Highly Assymetrical Wing Sail

[ancient kayaker]

The idea is to mount a wing on a Vee-mast that can be pivoted from side to side. When changing tack in this way, effectively the wing is flipped top to bottom, rather than side to side. Therefore it no longer has to be symmetrical and can instead adopt a more efficient profile such as those used on sailplanes. To eliminate problems controlling alpha, the wing has a small controlling foil mounted on a stub, operating like the tailplane of an aircraft, so alpha control is automatic.

It would be a practical sail for a small boat such as a kayak, because the thrust vector always points towards the pivot which is mounted low, reducing heeling. Same advantage as a kitesail but no launching problems. Obviously, multiple wings can be used, biplane, triplane, ad nauseum.

I plan to call it the SwingWing, assuming it works.

[marshmat]

I see no reason why it wouldn't work.

Difficulties might include: high stresses on the pivot fitting, leeway control (since it will lift the boat upward and laterally downwind, as well as forward) and you might need some kind of shock damping system for tacking- if that swings over too quickly, that's a fair bit of rotational inertia going in the wrong direction on a tack.

But I think those problems should be easy to overcome with a little ingenuity.

Doesn't that "Sailrocket" speed-record candidate have an angled wingsail that looks a little like this, but only one-directional (can't tack)?

Looking forward to a prototype!

[daiquiri]

I didn't ghave time to get too much into details of your idea, but at first glance I don't see why it shouldn't work. You'll have to resolve two problems, especialy if you plan to use it with a kayak hull:
1) the center of gravity of the rig is placed on the lee side, creating a heeling moment which will need to be countered. Maybe two small floats at the wing tips would help.
2) you need to give the skipper a mean to luff up the whole thing and stop the boat, even under moderately strong winds.
If anything else comes up to my mind, I'll get back. ;)

[ancient kayaker]

Marshmat: good point about the shock damping even on a small rig; the best time to flip the rig is during the turn. Also maybe a multiple pivoted lever arrangement of the wing supports so the CoG doesn't get so high when it is flipped, but it might be too complicated. I have a lot of respect for the kind of forces that even a small sail can generate!

I recall several advanced speed sailing designs in a magazine I read a few years back, some looked liked airplanes tethered to a float with a foil and one in particular was probably the "Sailrocket" that you mentioned; the vectors of the wing lift and foil reaction looked to be on the same axis. With the SwingWing it would be too complicated to arrange for that but it gets close. I thought an offset inclined leeboard or Bruce foil would react the remained heeling moment. If course if I wnated to get fancy I could sing the hydrofoil under the hull but ...

Daiquiri: I hadn't thought about the CoG offset, it depends on the weight of the rig which I haven't projected yet. This one is a bit further down the pipeline than current projects. This style of wing is easy to put into neutral, I can either change the control foil alpha to feather the wing or set the wing horizontal, or perhaps both. Feathering the wing would reduce thrust by the lift/drag ratio of the profile, if horizontal the center of thrust of that drag would be higher unless the wing support had the kind of multiple lever system mentioned above. Whatever I have, I would want to be able to dismantle it from the cockpit and store it on deck or toss it overboard in seriously bad weather conditions, for safety. Early days yet.

[Eric Sponberg]

A-K,

Look at photo 2.29 in C.A. Marchaj's book, "Aero-Hydrodynamics of Sailing", page 386 in the first edition. It is a picture of a catamaran called Tackwind that competed for the World Sailing Speed Record in 1974. The wing looks kind of like a surfboard. The lower end is rigged to one ama, and the midpoint of the wing is attached to a pivot on the top of the single mast. To tack, the upper end of the wing is pivoted down to the other ama, bringing the lower end up to the upper position. Overall, the wing is situated more upright than in your diagram. The text in the book uses this photo and idea in its discussion of 3-D flow over rigs.

Eric

[Erwan]

Hi everybody,

20 years ago I met a young Phd in fluid mecanics. He got an old Tornado hulls/ platform, with a short mast, and put on it a Deltaplane wing.

He experimented it on flat water low wind, and concluded it was very good.

Then, with another bunch of Phd, they build a C Class catamaran, with a pivoting wing, very asymetrical and slots.

When they go to Australia in the ?? early 90's I guess. The boat was able to point higher windward than the US or Aussie boat, but unfortunatly at half the speed.

For downind it was much worse, they had to sail close to the wind and again speed was half classic C-cat., They capsized, in light condition despite hight platform stability and low wind, due to not friendly-user rig manipulation, and the wing was destroyed immediatly.

