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Site is up on Wingsails

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Created by NelsonFoils 9 months ago, 4 Nov 2017
NelsonFoils
145 posts
4 Nov 2017 8:24PM
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www.mwsails.com/wingsail-story

BSN101
WA, 1233 posts
4 Nov 2017 8:57PM
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WOW! I had forgotten about this one.

Whos gonna be first?

gavnwend
NSW, 953 posts
5 Nov 2017 2:06AM
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Thought l knew it all about sail design until l read the link.wow!

Ezric
NSW, 168 posts
5 Nov 2017 10:35AM
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Very interesting. I like the inflatable pocket. No more sinking sail.

Send one to Luderitz quickly for testing.

John340
QLD, 1808 posts
5 Nov 2017 9:55AM
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The finished product looks great.

I have a few questions
- what are the comparative sizes of current PWA race sails to the 4.5 & 5.8 MW Storm?
- similarly, what are the expected wind range for each sail for a 85kg sailor on a 110lit slalom board?
- have you or other sailors used the Storm for GPS sailing and is there any GPS data available for these sessions?
- is there any leach twist or is it not necessary?
- do you have any video of the sail in use?
- is the specification for the mast unique to the Storm or can current constant curve masts be used?
- how does the sail account for different boom heights or is there only one height available?
-

NelsonFoils
145 posts
5 Nov 2017 8:10AM
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Have a look on the mens facebook page :

www.facebook.com/stanislav.mostoviy

There you will find answers and some rigging and sailing video's .

joe windsurf
1344 posts
5 Nov 2017 9:13AM
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you ship from NJ ??
max sail is 5.8 meters ?
at that price does it come with mast ?
if not - flex, cc or hard top ??
if i visit Long Island or CT - can go to NJ and try one ??
thanks
joewindsurfer.com

cammd
QLD, 1771 posts
5 Nov 2017 6:05PM
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John340 said..




The finished product looks great.

I have a few questions
- what are the comparative sizes of current PWA race sails to the 4.5 & 5.8 MW Storm?
- similarly, what are the expected wind range for each sail for a 85kg sailor on a 110lit slalom board?
- have you or other sailors used the Storm for GPS sailing and is there any GPS data available for these sessions?
- is there any leach twist or is it not necessary?
- do you have any video of the sail in use?
- is the specification for the mast unique to the Storm or can current constant curve masts be used?
- how does the sail account for different boom heights or is there only one height available?
-


I was on the site early this morning and they had one of those chat pop up boxes. I asked a couple of the same questions so I can answer these few questions that I asked
Mast is 460m sdm not specific to the sail so you can use your own existing mast
boom height is adjustable like normal sails
I also questioned the zippers given every one of my board bag zippers fail over time or get seized , the response was they use marine grade zippers and in 5 years of testing no zipper failures or problems.
Price is in USD, they can ship internationally and thats all I asked

Nice to be able to chat with the manufacturer though or I assume it was as the person on the other end was knowledgeable about windsurfing

Chris 249
ACT, 1505 posts
5 Nov 2017 7:55PM
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If figure 2A is correct, why do all my boat sails with tufts show attached flow on the windward side? The flow is clearly NOT turbulent as your figure shows, even when using a single surface sail with no wide luff pocket.

If figure 2A is correct, then all the CFD programmes that sail designers use are wrong and all the tens of millions of dollars that have been spent developing yacht sails have been burned by morons. I know some of these guys and they are not morons, nor at the people who run wind tunnels and develop CFD programmes.

If twin-surface sails are so much better, why have they failed so often (and yes, I have raced against them, and beaten them)?

How have your sails done in competition? Surely they must be winning every race they entered if your claims are correct?

Here's some pics of very simple single-surface sails. Note the tufts streaming aft, showing that the flow over the windward side is not turbulent as shown in your diagram.









Chris 249
ACT, 1505 posts
5 Nov 2017 8:26PM
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Here's other single surface sails showing lots of tufts on the windward side, all streaming with no indication of the turbulence your figure shows.







Those tufts are just ribbons of cloth, lying in the airflow. If the airflow stalls, as shown in your diagram, then the tufts whirl around. These tufts are all lying back, showing non-turbulent flow over the windward side of the luff rather than the vortices and turbulent flow shown in your diagrams.

