As it feels like this thread is approaching closure , and grappling for a practical value :
I'm buying a mainsail for my uni-rig F16. All the sails from the various manufacturers represent an invisible hierarchy of "best" to "worst" at hastening the force needed to move the boat forward in the wind conditions in which I intend to race.From the standpoint of pure consumerism and given the abundance of misconception about how sailboats move - how does one distinguish a smart (fast) sail from one cut by a minion of the church of equal transits (buy what's winning ?) ?
I'm pretty new to sailing , has the misinformation about how lift occurs manifest in wide spread purchase of bad sail designs in the past or am I safe assuming most sails offered are "smart"?
Regardless , loved this thread...
PK
scott@aa.washington.edu
Office: 101 Kirsten Wind Tunnel Building
He certainly has a credible location. Means I'm going to have to be reeeeeal certain about the email I'm going to send him about the Coanda effect. 
The two approaches, Newtonian and pressure must be compatible. They're both based on physical laws. That's the fallacy that I was getting at with the Coanda/F=ma argument. In all the presentations of that argument that I've seen, there is a lack of connection between all the downward deflected air and the wing itself. Then viscosity and "stickiness" gets brought into it as to how flow stays attached and, personally, I don't think that pans out, either. First, viscosity leads to boundary layers and boundary layers lead to separation. As for "stickiness," as opposed to a solid, a fluid, in and of itself -- the special case of surface tension excepted -- cannot support a load in tension or compression. It's like pushing a rope cut into 10 pieces. But surround that fluid that you are trying to apply a force to with a pressurized fluid of a same or different type and now it can support a load.
Worse, I'm going to go out on a limb, although I believe it's a short, sturdy limb and say that Eberhardt and the How Planes Don't Fly article are wrong in their description of the Coanda effect. If Coanda is viscosity/boundary layer driven, then the flow slows down, the bondary layer thickens and the flow separates and it sure doesn't seem like it would help in keeping flow attached on a nearly stalled wing! I'm going to have to ponder this one, but I suspect that in the water over the glass scenario, the flow leaves the faucet at atmospheric pressure, continues to accelerate down the glass due to gravity, decreasing its pressure to below atmospheric and the surrounding air pressure holds the stream against the glass until the boundary layer slows the flow too much and the stream separates from the glass. The water's surface tension would help keep the water attached to the glass, but surface tension sure doesn't have a role in the rotarless helicopter or the blown boundary layer referenced above. I'm not 100% percent on it, but I'd be willing to put money down on a claim that the water-jet-on-a-glass Coanda effect would not work nearly as well, if at all, on the space station.
Supernatural beings like fairies?
And since I'm disparaging other people's credentials and criticizing credentialed experts, I suppose I should toss my credentials into the mix. I have an MS in mechanical engineering, have been working in hydrodynamics for about 15 years and have designed and analyzed about 15 underwater vehicles of various types and speeds.
I haven't had time to read this whole thread but there are a few things that I have to through in after reading a few of steveh's posts. The reason the Bernoulli equasions don't seem to be accurate for a wing is because most people seem to think that if 2 paricles of air side by side strike the leading edge of a wing and one goes over the top of the wing and the other goes under the wing, the two particles must both meet back up at the exact same time at the trailing edge of the wing. This is an insane assumption. There is no law of physics that says this will happen. The equasions aren't wrong, the assumptions people are making are wrong.
Next, the relation between the Coanda effect and lift. The Coanda effect simply shows how air is accelerated by the wing. I don't mean slowed down or speed up, I mean that the direction of travel is changed. Remember that when you have a wing creating lift, there are only 2 elements interacting, the air and the wing. If the wing is creating lift it must be doing it by interacting with the air in some way. Lift is a force normal to the direction of air flow. The only possible way for a wing to create lift is if it creates an equal but opposite force on the air. That force is accelerating a mass of air downward. Contrary to some of the bizzare circulation theories, air must be deflected downward in order to create a force on the wing in the opposite direction.
