Soft Wing Sail

[Erwan]

Sorry, again I posted the msg before finishing.

So, In order to move from esoterical towards more rational understanding of fluid mecanics phenomenons, I ordered last saturday an used edition of:
"Foundations of Aerodynamics" "Bases of Aerodynamic Design"
Fourth Edition Arnold M. KUETHE & CHUEN-YEN CHOW.
I received it yesterday.. I hope it will help me to keep up with your expert's comments.

I was pleased to see reference of the S 1223, when I candidly started to investigate wing section for a A-Cat, I basically choosed wing sections from a aircraft-model list.
I choosed the S1223 for max lift
then the E 216 for max lift/drag ratio
and the MH 22 for minimun drag
with an ability to "morph" continuioulsy the wing from one section to another should provide the best all-round A-Cat sail, of course it was just to have the ideal and theorical benchmark not an actual project.

Now I have a lot of things to assimilate, but I will still scrutinize the forum
forum.

Cheers

EK

[tspeer]

Originally Posted by markdrela

Possibly. I tried adding more aft camber on the 5s airfoil, but it didn't get any better.

Actually, the 5s upper surface has only the slightest concavity. Coordinates attached. In any case, duplicating this sufficiently accurately on a soft sail with battens doesn't seem easy. One possibility might be to use lots of part-chord battens, from 90% to 100% chord, say, to enforce the aft camber.

Just for grins, I took the MLA5s coordinates, used QDES and MDES to smooth out some of the wiggles in the pressure distribution that were causing XFOIL fits, and then reflected the leading edge to form a wingmast with a thin sail behind it. The pressure distributions and boundary layer displacement are shown below.

As expected, the wingmast has a large separation bubble on the windward side. The pressures along the bubble are very similar to the hard windward surface, indicating that the design condition for the MLA5s is very near separation for the front half.

The lift of the wingmast section is fractionally less and the drag a couple counts more than the basic section, for 4% less L/D.

I think this shows that a wingmast/sail combination can come very close to the maximum achievable lift for a single element, provided that the lee contour can be shaped properly. That becomes a matter of what can be done with a membrane surface, since not all shapes are possible from a structural standpoint.

I think the key would be to use the three-dimensional aspects of the sail. Some leech tension could cause the slight cupping of the leech. The big problem is the flat shape in the aft half. Spanwise tension could help pull this area in. It's kind of like the shape you get when you let a full batten sail out until it presses against a shroud. With a lot of vertical tension, it might be possible to create a similar hard spot in the aft part of the section.

[tspeer]

Originally Posted by tspeer

...then reflected the leading edge to form a wingmast with a thin sail behind it. ...

Here are the coordinates for the mast itself.

[BigCat]

Actually, this wing sail design looks almost exactly like a drawing by Tom Speer on his website, however whereas his drawing indicates a pivoting wing mast and an almost flat sail aft of it, my drawing indicates a soft wing sail, and the wing portion is a soft sail wrapped around wing shapped batten parts. The after part of the sail is a flat sail attached to straight battens. Camber is induced by sheetlets which are part of the sheet which controls the sail. This sheetlet system is exactly that used in the junk rig.

The rig is held aloft by a simple fixed unstayed freestanding mast, as in the junk rig. In fact, the sail is a junk rig modified in two ways-the forward part of the sail is a wrap around wing, and the after part is hinged with a hinge that has only a small degree of freedom - 14% total, or 7% on each tack.

I did not invent the hinged junk rig-it has been used on a number of cruising yachts in recent years. A similar rig was independently invented called the Swing-Wing rig, but its forward wrap around section was not informed by aerodynamics and had a sharp leading edge, rather than a standard foil shape. These precedents give me complete confidence that the rig will be quite seaworthy and very easily tacked, reefed, and furled.

I am currently building a catamaran on which this rig will be used in the biplane, aka tandem configuration, and expect the boat to be sailing some time in 2010.

Tim Dunn, dunnanddunnrealtors.com/Catamaran.html

[tspeer]

This is how the sails are made for the Standart landyacht class. Teardrop-shaped forms are threaded over a round mast inside a luff pocket with a zipper down the side. The ends of the battens extend inside the pocket and are inserted into the formers. Luff tension maintains a wingmast shape between the formers.