Ian K
NSW, 2688 posts
5 Nov 2017 9:17PM
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Chris 249 said..











How do those boats even work without battens?

Fig 2 A is just a little bit of artistic licence in the overpowered, backhanded situation. It's pretty well established that there are advantages to be had with wingsails on the faster sailing craft.




NelsonFoils
145 posts
5 Nov 2017 6:32PM
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As long as the Aoa is high there will be perfect airflow on single surface sails winfward site (as all sailers know ) but if you have to let go the leading adge collaps ---> center of lift travels back ! = no big problem on a boat but out of controle for windsurfers !

From the site :

In general, sailing with wing is no different than with conventional sail. There is no adaptation period or change in sailing technique. Wing sail delivers better performance in all aspects. All lessons learned with regular sail will be greatly enhanced using wing. Wing doesn't have fatigue as traditional sail and it's very predictable in all conditions. Because wing has fixed center of lift, ride is much more stable and much easier. There is no back hand and back leg pressure, no leading edge stall, no sudden loss or gain in power. In fact it is so easy to handle that you will never shred skin on your hands. Wing easily outperforms any traditional sail of equal size, especially cross and upwind. Wing has near unlimited wind range. I mean, if you take wing on 45kt wind, you probably experience more problems with aerodynamics of your board and your own body than with wing. We all know that jibe is very difficult and advanced move and probably we all experienced the fact that in different wind condition jibe technique is different. This happens because traditional sail has different behavior on different conditions. Regular sail needs to be tuned up according to wind and water conditions, and with different tune it has different characteristics. Wing has only one setting for all conditions. Wing delivers that same performance and behavior in all winds. It does exactly what it is designed to do, pull forward. Compare to conventional sail, with wing it much easier to master perfect jibe as well as other sailing techniques.Is wing faster?Strait answer YES. Wing easily outperforms traditional sail of equal size with same sailor, board, mast, boom, and fin. But, if you expect that sailing the wing will instantly make you fastest guy on the bay, probably not. There will be a guy who is heavier, has bigger sail, smaller board, better skills, smaller fin, etc. and he will be faster than you sometimes. But you will go faster with wing than with your regular sail of equal size. Also because lift component is directed more forward you can use smaller fin. Coefficient of lift that wing generates is just 0.2 better than traditional sail generates at its best. Also wing has no fatigue. If you can utilize and use properly all advantages of the wing, than you will be faster than others. Who should consider wing sailing?Sailors who consider getting wing, should more take in account such values as stability, reliable ride in all winds, better performance, freedom of sailing, and perfecting sailing techniques. When sailing on a good windy day, you will see people go over 2- 3 conventional sail sizes, while you just having more fun with more wind on your wing. With wing you can go safe as fast as you can and as slow as you want. Wing is an engine, not a crazy machine.

Chris 249
ACT, 1505 posts
5 Nov 2017 9:43PM
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Ian K said..


Chris 249 said..













How do those boats even work without battens?

Fig 2 A is just a little bit of artistic licence in the overpowered, backhanded situation. It's pretty well established that there are advantages to be had with wingsails on the faster sailing craft.





But here's the world champion Moth- no wing, and it goes faster than the wings. The same thing happens in the A Class cats, and like the Moths they are normally faster than a Formula board.


As Tom Speer, a Boeing wing designer and one of the mainstays of the Oracle America's Cup wingsail design team, says "There's nothing magical about a rigid wingsail. The soft sail rig on USA 17 (ie the unlimited 90 foot tri that won the America's Cup) was faster than the wingsail in some conditions. Whether a wing or soft rig will be faster depends on the class constraints and the sailing conditions." For example, one major reason the AC boats have wings is because the structural loadings on a conventional vang and mainsheet are too much of a problem.

The only "small" boat in which wingsails are proven to be faster is the 25 foot C Class cat, but by modern standards they lack power downwind due to class rules; as Tom says. "their area limit makes it hard for them to be fully powered up on the runs." It's interesting to see that when a recent C Class cat raced against modern production cats with soft sails, the 25 foot C Class with its hyper-expensive wingmast was killed downwind by cheap 20-16 foot cats with spinnakers and "soft" sails.

