Carb Ice with the 0-200A

[stroutmail]

This is my second year with the S1 (SN 28). Plane came from Michigan and previous owner claims to never have had carb ice. I have not experienced it either.

Yet, I read so many stories of the 0-200 being an "ice maker" that I am always careful and vigilant. I try not to fly unless ambient and dew point differential is 15F (8C). I always use carb heat while decending in the pattern (turn it off on short final). On days that I suspect risk (see photo) carb-ice-potential-chart.jpg I also test carb heat just before takeoff if I have taxied a long way. (Like when doing pattern practice to a full stop.)

Just did a cross country with ambient of 45F and dewpoint of 28F. At 2500 AGL, outside temp had fallen to 37F. Clouds forming at 4000 AGL. Seemed like high risk (Serious icing while cruising per red chart) for carb ice when crusing at 2250 rpm, so I kept pulling carb heat about every ten minutes or so---and noticed no carb ice. (I run the 52 cartridge on the Sensenich adjustable--so 2250 is my 90-93 mph cruise. If I push the RPM up to 2500, I am way outside of the green arc. Not sure what condiitions are OK outside the green arc---I do know that in central PA below 4000 feet, my little cub moves around a lot--up/down, side to side. ( I dared not let the engine run below 2250. My preferred flying is a little slower 80-85 mph at 2150 RPM. )

Am I being too careful?

Is there an CC approval for a carb temp gauge or the optical sensor type for our cc11-100's?

Appreciate comments and discussion....

[Pete D]

I am not sure if there is a carb ice gauge approved for the Sport Cub. I have seen them in other airplanes but very rarely.

I have quite a bit of time in different Sport Cubs, mostly our Sn 71 which is an S2. I have had carb ice a few times, always in very wet conditions and typically only on the ground. My normal SOP is to taxi at a higher power setting in those conditions, turning the carb heat on to clear it as needed then turn it off. When I line up to take off I will set full power, turn carb heat on as long as needed to clear it up then carb heat off and release the brakes for the takeoff roll. I've never had it ice back up doing that. The conditions I had to do this in were heavy rain over night which soaked the grass so lots of water everywhere (vapor trails off everyone's props) but not actually raining when I was departing so once clear of the ground the moisture level went down significantly.

[stroutmail]

After quite a bit of research..a few conclusions.

1)Carb Air Temp gauges don't really indicate the temperature of the air flowing through the carb---they instead more closely indicate the temperature of the metal surface of the carb just below the throttle butterfly. The momentary temperature of the air itself can be considerably warmer or considerably colder. And, the temperature of the throttle butterfly is likley colder than temp indicated by the gauge, depending on the pressure drop past the butterfly. So the gauge is better described as simply Carb Temp Gauge. Applying full carb heat may raise carb air temp by 50-70 deg F, but may only raise the carb temp by 5-10 deg F.
2) The temperature drop past the throttle butterfly in most cases--during cruise settings is about 9 deg F. So, if the Carb Temp Gauge is reading 41 deg F or higher, it is likely that the throttle butterfly temperature is above 32 deg F---and ice would not form or stick to the plate. However, if the ambient air is cold enough (below 12 deg F) raising the temperature of the carb using carb heat could be counterproductive as it could result in raising the air temperature to a point where liquid condenses and ice forms on the throttle plate. So for preventing carb ice during some cruise conditions, the Carb Temp Gauge can be useful for indicating the effective use of carb heat.
3) Temperature drop from ambient, past the venturi and the throttle can be be 50 deg F or more. The drop in temp due to fuel vaporization and other factors is why carb ice is possible, even at ambients as high as 80 deg F.
4) 32 deg F is the melting point of water, but water can be supercooled and maintain a liquid state below 32 deg F.
5) There is some research that engine performance is enhanced, and lead deposits are reduced by using carb heat and raising carb temperature when ambient air is below 32 deg F.