[BigCat]

Originally Posted by tspeer

This is how the sails are made for the Standart landyacht class. Teardrop-shaped forms are threaded over a round mast inside a luff pocket with a zipper down the side. The ends of the battens extend inside the pocket and are inserted into the formers. Luff tension maintains a wingmast shape between the formers.

Hi, Tom - I couldn't make out if the luff extends forward of the mast on the landyachts. Mine stick forward enough to reduce the pressure on the sheets, under, of course, the same principle that reduces rudder loads of balanced rudders. I am using the Clark Y foil, as you recommended.

[tspeer]

Originally Posted by BigCat

Hi, Tom - I couldn't make out if the luff extends forward of the mast on the landyachts. Mine stick forward enough to reduce the pressure on the sheets, under, of course, the same principle that reduces rudder loads of balanced rudders. I am using the Clark Y foil, as you recommended.

The leading edge of the Standart sail does extend forward of the mast, but not by very much.

The balance of a wingmast with a sail is very different from that of an airfoil by itself. The sail pulls on the trailing edge of the wingmast, and the pressure distribution is different around the mast than for the isolated foil. You don't change the sheet loads appreciably by extending the leading edge of the sail forward of the mast, at least not if you're still keeping the mast near the forward half of the wing portion. The leech of the mainsail has more to do with sheeting loads than does the wingmast portion.

For a solid wingmast, flutter is a big concern when the mast is not restrained by the sail, such as when tacking. Mass-balancing of a wingmast goes a long way to eliminating flutter. For your soft wingmast, I don't know if flutter will be such a big issue or not, but if there's a way to mass-balance it, that would be beneficial.

[BigCat]

Hi, Tom - My planned intersection of the mast and the wing sections varies from right forward in the wing section at the bottom to slightly aft of center in the middle, to forward but not right forward in the top batten assembly, because the luff curves but the wing sections are identical. Because the leach curves, the straight / flat battens are of different lengths, giving each batten assembly different lengths. As a consequence, the point of maximum camber varies, from 38% aft of the luff to 55% aft of the luff.

[Asleep Helmsman]

I’ve been looking into various different designs for sails in the last few months. Starting from scratch allows you more freedom in the imagination department.

Have you guys installed any of these sails on multi-hulls?

In particular are any installed on day boats / racers?

I’m building a 30 foot catamaran; which should displace about 1500 lbs (681 Kilos), would you expect better light wind sailing, higher top speed, or both?

[BigCat]

Originally Posted by Asleep Helmsman

I’ve been looking into various different designs for sails in the last few months. Starting from scratch allows you more freedom in the imagination department.

Have you guys installed any of these sails on multi-hulls?

In particular are any installed on day boats / racers?

I’m building a 30 foot catamaran; which should displace about 1500 lbs (681 Kilos), would you expect better light wind sailing, higher top speed, or both?

Wingsails have mostly been used on large daysail boats, the kind designed to break records. google image search "wing sail catamaran" and you find many.

[Ilan Gonen]

Hello every body,

Just wanted to inform you that Omer wing sail mark II is out there sailing.

In order to adopt the wing to big boats, the system that supports the wing has been changed, the outer skin looks similar to mark 1, airfoil reduced to 11%, performance slightly better, the wing is lighter, simpler, easier to handle and to trim the sail cloth (three independent sails).

The tests have not been finished yet however, the results we already have are very good.

You are invited to visit my web site (www.omerwingsail.com) and see the new pictures in the gallery.

Ilan Gonen

[thefuture]

Whats a rough estimate of cost compared to a main and genoa?

[Ilan Gonen]

The main cost component is the carbon fiber mast. It is relatively expensive for very small boats and inexpensive for very big boats.
When the wing is installed on a new boat you save sails, furlers, winches, stays & shrouds, chain plates etc.
Also, using a free standing mast, that has no stays downward compression as in the case of standard rig, enables making the hull lighter and cheaper.
Overall – depends very much on the size of the boat.

[steveo-nz]

Are we likely to see this on race boats any time soon?? no doubt that would help to refine it even more

[Ilan Gonen]

Look at the article "Consequences" in Seahorse magazine, Jan. 2009. Although the article is about rigid wing sails rather than soft wings, it is interesting.