Despite the common belief that wingsails are more efficient and new, in many ways they are less efficient and they have been around for very close to 100 years, and almost universally failing. They simply do not work as well in most situations.

There's a lot of speed sailing going on. Why isn't this wingsail proving its performance on the water?

Chris 249
ACT, 1505 posts
5 Nov 2017 9:54PM
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NelsonFoils said..
As long as the Aoa is high there will be perfect airflow on single surface sails winfward site (as all sailers know ) but if you have to let go the leading adge collaps ---> center of lift travels back ! = no big problem on a boat but out of controle for windsurfers !

From the site :

In general, sailing with wing is no different than with conventional sail. There is no adaptation period or change in sailing technique. Wing sail delivers better performance in all aspects.

So you are saying that Boeing wing designers from America's Cup teams, MIT aerodynamics professors with world flight records and America's Cup experience are wrong? Really?

These guys tell us that wingsails do NOT deliver better performance in all aspects. Do you really think that Boeings are badly designed, that world record holding wings are badly designed and that the hundreds of millions of dollars the AC guys spent are all wasted and they have no idea of what they are doing?

All lessons learned with regular sail will be greatly enhanced using wing. Wing doesn't have fatigue as traditional sail and it's very predictable in all conditions. Because wing has fixed center of lift, ride is much more stable and much easier. There is no back hand and back leg pressure, no leading edge stall, no sudden loss or gain in power. In fact it is so easy to handle that you will never shred skin on your hands. Wing easily outperforms any traditional sail of equal size, especially cross and upwind. Wing has near unlimited wind range. I mean, if you take wing on 45kt wind, you probably experience more problems with aerodynamics of your board and your own body than with wing. We all know that jibe is very difficult and advanced move and probably we all experienced the fact that in different wind condition jibe technique is different. This happens because traditional sail has different behavior on different conditions. Regular sail needs to be tuned up according to wind and water conditions, and with different tune it has different characteristics. Wing has only one setting for all conditions.

So the C Class and America's Cup designers have been wasting the enormous amounts of money and effort they put into trailing edge flaps and twist controls? Really? They have been spending 50 years and hundreds of millions of dollars getting it wrong every single time?

Why did they do that? Why did Lindsay Cunningham, for instance, spend so much of his time working on Victoria 150's bellcranks? Do you think wingsail pioneer Lindsay is a fool?


Wing delivers that same performance and behavior in all winds. It does exactly what it is designed to do, pull forward. Compare to conventional sail, with wing it much easier to master perfect jibe as well as other sailing techniques.Is wing faster?Strait answer YES. Wing easily outperforms traditional sail of equal size with same sailor, board, mast, boom, and fin. But, if you expect that sailing the wing will instantly make you fastest guy on the bay, probably not. There will be a guy who is heavier, has bigger sail, smaller board, better skills, smaller fin, etc. and he will be faster than you sometimes. But you will go faster with wing than with your regular sail of equal size. Also because lift component is directed more forward you can use smaller fin. Coefficient of lift that wing generates is just 0.2 better than traditional sail generates at its best. Also wing has no fatigue. If you can utilize and use properly all advantages of the wing, than you will be faster than others. Who should consider wing sailing?Sailors who consider getting wing, should more take in account such values as stability, reliable ride in all winds, better performance, freedom of sailing, and perfecting sailing techniques. When sailing on a good windy day, you will see people go over 2- 3 conventional sail sizes, while you just having more fun with more wind on your wing. With wing you can go safe as fast as you can and as slow as you want. Wing is an engine, not a crazy machine.



If you are right, then people who design wings and wingsails are wrong - even the ones who are involved in enormous America's Cup campaigns. They say that wingsails are NOT always superior, and that they DO need to be tuned - which is why they spend enormous effort on flaps and twist. All that effort in tests, all those years of experience, all those Formula 1 and Boeing and world record aerodynamics experts involved, and still get it completely wrong? Really????

Do you really think that people like Lindsay Cunningham have been lying all this time when they talk about wingsail controls and their effects?

Orange Whip
QLD, 416 posts
5 Nov 2017 9:00PM
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Any chance of some video of the wings in action and some testimonials from those that have used them?

