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#1
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how a sail works, who can help me explain?
I hate to be the one to tell you this, but PIM is correct. Lift is to air as buoyancy is to water.
"Simple Simon" wrote in message ... I think you should do a little research into Bernouilli and Venturi. "PIM" wrote in message ... "Simple Simon" wrote The convex side of the sail or the leeward side directs the air over a longer path. This longer path for the air lowers the pressure because said air must move faster to cover the increased cord. Faster flow equals lower pressure. This low pressure combined with the normal or slightly increased pressure on the windward side is what creates lift. Dear Simon, I am not neglecting what happens on the leeward of the sail, the leeward of the sail is also deflecting air and thereby creating lift. as I am explaining in www.sailtheory.com/sail.html According the "longer path theory" you use it would not matter how much you pull your sail in, since there is always the same difference in pathlength between windward and leeward. Please read www.sailtheory.com/wrongtheory.html for more examples why it is wrong. The "longer path theory" is not easy to use and is wrong. It is the reason I started my site. Clearly I am not clear enough at this point Many agree with me that the longer path theory is wrong: jeff raskin: http://tinylink.com/?RD9ntJyTuz university frankfurt (under 2.2) http://www.informatik.uni-frankfurt..../MIS/mis6.html University of washinton: http://www.aa.washington.edu/faculty/eberhardt/lift.htm Bill beaty: http://www.amasci.com/miscon/miscon4.html#wing And so do the most aerodynamicists as far as I know. I tried to adjust above theories from a wing into a sail. Best Regards Pim -- Posted by news://news.nb.nu |
#2
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how a sail works, who can help me explain?
I don't hate to say it but you and PIM are BOTH incorrect.
You both have only a laymans idea of how a sail works. Fact: Venturi effect is proven and accepted Fact: Venturi effect causes lower pressure in the area of the venturi. Fact: Lower pressure is cause by the lower density of the gas molecules in the area. Fact: An object with low pressure on one side and higher pressure on the other side if free to move will move in the direction of the low pressure. THAT is how a sail works. All that other crap is extraneous to the situation at hand aboard a sailboat. There is no high-horsepower motor available to make the sail act as a plane like PIM suggests. All the force is generated by a difference in pressure between the leeward and windward sides of the sail which force acts against the foil in the water and the planeform of the hull to produce forward motion. "jlrogers" wrote in message .com... I hate to be the one to tell you this, but PIM is correct. Lift is to air as buoyancy is to water. "Simple Simon" wrote in message ... I think you should do a little research into Bernouilli and Venturi. "PIM" wrote in message ... "Simple Simon" wrote The convex side of the sail or the leeward side directs the air over a longer path. This longer path for the air lowers the pressure because said air must move faster to cover the increased cord. Faster flow equals lower pressure. This low pressure combined with the normal or slightly increased pressure on the windward side is what creates lift. Dear Simon, I am not neglecting what happens on the leeward of the sail, the leeward of the sail is also deflecting air and thereby creating lift. as I am explaining in www.sailtheory.com/sail.html According the "longer path theory" you use it would not matter how much you pull your sail in, since there is always the same difference in pathlength between windward and leeward. Please read www.sailtheory.com/wrongtheory.html for more examples why it is wrong. The "longer path theory" is not easy to use and is wrong. It is the reason I started my site. Clearly I am not clear enough at this point Many agree with me that the longer path theory is wrong: jeff raskin: http://tinylink.com/?RD9ntJyTuz university frankfurt (under 2.2) http://www.informatik.uni-frankfurt..../MIS/mis6.html University of washinton: http://www.aa.washington.edu/faculty/eberhardt/lift.htm Bill beaty: http://www.amasci.com/miscon/miscon4.html#wing And so do the most aerodynamicists as far as I know. I tried to adjust above theories from a wing into a sail. Best Regards Pim -- Posted by news://news.nb.nu |
#3
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how a sail works, who can help me explain?
You are making a mistake: why the air speeds up at leeward.
It has nothing to do with the length difference. If you do not want to leave your good old theory, please consider the one I suggest as an extra. my theory : "the sail deflects the air (on the windward side as well as on the leeward side)" It is very satisfying, it explains a lot. Any way, all theories are a simplification of the reality. more theories to describe the same are possible. The best theory is the one that is the simplest and explains the most. It does not mean all other theories are rubbish! By the way, how do you explain that a flatter sail sails better "pointing" close hauled as a deep(=curved) sail? The more curve the more force according your theory, so what is the use of flattening the sail? (my answer: www.sailtheory.com/sail.html#ch) In reply of your previous post: "Simple Simon" wrote in message Fact: Venturi effect is proven and accepted Venturi effect is in a pipe, in a venturi, There it is indeed proven and accepted. A sail is no venturi. Fact: Venturi effect causes lower pressure in the area of the venturi. yes. Fact: Lower pressure is cause by the lower density of the gas molecules in the area. density difference is not of importance. A keel works just as a sail prducing sideways lift, but density of water stays the same. Fact: An object with low pressure on one side and higher pressure on the other side if free to move will move in the direction of the low pressure. Yes. THAT is how a sail works. There is no venturi. There is a sail. That is the error. All that other crap is extraneous to the situation at hand aboard a sailboat. oh. There is no high-horsepower motor available to make the sail act as a plane like PIM suggests. I do not want to suggest a motor. Sorry if I did. (with "power" I mean energy/time, or force x speed, so not a motor, on my site you can read "force" instead of "power" in most places. It is a small translation error. "power" is in Dutch different from "motorpower" thanks for the hint. This helps improving my site ) All the force is generated by a difference in pressure between the leeward and windward sides of the sail yes, and these pressures are created by changing the direction of the wind locally. which force acts against the foil in the water and the planeform of the hull to produce forward motion. yes. Best regards, Pim www.sailtheory.com -- Posted by news://news.nb.nu |
#4
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how a sail works, who can help me explain?
