Aerofoils in heavy rain
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Aerofoils in heavy rain
Away from the breathless excitement of R&N and the Bali thread, what do the experts think of this? ('Avoid' if possible is taken as written......)
Looking at a few papers on the topic, I see figures for an 'up to 30% loss of lift at max alpha', a significant reduction in stall angle and a big increase in drag, particularly on a 'dirty' wing, all of which degrade the g/a performance. If you chuck in the simple downforce exerted by a heavy downpour which increases a/c weight...................................
I believe there has been 'advice' in the past on increasing speeds on approach in these conditions, but I am not aware of any specific guidance in Ops Manuals (in my time). Is it in place now? Should it be?
I think there was a brief discussion a few years back on PPrune.
Looking at a few papers on the topic, I see figures for an 'up to 30% loss of lift at max alpha', a significant reduction in stall angle and a big increase in drag, particularly on a 'dirty' wing, all of which degrade the g/a performance. If you chuck in the simple downforce exerted by a heavy downpour which increases a/c weight...................................
I believe there has been 'advice' in the past on increasing speeds on approach in these conditions, but I am not aware of any specific guidance in Ops Manuals (in my time). Is it in place now? Should it be?
I think there was a brief discussion a few years back on PPrune.
He should have asked a glider pilot then, they knew all along it has an effect, in some cases quite dramatic.
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OMG! Those flying airliners with laminar aeroprofiles in torrential rain are doooooomed!
Seriously,why fly through such heavy rain in the first place?
If downdraft were so so strong,wouldnt the PWS warned them of it?did they disregard it?did they usually disregard it?
Last edited by de facto; 16th Apr 2013 at 11:09.
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Interesting point about gliders.
I remember back in the '70s when the first glassfibre sailplanes were coming along that a slope-soaring Kestrel 19 had to land out when a rain shower came along and reduced lift to such an extent that the aircraft could no longer maintain lift on the slope and was too low to complete a circuit to land (at Challock 1976).
The effect of rain on the performance of the laminar flow glassfibre wing was significant.
KR
FOK
I remember back in the '70s when the first glassfibre sailplanes were coming along that a slope-soaring Kestrel 19 had to land out when a rain shower came along and reduced lift to such an extent that the aircraft could no longer maintain lift on the slope and was too low to complete a circuit to land (at Challock 1976).
The effect of rain on the performance of the laminar flow glassfibre wing was significant.
KR
FOK
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Originally Posted by de facto
If downdraft were so so strong,wouldnt the PWS warned them of it?did they disregard it?did they usually disregard it?
EDIT: Before you all relegate this to a 'gliding' problem, I suggest you do a bit of searching for research work on jet airliner wing sections.
Last edited by BOAC; 16th Apr 2013 at 12:35.
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... with my B737 hat on, I don't remember any guidance for adjustment of approach speeds due to precipitation, just the usual allowance for gusts up to a maximum figure.
Nor do I remember any talk during training of any significant adverse effects of rain on jet airliner wings?
Microbursts yes, but the direct effect of any rain associated with them, no.
Maybe 'scale' and speed dictate the likelihood of adverse affects due to rain rather than laminar flow aerofoil sections as such? - Big fast jets against slow small gliders?
KR
FOK
Nor do I remember any talk during training of any significant adverse effects of rain on jet airliner wings?
Microbursts yes, but the direct effect of any rain associated with them, no.
Maybe 'scale' and speed dictate the likelihood of adverse affects due to rain rather than laminar flow aerofoil sections as such? - Big fast jets against slow small gliders?
KR
FOK
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FOK - that is my point - there is no guidance. Have a look at this (wind tunnel) test by NASA from 1992 http://www.cs.odu.edu/~mln/ltrs-pdfs/tp3184.pdf
The theory of the effect may be fine, but the time duration of the effect equates to little effect for most high energy flight vehicles.
Seems like there should be lots of DFDR data in past accidents to support this ?
Seems like there should be lots of DFDR data in past accidents to support this ?
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Originally Posted by loma
but the time duration of the effect equates to little effect for most high energy flight vehicles
Folks, its not time to shoot down DP Davies yet, especially as his advice on necessity of utilizing perspective and balance when reflecting on aeronautical matters has been once again proven to be useful - by this thread.
Yes, rain will affect aerodynamic performance of any airfoil.
Yes, the effect was measured in aerotunnels.
Yes, it is significant on laminar aerofoils such as used on high performance gliders or Rutan's canards.