Circulation theories, CRACK SMOKING BS. Just a little bit of common sense will show that this idea is totally wrong. If there is a circulation around the wing that produces the lift then I should be able to destroy all lift by destroying the circulation. Since the "circulation" is from the trailing edge toward the leading edge on the bottom of the wing, all I should have to do is greatly accelerate the air under the wing from the leading edge toward the trailing edge to distroy the circulation. What if we bolt a jet engine under the wing to accelerate the air flow. By the reasoning of the circulation theory, every jet that has an engine mounted under the wing should never be able to get off the runway. By use of simple vector math you can show that a circulation plus a flow does not create lift. Some of the assumptions and leaps made by Mr. Gentry are soo wild I can't believe anyone would take him seriously.
I'm sure that many people will disagree with me on the circulation theories and I welcome your arguments but first I ask you to think for your self rather than blindly following the latest craze in lift theories. Does it make sense?
I never appreciated the circulation theories, but I do recognize that they can be used as mathematical describtions that will give accurate results. In a way it is not a explanation but a different type of model, one that can be useful in certain circumstances.
For the educated people among us. Complex numbers or imaginairy numbers are just plain BS in the real world but with this math structure we humans are able to solve many complicated problems. I feel circulation theories are comparable to that.
In all other aspects I'm with Steveh
Wouter
Our current summer feels much like winter. Cloudy and plenty of rain with regulary a storm coming through. Another wasted season.
Wouter
To clarify a little about pressure. Total pressure is static pressure plus velocity pressure. Velocity pressure acts in the direction of velocity while static pressure acts in all directions. A pitot tube measures total pressure at the tip (pointed into the air stream) and subtracts static pressure at right angles to velocity (through the little holes around the perimeter of the tube) to give you a reading of velocity pressure which is then allows calculation of velocity. That is assuming you connect both hoses to a manometer. If you increase velocity as in a venturi, there is a reduction in static pressure as it converts to velocity pressure where the velocity is higher (at the restriction). Reducing velocity, the pressure is reconverted to static pressure with some efficiency loss.
In a sail, increasing the velocity on lee side reduces the static pressure on that side compared to the static on the windward. That results in a force or lift which is the difference in the static pressures. I would believe there are other forces involved as well such as a portion of the velocity pressure on the windward side.
Howard
deseely,
Most of this has been covered and to my mind, the Coanda effect as a "how" or cause for the downward deflection is not only DOA, it's a misnomer. Effects can't cause things! Try this.
Bob: How does the air get curved downward going over a wing?
Joe: The Coanda effect.
Bob: How does the Coanda effect curve the air?
Joe: It's like water from a faucet flowing over a glass.
Bob: Ahhhh... But how does the air or water curve?
Joe: (head explodes)
That's pretty much Raskin's argument in a nutshell, but instead of his head exploding, he waves his arms around and says we don't need to know how it works, leaving us 
As for the crack smoking circulation theory, as Wouter said, circulation is just a mathematical and visualization tool, not a conspiracy. Check out Section 3.10 of See How It Flies for a very clear description of circulation. Circulation doesn't state that air moves from the trailing edge to the leading edge while an airplane is flying, it states that this kind of flow plus that kind of flow produces the same flowfield as a wing. In fact, circulation assumes that the forward flow under the wing from the TE to the LE is exactly cancelled out by the linear flow passing under the wing from the LE to the TE. You don't need a jet engine to cancel that forward flow, it's already done.
Ironically, a jetstream improperly placed under a wing could decrease lift in that region because of the...
...Coanda effect. 
I wish I was kidding.
Wouter,
One could say that the jib works in the mainsail's updraft and the mainsail in the jib's downdraft, but I miss the advantage of the combination.
If I look at the jib, it can be set in a more opened angle due to the main, but if I look at the mainsail, it needs to be moved closer to the centerline with a jib, compared to without it. Doesn't seem to work this way.
