Oh,
I guarentee your fuel burn will decrease if you leave the carb heat on also. A reason is because your % power output will be significantly reduced because the hot air is less dense, so to maintain a proper A/F ratio you will have to reduce fuel flow. I believe the same result can be achieved by reducing the throttle.

Walter Atkinson wrote:**My O 540 B4B5 is very susceptible to carb ice. I've notice it most at the low power settings I use for patrol work. The carb temp probe will be showing as high as 42 F and I will be losing m.p. due to carb ice. Maybe it's building up on the throttle body and not at the top of the venture where the probe is located**


THAT is a very good observation. That's INDUCTION icing--commonly on the air filter.

Now Walter, he's getting induction icing on the airfilter when the air temp down stream of the airfilter is 42 deg.? There should be almost no pressure drop from the filter, so where is the cooling effect coming from and what heated the air temp back up to 42deg? Oh and I'll bet if we asked him we would find out the FAT was at least in the 50's, but I'm shooting in the dark there.

a64pilot wrote:

Walter Atkinson wrote: MANY are now using Carb heat in cruise to improve fuel vaporization and improve F:A balance in carbed engines. MANY are able to run smoothly LOP as a result. The side benefit is that those who are doing this end up with a carb temp above freezing where it is not possible to have carb ice at all. Something to ponder......

Something else to ponder is that whenever you are using carb heat, you are bypassing the airfilter.

That's true, but it's usually at altitude where dust isn't much of a factor. It's also worth remembering that many engines don't have a filter at all and never have. The ones on the big, old radials would stop a small to medium sized bird. Everything else went right on through! <g>

a64pilot wrote:

Walter Atkinson wrote:**My O 540 B4B5 is very susceptible to carb ice. I've notice it most at the low power settings I use for patrol work. The carb temp probe will be showing as high as 42 F and I will be losing m.p. due to carb ice. Maybe it's building up on the throttle body and not at the top of the venture where the probe is located**


THAT is a very good observation. That's INDUCTION icing--commonly on the air filter.

Now Walter, he's getting induction icing on the airfilter when the air temp down stream of the airfilter is 42 deg.? There should be almost no pressure drop from the filter, so where is the cooling effect coming from and what heated the air temp back up to 42deg? Oh and I'll bet if we asked him we would find out the FAT was at least in the 50's, but I'm shooting in the dark there.

That's certainly a fair question, but we've seen ice accumulation on air filters when the OAT certainly should not have resulted in that. It's not always intuitive. Ice deposition is a result of a combination of issues besides OAT. I have a magnetic, automatic alternate air door on my engine. It has a light that comes on on the panel when the door is even cracked open a tiny bit. That light has come on indicating filter obstruction (ice) at all kinds of unexpected times! It has often been a head-shaker, but that's the observation. Sometimes I never see the airframe accumulation at all, but it's on the filter. Granted, it seems weird.

I'm not saying that's definitely what's going on, but it's a possibility. Also, throttle plate ice is "induction icing" as well... it's not carburetor icing.

a64pilot wrote:Oh,
I guarentee your fuel burn will decrease if you leave the carb heat on also. A reason is because your % power output will be significantly reduced because the hot air is less dense, so to maintain a proper A/F ratio you will have to reduce fuel flow. I believe the same result can be achieved by reducing the throttle.

Reducing the throttle will "choke" the engine of air. That increases pumping loses and makes the engine less efficient. It also does nothing to increase fuel vaporization. There's more to this than simply HP being produced.

I have an IO 540 (injected) and a few days ago I was experiencing a gradual lowering of MP and it was restored by pulling the Alt Air. It happened a few times on a 2 hr flight in light rain with OAT ~ 36F.

Norm

PS Sorry....I know this was a post re 180 hp Lycs but I couldn't resist.

I have experienced this power loss in rain or after a badly aimed hose at the wash rack. It only happens if you have the Paper air filter which swells when wet. There are other types available and certified.

I agree, but mine has a foam filter. I had a bad experience with a paper filter years ago in a Cessna 172 in heavy rain with it swelling up and closing off the air supply.

Hey guy's
Go back and study your material from the Air Force, Navy, Engine manufactures, Faa, Caa, etc etc.
The most prone time for carb icing is when the highest pressure difference exsist in the carb "LOW POWER SETTING". Wide open throttle is the least pressure difference.
Yes, IT can happen at other times BUT BUT BUT use your brain and what you have been taught.

I heard a story once that could be useful, I have not tried it.
Adjust carb heat as you would mixture when conditions exsist. Pull carb heat and when you furst notice an RPM drop stop and readjust now and then. Sounds easy enough.
I,m happy to say I have had my Maule in heavy icing conditions and not even a wimper. The only place I could of gathered ice would have been the air intake and it has never happened. My air intake is on the right side of the cowl and this could help prevent icing, I just don't know.
One time the icing was bad enough that when a blade would sling it off the dash would vibrate so badly I thought the instruments would fall out.

210TC wrote:The most prone time for carb icing is when the highest pressure difference exsist in the carb "LOW POWER SETTING". Wide open throttle is the least pressure difference.

RATZ. I guess Sir Isaac Newton was wrong. <g>

Venturi effect is greatest at higher flow--wide open throttle. That is when the temp drop is the greatest. Go back and read my explanation as to why we use carb heat during low power conditions.

It is that time again in the Pacific Northwest. Low temps and high humidity.

I was dodging snow showers yesterday ( in and out of rain snow mix) on the way from Snohomish to Scapoose putting along about 1000 ft with an OAT of about 32F.

Have to admit I was not keeping a close enough eye on the Man. pressure and was more concerned w/ maintaining visibility.

I set cruise about 20" 2100Rpm but when I looked over I had dropped to about 17" manifold pressure. Quick carb heat a little shudder and right back up to 20".

Had to clear the carb ice about four or five times in the space of about 45 minutes.

This is on a O-540A1J5D 235hp engine.

Ya'll be careful out there.

TD

TD

Is that a Continental engine?

flyer

flyer wrote:TD

Is that a Continental engine?

flyer

Lyc 0540 not Cont.

Just read some good info about some testing done in Canada. I think this was funded by the Canadian Gov.
Test were conducted on carb icing, a .00125 layor of Teflon was coated onto the throttle shaft and butterfly with superb results.
Ice does not stick to Teflon.

Update: the study was conducted in 1971 by the NRC National Research Counsel in Canada.
ANY airplane I own with a carb will get this treatment.