driesbabe

Hi Guys,

I am wondering about carb icing on our engines?
Here is the story. I am in the process of building a long-range plane. It will be something like a large trainer capable of carrying about 2,5L of fuel. The idea is to fly for a period f about 3 hours nonstop and making an aerial video of an Oldtimer rally that is going to attract hundreds of Oldtimers from around the world to Namibia.

The Engine will be a RCGF 26cc with rear carb, as they run very nicely and use very little petrol.
I am concerned that the carb might ice up. The temp when starting will be about 0 degrees Celsius and will not get much warmer than that throughout the flight of 2/12 too 3 hours.
The Carb will sit inside the airframe with the engine uncowled running upright.
Dose anybody here have any experience with anything like this?

Any help will be appreciated.

Regards
Andreas

mrbigg

My Feedback: (21)

No experience myself, but I remember reading a thread about a plane deadsticking and the carb icing up was thought to be the problem.

pe reivers

If the engine has to run without stopping and re-starting, remove the heat isolator block between carb and engine. That should do, but be prepared to fight vapour lock on hot restarts. (the engine will only start when cooled down completely)
Also use a modern racing oil that prevents carb sticking under wet conditions. This will keep the carb ice-free

Aussie Maddog

My Feedback: (16)

There are many factors in carb icing. Temperature being one of them. Humidity is also a very big factor.
Aircraft in tropical climates suffer from carb icing.
Partial throttle opening, creating a higher manifold vacuum (not sure about 2 strokes?) increases the likelyhood of carb ice.

Jburry

I was thinking about this last night too. PE's suggestion to remove the insulator is a good one, basically providing the carb with carb heat. Ducting some of the engine's cylinder cooling air past the carb might also help.

That said, I'm not sure there'd be a problem anyway. I'm gonna admit right now that I have no idea what the climate is like in Namibia. If it's jungle like, with frequent rain and lots of humidity and water, I'd worry about the possibility of carb icing. If, however, it's desert like dry, I doubt there'd be a problem. For a carb to freeze, the carb has to be cooled (by air expansion thru the venturi) to below the dew point and to below freezing. If the dew point is really low, carb ice can't happen.

Have any fliers in your area with gassers ever had a icing problem, or suspected that they did? After 10 to 20 minutes of flying, I'd expect that things are as hot or cold as they'll get all day.

Interesting question!

J

HornetFitter

My Feedback: (2)

driesbabe,

Here in Canada, we often run engines in conditions which are conducive to carburetor icing. The temperatures that this occurs most readily are +12c to -10c. Relative humidity will have alot to do with this, but it does not take much, when the temperatures are in the "window".
You will usually experience this when you first start up and are running at low power settings. THis is due to ice forming in the venturi area between the butterfly and venturi body.

Ways to minimize the problem;

Carb heat: Run a duct from the cooling fins of the cylinder to the inlet of the carb, or build a "heat stove" (shroud) around the muffler to preheat the inlet air.

Alcohol injection: Going to be difficult to do on a small engine, and not too good for a two stroke, as the alcohol will wash down the lubrication in the engine.

driesbabe

Thanks Guys,
Some very good info here.
As for the climate, it is very dry Desert where we will set of on the journey, so no problem there. BUT, and there always has to be one...! As we will be flying towards the see, we will more than likely encounter Fog. If it’s not visible, then it’s very humid anyway. The flight will start at about 3000 feet above see level, then go up to about 5200 feet above see level and then go back down to 1000 feet....on this down ward leg, that is where the fog will be.
The strange thing is the further we go into the desert, the more moist it gets. Namibia is a strange but beautiful place.
Regards
Andreas

altavillan

My Feedback: (1)

How deep into the fog before carb icing becomes problem #2?

driesbabe

Altavillan,
Thats what I would like to know also. The problem is that I can't try it before the acctual flight, as where I live there is no fog or moisture.
Meaning all test flights will be done in dry weather, also cold, but dry.

Then there is the problem of not knowing if there will be fog, there may be nothing, but the air will be moist, due to it being near to the coast.
regards
Andreas

HornetFitter

My Feedback: (2)

It depends on the ambient air temp... (see my previous post)

Jburry

He means how long before you don't have to worry about carb icing on that plane that you can no longer see, due to the fog.... that'd become problem #1!

I think....

J