Wing Sails

Don't know if you've run acrossthis variation or not. I've seen some inflatables used with windsurfers also.
I'm still drawing and thinking on my latest version. I hope to complete it and if I can figure out how display it on this forum, do so.
In short a fully rotatable wing mast which would set directly on deck. The cloth, or other material of the aft sail, would be fully battened. This has been used, or used in attempts before.
I saw an earlyer thread discuss the uncertainties of what airfoil shape would work best. It would be a heavy and involved practical experiment to investigate this with a real soft wing sail. I envision something using lasers to detect wind movement over the sail.
I've figured that induceing an assementrical curve to the sail and adjusting its width would be flexible enough of an approach to investigate what does work.
This shaping would be based on four c section vertical struts. Two would locate the front of the cloth. Pulling one edge forward and allowing the other to slack off will produce the shape of an assemtrical airfoil. The two other struts would be located arround 1/4 to 1/3 aft. The struts will be attached to the battens. These struts will be pulled forward and inboard, or allowed slack to let the negative air pressure pull it outboard.
The four c section struts will use a luffrope (not real sure this is the proper term) to both allow attachment to the sails forward edge, sides and to be used to hoist the sail. Supporting these struts from above, while allowing sufficient movement and maintaining even tension on the halyards is fairly clear. But not finalized yet.

 

Two interacting wings does have advantages. You could also add a slot/ small foil forward of the main wing. Its mechanism would take some thought though

 

Here is an interesting potential development:

http://www.liveyachting.com/wally-o...ing-sail-technology-for-large-cruising-yachts

 

New Wing

Thanks Doug
That looks like a very good simple setup. Performs too!
Having no luck loading images here. I did up a curvature mechanism model for my system and have three semifuzzy images on file here. I'm pleased with how it worked and see an improvement or two. It is possibly more than it needs to be.
Hope too see about progressing it. Right now Life is rompin and stompin on my time.

Ed W

 

Well, it CLAIMS that it performs.....
According to the claims made for the Omer wingsail, if you put an Omer wingsail on a Hobie 16, it would probably beat the fastest C Class cats in the world.

That seems.....shall we say, rather unusual, given that the C Class is a vastly more sophisticated and much larger boat that already has a wing rig.

Apparently, if you put an Omer wing rig on a 470, you would beat the 49ers quite easily. Hmmmmmmm.........................

Similarly, according to the Wally/Omer site, if you put an Omer wing rig on an A Class cat, you'd beat the other A Class cats by about 30%. However, when a very good sailor put a more sophisticated wing rig on an A Class cat, they got beaten by soft rigs. So how did that come about? According to the site, the A Class would have been the fastest small boat around a course in the world if it carried the less sophisticated Omer wing, so why did it get beaten by other As???

Funny thing, Omer was promising to provide us with results of his testing against a standard sistership back in 2008. Oh, and that was just after a BDF poster had pointed out that his polars (as posted on Omer's website) were wrong and Omer agreed. It seems that he may have fixed them, but certainly there were errors with the publically-provided information released earlier.

Racing sailors are very easy to convince,. It goes like this - you turn up to a race. You win that race easily. People go geezers, that was FAST!!!!!!

I wonder how the testing went when the Omer wingsail went racing?

 

You'll notice that the picture is not a real boat but a made up computer one.
You always have to be suspicious when you see this because usually it's just someones dream and will never get built.

These kind of uncontrolled wings are difficult to sheet accurately because of the narrow angle of attack that works best for them.
A much better scheme is to introduce a controlling surface, a tail if you like, to automatically keep the angle of attack constant, thus relieving the helmsman of having to do it manually all the time for every little windshift.

This kind of approach was used on the Walker wings, and my own wings. Some of which you can see on Youtube under "controlled wingsailing".

 

I've been thinking about wingsails for a while now. I read fantastic claims and occasionally see something that seems to work but not often. Theoretically they should outperform a conventional sail close to the wind although perhaps not on other points.

I used to design and build model gliders and sailplanes, and the wings were usually built concave on the underside, undercamber we called it back then, not sure if that term is correct or still used. They were claimed to be superior to flat-bottomed wing profiles although I never established that in practice. However an asymmetrical profile is better than a symmetrical one, dramatically so at low speeds, but not for aerobatics.

Since a boat's wingsail must take the wind on either beam it must be either symmetrical like an aerobatic wing, have a variable profile which can get complicated, or use slots to increase lift. A conventional cloth sail provides the desirable asymmetry automatically, but has difficulty maintaining shape very close to the wind unlike a wingsail. However, since the actual speed made good upwind can be improved by sailing a little further off the wind, this is moot.

The wingsail does not provide the same feedback as a sail, although the control problem has been addressed by a tailplane to control alpha as mentioned by windmaster. Again it must be changed to take the wind on the opposite beam which adds complexity. This may be the optimum concept for upwind work, short of going to the extremes illustrated in the last America's cup.

