Wing question
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shinysideup
New Member
Without getting into the aerodynamics of how it works, here is the basic answer.
It saves fuel, by making the wing more efficient, reducing drag.
Getting a little deeper into aerodynamics.
The wing tip vortices produced at the wing tip produce a large amount of drag. These vortices can be reduced to a minimum by creating another airfoil at the tip acting against the vortices. This minimizes the drag producing vortices by pushing air, much like a wing, toward the uprising vortices, and stops 'some' of their movement and redirects that airflow down, causing a little added lift.
It saves fuel, by making the wing more efficient, reducing drag.
Getting a little deeper into aerodynamics.
The wing tip vortices produced at the wing tip produce a large amount of drag. These vortices can be reduced to a minimum by creating another airfoil at the tip acting against the vortices. This minimizes the drag producing vortices by pushing air, much like a wing, toward the uprising vortices, and stops 'some' of their movement and redirects that airflow down, causing a little added lift.
seagull
Well-Known Member
Actually, the winglets work more like a sail on a boat that's tacking into the wind, providing foward thrust.
They also actually REDUCE, not INCEASE downward flow of the air aft of the wing (so much for the false theory of lift that many civilian CFIs teach of downward flow and "opposite and equal reaction")~
They also actually REDUCE, not INCEASE downward flow of the air aft of the wing (so much for the false theory of lift that many civilian CFIs teach of downward flow and "opposite and equal reaction")~
Sir_Captain
New Member
So using the "equal and opposite reaction" explanation for lift is also incorrect? On my Commercial checkride, the checkairmen wanted this explanation, over the others. He said it best describes how lift works.
So then, what IS an explanation that everyone will accept. It seems someone is always saying "so and so explantion of lift that CFI's teach is incorrect"! They should just write a book about what IS actually widely accepted and have us learn and later teach that.
So then, what IS an explanation that everyone will accept. It seems someone is always saying "so and so explantion of lift that CFI's teach is incorrect"! They should just write a book about what IS actually widely accepted and have us learn and later teach that.
NJA_Capt
Well-Known Member
[ QUOTE ]
...(so much for the false theory of lift that many civilian CFIs teach of downward flow and "opposite and equal reaction")~
[/ QUOTE ]
Huh? lost me with that one.
Lets keep it simple.....winglets reduce drag associated with wingtip votices.
Try this link.
http://www.airandspacemagazine.com/ASM/Mag/Index/2001/AS/htww.html
...(so much for the false theory of lift that many civilian CFIs teach of downward flow and "opposite and equal reaction")~
[/ QUOTE ]
Huh? lost me with that one.
Lets keep it simple.....winglets reduce drag associated with wingtip votices.
Try this link.
http://www.airandspacemagazine.com/ASM/Mag/Index/2001/AS/htww.html
shinysideup
New Member
[ QUOTE ]
Actually, the winglets work more like a sail on a boat that's tacking into the wind, providing foward thrust.
They also actually REDUCE, not INCEASE downward flow of the air aft of the wing (so much for the false theory of lift that many civilian CFIs teach of downward flow and "opposite and equal reaction")~
[/ QUOTE ]
Please, just for discussion purpouses here, expand on this. I cannot see what you are speaking of in this 'theory' that would make you think that down wash off the wing does not produce lift.
Equal and opposite reaction is required by any theory of lift to make it valid. You cannot describe lift just off of Burnulli's (sp) principal alone, or by the skipping stone theory alone, you must have an airflow over and under a wing which is redirecting airflow in a downward movement to create the upward force upon the wing aka Lift.
Burnulli's basic principal, incorrectly explained, says that High pressure seeks low pressure, and therefore the high below the wing seeks the low above the wing and 'Pushes' the wing up. Cannot happen Newton's LAW will not allow that. What that is saying is there is an upward airflow through the wing. If there is upward airflow then there must be a reactive downward force placed somewhere and the only thing that downward force would hit is the wing..... False Theory.
Newton's theory alone (aka impact theory, skipping stone), Incorrectly explained, says that the air impacting the lower side of the wing will be deflected downward and will push the wing up as the reactive force. The reason this theory is incorrect is that it does not take into effect the upper surface of the wing at all, and in this theory a piece of 3/4 inch plywood with the same lower surface of a Cessna wing will produce the same amount of lift as that Cessna wing.
