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Sailing against the wind depends on airfoil shape?
Hi,
I'm trying to understand how a boat can sail against the wind. Explanations on the internet usually go like this: "The sail has an airfoil shape, the air goes faster on one side than on the other, creating lift by Bernouilli's principle." But I know that for flying planes, the wing's airfoil shape is not essential (otherwise planes couldn't fly on their back): it's the angle of attack that matters. So I'm wondering if the same is true for sailing: would it be possible to sail against the wind with a sail that's a rigid flat surface, not an airfoil-shaped piece of cloth? Thanks, Axel |
Sailing against the wind depends on airfoil shape?
Axel Boldt wrote: Hi, I'm trying to understand how a boat can sail against the wind. Explanations on the internet usually go like this: "The sail has an airfoil shape, the air goes faster on one side than on the other, creating lift by Bernouilli's principle." But I know that for flying planes, the wing's airfoil shape is not essential (otherwise planes couldn't fly on their back): it's the angle of attack that matters. So I'm wondering if the same is true for sailing: would it be possible to sail against the wind with a sail that's a rigid flat surface, not an airfoil-shaped piece of cloth? Thanks, Axel Yes, but slowly - a flat surface is not an efficient aerofoil. A boat goes to windward by generating lift from its sail, just like an aircraft's wing. If you understand a wing you are 3/4 of the way there. Of course it generates drag as well; the resultant force from the sail will be pointing a bit behind right angles to the boom (the long hard thing usually made of wood or metal at the bottom of the sail) - in your "flat surface" case, a bit behind right angles to the surface. The force is angled sideways and forwards by controlling the amount the sail is directed away from the centre line of the boat. The forward vector of the force propels the boat forwards. The sideways vector is absorbed by the centreboard, keel, or sometimes just the shape of the hull, which acts as another aerofoil shape but underwater. (It's technically a hydrofoil, but most people think of a hydrofoil as something to lift the boat out of the water). Of course, in absorbing the sideways force the underwater parts of the boat create some drag. It's much easier to understand with a boat to look at and wave your hand over - or at least a piece of paper to scribble on! HTH Andy |
Sailing against the wind depends on airfoil shape?
"Axel Boldt" wrote...
I'm trying to understand how a boat can sail against the wind. Explanations on the internet usually go like this: "The sail has an airfoil shape, the air goes faster on one side than on the other, creating lift by Bernouilli's principle." But I know that for flying planes, the wing's airfoil shape is not essential (otherwise planes couldn't fly on their back): it's the angle of attack that matters. So An airfoil creates lift when the air flows across it. The amount of lift depends on the speed of the air flow, the shape of the airfoil, and the angle of attack. An airplane can fly on its back because the wing airfoil is rigid. It can create lift in the "wrong" direction if the angle of attack is high enough in the proper direction. Competitive acrobatic aircraft use airfoils that are nearly symmetric (same curve on top and bottom) for better performance up-side-down. Few wings are actually flat on the bottom; they just have less curve than on the top. Similarly, a sailboat can tack upwind by positioning the sail so the wind blows on the opposite surface, while positioning the sail over the hull so there is a net lift force in the desired direction. The sail then acts like the bottom surface of the airpalne as it fills on the opposite side. The sail assumes the same shape on the other side, and behaves like a symmetric airfoil. I'm wondering if the same is true for sailing: would it be possible to sail against the wind with a sail that's a rigid flat surface, not an airfoil-shaped piece of cloth? An airplane uses the engine to pull the airplane through the air, so lift can be created by a less efficient surface. A sailboat depends on the wind to provide the propulsive force, so it is much more difficult. While you might be able to make some net upwind progress with such a device, it would be slow and inefficient. |
Sailing against the wind depends on airfoil shape?
So
I'm wondering if the same is true for sailing: yes. |
Sailing against the wind depends on airfoil shape?
Yes, but slowly - a flat surface is not an efficient aerofoil.
not necessarily. at certain a of a it is more efficient. an s-shaped airfoil is more efficient. |
Sailing against the wind depends on airfoil shape?