Hope it can help

Regards

EK

[ancient kayaker]

Eric: it's a relief that it's been done before, it evidently works, no theoretical reasons why not, just practical challenges.

Erwan: do you know the cause of the capsize? I can speculate a couple of reasons:-

If they were using an asymmetrical wing with slots, assuming it had a fixed profile, then it must pivot laterally to change tack, same as I am contemplating. If control of the wing were lost during this operation, as Marshmat warned, it might well generate enough momentum to cause a capsize, although rig failure would be more likely.

There is an alternative possibility that sailors used to conventional sails might not expect, which has come out of my own theorizing. While beating, during a change of tack while the boat is headed directly upwind the real wind and forward speed produce a strong apparent wind; with a wing that could produce enough lift to cause a capsize with a near-vertical wing. Currently my plan is to set the wind in the midway horizontal position while turning into the wind, or feather the wing. Together with the a Bruce foil to offset heeling moment, I hope that will avoid a capsize.

For sailing downwind, I understand it is faster to tack in order to make use of the lateral component of the apparent wind.

[CT 249]

Interestingly, in the sailing craft which can cant its rig to windward most easily (the windsurfer) the development has moved the other way - towards an upright rig.

The original Windsurfer did (and still does) sail fastest in a breeze with the rig inclined steeply. However more modern boards keep the rig upright (in the sideways direction) and go extremely fast.

See top Formula racer Sean O'Brien's post about the techniques of the top sailors and how they try to combine an upright rig with the heeled body needed to generate power at

http://www.carbonsugar.com/racing/power-to-weight-your-stance-vs-antoines/#more-24

[ancient kayaker]

Interestingly, in the sailing craft which can cant its rig to windward most easily (the windsurfer) the development has moved the other way - towards an upright rig.

The original Windsurfer did (and still does) sail fastest in a breeze with the rig inclined steeply. However more modern boards keep the rig upright (in the sideways direction) and go extremely fast.

See top Formula racer Sean O'Brien's post about the techniques of the top sailors and how they try to combine an upright rig with the heeled body needed to generate power at

http://www.carbonsugar.com/racing/power-to-weight-your-stance-vs-antoines/#more-24

All small boat sailors hike out to use body weight to balance heeling force; windsurfers cant the rig windward to a degree to hike out further, but try to keep an upright rig for efficiency. If windsurfers had longer arms they wouldn't have to do that. Not sure why original Windsurfer is faster with rig inclined steeply unless the lift reduces hull drag.

Hiking on of a kayak is virtually impossible of course, at least for me - neither athletic or young. Part of reason for proposed concept; also hopefully can be smaller but still able to delivery performance of large sail.

[TeddyDiver]

How about small combined ama-winglets in both wingtips?

And now I noticed Daiquiri allready thought about similar thinghy.. ;)

[ancient kayaker]

Good point. there were several good ideas in Daquiri's post and I I didn't give that one its due. If they were light it might help keep a level keel, although a beam sea could push the kayak around a bit. Depends how far from the centerline they are, which in turn depends on wing area and aspect ratio, wing construction, "mast" weight, offset angle , all still up in the air (pun unintentional). My guess for rig moment is around 15 lb-ft; the kayak I plan to use is quite stiff by kayak standards but some of my other boats are tippy, that is about 60% of the available righting moment at the flood point. So something has to be done! On the other hand I may need a Bruce foil or two to offset residual heeling moment from the wing, in which case i can incorporate a float atop of the foil.

[CT 249]

All small boat sailors hike out to use body weight to balance heeling force; windsurfers cant the rig windward to a degree to hike out further, but try to keep an upright rig for efficiency. If windsurfers had longer arms they wouldn't have to do that. Not sure why original Windsurfer is faster with rig inclined steeply unless the lift reduces hull drag.

Hiking on of a kayak is virtually impossible of course, at least for me - neither athletic or young. Part of reason for proposed concept; also hopefully can be smaller but still able to delivery performance of large sail.

Yes, that's true. The point is that arguably, on the evidence of some of the most popular classes that have ever been sailed, significant windward cant (even when it increases RM) is a negative.

Frank Bethwaite found one problem - unless there are nice steady winds of reasonable strength, under the force of gravity an inclined sail inverts.

Dunno if the assymetry (in camber) is all that important. Fully battened sails often possess camber at all times however they are not always faster at low speeds (typical of a kayak) or shifty conditions.

As you can tell, I have reservations about highly-canted rigs.

[ancient kayaker]

Canting the rig is likely to reduce efficiency, I think that's a given. That may offset other benefits.