The way I understand lift, and the way I have always taught lift, takes principals from each, and explains it correctly:
Yes the airflow over the top of the wing decreases in pressure as the velocity of the air increases, this local pressure should not be compared to the local pressure below the wing, because it is shut off from that air mass because the wing is in the way. This local pressure is low relative to the air mass well above the wings surface, and High does seek Low, therefore there is a downward movement of air from well above the surface of the wing down toward the wing. Keep that in mind. As well as below the wing the local area just below the wing is High compared to the adjacent area well below the wing, High seeks low, and the air moves from near the wing downward toward the lower relative pressure well below the wing. (Draw this out it helps... Draw a wing cross section, Just below make an H (high pressure) and just above make a L (low pressure). Above the L on top make another relative H, and below the wing make a L below the H. Then draw arrows from the Hs to the Ls. From the top of the paper it should be H then L, then the wing, then H then L. This shows a downward flow of the air, and as the wing flys through this system, that downward system continues downward, giving the wing a reactive force up (aka LIFT)
Now, as for wing tips and vortices. There is some local air flow around the wing tip where the High pressure area below the wing can travel out around the wing tip to the local Low above the wing, causing the inward swirl we call vortices. A wing tip like the original question was asking about, will create a lateral flow of air off the end of the wing, going against the vortices and will minimize the vortices drag on the wing.
As for it creating a thrusting moment like a sail tacking into the wind, that theory cannot work, because there is no boat and Keel to help this "sail" on track to tack into the wind. Remember a sail boat with no keel cannot tack into the wind. Newton would not like that answer at all, the only way to create thrust is to accelerate the air to the aft, therefore creating a forward reactant force forward (thrust)????? I am open to that discussion, but I don't see it now.
Actually, the winglets work more like a sail on a boat that's tacking into the wind, providing foward thrust.
They also actually REDUCE, not INCEASE downward flow of the air aft of the wing (so much for the false theory of lift that many civilian CFIs teach of downward flow and "opposite and equal reaction")~
[/ QUOTE ]
Please, just for discussion purpouses here, expand on this. I cannot see what you are speaking of in this 'theory' that would make you think that down wash off the wing does not produce lift.
Equal and opposite reaction is required by any theory of lift to make it valid. You cannot describe lift just off of Burnulli's (sp) principal alone, or by the skipping stone theory alone, you must have an airflow over and under a wing which is redirecting airflow in a downward movement to create the upward force upon the wing aka Lift.
Burnulli's basic principal, incorrectly explained, says that High pressure seeks low pressure, and therefore the high below the wing seeks the low above the wing and 'Pushes' the wing up. Cannot happen Newton's LAW will not allow that. What that is saying is there is an upward airflow through the wing. If there is upward airflow then there must be a reactive downward force placed somewhere and the only thing that downward force would hit is the wing..... False Theory.
Newton's theory alone (aka impact theory, skipping stone), Incorrectly explained, says that the air impacting the lower side of the wing will be deflected downward and will push the wing up as the reactive force. The reason this theory is incorrect is that it does not take into effect the upper surface of the wing at all, and in this theory a piece of 3/4 inch plywood with the same lower surface of a Cessna wing will produce the same amount of lift as that Cessna wing.
The way I understand lift, and the way I have always taught lift, takes principals from each, and explains it correctly:
Yes the airflow over the top of the wing decreases in pressure as the velocity of the air increases, this local pressure should not be compared to the local pressure below the wing, because it is shut off from that air mass because the wing is in the way. This local pressure is low relative to the air mass well above the wings surface, and High does seek Low, therefore there is a downward movement of air from well above the surface of the wing down toward the wing. Keep that in mind. As well as below the wing the local area just below the wing is High compared to the adjacent area well below the wing, High seeks low, and the air moves from near the wing downward toward the lower relative pressure well below the wing. (Draw this out it helps... Draw a wing cross section, Just below make an H (high pressure) and just above make a L (low pressure). Above the L on top make another relative H, and below the wing make a L below the H. Then draw arrows from the Hs to the Ls. From the top of the paper it should be H then L, then the wing, then H then L. This shows a downward flow of the air, and as the wing flys through this system, that downward system continues downward, giving the wing a reactive force up (aka LIFT)
Now, as for wing tips and vortices. There is some local air flow around the wing tip where the High pressure area below the wing can travel out around the wing tip to the local Low above the wing, causing the inward swirl we call vortices. A wing tip like the original question was asking about, will create a lateral flow of air off the end of the wing, going against the vortices and will minimize the vortices drag on the wing.