Luiz
There is an AWFUL lot of bull sheeeet being thrown about here guys!! The best, truest and nicest answer is that the fairies were the ones what dun it!! And very nice little folk they are too, so DONT GET THEM ANGRY OR THEY WILL TAKE THEIR "LIFT" AWAY - SELECTIVELY, which means that when you are gliding in, quite nicely placed, towards the finish line and you think that you have a top place all wrapped up, it is then that the "lift fairies" will strike!!! And instead of having a favourable wind to cross the finish line with, you will be suddenly "lifted" almost straight up and thrown aback as you watch several other "believers in the powers of fairies" cross in front of you. So take care, you have been warned. (I have seen it happen many times – and that’s the truth -)
For the educated people among us. Complex numbers or imaginairy numbers are just plain BS in the real world but with this math structure we humans are able to solve many complicated problems. I feel circulation theories are comparable to that.
Wouter
There are actual real world physical phenomena described well by complex numbers such as electromagnetic wave theory, where electrical and magnetic sine wave constituents are said to be operating in planes 90* apart, thus creating a 'Z' axis. The X, Y and Z axis relate exactly as the plane of the real numbers intersects the imaginary.
Agree with you on the circulation theory, though. Many people completely misapprehend the intent of this theory thinking that it supposes the fluid is actually flowing backwards on the underside(??!!) instead of simply returning to the same energy state as before negotiating the foil.
Jimbo
First, Tami, that kills me, glad somebody said it (42..love it)
Second, I didn't read more than 30% of those long posts, I don't have the time (or attention span). Like my boss says, "get to the point".
Tami said it once, I said it once, read a Marchaj book, he's not written the "definitive" books on the subject for no reason.
I deleted my post explanation here, b/c.... I'm tired and don't feel like finishing it now.
In short, the circulation effect accelerates the air on the lee side in comparison to the windward side. SINCE THE LEEWARD FLOW IS FASTER, THE PRESSURE EXERTED (BERNI) IS LOWER ON THE LEE SIDE THAN THE WINDWARD SIDE. Berni is able to tell us the pressure differential b/c of the differing velocities. Berni, then tells us part of the lift coeff.
This guy uses the same type of information as Marchaj.
http:/
I can't find my Marchaj book otherwise I'd post a pic of the graphs of pressures and resultant vectors.
He did wind tunnel testing with pressure readings. It's hard to argue with numbers.
As he explains it, the jib pulls 4-5x harder per in^2 than the main does. The jibs main purpose is, however to aid in keeping flow attached to the lee side of the main thus reducing drag and increasing efficiency. It does decrease pointing ability, however provides quite a bit of driving force on reaches.
Was I pissy and terse, possibly.... am I about to get done with a week of AF inspections w/sh*tty inspectors and bogus findings... yes. Have I worked 50+hrs in 4 days and only had ~4-5 hrs of sleep/night... yes. I'm going to bed.
p.s. Under the "fallacies" section, he kills the Coanda argument.
http:/
Alright "smarty pants" TAMI, (who's a pretty boy then), we all know the answer (42) but what is THE question???????
I can only reiterate what has been said earlier (if you REALLY want to know about "lift" relative to sailing)
READ C.A.MARCHAJ !!!!!!!!!!!!
Jimbo,
You misunderstood my statement. I myself wrote :"this math structure we humans are able to solve many complicated problems". Sound like "... actual real world physical phenomena described well by complex numbers ... " to me.
What I was referring to is that an imaginairy number has no meaning in the real world. Example. If a wave has a frequency of say 10 Hertz that we know what that physically means. If however a wave has a frequency of say (10 + 4J) (= imaginairy number, with the J identifying the imaginairy part and the 10 being the real part) than nobody knows what that means in physical terms. Nor does such a wave form exist in the real world or can ever be made to exist. Such a construction that is very much possible in mathematical terms, is simply non-existant (impossible) in the real world where ONLY REAL numbers exist. That is why I say that an imaginairy number is just plain BS in the real world. It is as concrete in the real world as little wood elfs.
