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CoolGuy
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Water On Top Of The Wings, Not Blowing Off?

Mon Mar 05, 2007 8:19 am

There was some water on top of the wings of a 733 (just had a deicing, and snowing), and it looked like it was trickling down the wing very slowly, and this was at cruising speed/altitude. I would have expected the water to have been blown off the wing by 500kts air. I'm guessing there's some interesting airflows going on above the wing. Perhaps something that demonstrates Bernoulli's Principle well?
 
2H4
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RE: Water On Top Of The Wings, Not Blowing Off?

Mon Mar 05, 2007 8:23 am




Quoting CoolGuy (Thread starter):
Perhaps something that demonstrates Bernoulli's Principle well?

I'd say it demonstrates the boundary layer, rather than Bernoulli's principle....


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boeingfixer
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RE: Water On Top Of The Wings, Not Blowing Off?

Wed Mar 07, 2007 1:07 am

Quoting CoolGuy (Thread starter):
There was some water on top of the wings of a 733 (just had a deicing, and snowing), and it looked like it was trickling down the wing very slowly, and this was at cruising speed/altitude.

What you probably saw was the residual de-ice fluid. If you were just de-iced(Type I Fluid), and if it was snowing, the aircraft would have been Anti-Iced(Type IV Fluid) as well. The only contamination on the wing should be suspended in the Type IV fluid and shear off on the takeoff roll. What's left is the Type I fluid underneath which is fairly thick compared to water. This fluid slowly flows across the wing in flight. Water OTOH, would have frozen to the wing at cruise altitude and eventually sublimate.

Cheers,

John
Cheers, John YYC
 
newagebird
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RE: Water On Top Of The Wings, Not Blowing Off?

Wed Mar 07, 2007 9:50 am

Hey
The reason it wasn't moving was due to boundary layer, i found out to my surprise that if you left dust on a wing and flew, when you get back on ground its still gunna be there. This is because there is a layer of air above the wing that is stationary despite the speed the wing is travelling.
Just in care youre interested, the boundary layer is of prime concern to lower aircraft drag. Thick boundary layer = more drag means less range  Sad

Cheers newagebird
 
2H4
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RE: Water On Top Of The Wings, Not Blowing Off?

Wed Mar 07, 2007 10:05 am




Quoting Newagebird (Reply 3):
i found out to my surprise that if you left dust on a wing and flew, when you get back on ground its still gunna be there.

Likewise with cars. Drive on a dusty dirt road, then blast down the freeway, and your car will still be dusty afterward.


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boeingfixer
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RE: Water On Top Of The Wings, Not Blowing Off?

Wed Mar 07, 2007 10:30 am

Quoting Newagebird (Reply 3):
Hey
The reason it wasn't moving was due to boundary layer, i found out to my surprise that if you left dust on a wing and flew, when you get back on ground its still gunna be there. This is because there is a layer of air above the wing that is stationary despite the speed the wing is travelling.

Thank you.... I do know what the Boundary Layer is.  Wow!

I was making the point that you won't have liquid water on your wings at B733 cruising altitudes. What CoolGuy saw was de-ice fluid, which has a higher viscosity than water and takes a long time to evaporate. Water would either evaporate(if not replenished) or if it's ice, sublimate.

BTW, dust and water are not a good comparison. The boundary layer still has airflow and will evaporate or sublimate water on the top of the wing.

Cheers,

John
Cheers, John YYC
 
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Starlionblue
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RE: Water On Top Of The Wings, Not Blowing Off?

Wed Mar 07, 2007 10:49 am

I'll just add my anectode. The BA 772 I was on had to be deiced and anti iced for about 40 minutes (yes I checked) last Monday at JFK. As we were approaching Ireland I looked out over the wing. Sure enough, there was still green fluid hanging on for dear life between the flap slots.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
CoolGuy
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RE: Water On Top Of The Wings, Not Blowing Off?

Thu Mar 08, 2007 3:12 am

This is really interesting. I had no idea about the boundary layer. I'll have to read up on it!

One other question comes to mind. If it were raining, then there would be water on the wing. Why doesn't it freeze when the plane reaches higher altitudes?
 
boeingfixer
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RE: Water On Top Of The Wings, Not Blowing Off?

Thu Mar 08, 2007 8:06 am

Quoting CoolGuy (Reply 7):
One other question comes to mind. If it were raining, then there would be water on the wing. Why doesn't it freeze when the plane reaches higher altitudes?

Easy answer, it doesn't rain at higher cruising altitudes so you won't have water on the wings. The OAT(Outside Air Temperature) is too cold to support liquid water at altitude. Using the ISA(International Standard Atmosphere) the OAT at 33,000 ft is -50.4 degrees C. Rain at lower altitudes will remain liquid until the TAT(Total Air Temp. = OAT + Ram Air Temp Rise) of the airframe is below freezing and the water will then freeze as well. There is the possibility of super cooled droplets but they will also freeze on contact. Using Leading Edge Anti-Ice keeps the leading edges clean while any rain that has streaked back will freeze and sublimate(goes from a solid to gas without first becoming liquid).

Cheers,

John
Cheers, John YYC
 
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HAWK21M
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RE: Water On Top Of The Wings, Not Blowing Off?

Thu Mar 08, 2007 11:47 am

Moisture held on due to Boundry Layer Effect of the Surface of the Wing.Remember Dust on an Aircraft never blows away in Flight.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
CoolGuy
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RE: Water On Top Of The Wings, Not Blowing Off?

Thu Mar 08, 2007 2:09 pm

I don't think I understand. I was referring to rain at ground level. When the plane reaches higher altitudes, won't the water all over the aircraft still be there and subsequently freeze?
 
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HAWK21M
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RE: Water On Top Of The Wings, Not Blowing Off?

Thu Mar 08, 2007 8:37 pm

Quoting CoolGuy (Reply 10):
don't think I understand. I was referring to rain at ground level. When the plane reaches higher altitudes, won't the water all over the aircraft still be there and subsequently freeze?

Not if De-iced on Ground.
regds
MEL
I may not win often, but I damn well never lose!!! ;)
 
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Starlionblue
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RE: Water On Top Of The Wings, Not Blowing Off?

Thu Mar 08, 2007 10:13 pm

Quoting CoolGuy (Reply 10):
I don't think I understand. I was referring to rain at ground level. When the plane reaches higher altitudes, won't the water all over the aircraft still be there and subsequently freeze?

Good catch. AFAIK there are two cases:

1. Well above freezing on the ground. Water will blow off the wings. I assume any water left will be so little it won't have an impact.
2. Around freezing on the ground. Freezing rain/sleet/snow would adhere to the wings. Aircraft needs to be both deiced (remove gunk) and anti-iced (ensure new gunk doesn't stick).
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

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