As for it creating a thrusting moment like a sail tacking into the wind, that theory cannot work, because there is no boat and Keel to help this "sail" on track to tack into the wind. Remember a sail boat with no keel cannot tack into the wind. Newton would not like that answer at all, the only way to create thrust is to accelerate the air to the aft, therefore creating a forward reactant force forward (thrust)????? I am open to that discussion, but I don't see it now.
jrh
Well-Known Member
I'm going to jump into this never-ending debate. First, let me say what I _teach_ and how I explain lift to students. Then I'll say what I _believe_ in.
I teach that lift is primarily produced by the Coanda Effect. Just google "Coanda effect" to learn the details of this principle.
Basically, Coanda effect explains why fluids have a tendency to adhere to a surface, as long as that surface does not curve too sharply. As air flows over the top surface of a wing, it tends to follow that curve. I don't understand why. I just know it does. When the air reaches the back of the wing, it continues downward. Because of Newton's Third Law, this overall downward motion of the air must have an opposite reaction. That reaction is the wing being forced upward. Lift.
To see this effect for yourself, dangle the backside of a spoon against a stream of water from a faucet. As soon as the water touches the spoon, it will be deflected towards the spoon and the spoon will be pulled into the stream of water.
I like the explanation of Coanda effect because it can be used to explain things like stalls. Fluids can only adhere to a curve up to a given "steepness." This explains why almost all wings stall at a 16-20 degree AoA. It also explains accelerated stalls in any flight attitude. It also explains why the density of air affects lift.
I use Bernoulli's Principle to explain wingtip vortices. Once again, I don't believe in the explanations of using a second upside down wing to show how you could say air is flowing through a constricted pipe. I think that's garbage. I also don't believe in any of those explanations of air is moving faster over the top of the wing because it has a larger distance to travel. It does move faster over the top of the wing, but not because of the longer distance. I don't understand why it moves faster--I just know that distance has nothing to do with it.
The bottom line is that there is, indeed, lower pressure on top of the wing. Because of this pressure differential, air "wraps up" around the wingtip from underneath the wing where there is higher pressure. Because the wing is constantly moving, by the time the air rotates from the underside to the top side, the wing has gone past. Hence, spirals are created. Why does this create drag? Because any air flow less than smoothly straight back uses energy. Wasted energy is drag.
That's what I teach.
For what I believe in, I've stopped trying to figure it out. I don't know how lift is produced. I've done a fair amount of reading and research trying to figure it out, and I've come to the conclusion that both the Coanda effect/Newton's Third Law and Bernoulli's Principle don't completely explain lift. From the reading I've done, I've concluded that only advanced math and physics can accurately describe lift. I need to learn more in that area, but haven't had the time. I think Coanda effect and Bernoulli's Principle are just flawed explanations passed on through generations of pilots and flight instructors who don't have a solid understanding of lift themselves (myself included).
Some references for further reading:
http://www.amasci.com/wing/airfoil.html (An EXCELLENT resource for both explanations. This convinced me that math is the only way to accurately explain lift)
http://www.aa.washington.edu/faculty/eberhardt/Lift_AAPT.pdf
http://www.aeronautics.ws/blunder1.html
(These two sites give good support to Coanda)
I teach that lift is primarily produced by the Coanda Effect. Just google "Coanda effect" to learn the details of this principle.
Basically, Coanda effect explains why fluids have a tendency to adhere to a surface, as long as that surface does not curve too sharply. As air flows over the top surface of a wing, it tends to follow that curve. I don't understand why. I just know it does. When the air reaches the back of the wing, it continues downward. Because of Newton's Third Law, this overall downward motion of the air must have an opposite reaction. That reaction is the wing being forced upward. Lift.
To see this effect for yourself, dangle the backside of a spoon against a stream of water from a faucet. As soon as the water touches the spoon, it will be deflected towards the spoon and the spoon will be pulled into the stream of water.
I like the explanation of Coanda effect because it can be used to explain things like stalls. Fluids can only adhere to a curve up to a given "steepness." This explains why almost all wings stall at a 16-20 degree AoA. It also explains accelerated stalls in any flight attitude. It also explains why the density of air affects lift.