No, there are no modern airliners using laminar wings. Certain Tolouse based brand claims their planes do but while this might not be entirely marketing hype, there are no incidents showing they lose performance or their control forces/efficiency alters in precip. Mind you: some of their make and models are almost tragically underpowered.
No, there are no airliner accidents or incidents where high rate of precipitation was proven to be decisive factor. Even when extreme rain caused both engines to flame out, aeroplanes were controllable down to ground/water contact, outcome largely dependent on the quality of the terrain below. Anyway, there is not much point in worrying about loss of performance due to wet wing if you find yourself in microburst.
Paper quoted that states there were some a) doesn't provide any reference for the claim b) is published via Azerbaijan based pay-to-publish operation that organizes conferences used just to pad the CVs, despite the claim its journals seem not to be peer reviewed at all and consequently has pretty bad reputation in scientific circles.
Yes, rain will affect aerodynamic performance of any airfoil.
Yes, the effect was measured in aerotunnels.
Yes, it is significant on laminar aerofoils such as used on high performance gliders or Rutan's canards.
No, there are no modern airliners using laminar wings. Certain Tolouse based brand claims their planes do but while this might not be entirely marketing hype, there are no incidents showing they lose performance or their control forces/efficiency alters in precip. Mind you: some of their make and models are almost tragically underpowered.
No, there are no airliner accidents or incidents where high rate of precipitation was proven to be decisive factor. Even when extreme rain caused both engines to flame out, aeroplanes were controllable down to ground/water contact, outcome largely dependent on the quality of the terrain below. Anyway, there is not much point in worrying about loss of performance due to wet wing if you find yourself in microburst.
Paper quoted that states there were some a) doesn't provide any reference for the claim b) is published via Azerbaijan based pay-to-publish operation that organizes conferences used just to pad the CVs, despite the claim its journals seem not to be peer reviewed at all and consequently has pretty bad reputation in scientific circles.
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Clandestino -
"its not time to shoot down DP Davies yet," - it's just that he said "This has no significant effect on the aeroplane", you said "Yes, rain will affect aerodynamic performance of any airfoil" - which is it?
Are you saying that Nasa also "has pretty bad reputation in scientific circles."?
The NASA paper tested "a cambered airfoil representative of typical com-
mercial transport wing sections" - NB not laminar flow.
The NASA summary
"The results obtained for various rain intensity levels and tunnel speeds
showed signifi cant losses in maximum lift capability and increases in drag for a given lift as the liquid water content was increased. The results obtained on the landing con guration also indicate a progressive decrease in the angle of attack at which maximum lift occurred and an increase in the slope of the pitching-moment curve as the liquid water content was increased."
I think on balance NASA wins over Mr C.
"its not time to shoot down DP Davies yet," - it's just that he said "This has no significant effect on the aeroplane", you said "Yes, rain will affect aerodynamic performance of any airfoil" - which is it?
Are you saying that Nasa also "has pretty bad reputation in scientific circles."?
The NASA paper tested "a cambered airfoil representative of typical com-
mercial transport wing sections" - NB not laminar flow.
The NASA summary
"The results obtained for various rain intensity levels and tunnel speeds
showed signifi cant losses in maximum lift capability and increases in drag for a given lift as the liquid water content was increased. The results obtained on the landing con guration also indicate a progressive decrease in the angle of attack at which maximum lift occurred and an increase in the slope of the pitching-moment curve as the liquid water content was increased."
I think on balance NASA wins over Mr C.
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posted this on the 'other' thread, but may be more appropo here...
The mechanics of the weather radar and wind shear alert system. Doesnt the windshear alert use the weather radar? I am aware that some models use a l@ser system for windshear, I am just not positive about the connection between the 2 systems.
If the settings for the weather radar had been to look up, with the windshear system auto engage at 2500 feet, does this automatically reposition the dish?
In regards to this thread...wet wings and Reynolds numbers...CFD gone mad in regards to Bernoulli vs Newton..
NASA and wind tunnels...interesting concept, but in reality, its all smoke and mirrors.
In working with some testing, I just found out that there has NEVER been a model tested in a crabbing position..NEVER. Makes you wonder...
The mechanics of the weather radar and wind shear alert system. Doesnt the windshear alert use the weather radar? I am aware that some models use a l@ser system for windshear, I am just not positive about the connection between the 2 systems.
If the settings for the weather radar had been to look up, with the windshear system auto engage at 2500 feet, does this automatically reposition the dish?
In regards to this thread...wet wings and Reynolds numbers...CFD gone mad in regards to Bernoulli vs Newton..
NASA and wind tunnels...interesting concept, but in reality, its all smoke and mirrors.