Did I loose any of the other guys yet ? Yep we are talking about imaginairy numbers, no kidding they really do exist in mathematics and are quite helpful, especially in the analysis of oscillating systems.
So for you guys the answer to how can imaginairy numbers be helpful in real life problems ? Because any system that initially is worded in real valued equations will produce real valued answer even though the path in between is using imaginairy numbers. In such a case the imaginairy numbers occur in what is called complex conjugate pairs. Example : whenever the number 10 + 4j arises than somewhere else its mirror image 10 - 4j arises as well; that is when the original problem is real valued. The math structure around these numbers keeps the pair linked to one-another so they constantly are added/subtracted or multiplied with eachother. Often right before the final sought after answer, which always is a value with meaning in the real world, the two mirror images are added or multiplied by one another resulting in a real valued number.
example : (10 + 4j) + (10 - 4j) = (10 + 10) + (4j - 4j) = 20 + 0J = 20 = real value.
Similar thing happens when multiplying to mirror complex numbers.
The structure that enforces this behaviour is linked to wether a problem exist in the real world. If the final answer is NOT a real value then either you have made a calculation error or the original problem you were analysing simply does NOT exist in the real world.
Funny stuff this is, right ?
Who said Mathematics are boring ? The further you get into studying mathematics to more wild the phenomenons get. You just need a good teacher to get through the basics after that it gets mind blowing
Wouter
I`ll go back to my reference to Dennis Pagen, who wrote "Understanding the sky", wherein he explains how thermals are formed, which is kinda important to free-flying people, and therefore relevant in this thread.
I won`t get into it in detail, suffice to say that thermals are really just a whole lot of hot air.
Which brings me to my point : If this thread was on a paragliding forum, we`d all be at cloudbase by now.
Complex numbers, real numbers and even integers are all human conceptual/modelling devices; none of them "exist" in the real world... 
Will
Again I only ask that people think for them self. We have all read Marchaj's books. I have every book he wrote. Marchaj didn't come up with these theories, he only rewrote them. Secondly your referance to John Denker's page does not in any way "kill" the Coanda arguement. I have read all of Denker's theories and again he did not create them, he simply restates them. Denker's barn door analogy is an excellant example of how wrong he is. The air flow "or water" will adhear to a flat plate at low angles of attack. If you don't believe it, try it in the sink with a sheet of plastic or metal. One of the mistakes he makes is using a fast stream that is broken and full of air. Just like a cavitating prop, the water will not adhere as well when mixed with air. Again the coanda effect doesn't create lift. Changing the direction of the air flow does. You can't just say that Newtonian physics does't apply to wings. It does, it always has and always will. The ONLY way to create lift is by changing the direction of the fluid flowing past the wing. The forces must be equal and opposite each other. Another on of the completely ridicules arguments by the "circulation beleivers" is that air is like "be bees" shot from a gun and bouncing off the bottom of the wing. I think we have all seen the diagrams of the wing with the be bees flying at it. There explination is that the only the air that strikes the bottom of the wings would change direction and therefore Newtonian physics can only account for a fraction of the lift. Use a little bit if common sense here and look at there diagram. If air were like be bees, there would be a perfect vacuum behind the wing because the wing has deflected those be bees away. Air is not like be bees, it's a fluid. Take a look at any of the diagrams in Marchaj's books of the fluid flow around a wing or sail. Look at the direction of the free fluid flow well ahead of the wing and look at the direction of flow behind the wing or sail. If there is lift, there is a directional change in the fluid flow. This whole circulation theory comes out of a misunderstanding of the Kutta-Joukowski lift on a rotating cylinder. The rotation of the cylinder is causing a change in the directional flow of the fluid flowing past the cylinder. See this link for a complete explination. http:/
Will R wrote:
and
I haven't picked up a Marchaj book in about 15 years, but I doubt he uses the unequal flowpath theory. If he does, I think I'll take a pass.
I'm sorry about being longwinded, but it takes a bit of explanation and detail to dispell myths and present (I hope) a clear and correct explanation. The true situation is a bit more complicated than just saying, "Unequal flowpaths!" or "Coanda!" or "Bernoulli!" and not nearly as sexy as those East European or Italian names.