I use Bernoulli's Principle to explain wingtip vortices. Once again, I don't believe in the explanations of using a second upside down wing to show how you could say air is flowing through a constricted pipe. I think that's garbage. I also don't believe in any of those explanations of air is moving faster over the top of the wing because it has a larger distance to travel. It does move faster over the top of the wing, but not because of the longer distance. I don't understand why it moves faster--I just know that distance has nothing to do with it.
The bottom line is that there is, indeed, lower pressure on top of the wing. Because of this pressure differential, air "wraps up" around the wingtip from underneath the wing where there is higher pressure. Because the wing is constantly moving, by the time the air rotates from the underside to the top side, the wing has gone past. Hence, spirals are created. Why does this create drag? Because any air flow less than smoothly straight back uses energy. Wasted energy is drag.
That's what I teach.
For what I believe in, I've stopped trying to figure it out. I don't know how lift is produced. I've done a fair amount of reading and research trying to figure it out, and I've come to the conclusion that both the Coanda effect/Newton's Third Law and Bernoulli's Principle don't completely explain lift. From the reading I've done, I've concluded that only advanced math and physics can accurately describe lift. I need to learn more in that area, but haven't had the time. I think Coanda effect and Bernoulli's Principle are just flawed explanations passed on through generations of pilots and flight instructors who don't have a solid understanding of lift themselves (myself included).
Some references for further reading:
http://www.amasci.com/wing/airfoil.html (An EXCELLENT resource for both explanations. This convinced me that math is the only way to accurately explain lift)
http://www.aa.washington.edu/faculty/eberhardt/Lift_AAPT.pdf
http://www.aeronautics.ws/blunder1.html
(These two sites give good support to Coanda)
seagull
Well-Known Member
<sigh> These last several posts are, unfortunately, so typical of what is wrong with the bulk of civilian training (and I came from that background, before you try to cast stones). There really is no debate, except for amongst people that do not understand the principles involved.
Look at the following threads, then resume your debate (I hope they come across as a link, otherwise, perhaps someone else can fix them):
http://jetcareers.com/forums/showflat.php?Cat=&Board=UBB8&Number=225834&Forum=f8&Words=newton&Searchpage=0&Limit=25&Main=225834&Search=true&where=bodysub&Name=&daterange=1&newerval=1&newertype=y&olderval=&oldertype=&bodyprev=#Post225834
http://jetcareers.com/forums/showflat.php?Cat=&Board=UBB8&Number=224745&Forum=f8&Words=newton&Searchpage=0&Limit=25&Main=224395&Search=true&where=bodysub&Name=&daterange=1&newerval=1&newertype=y&olderval=&oldertype=&bodyprev=#Post224745
http://jetcareers.com/forums/showflat.php?Cat=&Board=UBB8&Number=269454&Forum=f8&Words=newton&Searchpage=0&Limit=25&Main=268876&Search=true&where=bodysub&Name=&daterange=1&newerval=1&newertype=y&olderval=&oldertype=&bodyprev=#Post269454
Look at the following threads, then resume your debate (I hope they come across as a link, otherwise, perhaps someone else can fix them):
http://jetcareers.com/forums/showflat.php?Cat=&Board=UBB8&Number=225834&Forum=f8&Words=newton&Searchpage=0&Limit=25&Main=225834&Search=true&where=bodysub&Name=&daterange=1&newerval=1&newertype=y&olderval=&oldertype=&bodyprev=#Post225834
http://jetcareers.com/forums/showflat.php?Cat=&Board=UBB8&Number=224745&Forum=f8&Words=newton&Searchpage=0&Limit=25&Main=224395&Search=true&where=bodysub&Name=&daterange=1&newerval=1&newertype=y&olderval=&oldertype=&bodyprev=#Post224745
http://jetcareers.com/forums/showflat.php?Cat=&Board=UBB8&Number=269454&Forum=f8&Words=newton&Searchpage=0&Limit=25&Main=268876&Search=true&where=bodysub&Name=&daterange=1&newerval=1&newertype=y&olderval=&oldertype=&bodyprev=#Post269454
seagull
Well-Known Member
Incidentally, the above also demonstrates the general misunderstanding of what Newton's 3rd law really means. Through that, you would think that a balloon that is untied moves because of a reaction to the air moving out of the nozzle. Not true at all! The balloon moves because it is pushed. In fact, that's why anything moves. It is pushed and it reacts to being pushed. The fact that the thing pushing also "feels" that it is being pushed does not change that fact. Newton's 2nd law applies more directly than the 3rd, and is also where we get Bernoulli to work for us.