NelsonFoils
145 posts
5 Nov 2017 7:07PM
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on :

www.facebook.com/stanislav.mostoviy

Video's of testing and lots of info on the wing

NelsonFoils
145 posts
5 Nov 2017 7:18PM
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Do you really think that people like Lindsay Cunningham have been lying all this time when they talk about wingsail controls and their effects?


I don't think anybody is lying , I only know , after 46 years of sailing and windsurfing : No Control = No Speed , No Fun , for us mortels with a small hobby budget and this new wingsail is the biggest step in years ...

Its is not a $ millions sponsered project with tons of carbon and lots of controls where you have to be a "BIKER" to win a race .
It's made for having fun ( one sail per session ) with a sail with automatic gearbox ...

BSN101
WA, 1233 posts
5 Nov 2017 7:37PM
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This has to go on a foil board!

Such a a great journey to finally be able to offer something new to us.

Not a multi million $ corp with R&D in 5star Hotel.

A fellow sailer with an idea and ability determination to follow it through, well done.

To to get it out in the market place in Aust we need to see it in the flesh, that's the hard bit.

NelsonFoils
145 posts
5 Nov 2017 7:48PM
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They ship world wide ...


www.mwsails.com/shop

CJW
NSW, 1446 posts
5 Nov 2017 11:34PM
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I don't think anyone could realistically argue with a straight face that in 99.9% of conditions a wing sail isn't going to be more efficient on a craft that develops high apparent wind, IE an AC50. There are simply too many efficiency gains to ignore in something that can travel 3 or 4 times the windspeed, a soft sail isn't going to be even in the same league. However, as stated above to maintain this efficiency requires extreme attention to twist, camber, AoA etc which is why they are effectively sailed by a computer; someone following what the computer tells them what to do anyway ;)

I think if someone developed a wing sail for a moth that had a huge, easily manageable tuning range it would be faster (if dialled in) in almost every condition...but it doesn't exist and poses lots of other problems like cost, longevity, how hard it is to tune etc. Just look at the effort they go to end plating sails to booms, decks, tramp aero etc all in the name of efficiency.

It's an interesting idea but i'm somewhat sceptical that this particular iteration of a wing much more efficient and has a sufficiently wide range that we'll all ditch out 5, 6, 7, 8... etc size sails. End of the day lift is in part a function of area and a 5.8 != 8.5 in 10kts, right?

John340
QLD, 1808 posts
6 Nov 2017 8:57AM
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I'd like to see a comparison with current PWA race sails on a 130 to 140 deg GPS speed course.

Chris 249
ACT, 1505 posts
6 Nov 2017 11:03AM
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Actually CJW, as already quoted, some of the AC wingsail designers DO in fact say that wingsails are NOT more efficient 99.9% of the time on such craft. To repeat, one of them said "There's nothing magical about a rigid wingsail. The soft sail rig on USA 17 (ie the unlimited 90 foot tri that won the America's Cup) was faster than the wingsail in some conditions. Whether a wing or soft rig will be faster depends on the class constraints and the sailing conditions."

To go into more detail from the same source, namely Tom Speer of Boeing and Oracle's America's Cup team, here's him writing about a windsurfer wingsail 15 years ago; "The typical argument goes something like this, "Aicraft wings are more efficient than sails. Aircraft airfoils are thick, double surface sections with modest camber. If a sail has thickness and a double surface it will be better than a single surface sail." The problem with this is that it doesn't take into account the different requirements for wings and sails. Plus, aerodynamic tests and calculations invariably show that for any given design point, a thinner airfoil will outperform a thick one. So why use a double surface sail?

I can only think of three reasons to have a thick foil:
1) The depth is necessary for structural stiffness,
2) A sharp leading edge loses out on leading edge suction, which results in an increase in drag,
3) The airfoil has to operate over a wide range of angles of attack.
Other than these factors, a thick section will generally have more drag and less maximum lift than a thin section.

An aircraft has to operate at a very low angle of attack in cruise because it can't change its wing area, the lift has to equal the weight, and the only way match the weight at high speed is to use a low lift coefficient. It's the optimization for cruise that drives the airfoils to a semi-symmetrical shape. However, for landing, airplane designers do everything they can to change to a highly cambered shape to produce high lift. And when the wing is configured for high lift, drag is actually helpful because it makes the landing glidepath steeper.