You think it's BS? Fine, present your case. But referencing this or that expert does not necessarily mean that there's understanding. I've read Rick's cat racing book, but until I can successfully apply it, I sure won't feel like I understand it. Don't like it, find it boring, think it's all hot air, well, there's a thread full of pithy rejoinders on light air racing to enjoy.
deseely,
That rotating ball example you linked IS a real world example of circulation. If that Java simulator could be set to a straight line flow of zero when you spun the ball, you would have a rotating, circular flow in the direction of rotation, i.e. circulation. Add the straight flow and you get lift. Straight flow plus circulation generates lift is the circulation theory. What's the issue with this?
No problem with it Steve, in the real world a spinning cylinder or ball in a flow will produce lift but that is becauce it alters the direction of the fliud flow. The vector addition of a circulation plus a flow does not. The key here is that the fluid produced a force on the cylinder or ball and the ball or cylinder provided an equal but opposite force on the fluid flowing past it.
10 Steps to Circulation Enlightenment
1. Obtain CAD program
2. Draw circle of radius 5
3. Draw rotation vectors tangent to circle of length 0.5 pointing in clockwise direction
4. Draw horizontal linear flow vectors of length 1.41 at the tip of each rotation vector pointing right (the length makes it easy later)
5. Draw the resultant flow vectors
6. Measure the length of each resultant flow vector
7. Assume upstream pressure of 1 and density of 1
8. Using the upstream pressure and velocity and the velocity vector measurements in the Bernoulli equation, calculate the pressure at each point
9. Plot results on corresponding points
10. Analyze pressure field and determine that the lower pressure values above and the higher pressure values below will result in lift
Almost as hot as the Nacra 580.
That's it, I'm goin' to Disney World.
Altering the direction of flow is the function of a foil. By altering the direction (velocity) of the flow, lift is converted from the kinetic energy of the flow. The spinning cylinder or ball is a type of foil.
The spinning ball alters the flow because the flow adheres to the ball on the retreating side more than on the advancing side or more than it would on a stationary example. This increased adhesion prevents the flow from separating from the cylinder, thus it follows the cylinder's surface and it undergoes a continuous change in velocity (acceleration) as it does so. Lift is a reaction to this acceleration and the boundary adhesion.
Jimbo
I see you went to visit the big rat. Hope he didn’t gnaw too big a hole in your wallet. Looks like Jimbo is among the ever growing number of people who have realized that lift is just simple Newtonian physics. My sail puts a force on the air that passes by it and the air puts an equal and opposite force on my sail. That’s all, nothing more. I’ve been struggling with this concept of lift for about 15 years (since college) and I would have to say that I didn’t come to this conclusion until about a year ago. Sometimes the simplest answer is the correct one.
I’m so glad you have discovered 10 OF THE 12 steps to enlightenment. I hate to tell you Steve but once you start drawing diagrams, you can’t help but see the flaw in the circulation theory. To start out let’s place your diagram in front of you with the flow from left to right and the circulation clockwise. Now to the right of your diagram lets put a velocity vector to represent the flow after interacting with the circulation. If you add your 4 resulting vectors together and divide by 4 to get an average velocity vector after circulation, you will notice that the circulation cancels itself out. The flow before is exactly the same as the flow after and the circulation has no net effect on the flow. This was probably obvious to you before you started since circulation has no net direction of flow. If you sit down with the diagram you just drew and the flow diagrams from the actual experiment and ask yourself 1. Why is the flow in my diagram different from the actual flow? 2 If there is a pressure difference then why don’t I see a net change in my velocity vectors indicating an equal and opposite force being placed on the air? Why don’t my forces balance out?