The balloon moves because it has pressure on one side that is pushing that is unopposed by the pressure on the opposite side where the nozzle is. The better the nozzle is designed, the less back pressure there is as the air passes through it, so the great the inequality of pressure.
The wing moves because pressures on it are not equal.
Winglets work because the relative flow leaves a net lift vector inward and slightly forward, the latter part being what makes the forward "thrust". The inward part leads to the wing bending moments that can reduce max speeds for the wing under certain conditions (such as less fuel towards the tips to counter it).
The downward flow of air aft of the wing is after the fact, as is the reduction of vorticies from a winglet. Those airflow patterns are a RESULT of the lift or drag reduction, respectively, and not the CAUSE of those effects.
And no, you don't need math to explain lift, only to quantify it.
The balloon moves because it has pressure on one side that is pushing that is unopposed by the pressure on the opposite side where the nozzle is. The better the nozzle is designed, the less back pressure there is as the air passes through it, so the great the inequality of pressure.
The wing moves because pressures on it are not equal.
Winglets work because the relative flow leaves a net lift vector inward and slightly forward, the latter part being what makes the forward "thrust". The inward part leads to the wing bending moments that can reduce max speeds for the wing under certain conditions (such as less fuel towards the tips to counter it).
The downward flow of air aft of the wing is after the fact, as is the reduction of vorticies from a winglet. Those airflow patterns are a RESULT of the lift or drag reduction, respectively, and not the CAUSE of those effects.
And no, you don't need math to explain lift, only to quantify it.
shinysideup
New Member
[ QUOTE ]
Winglets work because the relative flow leaves a net lift vector inward and slightly forward, the latter part being what makes the forward "thrust". The inward part leads to the wing bending moments that can reduce max speeds for the wing under certain conditions (such as less fuel towards the tips to counter it).
The downward flow of air aft of the wing is after the fact, as is the reduction of vorticies from a winglet. Those airflow patterns are a RESULT of the lift or drag reduction, respectively, and not the CAUSE of those effects.
[/ QUOTE ]
[ QUOTE ]
They also actually REDUCE, not INCEASE downward flow of the air aft of the wing (so much for the false theory of lift that many civilian CFIs teach of downward flow and "opposite and equal reaction")~
[/ QUOTE ]
Alright, I am listening, but you are contradicting yourself here. If the wing-lets reduce the downward flow of air aft of the wing, how then can they create a a lift vector inward and forward. This doesn't make sense to me. The Newton's Laws are LAWs not theories, and we do still need to have an equal system here, but those two go with each other?
As for Coanda Effect, this is also very viable, and does give a good method of explanation of lift. But, it doesn't complete the equation, neither does my last example either, but they are very complimentary.
Winglets work because the relative flow leaves a net lift vector inward and slightly forward, the latter part being what makes the forward "thrust". The inward part leads to the wing bending moments that can reduce max speeds for the wing under certain conditions (such as less fuel towards the tips to counter it).
The downward flow of air aft of the wing is after the fact, as is the reduction of vorticies from a winglet. Those airflow patterns are a RESULT of the lift or drag reduction, respectively, and not the CAUSE of those effects.
[/ QUOTE ]
[ QUOTE ]
They also actually REDUCE, not INCEASE downward flow of the air aft of the wing (so much for the false theory of lift that many civilian CFIs teach of downward flow and "opposite and equal reaction")~
[/ QUOTE ]
Alright, I am listening, but you are contradicting yourself here. If the wing-lets reduce the downward flow of air aft of the wing, how then can they create a a lift vector inward and forward. This doesn't make sense to me. The Newton's Laws are LAWs not theories, and we do still need to have an equal system here, but those two go with each other?
As for Coanda Effect, this is also very viable, and does give a good method of explanation of lift. But, it doesn't complete the equation, neither does my last example either, but they are very complimentary.
seagull
Well-Known Member
It is not contratictory at all. The lift created by the winglets is not in an upward direction, but rather, inboard and forward. It works exactly like a sail on a sail boat as you tack into the wind. The "keel" is the wing itself, it can't turn. After the fact, it does reduce downwash and the vorticy, but that is not how the force that is helping is created, it is a result of it. I am not sure how else to explain it, I think you are having trouble letting go of the (incorrect) explanations that you've held onto for so long. Not uncommon, it is a paradigm shift.