SonexBuilders.net

Hey guys,
So I know the official word from the Sonex folk is that Carb heat is not needed due to the design of the aeroinjector and such. However, after spending some time researching the issue, and reading William Wynnes experience, I have to say the issue concerns me a bit.

I did Research on Jeff's Crash of sonex 604 here:
http://www.sonex604.com/crash.html

The opinion of some folk online was that its a classic carb heat failure. Engine had no damage, had compression, fuel and spark. It died on a power off descent and thats classic times of carb ice accumulation.

So the OFFICIAL cause of the crash is undetermined, and the official opinion of the Sonex guys is that it cannot ice over, but the whole thing has mixed opinions online. I was not even able to find any results on any options if you want to install carb heat.

What are your guys opinion on this?

Thanks
Abe

Abe, I am not an expert on the AeroCarb (AC)/Carb ice situation but I can only offer my operational experience.

I have about 270 hours on my AC and Jabiru with no carb heat and no carb ice problems. I operate mainly in the south where it's warm most of the time but also humid. I must say that I have been concerned a few times while in a desceding with 50-60F outside temp with near 100% humidity but I have never noticed any signs of carb ice. I'll add that I rarely descend a long time at idle as I try to keep my cylinders warm.

It may indeed take a "perfect storm" of things to produce ice in these things otherwise I'm sure that there would be more reported problems. Does anyone know the temp/humidity that Jeff experienced on the descent? Was he at idle?

N111YX wrote:Does anyone know the temp/humidity that Jeff experienced on the descent? Was he at idle?

This is what he wrote on his website about the experiance:

...I was cruising at 8,500 ft MSL and had the airport in sight approximately 30 miles out. At about 10 miles out, I reduced power from cruise power to a descent power setting, and began my gradual descent into MEZ. After 2 or 3 minutes of descending, at about 5,000 ft, the engine suddenly lost power. It continued to run, but was not producing any significant power. I attempted to restore power by adjusting the throttle, mixture, and mag switches, but after 30 seconds or so, the engine died completely. I was able to restart it once, but it barely ran, and died for good after 10 seconds or so...

I've always wondered if one possible reason why there's no carb ice issues is that we draw air from inside the cowling where the air is warmer rather than having some kind of ram air scoop to draw in cold air.

I also didn't install a carb heat setup but I've been doing some final engine tweaking and have noticed that some condensation has been forming on the bottom of the Y pipe just above where the Aeroinjector is attached. That does have my attention... I'm hoping the diameter of the pipes themselves, along with them staying warm next to the engine will keep carb ice from being an issue.

Maybe it was carb ice but then again maybe not. If I remember correctly, Jeff never tried to restart the engine after he got it back on the ground. There is no way to tell if it was carb ice, something broken inside the engine, something in the gas tank temporarily plugging the screen, etc. Way too many possibilities to tell what the cause could have been. I'll have to do some searching on the yahoo groups but I am pretty sure someone at one point put a termocouple by the inlet to the carb to measure the temperature of the air that was being ingested. I believe it was pretty high (100 degrees rings a bell) and deemed to be way too warm for ice to possibly form. I'm not saying it isn't possible, just probably not likely.

Keith
#554

I think there is something to be said for the factory planes.. being based out of Oshkosh where it is really cold for most of the year and right next to a lake where it is nice and humid.. They fly the factory planes all the time and have never experienced carb ice. I doubt they would hide the fact if they ever have.

MichaelFarley56 wrote:I've always wondered if one possible reason why there's no carb ice issues is that we draw air from inside the cowling where the air is warmer rather than having some kind of ram air scoop to draw in cold air.

I was thinking the exact same thing. The aerocarb will not even work with a ram air induction.

142YX wrote:

MichaelFarley56 wrote:I've always wondered if one possible reason why there's no carb ice issues is that we draw air from inside the cowling where the air is warmer rather than having some kind of ram air scoop to draw in cold air.

I was thinking the exact same thing. The aerocarb will not even work with a ram air induction.

Several people have added NACA ducts to their cowl leading to an enclosed chamber for the air filter. Not ram air, but certainly cold(er) air. I have not heard of these setups having problems either. Maybe just lucky so far, though.

Anyone who says an Aerovee installed in a Sonex doesn't have carb heat is mistaken. In fact, it has full time carb heat...you can't shut it off. All the heat from the engine and the exhaust pipes flows over and into the carb intake. Someone once reported that they installed a temp sensor and never saw temps below 100 degrees in the carb.

Andy Walker wrote:
Several people have added NACA ducts to their cowl leading to an enclosed chamber for the air filter. Not ram air, but certainly cold(er) air. I have not heard of these setups having problems either. Maybe just lucky so far, though.

My plane has "fresh air" flowing to the carb. I did it similar to the way Jeff Shultz described...added a small shroud around the carb air filter with a Scat tube from the air duct at the oil cooler. How effective it is I can't measure....I didn't see any change or improvement from before.