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[7JD]

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[Ed Cesnalis]

Descending from 9,500 to 800' is one I do often. I retard my throttle until I have a 500'/min descent. The throttle is only partially closed, far from 'a touch open' That seems to match the descent profile that I get from my 496 ( perhaps 500 fpm is a setting somewhere? )

 

Using carb heat makes sense on descents and landing approaches with traditional aircraft engines, the jury seems to be still out with a 912. If you don't use it routinely then you should have in your mind that you will use it if carb icing symptoms develop. I think its safest to just use it, if you are not in the habit carb heat may not occur to you when you do need it.

[Jim Meade]

Does anyone know of anyone who has a carb temp gauge on the 912, and if so, what kind of readings does it yield?

[Flying Bozo]

What are the symptoms of carb ice in the CT... The carb is self adjusting for altitude so I don't know how the carb ice would look any different to the carb than a change in altitude. I don't think I have ever had carb ice in the CT but can't say that I would know it or not. Comments on this would be helpful.

Larry

[josjonkers]

What are the symptoms of carb ice in the CT... The carb is self adjusting for altitude so I don't know how the carb ice would look any different to the carb than a change in altitude. I don't think I have ever had carb ice in the CT but can't say that I would know it or not. Comments on this would be helpful.

Larry

I "think" I have only experienced this once going into Helena, Mt. In descent I noticed an engine sputter/hickup. Just a burb with a noticeable drop in rpm for maybe 0.5 seconds. And then it was smooth again . Did pull the carb heat just in case.

[Ed Cesnalis]

Pressure differential acts on the diaphragm / needle jet to provide leaning at altitude when throttle is not wide open. The carbs wouldn't be fooled by icing.

 

Icing will richen the mixture and cause rough running and if allowed to develop eventually stop the engine. If one carb iced before the other it could cause violent shaking?

[C ICEY]

flying in BC, seasonally we get lots of icing conditions that appear to turn the Cessna pilots white. Cool to cold temps and high humidity. I have never experienced icing with the CT. When temps dip, I cover the rad with strips of aluminum tape and that keeps the oil and cht temps the same as summer.

[Rich]

Good afternoon,

 

If I was descending from any altitude from cruise RPM I'd use carb heat every time.

I don't think there's anything to gain by not using it in a descent but a lot to loose if you get carb ice without enough time or altitude to clear it.

 

Also, if I was in cruise and noticed my RPM's dropping, (the first sign of carb ice) I'd apply carb heat. The RPM's may drop a little more when applied while the melted ice goes through the induction system but will clear rapidly.

 

I don't know if the water jackets around the carbs in my 912ULS is an option that the dealer installed or if it's standard on the 2012 + models. The water jackets that allow warm coolant to flow around the carbs will help prevent carb ice with no reduction in RPM, as there's no warm air ingested in the induction system.

 

I've had carb ice develop in cruise while flying a C-172 over the Catskill Mts. in NY.

So far, with 106 hours on the 912 ULS I haven't had a problem.

 

Rich

 

 

[Roger Lee]

The hot water jackets should keep all your carb ice at bay.

 

Ed is right that it works on the air sie of the mixture and makes the engine really rich and it can get so rich it won't fire.

 

It can't hurt anything to use carb heat on a decent.

 

Variable throat carbs aren't as susceptible to get icing like a standard carb, but it can and does happen.

 

912's in the UK where the conditions are ideal as lot more often can and do see some carb ice at times.

Since the inception of the 912 (late 1989) very few have ever had carb heat and most have done very well, but planes are different now days and we're supposed to be better educated about carb ice.

 

Our CT carbs get quite hot, but I have never measured the temps. After I heal up a little maybe a little research project might be fun. Here in the southwest US carb and 8-10% humidity carb ice usually isn't a worry. I haven't heard of any CT's going down because of carb ice. I'm sure sometimes people want to blame carb ice, but it's hard to prove. It is usually pointed to as a culprit when they can't find anything else.

 

 

Wikipedia:

Carburetor, or carb icing, is an icing condition which can affect any carburetor under certain atmospheric conditions. Carburetor icing occurs when there is humid air, and the temperature drop in the venturi causes the water vapor to freeze. The ice will form on the surfaces of the carburetor throat, further restricting it. This may increase the Venturi effect initially, but eventually restricts airflow, perhaps even causing a complete blockage of the carburetor. Icing may also cause jamming of the mechanical parts of the carburetor, such as the throttle, typically a butterfly valve.

While it applies to all carburetors, it is of particular concern in association with piston-powered aircraft, especially small, single-engine, light aircraft. Aircraft powered by carbureted engines are equipped with carburetor heat systems to overcome the icing problem. In cars, carburetor icing can occasionally be a nuisance. The inlet manifold and parts of the carburetor often have warm water from the cooling system or exhaust gas circulating through them to combat this problem. Motorcycles can also suffer from carburetor icing, although some engine designs are more susceptible to it than others. Air-cooled engines may be more prone to icing, due to the absence of warm coolant circulating through the engine.