The requirements for a sail are quite different. The sail needs to produce high lift with as little drag as possible. The sail doesn't need to operate at low angles of attack because if you are that overpowered, you'll reduce the area by reefing. It's much better to use a smaller area near its maximum lift than a large area that's lightly loaded, because the smaller area has less parasite drag (less wetted surface). The sail does have to perform well for a certain range below max lift, but that range is nowhere near as great for a sail as for an aircraft.

The ideal shape for high lift would be a thin, highly cambered airfoil. This is provided very well by traditional single surface sails. Such a sail has a narrow groove, however. If the sail is operated at too high an angle of attack, the flow separates on the lee side and the sail stalls. If the sail is operated at too low an angle of attack, the flow will separate on the windward side, just behind the leading edge. This causes drag." (My emphasis)

Completely agree that wingsails require intense attention to twist and camber, which is why it's odd that this sail appears to ignore such things. It's also a concern that one diagram claims that the sail is more efficient because of the vector of forces normal to the windward side, when people like Mark Drela say that such things are irrelevant. Drela is an MIT professor of aerodynamics, who holds world records for human powered boats and aircraft as well as being involved in AC designs.

I may seem to be negative, but our MW sails mate insults people like world record holding aerodynamics professor Mark Drela and Boeing wing designers by claiming that they are "desperate" when they create AC wingsails. So basically, he reckons that he can get it right when the people who have been working on these rigs, often with enormous resources, have been getting it wrong for almost 50 years.....

One of the cards that wingsail promoters often play is claiming that people are too conservative to adopt their ideas. For one, that's pretty obviously wrong - look at the reaction to this sail both in the earlier thread here and in the Dutch thread some have linked to. Lots of people are excited.

The other issue is that wingsails have been around for eons (I had a mate who had one in about 1972) and SOME of them have been known to work in SOME boats for years, so they are far from new and therefore conservatism isn't the issue. What is the issue is that time and time and time again, we have been promised the earth by wingsail designers and they have failed to deliver. They also tend to promote their ideas by denigrating other rigs and designers, just as MW does with his sneering and dismissive references to the America's Cup and C Class wingsail designers.

I tend to think the conservatism comes from people who keep on thinking that wingsails are better even when the experts who design them say that thin sails are better in some ways.

Ben1973
71 posts
6 Nov 2017 8:21AM
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A wing sail if made right should always be faster at pretty much all wind speeds but they have many draw backs. The big one is they are much harder to get the best from.
To make one that really works on a windsurfer I think you are going to have to start from scratch and not try to work around existing mast and booms etc.
A wing sailed Moth would beat a conventional one but it's being held back by the sailor not the tech.

Gorgo
VIC, 3978 posts
6 Nov 2017 11:23AM
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Is there really a market for a sail that has 24 steps to rig it? (27 steps if you count all the pages).

Add to that the almost unreadable www.mwsails.com/wingsail-story and you'd have to be suspicious about the reality of the product.

Chris 249
ACT, 1505 posts
6 Nov 2017 11:29AM
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benpei said..
A wing sail if made right should always be faster at pretty much all wind speeds but they have many draw backs. The big one is they are much harder to get the best from.
To make one that really works on a windsurfer I think you are going to have to start from scratch and not try to work around existing mast and booms etc.
A wing sailed Moth would beat a conventional one but it's being held back by the sailor not the tech.



But that's not what the people who design the best wingsails say. So why should we assume that Boeing wing designers and aerodynamics professors who design America's Cup wingsails and world record breaking aircraft wings are wrong?

The Moth guys do NOT say that the Olympic gold medallists who use wingsails are holding them back as far as I can find out. If that was the case, why wouldn't Goodison etc get wingsails?

Ben1973
71 posts
6 Nov 2017 8:45AM
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Chris 249 said..

benpei said..
A wing sail if made right should always be faster at pretty much all wind speeds but they have many draw backs. The big one is they are much harder to get the best from.
To make one that really works on a windsurfer I think you are going to have to start from scratch and not try to work around existing mast and booms etc.
A wing sailed Moth would beat a conventional one but it's being held back by the sailor not the tech.




But that's not what the people who design the best wingsails say. So why should we assume that Boeing wing designers and aerodynamics professors who design America's Cup wingsails and world record breaking aircraft wings are wrong?

