rotax 912 engine resistance to water ingestion

You don’t ever hear about a piston aircraft engine stopping because of flying through heavy rain. However, I remember reading the POH of a Cessna 172 and there was instruction to use carb heat as an alternate intake source in very heavy rain, so it is something manufacturers consider, or should consider. Certified aircraft certainly have designed in safeguards against excessive water ingestion. This can be simple design elements that let water drain back out of air intake by gravity. Simply put, the air intake is often lower than the carb or air box, and gravity solves the problem. There can also be drain back holes is key places.  What you don’t want is a design that lets water accumulate in the air duct and drain downward into the carb or air box.  Water is much more dense than air, and it does not take much of an upslope to separate the two. The C172 I mentioned earlier has the carburetor below the engine, but the air intake is even lower in the cowl so any water pushed in by airflow just drains back out. I believe there are drain holes in the filter box also, which is low in the front of the cowl.

My Bristell 912iS has the induction air intake through a NACA vent on the side of the cowl, and it’s about 6” lower than the throttle body. The air hose then goes up vertically from the filter box to the throttle body, so it’s unlikely there could be strong enough intake airflow to carry any water that got through the filter up into the air box. Rather, it would just drain back out the NACA duct. The filter is slightly recessed in the NACA duct, and is the washable type. The filter is lightly oiled so it rejects the water, and the airflow would keep it cleaned out well enough for the engine to breathe. Lastly, A piston engine will accept some moisture into the combustion chambers and handle it fine. The bottom line is, unless the aircraft has a poorly designed induction intake air system, water ingestion is not a problem.  

Everything Jeff B said.  

Plus:

I believe that water injection was deliberatly used, on high performance piston engines (both aircraft & race car) - moral of the story your Rotax will tolerate any amount of atmospheric water (as vapour) and may even run better. Liquid water & ice formation, it may object to, as Jeff mentioned.😈

Yes Sean, I remember the water injection craze in high performance automotive (and other) engines. A few manufacturers actually delivered cars with it stock! You could buy kits at your local speed shop that used a 50/50 mix of alcohol and water. The idea was that it cooled the intake pathway, and acted as an anti-knock agent so you could run more compression and timing advance. I think I even tried one once on a 1972 Plymouth Roadrunner. It did not do much on that car, but it looked cool. Funny, I think it even had a switch in the car marked “water injection”, that was the best part. Then there was the bag of ice on the intake manifold trick to make the intake charge more cold and dense. Not practical, and you only got one 1/4 mile run out of the ice.  

https://en.wikipedia.org/wiki/Water_injection_(engine)

thanks.

I remember reading that one of the first turbo car - oldsomobile jetfire - use a "Turbo rocket fluid", which was a mix of methyl alcohol and water https://silodrome.com/oldsmobile-jetfire-turbo-rocket-v8-engine/ 

Also in '80 Ferrari use a water injection system in his formula1 racing turbo engine . it is called "emulsystem 80" and was used to solve detonation problem at high boost level. with this system it wins montecarlo GP (the worst circuit for a turbo engine) and spain Gp in a row.