If you understand a wing you are 3/4 of the way there.
no, 100%. airfoils don't know whether they are vertical or horizontal. |
Sailing against the wind depends on airfoil shape?
Of course it generates drag as well;
just as true of a sail as an aircraft wing. For the same reasons. |
Sailing against the wind depends on airfoil shape?
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Sailing against the wind depends on airfoil shape?
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An airplane uses the engine to pull the airplane through the air, so lift can
be created by a less efficient (sic) surface. A sailboat depends on the wind to provide the propulsive force, so it is much more difficult. An aircraft wing is one hell of a lot more efficient at creating lift as compared to drag than a sailboat sail is. A sail has a pretty miserable L/D ratio, but a sail doesn't weigh much, it can be shortened for greater wind speeds, or more sail put up for lesser wind speeds, can be stored easily, costs less and a whole bunch of other things practical on a sailboat. |
On 14 Aug 2004 12:40:52 GMT, (JAXAshby) wrote:
If you understand a wing you are 3/4 of the way there. no, 100%. airfoils don't know whether they are vertical or horizontal. So? so, if you undestand a wing you 100% of the way there, not 3/4. The keel must be taken into consideration when sailing upwind. Airplanes move in one medium, sailboats move in two. Jack __________________________________________________ Jack Dale Swiftsure Sailing Academy Director/ISPA and CYA Instructor http://www.swiftsuresailing.com Phone: 1 (877) 470-SAIL (toll free) __________________________________________________ |
Thanks a lot for the illuminating answers. I read somewhere that the
"sail-as-airfoil" trick is a rather recent one, and that formerly people would just let the wind push them around. Is that true, and if yes, how recent is the invention? Thanks, Axel |
no, the keel has not a thing to do with understanding how a sail works.
nothing. it does have something to do with how a sailboat works, but not a thing on how a sail works. If you understand a wing you are 3/4 of the way there. no, 100%. airfoils don't know whether they are vertical or horizontal. So? so, if you undestand a wing you 100% of the way there, not 3/4. The keel must be taken into consideration when sailing upwind. Airplanes move in one medium, sailboats move in two. Jack _________________________________________________ _ Jack Dale Swiftsure Sailing Academy Director/ISPA and CYA Instructor http://www.swiftsuresailing.com Phone: 1 (877) 470-SAIL (toll free) _________________________________________________ _ |
sails always worked as sails work. the thinking about them has changed, but
airfoils are airfoils, and have been since birds learned to fly a bit back. Thanks a lot for the illuminating answers. I read somewhere that the "sail-as-airfoil" trick is a rather recent one, and that formerly people would just let the wind push them around. Is that true, and if yes, how recent is the invention? Thanks, Axel |
Are you claiming the keel has nothing to do with going upwind? How jaxian of
you to say that. "JAXAshby" wrote in message ... no, the keel has not a thing to do with understanding how a sail works. nothing. it does have something to do with how a sailboat works, but not a thing on how a sail works. If you understand a wing you are 3/4 of the way there. no, 100%. airfoils don't know whether they are vertical or horizontal. So? so, if you undestand a wing you 100% of the way there, not 3/4. The keel must be taken into consideration when sailing upwind. Airplanes move in one medium, sailboats move in two. Jack _________________________________________________ _ Jack Dale Swiftsure Sailing Academy Director/ISPA and CYA Instructor http://www.swiftsuresailing.com Phone: 1 (877) 470-SAIL (toll free) _________________________________________________ _ |
Square-rigged boats could sail no higher than a beam reach. However, the sails
were not flat, and they were trimmed appropriately to allow the boats to be sailed other than dead downwind. I don't recall the date triangular sails were invented, but they were the dawn of upwind sailing in the west; junk rigs enabled upwind sailing in the east. "Axel Boldt" wrote... Thanks a lot for the illuminating answers. I read somewhere that the "sail-as-airfoil" trick is a rather recent one, and that formerly people would just let the wind push them around. Is that true, and if yes, how recent is the invention? |
On 14 Aug 2004 17:19:25 GMT, (JAXAshby) wrote:
no, the keel has not a thing to do with understanding how a sail works. nothing. it does have something to do with how a sailboat works, but not a thing on how a sail works. You are correct. But the initial posting was :"I'm trying to understand how a boat can sail against the wind." Understanding the sail as airfoil is not 100% of the answer. One must also consider the effect of the keel. Jack __________________________________________________ Jack Dale Swiftsure Sailing Academy Director/ISPA and CYA Instructor http://www.swiftsuresailing.com Phone: 1 (877) 470-SAIL (toll free) __________________________________________________ |
no [head shakes], jeffies. I did not say that. please ask your wife to read
it for you. Are you claiming the keel has nothing to do with going upwind? How jaxian of you to say that. "JAXAshby" wrote in message ... no, the keel has not a thing to do with understanding how a sail works. nothing. it does have something to do with how a sailboat works, but not a thing on how a sail works. If you understand a wing you are 3/4 of the way there. no, 100%. airfoils don't know whether they are vertical or horizontal. So? so, if you undestand a wing you 100% of the way there, not 3/4. The keel must be taken into consideration when sailing upwind. Airplanes move in one medium, sailboats move in two. Jack _________________________________________________ _ Jack Dale Swiftsure Sailing Academy Director/ISPA and CYA Instructor http://www.swiftsuresailing.com Phone: 1 (877) 470-SAIL (toll free) _________________________________________________ _ |
Axel Boldt wrote:
Thanks a lot for the illuminating answers. I read somewhere that the "sail-as-airfoil" trick is a rather recent one, and that formerly people would just let the wind push them around. Is that true, and if yes, how recent is the invention? Thanks, Axel umm... it's probably a "AD" date rather than a "BC" but there are designs of sails which are pretty ancient that do run as proper airfoils, not just a drag device. The Arab Lateen rigs are I think pretty old, as an example. Remember what Cook found in the south seas? The native canoes "went about three miles to our two" - European rigs were not the hottest thing at the time. Andy. |
my statement was in respone to the secondary posting that said understanding
wing arifoils was 3/4 of understanding sail airfoils. no, the keel has not a thing to do with understanding how a sail works. nothing. it does have something to do with how a sailboat works, but not a thing on how a sail works. You are correct. But the initial posting was :"I'm trying to understand how a boat can sail against the wind." Understanding the sail as airfoil is not 100% of the answer. One must also consider the effect of the keel. Jack _________________________________________________ _ Jack Dale Swiftsure Sailing Academy Director/ISPA and CYA Instructor http://www.swiftsuresailing.com Phone: 1 (877) 470-SAIL (toll free) _________________________________________________ _ |
Axel
First please realize that the brother Wright had to reinvent aerodymanics whent hey found out the all the material that they had collected was junk. (Mr. langley didn't like them very much.) They were also the first people to build and used a wind tunnel (they built three in total) to any advantage. The "sail as a foil" convention can not really be tied down easily, but the oldest paper in my library is from the mid-teens and contains some things that are now known to be in error. A book that I have was written in the mid-twenties and it is hard to tell the difference between the going to weather part of this book and my newer ones. From the things that I was taught by much older people about a half a century ago, the understanding of the function both square and fore-and-aft rigged sails is not recent, but the language to describe it is (realiviely). Matt Colie Lifelong Waterman, Licensed Mariner and Perpetual Sailor Axel Boldt wrote: Thanks a lot for the illuminating answers. I read somewhere that the "sail-as-airfoil" trick is a rather recent one, and that formerly people would just let the wind push them around. Is that true, and if yes, how recent is the invention? Thanks, Axel |
John,