The Moth guys do NOT say that the Olympic gold medallists who use wingsails are holding them back as far as I can find out. If that was the case, why wouldn't Goodison etc get wingsails?


A wing sail is a very different beast to use, you may be the best sailer out there with a convention sail but that doesn't mean you can get the best out of a wing without a lot of pratice.

But again a wing sail should be faster IF made and used right

CJW
NSW, 1446 posts
6 Nov 2017 12:00PM
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I'm actually interested in what conditions they reckon the soft sail was actually faster on USA-17, I'm thinking it could only have been super marginal conditions such as <4kts true wind? As soon as you develop any meaningful apparent wind I find it very difficult to believe it would be faster. The biggest problem with huge soft sails is rig control, this is the advantage of a wing on say an AC50, they have massive control over the shape of the foil, you just don't have that with a soft sail and lack of foil control ultimately = drag, particularly on the more efficient high aspect rigs of today. I'd hate to see what the backstay and vang loads are on a big maxi like wild oats but it must be scary.

Even Moths' are encountering this issue now, the top guys now are running insane vang loads with ~50:1 purchase ratios, this is all in the name of rig control and efficiency right? I completely agree though that a wing sail on a moth is a ridiculous notion as it just introduces cost and complexity issues that are stupid for marginal gains.

Like I said I'd be very surprised if this particular design takes off as I don't see that any advantage outweighs the complexity and at the performance end of the scale the size range is too limited; maybe in the speed sailing world? Is it also that far removed from the top end race sails of today with their huge luff pockets (NP:Evo, Severne Reflex etal), sure slightly more rigid foil but is it any more efficient?

Chris 249
ACT, 1505 posts
6 Nov 2017 12:55PM
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Select to expand quote
benpei said..


Chris 249 said..



benpei said..
A wing sail if made right should always be faster at pretty much all wind speeds but they have many draw backs. The big one is they are much harder to get the best from.
To make one that really works on a windsurfer I think you are going to have to start from scratch and not try to work around existing mast and booms etc.
A wing sailed Moth would beat a conventional one but it's being held back by the sailor not the tech.






But that's not what the people who design the best wingsails say. So why should we assume that Boeing wing designers and aerodynamics professors who design America's Cup wingsails and world record breaking aircraft wings are wrong?

The Moth guys do NOT say that the Olympic gold medallists who use wingsails are holding them back as far as I can find out. If that was the case, why wouldn't Goodison etc get wingsails?




A wing sail is a very different beast to use, you may be the best sailer out there with a convention sail but that doesn't mean you can get the best out of a wing without a lot of pratice.

But again a wing sail should be faster IF made and used right



Again, Benpei, you're saying one thing and the aerodynamics guys who design the wingsails say another thing. Are you seriously claiming that you know more about wingsail design performance than the guys who get to spend tens of millions designing them, testing them, building them and sailing them?

Really?

Ian K
NSW, 2688 posts
6 Nov 2017 1:02PM
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Maybe we should look at birds and bats to get the tuning and construction issues out of the way. Archaeopteryx goes back 150 million years. That's a lot of time for experimenting and fine tuning. Bats only go back 50 million years, still enough time to perfect the single skin foil you'd reckon. The bird wing is 3d for a good percentage of the chord.


Bats do pretty well but.

Fastest- Peregrine falcon

"The peregrine is renowned for its speed, reaching over 320 km/h (200 mph) during its characteristic hunting stoop (high speed dive)"


Fastest over long distance: Great Snipe

"The birds traveled up to 4,200 miles (6,760 kilometers) at an average speed of 60 miles (97 kilometers) an hour."

Highest : R?ppell's griffon vulture

" A R?ppell's vulture was confirmed to have been ingested by a jet engine of an airplane flying over Abidjan, Ivory Coast on November 29, 1973 at an altitude of 11,300 m (37,000 ft)."






Chris 249
ACT, 1505 posts
6 Nov 2017 1:20PM
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Select to expand quote
CJW said..
I'm actually interested in what conditions they reckon the soft sail was actually faster on USA-17, I'm thinking it could only have been super marginal conditions such as
Even Moths' are encountering this issue now, the top guys now are running insane vang loads with ~50:1 purchase ratios, this is all in the name of rig control and efficiency right? I completely agree though that a wing sail on a moth is a ridiculous notion as it just introduces cost and complexity issues that are stupid for marginal gains.