"PIM" wrote in message ... By the way, how do you explain that a flatter sail sails better "pointing" close hauled as a deep(=curved) sail? The more curve the more force according your theory, so what is the use of flattening the sail? (my answer: www.sailtheory.com/sail.html#ch) You forget an important concept that of drag. A foil is a compromise between lift and drag. NACA did extensive studies on differently shaped foils and it was all about lift vs.drag. One can make a foil with maximum lift but if it also has maximum drag it will not function very well. If a foil is to full in higher winds it creates more drag. a flatter foil creates less lift but proportionately less drag so overall it is more efficient. A sail is no venturi. Yes it is. Take a venturi. Cut it and unroll it so it is spread out. It is still a venturi but just not a cylindrical venturi. Air molecules don't know if they are passing over a curve in a closed cylinder or a curve in a spread out cylinder. View the sail as a spread out cylinder. Fact: Lower pressure is cause by the lower density of the gas molecules in the area. density difference is not of importance. A keel works just as a sail prducing sideways lift, but density of water stays the same. Density is all important because things happen on a molecular level. It is a fact of physics that lower density equals lower pressure. The measure of pressure of a gas tells you its density. Fact: An object with low pressure on one side and higher pressure on the other side if free to move will move in the direction of the low pressure. Yes. THAT is how a sail works. There is no venturi. There is a sail. That is the error. Incorrect as explained above with respect to the opened and spread out cylinder and how molecules of air see no difference. |
#5
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how a sail works, who can help me explain?
Will move in the direction of the lower pressure
Why in the hell couldn't you see that when we were talking about weather systems? OT |
#6
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how a sail works, who can help me explain?
Some questions on Lift as applied to sail?
If Bernoulli is wrong and Newton's Law of ACTION & REACTION is what creates Lift, why then , when a sail is at maximum lift do the tell-tale at the leech of the sail stream back off the sail, as describe by Bernouli and not fly at a 90 degree angle as described by Newton's downdraft and updraft? If Newton's Law of Action & Reaction is correct (I'm not saying it is wrong) then the action has to be on the convex side of the sail ( Action- downdraft) to create the reaction on the concave side (Reaction- Updraft or Lift) Why then do we look for the tell-tales to be streaming backwards when sailing. Seems to me they should be forced straight into the sail in various direction Also, If Newton's Law is correct that should make the convex side of the sail the windward side and the concave side the Lee side ( Action_Reaction) How can this be if the boat is traveling in the direction of the convex side ( The Newtonian windward side) If, as Pim, logic of a flat sail is the desired shape for upwind performance, then why wouldn't a flat piece of plywood work best when tacking up wind? ( Just maybe, Bernoulli isn't wrong for how a sail works?) These are some question in my mind. Maybe some of you Flight Wizards have answer for me before I completely abandon " Bernoulli" Ole Thom |
#7
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how a sail works, who can help me explain?
"Thomas Stewart" wrote in message ... These are some question in my mind. Maybe some of you Flight Wizards have answer for me before I completely abandon " Bernoulli" You may as well abandon Bernouilli (note correct spelling) because you have already abandoned reason. Your motor sailer proves it. |
#8
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how a sail works, who can help me explain?
Lift is to air as Buoyance is to water
Oh Oh! Maybe in lighter than air. Newton's second Law is; Lift= mA. The mA is for; m= mass A= acceleration Buoyance needs no acceleration. Ole Thom |
#9
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how a sail works, Windtunnel Tests.
Maybe this will help everybody:
http://www.wb-sails.fi/news/99_4_Win...es/Movies.htm# "Thomas Stewart" wrote in message ... Lift is to air as Buoyance is to water Oh Oh! Maybe in lighter than air. Newton's second Law is; Lift= mA. The mA is for; m= mass A= acceleration Buoyance needs no acceleration. Ole Thom |
#10
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how a sail works, Windtunnel Tests.
Movies don't work.
"jlrogers" wrote in message ... Maybe this will help everybody: http://www.wb-sails.fi/news/99_4_Win...ies/Movies.htm |
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