Carb Ice in Climb

[DanBrown]

Last week we had 100 F on the ground with high humidity. Going NE over NJ at 5500 feet to keep cool, a scattered layer was ahead at my altitude, so I climbed to get above it. Climbing through 6000 the rpm started dropping and running rough (OAT about 75 F). Carb heat for a minute cleared it up, but I kept having to add heat a couple more times before I got to cruise at 7500.

I have never had icing before on the A65-8, and never before in a climb. Any thoughts on the cause, or would you consider this normal????

[Pearson]

Re: Carb Ice in Climb

You got carb ice because the temperature and humidity were just right. You didn't do anything wrong, just flew in the right conditions for carb ice forming.
I think what you experienced is exactly the way carb icing works on the Taylorcraft. The visual ques were there, but who has the experience to read them. Seeing the scattered layer ahead at your altitude, will next time be your que to be alert to possible carb ice. I have experienced it my self in early morning departures where there were low clouds below me. Keep your plane in good shape so that when it happens, turning on the carb heat will cure the problem. It saved my bacon that day, that is for sure.

[Len Petterson]

Re: Carb Ice in Climb

Remember this number : It takes 72 Deg F to evaporate fuel in a carburator!
75 deg F out side temperature - 72 lets say it equal 0 deg ( + - some degrees for errors) = ice!
= high O factor!!!!
Winter senario: ( Note fictius numbers) you flying allong and you commoing for the circuit, applies carb heat it is 10 deg F outside temp your heated air in the intake is 52 F and you pull the carbheat. There is point in time there the two shall meet at the frezzing point, so in the winter you can make carbice by applying carbheat.
Len

[DanBrown]

Re: Carb Ice in Climb

Thanks guys. In 1000 hours flying behind a carburetor (out of 1900 total) the right conditions of temperature and moisture content finally occurred to ice me up. It shows again how flying teaches us new stuff, or makes us re-learn things we have forgotten.

[Jim Hartley]

Re: Carb Ice in Climb

I am a liberal when it comes to carb heat...always testing!

You just never know ...!

Jim

[Steve Green]

Re: Carb Ice in Climb

Len, Do you have any documentation or sources for the [72 degree drop to evaporate fuel]? That would be a great teaching tool for my students, but I know at least one of them will want to know where that came from. I can't recall seeing that specific number anywhere.

For example, the Jepp pvt pilot book calls it a "sharp temperature drop" and that "ice is most likely to occur when temperatures are below 21C (70F) and relative humidity is above 80%." Any sources would be most appreciated.

[magman]

Re: Carb Ice in Climb

Some of the Temp Drop is caused by the the action of the Venturi ceating a

Low Pressure. When you compress air it gets HOT & expanding it makes it COLD.


The remainder of the Temp Drop comes from the Fuel evaporating into the Air.

Latent Heat of Evaporation is the term I have heard it referred to.

The Evaporation process requires Heat to convert from Liquid to a Gaseous

state.

It's the same you would feel with alcohol being rubbed on your skin.

The Heat is extracted from the Air & a Temp Drop results.


It you run an engine in the Summer & check the Carb you may notice

the upper portion is covered with frost because of these 2 factors.

The numbers are NOT constant.

The tendency for a fuel to evaporate is measured & referred to as "Reid Vapor

Pressure " or RVP.

High OAT air can also hold less H2O than Cold air.

[jim cooper]

Re: Carb Ice in Climb

6-7000 feet in a T-Craft?! Thats nose bleed time for me. I'm usually at 1500-2500 max. In this hot weather I remain in the car. I hope you stopped at Massey Air museum in Massey, Md., nice people, great airplanes. 450 Stearman, NICE Stinson Gull wing, etc. (Just off Rt. 301, look for C-47 parked near office.) Best, Jim C. (P.S. , I check the carb heat often and always go for it if an RPM drop occurs.)

[DanBrown]

Re: Carb Ice in Climb

Hi Jim -- Well, I usually like to be down low, but it gets pretty uncomfortable with the OAT above 90 and having the window in the top too. The T-Craft performed real nice at 7500 (actual density altitude more like 9000) -- got 80 indicated which works out to over a 100 true.

[Len Petterson]

Re: Carb Ice in Climb

I have no documentation on the temperature, I was told it in my flying lessons back in 1980 flying behind a C 85. It held true ( 72F + - a rule of thump) I seen it happen in other aircrafts, a C 150 with a O 200 and my friends T18 with a O 290 Gpu and converted carb from a O 320.
Last week he supected carb ice as the engine stalled on taxying in after landing. Started rigth up agin but ran ruff for a short while.
75F and close 100% humitety.
You Rotax 2 strokers keep in mind it takes even more heat to evapurate the gas oil mixture. I used to race a Saab in Sweden with 3 cyl 2 stroke, no carb heat no go! Ok, we used 3% SAE 50 for oil back when, but keep it in mind.
No extra clean 2 stoke oil mixed 40 or 100 - 1 mix back when.
Len