Like I said I'd be very surprised if this particular design takes off as I don't see that any advantage outweighs the complexity and at the performance end of the scale the size range is too limited; maybe in the speed sailing world? Is it also that far removed from the top end race sails of today with their huge luff pockets (NP:Evo, Severne Reflex etal), sure slightly more rigid foil but is it any more efficient?


You're quite right about the structural issues, which as Tom Speer says, is the main reason why USA 17 went for the solid wingsail. But reading what experts like Speer say indicates that there's not really any reason why soft sails are only faster in super marginal conditions.

For example, Mark Drela has noted how adjustable good soft sails are, compared to wingsails; "Sails are wings in that they must provide lift with a minimum of drag, but their design and operation is much more complicated. There are many constraints, the major one being a maximum heeling moment the sail can be allowed to generate (analogous to limiting the root bending moment on a glider). Exceed this and the boat falls over. This is mainly what limits the sail's aspect ratio. "

"On an America's Cup boat (NOTE - THIS IS AN OLD QUOTE AND HE WAS REFERRING TO SOFT-SAILED MONO AC BOATS), each sail's shape can be altered considerably in many different ways by pulling on control ropes. Angle, twist, camber magnitude, camber distribution, are continually adjusted for each sail by a dedicated crew member. Makes a glider's trim flap look kinda trivial." ((My emphasis)

As Speer says on the same subject " A soft sail allows the possibility of changing the camber of a thin airfoil, which can greatly extend the low-drag range if done appropriately. So a thin airfoil which always has the appropriate camber shape dialed in at any given operating point will in general be superior to a thick airfoil." (my emphasis)

Professor Drela (who, by the way, is a hands on guy who has been aboard his own designs when they broke world records) says things such as "Thin airfoils are capable of the highest CL and CL/CD values,.....The airfoil has attached flow only in the range alpha = 11-15, or CL = 2.65 - 3.05 , in which the L/D is phenomenal" although he does note that this is within a narrow range of angles of attack. (my emphasis)

As Speer notes, the actual thickness of a wingsail is not always an advantage, and of course it comes with other issues like extra weight (which causes pitching);"The notion that because aircraft wings are very efficient and have thick sections, while sails have thin sections and generally lower lift/drag ratios, and therefore a thick sectioned sail will aerodynamically superior to a sail rig with a thin section simply because it is thick, is a mistaken idea. Airplanes have thick sections because they are structurally stronger and because they have to operate efficiently at low lift coefficients in cruise. This is generally not the case for most sailing craft, except for very high-speed craft like landyachts and iceboats." My emphasis. Note that the high-end landyachts and iceboats he normally refers to are capable of much higher speed than windsurfers,

So leading minds in the area have told us time and time and time again that there is no intrinsic reason why wingsails are faster.







Pacey
WA, 45 posts
6 Nov 2017 1:34PM
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From the web site - "This is first in the world asymmetrical, reversible, soft wing windsurfing sail."

No, Graeme Attey built a full double surface, reversible sail much like the MWsails wingsail in 1985, and it was sailed at the Useless Loop speed trials that year. I did couple of runs with it and although a pleasure to sail downwind, it wasn't any faster than the conventional rigs at the time (which weren't nearly as good as current rigs). Where that rig did excel was sailing upwind back to the start of the speed run - the sail was amazing, light in the hands, high and fast.

But this is the crux of the matter, thicker wings excel at low lift to drag ratios, whereas soft sails excel at generating high lift coefficients, which is what you need for reaching. USA 17 achieved high camber and high lift coefficients by having a two element rig with a slot between them, in the shot below you can see that the angle between the leading and trailing elements is about 45 degrees, and the overall camber in the base of the rig is probably more than you would get in a camber induced slalom sail.


So yes, the MWsails wingsail will be great upwind, but probably no faster (and possible worse) than current sails downwind, and probably have less low-end power and wind range due to lack of camber.

As to the high aspect ratio, there are good reasons why modern slalom sails have tended towards lower aspect ratios, it would be a good idea to study and understand why this has happened, and why lowering centre of effort may give benefits that outweigh the increase in induced drag.



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"Site is up on Wingsails" started by NelsonFoils