Leaving the question of sailing close to the wind, on a reach the drag and its contribution to leeway are less important, and downwind drag is actually beneficial. Sailing at these points the wingsail could be expected to be handicapped, and in most cases I know about, that seems to be the case. The best thing for downwind should be a parachute, and a fabric wing can approximate one of those quite well.

Things change for a really efficient hull and sail combination, especially if the boat is good enough to benefit from tacking downwind and can go faster than the wind on some points. As the boat begins to "make its own wind" as the saying goes, the wingsail should come into its own, but modern sails are still hard to beat and have advantages for reefing and furling. For that reason, I expect to see combinations of rigid wing and fabric sail virtually take over in competitive sailing unless prohibited by the rules. p.s., Tom Speer's (post #166) at http://www.boatdesign.net/forums/sailboats/americas-cup-whats-next-31489-12.html notes control forces for a wingsail can be significantly less than for a fabric sail.

The nail in the coffin as far as I am concerned is, to benefit from the reduced drag of the wingsail, the rest of the boat must be also designed to reduce aerodynamic drag, or there is little point in the exercise. I suspect this is a major reason why wingsails often deliver disappointing results. I was planning to try out one on a kayak, until I realized that, sailing upwind, the drag of my body and head sticking up above the deck would completely overwhelm any gain in efficiency I might get from the wingsail.

 

I believe a tail was folded into Bernard Smith's work in the early sixties. The local library system had a copy of his "40 Knot Sailboat". Interesting, but as a proa design, tacking was an involved thing.

Hopefully Omar's sail will eventuall show it's worth, or lack thereof.

Consider the wasted effort to produce a Halfnium nuclear grenade. A bad idea from several points of view, evidence submicroscopic. Yet an amazing amount of federal cash was spent on it.

Despite a fair amount of thinking and calculating, the best ways forward right now may just show us were we are mistaken. More real world experience is needed.

Terry, the thing that a rotatable wing would allow is to produce dynamic lift from an aft wind. This is different from the using a parachute, spinnacker, mainsail ~ 90 degrees to the apparent wind.

I hope I can get back to this sometime soon. A worthy endevor, and a whole lot less damaging than a nuclear handgrenade.

 

Windmaster; you may feel free to question the knowledge or experience of any one on the forum except TSpeer. He is our resident guru who is very much respected and believed.

 

Quite right. I agree. Didn't mean to question anything he said. Hope there was no misunderstanding.

 

Quite so; they can all be operated at low alphas at any point of sailing. Be careful playing with those grenades now!

In my early thoughts about wingsails I read Peter's accounts of experiments using tailplanes. It seemed to me it would simplify control and increase safety. For competitive sailing the constant alpha would be a disadvantage and the tailplane would need to be varied over a continuous range rather than have two fixed positions plus a neutral setting. For sailing directly downwind - before I heard about tacking - I assumed the wingsail would be used 90 deg to the AW for maximum drive, and was considering an arrangement similar to the dethermalizer used in competition model sailplanes, at least many years ago.

The technique of tacking downwind renders that unnecessary as well as being far quicker. If the boat is fast enough to beat the wind then there is no need to gybe either.

 

Tails and direct control are not mutually exclusive. Some friends and I built a landyacht with a tail-controlled rigid wing. The controls were arranged so that the pilot could control flap and tail separately or gear the flap and tail together as one control with a variable ratio between them. The tail control worked very well. It was able to control the angle of attack in lighter winds than the yacht could sail, and in fact became a gigantic Windex. The gust response was very good, immediately sheeting out as the gust increased the apparent wind angle. Actually, the gust response was too good - when the gust hit, the yacht did not get the punch of acceleration that it usually did.

Because the tail boom passed directly over the pilot's head, pilots found there was a third method of control we designers hadn't thought of. Pilots discovered their preferred way of sailing was to neutralize the tail and simply reach up and grab the tail boom to position the wing. Balanced by the tail, it only required finger-tip pressure to move the wing. By manually controlling the wing, the pilots were able to get exactly what they wanted from it.

 

I'm not sure what you mean by this. When sailing "with an aft wind" with a kite or a spinnaker you do produce dynamic lift. Many people don't understand how sails like spinnakers are used.

 

Not only that, but the perforance gain claims seem pretty outlandish.

I look forward to seeing some two boat testing.

 

Now that is very interesting, if the tail can be fixed things get simpler. The arrangement for controlling the boom would have to be able to push the boom out as well as pull it in, but in practice it would not be a problem in a high speed craft as the apparent wind would not be far off the bow at speed. It suggests an offshoot of BMW Oracle's computer control requiring less power to operate the sail, allowing smaller, battery-powered servos. Might bring it within the range of us poor folk!