This is a common mis-conception. The truth is that most merchant vessels could do only do 160 deg between tacks, but many other square sails could do well better than that. It just took a lot of manpower and money to handle the extra rigging that would tighten the luff. Vikings with wool sails reports taht they could manage about 120 and that was not equaled until the fore and aft rigged schooners appeared in the early nineteenth century. Matt Colie Lifelong Waterman, Licensed Mariner and Perpetual Sailor John Weiss wrote: Square-rigged boats could sail no higher than a beam reach. However, the sails were not flat, and they were trimmed appropriately to allow the boats to be sailed other than dead downwind. I don't recall the date triangular sails were invented, but they were the dawn of upwind sailing in the west; junk rigs enabled upwind sailing in the east. "Axel Boldt" wrote... Thanks a lot for the illuminating answers. I read somewhere that the "sail-as-airfoil" trick is a rather recent one, and that formerly people would just let the wind push them around. Is that true, and if yes, how recent is the invention? |
Jax,
Maybe I didn't word it clearly. I said "A boat goes to windward by generating lift from its sail, just like an aircraft's wing. If you understand a wing you are 3/4 of the way there." I meant 3/4 of the way towards understanding how a boat goes to windward - not 3/4 of understanding sail airfoils. The other 1/4 being to turn it on its end and match it with a keel, centreboard etc. But this isn't helping Axel very much. Do you know of any good online diagrams we could point him at? I admit I can't be bothered to search for one... And. JAXAshby wrote: my statement was in respone to the secondary posting that said understanding wing arifoils was 3/4 of understanding sail airfoils. |
andy, lift is lift. airfoil or water foil or ethylenglchol or methanol or
whatever. Jax, Maybe I didn't word it clearly. I said "A boat goes to windward by generating lift from its sail, just like an aircraft's wing. If you understand a wing you are 3/4 of the way there." I meant 3/4 of the way towards understanding how a boat goes to windward - not 3/4 of understanding sail airfoils. The other 1/4 being to turn it on its end and match it with a keel, centreboard etc. But this isn't helping Axel very much. Do you know of any good online diagrams we could point him at? I admit I can't be bothered to search for one... And. JAXAshby wrote: my statement was in respone to the secondary posting that said understanding wing arifoils was 3/4 of understanding sail airfoils. |
On 16 Aug 2004 01:38:25 GMT, (JAXAshby) wrote:
andy, lift is lift. airfoil or water foil or ethylenglchol or methanol or whatever. Sails are asymmetrical, keels are symmetrical. Makes a difference. But to sail upwind effectively you need both sails and a keel. Ergo - sails are not 100%. Downwind is another issue. I watch Lasers raise their keels on a leeward leg. Jack __________________________________________________ Jack Dale Swiftsure Sailing Academy Director/ISPA and CYA Instructor http://www.swiftsuresailing.com Phone: 1 (877) 470-SAIL (toll free) __________________________________________________ |
jack, you also need air breath, a hull that floats, a rudder, sunscreen
protection and maybe condoms if you might get lucky. However, none of those in anyway affect how the airfoil on a sail works, which is 100% the same as the way the the airfoil on a wing works. andy, lift is lift. airfoil or water foil or ethylenglchol or methanol or whatever. Sails are asymmetrical, keels are symmetrical. Makes a difference. But to sail upwind effectively you need both sails and a keel. Ergo - sails are not 100%. Downwind is another issue. I watch Lasers raise their keels on a leeward leg. Jack _________________________________________________ _ Jack Dale Swiftsure Sailing Academy Director/ISPA and CYA Instructor http://www.swiftsuresailing.com Phone: 1 (877) 470-SAIL (toll free) _________________________________________________ _ |
You guys are getting boring. Maybe the two of you can get together by
ganging up on me! :-) "JAXAshby" wrote in message ... jack, you also need air breath, a hull that floats, a rudder, sunscreen protection and maybe condoms if you might get lucky. However, none of those in anyway affect how the airfoil on a sail works, which is 100% the same as the way the the airfoil on a wing works. andy, lift is lift. airfoil or water foil or ethylenglchol or methanol or whatever. Sails are asymmetrical, keels are symmetrical. Makes a difference. But to sail upwind effectively you need both sails and a keel. Ergo - sails are not 100%. Downwind is another issue. I watch Lasers raise their keels on a leeward leg. Jack _________________________________________________ _ Jack Dale Swiftsure Sailing Academy Director/ISPA and CYA Instructor http://www.swiftsuresailing.com Phone: 1 (877) 470-SAIL (toll free) _________________________________________________ _ |
