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Vapor - Dangerous?


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I know that ship screws can produce an effect called "cavitation". Because of the rapid pressure changes caused by the screw blades moving through the water, a lot of tiny "bubbles of vacuum" are produced. When these collapse/implode they cause strain and wear on the screw's material.

 

Now, those vapor trails, and perhaps more relevant, those vapor effects on the whole wing surface of fast moving aircrafts are caused by the temperature change (cooling) when the air pressure drops on the wing surface at certain maneuvers and the water in the air condenses.

 

Now I wonder, if these effects might have an ill effect on the plane, perhaps roughly comparable to these cavitation effects? Perhaps the water vapour as such is not so dangerous, but what about the cooling effect? Can that cause problems, maybe higher chances of icing? Or has the sudden pressure changes at the wing surface some ill effect on the material?

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The associated changes in pressure/temperature are fairly small and won't cause an issue in most cases. You won't get cavitation because the plane isn't relying on buoyancy.

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The ill effects of caviation are caused by the enourmous pressure spike that results when the gas bubbles collapse. Since the creation of these pressure spikes depends on the incompressibility of water, this effect is not possible in air.

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  • 2 weeks later...

yup, Cavitation is part of a Fluid Dynamic, doesnt happen in air.

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yup, Cavitation is part of a Fluid Dynamic, doesnt happen in air.

 

Air is also a fluid. ;) The reason why this can't happen in air is simply because air is already a gas, it can't form gas bubbles, as well as being compressible as compared to a liquid.


Edited by sobek

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Cavitation.... very dangerous for a sub under sea.

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Air is also a fluid. ;) The reason why this can't happen in air is simply because air is already a gas, it can't form gas bubbles, as well as being compressible as compared to a liquid.

Yeah, and that was the starting point of my thoughts ...: a gas just changes its density (and temperature) but is somewhat a similar effect. Or the cause is similar. Roughly. Whatever ... and I wondered, what else here could be comparable - like the ill effects. :-)

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Air is also a fluid. ;) The reason why this can't happen in air is simply because air is already a gas, it can't form gas bubbles, as well as being compressible as compared to a liquid.

 

wooooosh...... that was the sound of your knowledge flying over my head... :pilotfly:

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Cavitation.... very dangerous for a sub under sea.

 

in terms of it will give the bad guys a source to lock onto, same with a fart from Buckman

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  • 1 month later...
I know that ship screws can produce an effect called "cavitation". Because of the rapid pressure changes caused by the screw blades moving through the water, a lot of tiny "bubbles of vacuum" are produced. When these collapse/implode they cause strain and wear on the screw's material.

 

Thats not correct. A fluid has a constant energy. This energie konsists of Pressure, Temperature and Speed. Because of the high speed of the Blade the pressure suddenly drops, leading the fluid to vaporize. So thats no vacuum! The damage is caused by these Vaporbubbles popping because they are smashed under the Pressure of the surrounding fluid.

 

Now, those vapor trails, and perhaps more relevant, those vapor effects on the whole wing surface of fast moving aircrafts are caused by the temperature change (cooling) when the air pressure drops on the wing surface at certain maneuvers and the water in the air condenses.

 

Now I wonder, if these effects might have an ill effect on the plane, perhaps roughly comparable to these cavitation effects? Perhaps the water vapour as such is not so dangerous, but what about the cooling effect? Can that cause problems, maybe higher chances of icing? Or has the sudden pressure changes at the wing surface some ill effect on the material?

As there are no bubbles that kind of implode like in the cavitation effect, there is no damage caused.

 

The temperature should remain almost constant. If something vaporizes, it absorbs heat to reach the energy-rich state of vapour. But in this case the water condensates.

 

The effect is caused by pressuredifference. It's the same effect that can be seen at the mach barrier. Because of the large pressuredrop right after the compression at the mach cone the partial pressure of the water is greater than the saturation pressure, so it condensates.


Edited by Maverick-X
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Or has the sudden pressure changes at the wing surface some ill effect on the material?

 

No , it doesn't effect the material , but on the fastener holes over time ..... but as an aircraft gets older , it tends to suffer from fuel leaks if its a wet tank , possibily this may lead to some thinking of material damage . This is probably down to wing stress's , material movement , condition of sealing of fastner heads (tankside) . A typical repair is going inside the fuel tank , locating the fasteners and replacing them . Resealing the new fastener and doing a leak check . If the leak persists , oversize the hole and install an oversize fastener and resealing it again ..... If the leak persist's , retire to a bar and drink copious amounts of beer .

 

Wing is generaly made from 7075 aluminium , as opposed to 2024 for fuselage skins , ribs and stringers are 7075 .

 

7075 is more brittle that 2024 , but has better flexibility , but also prone to cracking .

 

We used to have aircraft with ice shields about 10 feet aft of the pax door ..... they didn't look great because they were doing their job properly . But the amount of letters the company received from the public , saying that their aircraft were flying around with cracks in their body , forced the company to get labels printed up saying " ICE SHIELD PROTECTION " ..... the letters stopped !


Edited by badger66
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Now I wonder, if these effects might have an ill effect on the plane, perhaps roughly comparable to these cavitation effects? Perhaps the water vapour as such is not so dangerous, but what about the cooling effect? Can that cause problems, maybe higher chances of icing? Or has the sudden pressure changes at the wing surface some ill effect on the material?

 

To what everyone else said, I'll just add that the pressure drop and cooling effects are there all the time. Condensation only makes them visible to the naked eye. If anything, the cooling effect is reduced by condensation since that process releases energy.

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If anything, the cooling effect is reduced by condensation since that process releases energy.

 

:thumbup: Best answer.

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