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Rain & engines


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I was wondering. How does an engine not flame out when it is passing through rain? Whether that be a Cessna 172, a King Air turbo prop or a 737. I know next to nothing about car engines let alone an aircraft engine. I would assume the 172 has a carburetor and all I know is that for me personally I have to keep the lawn mower covered so that rain/snow doesn't get in the carburetor. That's all I know. With a turbo prop and a 737 I'm sure that's competently different. But I do know the gas in the engine is ignited and mixed with air. Which has me wondering why very heavy moist air doesn't cause a flame out?

 

Thanks for your responses in advance.

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If you're just talking about humidity, does a campfire go out when it's humid? Earlier 172s had carburetors, later ones have fuel injection instead. But car or 172, if you splash enough water (lots and lots) under the hood (into the cowling) and it gets into the air intake in large quantities, it will indeed drown the engine, and the hood/cowling serve the same purpose (in that sense) as your cover over the lawn mower. But rain (even a gully washer) and high humidity don't get that amount of water to them (but drive through a foot of water at some speed and you might splash up enough to do it). Humidity does have some minor effects on engines, as do temperature and altitude (air density), but engineers design around that.

 

Turbine engines are a bit different, but they are designed such that little water can get to the combustion chamber, and the heat in there would largely counteract the little that does (but they can flame out if truly HUGE amounts of water get in there).

 

Larry N.

As Skylab would say:

Remember: Aviation is NOT an exact Science!

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I don't think they need such a thing on the fast-movers, but US Navy H-60 engines have what're called Swirl Vanes on the intake. They make the incoming air go around a plenum on the outside of the engine, thus removing centrifugally (sp?) particles of dirt, leaves, twigs, and water. So, even if they fly into a heavy spray area aft of the ship on landing, like a wave's spray, or the boat's wake spray, the majority of the water is removed from the air before it even gets to the first compressor stage.

Rupert knows as well as anyone how much spray a helicopter can ingest without much trouble. A slight miscalculation figuring power available vs power required, and when the leave the ground effect of the deck, they can sink down until the gear/skids are literally in the water, hopefully then picking up enough lift from their forward motion to fly up and out of the trouble. Imagine the spray the rotor wash causes for the engines to breathe in THAT situation!

Also, don't forget that jet engines are HOT. Even the compessor stages, since they squeeze the air so hard, make the air very hot, before it even gets to the burner cans. This would tend to make the water a vapor, rather than liquid droplets. And the burner cans are REALLY hot. This is why airport crash crews use foam on the engines, to choke off the air. It would take a LOT of water introduced very quickly to "put out" a jet engine.

A rain storm, even a "toad-strangler", as they say, isn't enough to cause a jet to flame out. There are other effects of rain storms that DO cause planes problems, though. The rain falling down makes the air around it follow suit, creating some very strong down-drafts. Not good for a plane that's gotten low-n-slow for landing, or that is climbing out on take-off. Especially with the advent of the never-to-be-sufficielntly-cursed noise abatement requirements. Pilots don't like them, generally, as the procedures call for engine power reduction and a max rate of climb right off the ground. Add a sudden downdraft from a rain storm, or worse, a thunderstorm, and you have a recipe for disaster. At least that's what I heard from my father and his friends, and he was a UAL pilot. Pilots are normally taught to go around or over a thunderstorm, never through.

A sudden wind-shear also has it's own problems to add. The real fear of pilots of commercial aircraft, though, is flying into the ash-cloud of a volcano. THAT will kill a jet engine faster than nothing else. And, if there's enough ash ingested, there's no hope for a relight. Bad scene...

Have fun!

Pat☺

[sIGPIC][/sIGPIC]

Had a thought...then there was the smell of something burning, and sparks, and then a big fire, and then the lights went out! I guess I better not do that again!

Sgt, USMC, 10 years proud service, Inactive reserve now :D

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