The invention goes back at least as far as the "Boomarang", Chinese Junk
Rig, Lateen Rig, Polynesian Claw Sail; All before the time of Common Age. The Europeans didn't have knowledge of it until 1000's of years later Ole Thom |
Hey Guys,
Don't you know Jax well enough by now. If he has an answer, he'll sure hell modify the question to fit his answer. Re-quoting the original question does absolutely no good. OT |
if you know the olde fart well enough, you notice olde thom doesn't make much
sense in any post after about 4:00 in the afternoon. From: (Thom Stewart) Date: 8/17/2004 ------------------ 10:26 PM -------------------- Eastern Daylight Time Message-id: Hey Guys, Don't you know Jax well enough by now. If he has an answer, he'll sure hell modify the question to fit his answer. Re-quoting the original question does absolutely no good. OT |
The answer to your question, is yes. Sails are made from dacron for ease of
handling & shortening, and cost. Many examples of rigid-wing vessels exist, I suggest doing a search on that. They often use fairings at the leading edge, or movable trailing edges to fine tune the foil. An aircraft can fly inverted, because its angle-of-attack changes to suit the correspondingly lower efficiency of the foil in this position. As others have noted, acrobatic craft often employ nearly symmetrical foils for this reason. A normally profiled foil will fly inverted, but inefficiently, and at a much lower VMG due to the increased drag from the higher angle of attack. Try some "Bernoulli experiments for kids",and you will reach a better understanding. "Axel Boldt" wrote in message m... Hi, I'm trying to understand how a boat can sail against the wind. Explanations on the internet usually go like this: "The sail has an airfoil shape, the air goes faster on one side than on the other, creating lift by Bernouilli's principle." But I know that for flying planes, the wing's airfoil shape is not essential (otherwise planes couldn't fly on their back): it's the angle of attack that matters. So I'm wondering if the same is true for sailing: would it be possible to sail against the wind with a sail that's a rigid flat surface, not an airfoil-shaped piece of cloth? Thanks, Axel |
just dipsquats who pretend to know things they utterly and knowingly ignorant
of. ac, you lack totally and utterly ANY understanding of what is going on -- airfoilwise -- on either or, same same, a sailboat sail. ac, the ng askes that you NEVER post on this subject again. for the obvious reason. Jax, Do you intend to annoy people, or is it just by accident? |
JAXAshby wrote:
ac, you lack totally and utterly ANY understanding of what is going on -- airfoilwise -- on either or, same same, a sailboat sail. ac, the ng askes that you NEVER post on this subject again. for the obvious reason. Jax, Do you intend to annoy people, or is it just by accident? |
I beg to differ.
And someone with the necessary training to make a statement such as yours would use far more decorum. Love the 100% refutations! (as above). They really get your point across. Not quite the point you think you're making, though... "JAXAshby" wrote in message ... ac, you lack totally and utterly ANY understanding of what is going on -- airfoilwise -- on either or, same same, a sailboat sail. ac, the ng askes that you NEVER post on this subject again. for the obvious reason. From: "AC" Date: 8/21/2004 5:50 PM Eastern Daylight Time Message-id: The answer to your question, is yes. Sails are made from dacron for ease of handling & shortening, and cost. Many examples of rigid-wing vessels exist, I suggest doing a search on that. They often use fairings at the leading edge, or movable trailing edges to fine tune the foil. An aircraft can fly inverted, because its angle-of-attack changes to suit the correspondingly lower efficiency of the foil in this position. As others have noted, acrobatic craft often employ nearly symmetrical foils for this reason. A normally profiled foil will fly inverted, but inefficiently, and at a much lower VMG due to the increased drag from the higher angle of attack. Try some "Bernoulli experiments for kids",and you will reach a better understanding. "Axel Boldt" wrote in message om... Hi, I'm trying to understand how a boat can sail against the wind. Explanations on the internet usually go like this: "The sail has an airfoil shape, the air goes faster on one side than on the other, creating lift by Bernouilli's principle." But I know that for flying planes, the wing's airfoil shape is not essential (otherwise planes couldn't fly on their back): it's the angle of attack that matters. So I'm wondering if the same is true for sailing: would it be possible to sail against the wind with a sail that's a rigid flat surface, not an airfoil-shaped piece of cloth? Thanks, Axel |