But despite all the limitations and complexity, I am convinced the additional data provided by the gauge is valuable. It provides one more data point for decisions regarding the use of carb heat--especially during cruise.

So, I submitted an MRA to Cubcrafters (my plane is a S-LSA) for authorization to install a carb temp gauge.

[stroutmail]

Wow. "vapor trails from props". That would be a sure sign of 100% humidity!

SA_029.pdf

Above is a link to a NTSB Alert that got my attention. The Alert provides links to FAA Advisories.

[stroutmail]

Carb Air Temp Ga 3.png

I submitted an MRA to Cubcrafters (my plane is a S-LSA) for authorization to install a carb temp gauge. (see previous post)

There are several options.

Each contains essentially three components: A Gauge, Wiring, and a Probe.

I decided that a Thermistor probe was better than a Thermocouple for this temperature range-more accurate and more stable.

I did not want to eliminate any of the gauges now in the panel. So my only choice would be to mount gauge above the glare shield or below the panel. (If I did, a complete engine data management 3 1/8 gauge from Electronics International would have been my choice, despite that they use a Type K thermocouple probe. I also would have considered one of UMA's 3 in 1 gauges.)

UMA Instruments offered a 1.25" diameter guage (slightly larger face than the pocket thermometer I use to check AC duct temps..about same size as wristwatch face.) that could be easily mounted under the panel without interfering with my knees.

UMA Instruments offers a thermistor probe.

With or without the Carb Temp Gauge, I will continue to use the same procedures: 1) "Apply Carb Heat on Downwind, before dropping RPM below 2000, Remove Carb Heat on Short Final"; 2) "Apply Carb Heat before Takeoff when conditions merit..remove carb heat during takeoff"; and 3) Monitor OAT and Dew Point Spread AT CRUISE ALTITUDE; and 4) Closely monitor cruise RPM for signs of carb ice: and 5) Without carb temp gauge..periodically pull carb heat during cruise. AND during long descent..leaving it on for at least 15-20 seconds and leaning the mixture while on. (This activity during cruise would be less necessary or not at all with the gauge.) And, even with a Carb Temp Gauge, only consider using partial carb heat during steady state cruise--all other times "Apply full carb heat when risk of carb ice is high".

[stroutmail]

Here is a pretty good video on carb ice..the Cessna 140 he is flying, with a Continental C85 is pretty close comparison to the Sport Cub. Note it is the increase in RPM after using carb heat in cruise that confirms ice was there. It was the small drop in RPM (almost simulating throttle reduction) when throttle was fixed (in conditions where ice is possible) that created suspicion that carb ice was present in cruise.



In my part of the country, that range of temp and humidity where carb ice is possible covers most of the whole calender.

[stroutmail]

Here is an article that shows the basics of a carb air temp gauge for a 0-200 with a MA-3SPA Marvel (Precision) Carb.

https://msacarbs.com/product/ma-3spa...retor-10-5067/

http://www.pielandings.com/q200/carb_air_temp.html

Always amazing to me, the creative energy of the experimental aircraft world! (I prefer a more sophisticated "factory" specifically engineered product.)

One of the questions I had about the install was the probe---his homemade probe made it seem quite simple.

He gives some flying experience with the gauge which I found quite useful.

[stroutmail]

https://airfactsjournal.com/2019/11/that-other-ice/

This article showed up in my inbox. This guy was plagued with carb ice.

[stroutmail]

Here is a link to a recent and very interesting read about carb ice. Reinforced my opinion that carb temp gauge is an important safety tool.

https://airfactsjournal.com/2019/11/that-other-ice/
https://airfactsjournal.com/2019/11/that-other-ice/

[stroutmail]

http://https://www.reddit.com/r/flying/comments/du3rvx/i_declared_an_emergency_today/?utm_medium=android_app&utm_source=share

Another article about carb ice with 0-200. Central Texas is not a place you normally think has high humidity.