

don't try to out-think the POH

follow the POH

 

[Vortilon]

Follow the manufacturer's recommendation....period!

 

[bobbysamd]

Carb heat

The reason for using carb heat is to prevent the formation of venturi ice. Engine temp has nothing to do with carb ice formation. Use the carb heat as you, and I, and everyone, were trained.

Case in point. I was tooling around one spring day in a 172 in Oklahoma. The day was humid, as are most days in Oklahoma. I am sure the OAT was between the classic 32 degrees and 70 degrees. I was flying at ordinary cruise, using 2400 rpm. I was losing power and couldn't figure out why. When I advanced the throttle, I wasn't getting more revs. Then, the light (in my mind) came on. I opened the carb heat fully, and the power came back shortly.

Hope that helps.

 

[mar]

What they said.

It's good advice to follow the book. Nobody knows the machine as well as the people who built it.

Not only that, but it gets the legal monkey off your back. If something were to happen and it was discovered you didn't follow SOP then the monkey gets on your back again.

And I've only heard of one condition where carb heat is a bad idea: When the OAT is -40C and you actually warm up the air in the venturi to -10C to 0C and increase your chance of carb ice...

...or that could just be a hunk of pilot lore that ain't true. I don't know.

Some airplanes have a carb temp gauge. Very handy. Fly safe.

 

[FracCapt]

I never fully realized how much the temp drops in a carb, or what kind of conditions could really produce temps low enough for carb ice, until I started flying helicopters with carbs, and a carb temp gauge. It was an eye opener when I saw temps of around 0 degrees C on the carb temp when it was 30C outside.

 

[xrated]

All posts here have a valid point. Good advice all around. I've got a lot of experience in Cessnas and fact of the matter is, it doesn't hurt to use it. In fact, in the last Cessna I flew, It didn't even have a carb heat controll but I incorporated into my flow so I wouldn't forget it on the next plane I flew.

Well here I am in training on a new aircraft. A budy of mine, (who has about twice the experience as I do, and was on the fast track to greatness.....if you could call #2 great, at a previous little know carrier in the midwest), told me the instructors would be impressed if I used carb heat on all approaches regardless of temp or humidity. I took his advice. The only problem is, I haven't read about Carb heat in the systems books and the instructors haven't told me where the carb heat controll is? I ask, and they look at me like was some bald funny looking ex 767/MD-80 pilot.

If anybody could help me out on this problem, I'd be happy to hear all advice.

Can carb ice form on an V2500-A1 or A-5 when the temps in PHX are 110 and the humidity is 10%?

Thx in advance

CARB HEAT

 

[steveg]

Ignore the bitterness from xrated. He got in trouble today for opening the window and yelling "Clear". Just remember, Wx, box brief, flow, gumps.

 

[steveg]

ps. You know what they say about bald pilots with more experience?

 

[rumpletumbler]

Check this out....

http://www.whittsflying.com/page5.715CarburetorIce and Heat.htm#Carburetor Ice and Heat

 

[dtoften]

If I remember correctly, it's 2,000 rpm the beginning of the green arc? So no carb ice needed? One possible solution, if below green arc, is to lean the carb with carb heat on.

 

[Lead Sled]

Can carb ice form on an V2500-A1 or A-5 when the temps in PHX are 110 and the humidity is 10%?

To answer your question, probably not. You can't freeze what's not there and with an OAT of 110 F, I don't believe that you're going to get enough temperature drop in the venturi to get what water vapor is present to freeze.

That being said, I'll echo what others have posted on this thead...

What does you POH say about the use of carb heat? Reread your manual and then answer your own question.

Some manuals give you the option, others do not. For example, I happened to grab the manual for a Super Cub I used to tow gliders with. The Lycoming O-320 isn't especially prone to icing and this fact is reflected in the following statements:

"Unless icing conditions in the carburetor are severe, do not cruise with the carburetor heat on. Apply full carburetor heat only for a few seconds at intervals determined by icing severity."

"During approach... the carburetor heat need not be used unless icing conditions prevail, but the engine should be cleared frequently by opening the throttle."

Granted, those quotes were from a Super Cub manual, but you'll find similar statements for most aircraft powered by carbureted Lycomings. Continential powered aircraft are a different breed of cat and typically require the use of carb heat. Again, read the friggen manual and don't read more or less into it. (Pilot's have a bad habit of thinking that they know more than the aircraft engineers, designers, and test pilots that wrote the manuals.)

Lead Sled

 

[A Squared]

Granted, those quotes were from a Super Cub manual, but you'll find similar statements for most aircraft powered by carbureted Lycomings. Continential powered aircraft are a different breed of cat and typically require the use of carb heat. Again, read the friggen manual and don't read more or less into it. (Pilot's have a bad habit of thinking that they know more than the aircraft engineers, designers, and test pilots that wrote the manuals.)

Lead Sled

There's probably some truth to those observations about lyc. vs. cont. but like all generalizations, they can be deceptive. A friend has a Pa-12 with a 160 hp lyc 320 (don't recall the dash model) he's owned the thing for decades, never has any problem with ice. He had it rebuilt and the induction system was changed a bit, don't recell the details of the changes but it became a regular ice monster. He's always fiddling with carb heat to keep it from icing up. same exact engine, same exact carb, different induction ducting.