Are you the "ng"? I hope not, since if you are, that would make you some
sort of one-sentence-replying dictator, expecting everyone else to understand your prophetic one-liners. "JAXAshby" wrote in message ... ac, you lack totally and utterly ANY understanding of what is going on -- airfoilwise -- on either or, same same, a sailboat sail. ac, the ng askes that you NEVER post on this subject again. for the obvious reason. From: "AC" Date: 8/21/2004 5:50 PM Eastern Daylight Time Message-id: The answer to your question, is yes. Sails are made from dacron for ease of handling & shortening, and cost. Many examples of rigid-wing vessels exist, I suggest doing a search on that. They often use fairings at the leading edge, or movable trailing edges to fine tune the foil. An aircraft can fly inverted, because its angle-of-attack changes to suit the correspondingly lower efficiency of the foil in this position. As others have noted, acrobatic craft often employ nearly symmetrical foils for this reason. A normally profiled foil will fly inverted, but inefficiently, and at a much lower VMG due to the increased drag from the higher angle of attack. Try some "Bernoulli experiments for kids",and you will reach a better understanding. "Axel Boldt" wrote in message om... Hi, I'm trying to understand how a boat can sail against the wind. Explanations on the internet usually go like this: "The sail has an airfoil shape, the air goes faster on one side than on the other, creating lift by Bernouilli's principle." But I know that for flying planes, the wing's airfoil shape is not essential (otherwise planes couldn't fly on their back): it's the angle of attack that matters. So I'm wondering if the same is true for sailing: would it be possible to sail against the wind with a sail that's a rigid flat surface, not an airfoil-shaped piece of cloth? Thanks, Axel |
ac, beg all you want, but you learned what little have from a popular science
magazine article long ago. you are an idiot. would you feel better if the world referred to you as a "special learning" student instead? You know, decorum and all. From: "AC" Date: 8/22/2004 11:23 PM Eastern Daylight Time Message-id: I beg to differ. And someone with the necessary training to make a statement such as yours would use far more decorum. Love the 100% refutations! (as above). They really get your point across. Not quite the point you think you're making, though... "JAXAshby" wrote in message ... ac, you lack totally and utterly ANY understanding of what is going on -- airfoilwise -- on either or, same same, a sailboat sail. ac, the ng askes that you NEVER post on this subject again. for the obvious reason. From: "AC" Date: 8/21/2004 5:50 PM Eastern Daylight Time Message-id: The answer to your question, is yes. Sails are made from dacron for ease of handling & shortening, and cost. Many examples of rigid-wing vessels exist, I suggest doing a search on that. They often use fairings at the leading edge, or movable trailing edges to fine tune the foil. An aircraft can fly inverted, because its angle-of-attack changes to suit the correspondingly lower efficiency of the foil in this position. As others have noted, acrobatic craft often employ nearly symmetrical foils for this reason. A normally profiled foil will fly inverted, but inefficiently, and at a much lower VMG due to the increased drag from the higher angle of attack. Try some "Bernoulli experiments for kids",and you will reach a better understanding. "Axel Boldt" wrote in message om... Hi, I'm trying to understand how a boat can sail against the wind. Explanations on the internet usually go like this: "The sail has an airfoil shape, the air goes faster on one side than on the other, creating lift by Bernouilli's principle." But I know that for flying planes, the wing's airfoil shape is not essential (otherwise planes couldn't fly on their back): it's the angle of attack that matters. So I'm wondering if the same is true for sailing: would it be possible to sail against the wind with a sail that's a rigid flat surface, not an airfoil-shaped piece of cloth? Thanks, Axel |
certainly no expects you to understand, ac, one liners or ten thousand.