Let’s start with the flow diagrams. First you are using a pure circulation with no physical object in the middle, where as a spinning rod is used in the actual experiment. Not a big problem. It’s not the flow around a stationary rod that is important, it’s the circulation created by spinning the rod and how it reacts with the flow that we want to look at. Look at the velocity vector on the left and right of your diagram then look at the flow lines from the actual experiment. Do you notice anything? In your diagram the flow has no net change in velocity after interacting with the circulation. In the actual experiment you will notice that the flow lines have changed directions after interacting with the circulation. How could we make your diagram more accurately depict the true flow? Go back in to your cad drawing and let’s make a change to your circulation. On the left side of your circle your circulation vector has a length of 0.5 pointing up. Let’s change it to 0.2. Now let’s change the circulation vector on the right to 0.8. Notice that I didn’t change the vector on top or bottom that gave you the pressure difference. Now redraw the resulting vectors and the vector that represents the flow after interacting with the circulation. Now you will notice that there is a change in the direction of the velocity vector of the flow after interacting with the “circulation” and it is in the same direction of the flow line depicted from the actual experiment. Now your diagram agrees much more accurately with actual flow lines. Now let’s look at the force balance. Sum the resultant vectors around your circulation. You will notice that there is a component that is now pointing down. The change in the direction of the velocity vector was caused by a force. You will notice that the direction of force on the flow is down and an equal but opposite force is applied to the circulation. The direction of the force on the circulation coincides with the difference in pressure. Now your diagram agrees with the actual flow lines and the forces balance out correctly not to mention that the pressure difference above and below the “circulation” agrees with the forces indicated by the velocity vectors. Everything agrees except you no longer have pure circulation. In fact you will notice that there can’t be any forces on the wing or rod if there is pure circulation because no forces can be transmitted to the flow. The original diagram that you drew with pure circulation won’t ever exist without another component introduced into the flow to force that condition but we can go into that in the future. It may take a few days, a few beers and lots of paper to digest all of this.
Pardon my amusement here but you don't need any knowlegde of physics to come to that conclusion. This is like saying that when you put your hand in the fire your hand will be heated up and the fire will get cooled. Leaving us no further in understanding WHY this is the end result of such an action. In effect everybody knows that a car will accellerate when you press on the gas pedal but doesn't mean that everybody understands what happens between pressing the peddle down and the car accellerating.
In short, you haven't provided much clarity to the issue apart form something that is almost obvious.
Also I think that a quatum physicist will have a problem or two with your statement that it is all JUST Newtonian physics.
The point you are still trying to make about circulation theory is still a mute point as it is nothing more than a different mathematical model of the same lift producing proces. It is not an explanation but rather a way of looking at that proces from a modelling (mathematical) viewpoint with certain characteristics. In some applications it is handy, in most however it is not. There is not much point in disproving as it very much is mathematically correct. Meaning that the results acquired by using this model are accurate. It is just like prefering to say that 2 = (2*7 - 4) / 5 instead of 2 = 1 + 1, both are correct expressions although the first isn't very practical at first sight but never the less could be very handy in certain special cases.
Wouter
"That's it, I'm goin' to Disney World" was rhetorical. I did the vector math (with 23 points, not 4), worked up an Excel sheet and I got lift. In addition to no net flow deflection, I also got no drag, so what good is this circulation nonsense?
Oh yeah, I got lift. And without all that mess of viscosity, Reynolds number, boundary layers, separation points and 3D, Navier-Stokes CFD codes. The spinning cylinder example you posted earlier doesn't have any net deflection, either, nor any drag.
deseely, my question for you is, how does all that downward deflected air from simple Newtonian physics hold up the airplane? In F=ma, how do you measure or estimate mathematically the mass of air moved and its acceleration in order to calculate your lift force? Also, how and where is that lift force applied to the wing?
Crack smoking circulationists have used circulation and idea of superposition of flows to develop a very successful aerodynamic modeling tool called panel methods** for estimating forces on a body. Including in three dimensions. If they can do it, I would hope that simple Newtonian physics could do the same.
** - PMARC is just an example. I liked it because in the description, they use the term "ficticious flow." So what comes from circulation really is cracksmoking bs.