I have a Cessna 180 with a continental 0-470-R and the *only* time in 12 years I have had a hint of carb ice was one misty, rainy/snowy 33 degree October morning departing a river in western Alaska By contrast, an acquaintence has the same exact engine (right down to the dash model) in an early model 182 (similar, but slightly differnet induction sys.) and it makes carb ice at the drop of a hat. My point is that carb ice is a much more complex issue than merely engine manufacturer.

 

[Lead Sled]

There's probably some truth to those observations about lyc. vs. cont. but like all generalizations, they can be deceptive...
My point is that carb ice is a much more complex issue than merely engine manufacturer.

Exactly. If you reread my quote I used the words "most" and "typically", I also told them to read the manual. Even most manuals leave some wiggle room for individual cases. (When it comes to aviation, the words like "always" and "never" are seldom appropriate.) You are absolutely correct when you state that carb ice is "a much more complex issue than merely engine manufacturer." My point is that when all else fails, read the friggen manual. If the manual calls for carb heat on approach and it just so happens to be 110F outside, then ice or not, use the heat.

Lead Sled

 

[mtrv]

There's probably some truth to those observations about lyc. vs. cont. but like all generalizations, they can be deceptive. A friend has a Pa-12 with a 160 hp lyc 320 (don't recall the dash model) he's owned the thing for decades, never has any problem with ice. He had it rebuilt and the induction system was changed a bit, don't recell the details of the changes but it became a regular ice monster. He's always fiddling with carb heat to keep it from icing up. same exact engine, same exact carb, different induction ducting.

I'm new here, but will mention a few facts regarding Lycoming, Continentals, & ice.

The reason you don't see "carb heat" as a usual step in the landing checklist for a Piper Warrior/Archer is that the Lycoming's carb is bolted directly to the engine's oil sump, which transfers some engine heat to the carb body. Helps with preventing icing, but has the downside of slightly lower horsepower.

The Continental, as used in older Cessna's has a carb mounted to the intake piping & absorbs less heat.

My preference with Lyc's and high altitude airports is to leave the carb heat off during an approach. If it's by chance left on during a go-around, it's just robbing needed power.

 

[I.P. Freley]

My preference with Lyc's and high altitude airports is to leave the carb heat off during an approach. If it's by chance left on during a go-around, it's just robbing needed power.

Hmmmm... The only airplane manual I have handy is a C-172N manual, and on the "Balked Landing" procedure it sez "Carb Heat- Cold" as the second item, right after full power. I seemed to remember that this was a standard procedure for ANY airplane with carb heat, and that's just part of the program. It would seem doubtful that you'd crash and burn because of the one second interval between pushing that throttle full up and turning the carb heat to cold.

When I taught, I always told the students to use the heat. Always. Then again, I didn't live or teach in an area like Phoenix, where I imagine it's not as much an issue.

 

[mtrv]

Hmmmm... The only airplane manual I have handy is a C-172N manual, and on the "Balked Landing" procedure it sez "Carb Heat- Cold" as the second item, right after full power. I seemed to remember that this was a standard procedure for ANY airplane with carb heat, and that's just part of the program. It would seem doubtful that you'd crash and burn because of the one second interval between pushing that throttle full up and turning the carb heat to cold.

The factory Piper Archers POH, states "On......... if required" for landing. You'll seldom find "carb heat on" in the many checklist's for Warriors & Archers on the web. It's in "none" of my checklist's from student days, while it's in all my older Cessna checklist's.

In the homebuilt/experimental sector, many use "carb heat- on" as part of the landing checklist while using Lycomings, but many others don't. As I have a Lyc & am use to Pipers, I don't either.

 

[I.P. Freley]

The factory Piper Archers POH, states "On......... if required" for landing.

Right, and that -N manual I told you about sez "Carburetor Heat- As required".

My point is that your procedure for a balked landing or a go-around should always, ALWAYS include "Carburetor Heat- OFF", or "cold", to remind you to go for it even if you didn't turn it on while setting up for landing. What I'm saying is that the argument "carb heat will reduce your available power on a balked landing" is irrelevant if you trained to turn it off as part of a balked landing/go-around.

For purposes of comparison, our call at acceleration height is "Flaps Up, Climb Power, Climb Checklist"... Perhaps twice out of the 2000 legs in this airplane have the flaps been anywhere but "up" already, but we always check it anyway for that one-in-a-thousand event where they're extended for takeoff.

 

[Lead Sled]

You'll seldom find "carb heat on" in the many checklist's for Warriors & Archers on the web.

Actually, I find this kind of funny. There's nothing wrong or nothing to stop you from modifying checklists used in aircraft operated under Part 91. It's actually done all of the time with bizjets. (Part 121 and 135 aircraft do it as well, but they have to go through an approval process.) The one thing you have to very careful with is that if you elect to change one of the checklists you keep the "intent" of the checklist intact. The controlling document is the FAA approved flight manual (if the airplane has one - some older types don't). I've seen guys call for carb heat on Cherokees on every approach because "the Cessna 150 that I used to fly used to ice up all of the time". I've also seen guys omit the heat on airplanes that called for it because "I've never had it ice up on me yet". If you use a checklist that you downloaded from the 'net or got from any other source besides the flight manual make sure you verify that it contains all of the appropriate items. If there's an accident, you will have to account for the checklist that you were using.

Lead Sled