From: "AC" Date: 8/23/2004 12:13 AM Eastern Daylight Time Message-id: Are you the "ng"? I hope not, since if you are, that would make you some sort of one-sentence-replying dictator, expecting everyone else to understand your prophetic one-liners. "JAXAshby" wrote in message ... ac, you lack totally and utterly ANY understanding of what is going on -- airfoilwise -- on either or, same same, a sailboat sail. ac, the ng askes that you NEVER post on this subject again. for the obvious reason. From: "AC" Date: 8/21/2004 5:50 PM Eastern Daylight Time Message-id: The answer to your question, is yes. Sails are made from dacron for ease of handling & shortening, and cost. Many examples of rigid-wing vessels exist, I suggest doing a search on that. They often use fairings at the leading edge, or movable trailing edges to fine tune the foil. An aircraft can fly inverted, because its angle-of-attack changes to suit the correspondingly lower efficiency of the foil in this position. As others have noted, acrobatic craft often employ nearly symmetrical foils for this reason. A normally profiled foil will fly inverted, but inefficiently, and at a much lower VMG due to the increased drag from the higher angle of attack. Try some "Bernoulli experiments for kids",and you will reach a better understanding. "Axel Boldt" wrote in message om... Hi, I'm trying to understand how a boat can sail against the wind. Explanations on the internet usually go like this: "The sail has an airfoil shape, the air goes faster on one side than on the other, creating lift by Bernouilli's principle." But I know that for flying planes, the wing's airfoil shape is not essential (otherwise planes couldn't fly on their back): it's the angle of attack that matters. So I'm wondering if the same is true for sailing: would it be possible to sail against the wind with a sail that's a rigid flat surface, not an airfoil-shaped piece of cloth? Thanks, Axel |
Oooohh, great - name calling. Now, we're really expressing ourselves well,
aren't we? I can tell the limitation of your cred's by your grammar. I bet you can't tell what mine are... You can click on as many hyperlinks as you want, and be a wannabe pilot all your life, but still not receive basic physics training, that's a two-way experience. "JAXAshby" wrote in message ... just dipsquats who pretend to know things they utterly and knowingly ignorant of. ac, you lack totally and utterly ANY understanding of what is going on -- airfoilwise -- on either or, same same, a sailboat sail. ac, the ng askes that you NEVER post on this subject again. for the obvious reason. Jax, Do you intend to annoy people, or is it just by accident? |
hehehe, I bet the group can work out who is the faker...
Go back & hide behind your PC. You obviously aren't supplying the group, or anyone else anything of use, nor substance. Why not cut & paste your reactionary diatribe in another newsgroup? It'll make just as much sense there! "JAXAshby" wrote in message ... ac, beg all you want, but you learned what little have from a popular science magazine article long ago. you are an idiot. would you feel better if the world referred to you as a "special learning" student instead? You know, decorum and all. From: "AC" Date: 8/22/2004 11:23 PM Eastern Daylight Time Message-id: I beg to differ. And someone with the necessary training to make a statement such as yours would use far more decorum. Love the 100% refutations! (as above). They really get your point across. Not quite the point you think you're making, though... "JAXAshby" wrote in message ... ac, you lack totally and utterly ANY understanding of what is going on -- airfoilwise -- on either or, same same, a sailboat sail. ac, the ng askes that you NEVER post on this subject again. for the obvious reason. From: "AC" Date: 8/21/2004 5:50 PM Eastern Daylight Time Message-id: The answer to your question, is yes. Sails are made from dacron for ease of handling & shortening, and cost. Many examples of rigid-wing vessels exist, I suggest doing a search on that. They often use fairings at the leading edge, or movable trailing edges to fine tune the foil. An aircraft can fly inverted, because its angle-of-attack changes to suit the correspondingly lower efficiency of the foil in this position. As others have noted, acrobatic craft often employ nearly symmetrical foils for this reason. A normally profiled foil will fly inverted, but inefficiently, and at a much lower VMG due to the increased drag from the higher angle of attack. Try some "Bernoulli experiments for kids",and you will reach a better understanding. "Axel Boldt" wrote in message om... Hi, I'm trying to understand how a boat can sail against the wind. Explanations on the internet usually go like this: "The sail has an airfoil shape, the air goes faster on one side than on the other, creating lift by Bernouilli's principle." But I know that for flying planes, the wing's airfoil shape is not essential (otherwise planes couldn't fly on their back): it's the angle of attack that matters. So I'm wondering if the same is true for sailing: would it be possible to sail against the wind with a sail that's a rigid flat surface, not an airfoil-shaped piece of cloth? Thanks, Axel |
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