[Roger Lee]

Carburetor Icing

 

by FLIGHT LEARNINGS

in AIRCRAFT SYSTEMS

 

As mentioned earlier, one disadvantage of the float-type carburetor is its icing tendency. Carburetor icing occurs due to the effect of fuel vaporization and the decrease in air pressure in the venturi, which causes a sharp temperature drop in the carburetor. If water vapor in the air condenses when the carburetor temperature is at or below freezing, ice may form on internal surfaces of the carburetor, including the throttle valve. [Figure 6-11]

 

Figure 6-11. The formation of carburetor ice may reduce or block fuel/air flow to the engine.

 

The reduced air pressure, as well as the vaporization of fuel, contributes to the temperature decrease in the carburetor putting you at risk for carburetor icing. Ice generally forms in the vicinity of the throttle valve and in the venturi throat. This restricts the flow of the fuel/air mixture and reduces power. If enough ice builds up, the engine may cease to operate. Carburetor ice is most likely to occur when temperatures are below 70 degrees Fahrenheit (°F) or 21 degrees Celsius (°C) and the relative humidity is above 80 percent. Due to the sudden cooling that takes place in the carburetor, carburetor icing can occur even with temperatures as high as 100 °F (38 °C) and humidity as low as 50 percent. This temperature drop can be as much as 60 to 70 °F (15 to 21 °C). Therefore, at an outside air temperature of 100 °F (37 °C), a temperature drop of 70 °F (21 °C) results in an air temperature in the carburetor of 30 °F (-1 °C). [Figure 6-12]

 

 

Figure 6-12. Although carburetor ice is most likely to form when the temperature and humidity are in ranges indicated by this chart, carburetor ice is possible under conditions not depicted.

 

The first indication of carburetor icing in an aircraft with a fixed-pitch propeller is a decrease in engine rpm, which may be followed by engine roughness. In an aircraft with a constant-speed propeller, carburetor icing is usually indicated by a decrease in manifold pressure, but no reduction in rpm. Propeller pitch is automatically adjusted to compensate for loss of power. Thus, a constant rpm is maintained. Although carburetor ice can occur during any phase of flight, it is particularly dangerous when using reduced power during a descent. Under certain conditions, carburetor icing could build unnoticed until power is added. To combat the effects of carburetor ice, engines with float-type carburetors employ a carburetor heat system.

 

 

 

 

Read more http://www.flightlea...rburetor-icing/

[WmInce]

Carburetor Icing

by FLIGHT LEARNINGS

in AIRCRAFT SYSTEMS

 

Thanks for posting that Roger.

Clear as mud now.

[Ed Cesnalis]

Symptoms of carb icing are running rough and losing power. Both attributes of disruption in atomized fuel flow to the intake manifold that feeds the pistons. I have heard the CT is better than other planes regarding carb ice. But you can recognize the symptoms mainly by loss of power, and that is a bad thing obviously on takeoff.

 

You need a venturi effect to encourage carb ice, that means a closed or partially closed throttle, it is a concern on descents and landing approaches but not on takeoffs. In fact takeoffs should be done with carb heat off to maximize power.

[Roger Lee]

The 912 doesn't get the same affect as a Continental or Lycoming or some other air cooled engine from activating the carb heat. Carb heat is safe anytime on the 912. Many people do a carb heat check before take off on a 912 and never even notice an rpm drop. Use it if you need it. Carb ice doesn't form on climb out. It may have formed sitting on a ramp and you may feel it on take off, but evidence has shown it doesn't form on climb out. Carb ice isn't very high up on my look out list while flying, but that doesn't mean to be uneducated about it and knowing what to do just in case so this should be in your mental file cabinet.

[Dan Kent]

I believe another response to carb icing is to go to full throttle while applying carb heat. A wide open throttle reduces pressure drop in the carb which will raise temp (or reduce temp reduction).

[Doug G.]

If I understand correctly carb heat on an SW simply means the air is not going through the filter. On the CTLS heated air comes from the muffler shroud. Is this understanding correct?

[Roger Lee]

The SW has a trap door on the bottom of the air intake housing that just lets hot air in from the cowled area. The LS comes from the muffler, but neither carb heat goes through the air filter. The LS only goes through the Rotax air box.

[Doug G.]

Yes, I mis-stated the air filter comment. I know they both take the filter out of the intake circuit. So the SW depends on the warmth inside the cowling to provide heat. I wonder how much difference that would be on a cold day up north? It seems to have worked though.

Was the change just to be in line with the common carb heat practice, or was there a problem that caused them to change it on the LS?

[Roger Lee]

FD just started using the Rotax airbox which was more inline with others