In working with some testing, I just found out that there has NEVER been a model tested in a crabbing position..NEVER. Makes you wonder...
Last edited by FlightPathOBN; 16th Apr 2013 at 22:55.
Let me pass on an actual observation of rain on a wing - from a perspective not available from the front office....
Right in the middle of my primary flight training, I flew as pax on (coincidentally) a 737 from MEM to IND. On approach, IND had numerous summer thunderboomers in the area, with ceilings under the CBs at about 4000, and intermittent strong downpours (we passed through about 5 on the inbound leg to 23R).
Each time we entered the heavy rain, I could see, from my window seat just above the right wing, a "bead" of water pulsating along the leading edge of the deployed slat. Or at least the "edge" that I could see (the actual leading edge was likely so low as to be out of sight from my location about 6 feet back).
That build-up of water pulsated between 1 and 2 inches in thickness (2.5-5cm) in the heaviest parts of the rain; reducing, of course, to nothing when we exited each rain column.
For a beginning pilot, it was an impressive demonstration of just how much water can build up from the forward movement of the wing through a torrential downpour.
Right in the middle of my primary flight training, I flew as pax on (coincidentally) a 737 from MEM to IND. On approach, IND had numerous summer thunderboomers in the area, with ceilings under the CBs at about 4000, and intermittent strong downpours (we passed through about 5 on the inbound leg to 23R).
Each time we entered the heavy rain, I could see, from my window seat just above the right wing, a "bead" of water pulsating along the leading edge of the deployed slat. Or at least the "edge" that I could see (the actual leading edge was likely so low as to be out of sight from my location about 6 feet back).
That build-up of water pulsated between 1 and 2 inches in thickness (2.5-5cm) in the heaviest parts of the rain; reducing, of course, to nothing when we exited each rain column.
For a beginning pilot, it was an impressive demonstration of just how much water can build up from the forward movement of the wing through a torrential downpour.
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In working with some testing, I just found out that there has NEVER been a model tested in a crabbing position..NEVER. Makes you wonder...
"This has no significant effect on the aeroplane", you said "Yes, rain will affect aerodynamic performance of any airfoil" - which is it?
Also, in my level 4 English there exists such a thing as insignificant effect so "it will affect" and "it has no significant effect" are not at all contradictory, but then I'm no native speaker and might be wrong.
Are you saying that Nasa also "has pretty bad reputation in scientific circles."?
Originally Posted by Ismail, Yihua, Ming, Bakar
We believe that the results showed in this paper will be useful for the designer of the commercial aircrafts and UAVs, and will be helpful for training of the pilots to control the airplane in heavy rain.
Them scientists found out the way to help pilots control the aeroplane in heavy rain and zee pilots don't care about it! Is the denial of industry there actually is a problem sign of worldwide conspiracy?
cambered airfoil representative of typical com-
mercial transport wing sections" - NB not laminar flow.
mercial transport wing sections" - NB not laminar flow.
A UK AIB report mentions this phenomenon:
What do you mean?
From what I've seen, every wing section seems to have a different reaction to contamination and it's not obvious what it might be until it happens.
I have flown many gliders in precipitation of all descriptions and it's not always the highly laminar flow wings that are affected the most. One particular model with a fairly thick, high lift section vibrated and headed earthwards after a few tiny drops. Mine with a modern, thin 90%+ laminar profile seems to be much more resistant: I've seen water cascading in floods off the wing and the handling doesn't really suffer.
With typical airliner sections, there probably is an effect but it's masked by the amount of power available and the scale of the wing, I feel. If it were that pronounced, you'd have a performance decrement to apply taking off in rain or after de-/anti-icing. We know that hard, irregular deposits are bad and take great pains to rid the airframe of them but are less concerned with liquid ones - think how many takeoffs are made in rain every day without issue. It seems that a wet runway is much more relevant than wet wings.
I have flown many gliders in precipitation of all descriptions and it's not always the highly laminar flow wings that are affected the most. One particular model with a fairly thick, high lift section vibrated and headed earthwards after a few tiny drops. Mine with a modern, thin 90%+ laminar profile seems to be much more resistant: I've seen water cascading in floods off the wing and the handling doesn't really suffer.
With typical airliner sections, there probably is an effect but it's masked by the amount of power available and the scale of the wing, I feel. If it were that pronounced, you'd have a performance decrement to apply taking off in rain or after de-/anti-icing. We know that hard, irregular deposits are bad and take great pains to rid the airframe of them but are less concerned with liquid ones - think how many takeoffs are made in rain every day without issue. It seems that a wet runway is much more relevant than wet wings.