Based on aerodynamic data provided in another thread, assymmetry improves lift/drag ratio. Profiles with undercamber are commonly found on low speed aircaft where /drag ratio is important such as gliders and performance model aircraft. However, the profile shape can be quite critical and perhaps a battened sail does not always reproduce the optimum profile. Hopefully, I will be able to try this out in the summer as I will be building a sail rig for the kayak soon, and if I can figure out the mechanics I will make an alternative wing sail for it. The proof of the pudding as they say, is in the eating. Or as an American might say, I'm from Missouri.

[Chris Ostlind]

Couple of things...

What holds the wing at the desired angle?

What happens to the control foil as the wing is swung over the top to the other side? You show it near the top of the sail in your diagram.

Chris

[ancient kayaker]

The control foil acts like the tailplane of an aircraft, its angle with regard to the wing determines the wing's alpha; the wing is free to pivot about its average center of lift. In this case it will experience off-axis wind as in an aircraft that is yawing, but I expect it will still work, it will appear to be half of a swept wing. As the wing is swung over the top it will still behave in the same way, except in the top position the lift will be purely vertical.

[TeddyDiver]

. If they were light it might help keep a level keel, although a beam sea could push the kayak around a bit.

I think the ama is perfect for balancing the CE being so much on the same side. Might even be handy having some kind of rudder out there to assist steering and maybe even use it as assist brake in sudden gusts..

[ancient kayaker]

Eric: I looked for "Aero-Hydrodynamics of Sailing" -it is too rich for my purse but Tackwind sounds like what I am proposing.

Teddy: balancing the CE should not be a big issue as the wing's lift vector points at the mast's pivot, at the center of the deck. The weight of the overhead rig may be a problem but looks doable if I use my most stable kayak; I think I can bring the moment down to about 25% of the boats limit. The ama's on the wingtips are out for weight reasons. If they are inflatable their weight could be tolerated but they would then only be of value to avoid a capsize, not for actual sailing and the top one would catch the wind. For steering I was planning to use http://www.boatdesign.net/forums/sailboats/articulated-sailboat-24598.html concept turning the entire rig including hydrofoil(s) with a fixed skeg to keep the hull in line.

It is starting to look weird: I like that.

[Chris Ostlind]

Couple of things, AK...

I can't recall seeing the amas in your plans and have no idea as to what size of a form you might be suggesting.

At the speeds at which you will likely be traveling, I tend to believe that the ama forms required for sailing will not create as much of a source of form drag as suspected. I'm guessing, then, that you are planning on doing a good bit of body english to take care of things while the foils get hooked-up?

Your most stable kayak...? How is that going to effect drag, as opposed to the possible drag from a raised ama?

There is potential here, to be sure. Perhaps some additional drawings depicting various size relationships, etc., could help me to better visualize the design better.

ChrisO

[TeddyDiver]

It is starting to look weird: I like that.

Me too:D
With CE I meant more it being far lee side so you need at least a sheet to hold it in right angle otherwise it'll turn forward..

[ancient kayaker]

Chris: there were no amas in my original plans; the concept is still in motion as I get inputs. My best kayak sail was only 15 sq ft, lost in a fire alas. That was decent for run and reach but inefficient upwind. A wing about the same size, weight permitting, should work better.

The amas I referred to are the wingtip mounted floats suggested by Daiquiri and Teddy.

Bruce foil(s) will take care of any wind-generated heeling moment; I used one with the old sail and that was safe and easy to use. “Body English” can balance the offset rig weight, just lean over a few inches, or I could put small ama(s) on the Bruce foil outrigger(s).

Drawing isn’t my strong suit but I should have something soon, however I first want to design a lightweight sail; low-tech; I don’t want to get into composites - looking at beefed-up model plane construction. I am also still finalizing my design for the kayak attachment and blending in the articulated sailboat concept.

Teddy: sorry - I misunderstood you. The pivot has a fore-and-aft axis with enough length to react the moment generated by the wing's forward thrust. A hard stop will prevent the mast from over-travel sideways. I am looking at wing dihedral as a means to automate the flipping of the wing during changes of tack, I need to do some modelling but my memories of tow-launching model gliders suggest it will work. If that works OK I don't think there will be a need for a sheet unless it has to be pulled all the way down to the stop and lashed.

[ancient kayaker]

Here's a sketch. This incorporates the concepts of the following threads which may help understanding the entire concept:

http://www.boatdesign.net/forums/sailboats/sailing-kayak-project-24541.html
http://www.boatdesign.net/forums/sailboats/articulated-sailboat-24598.html

[tspeer]

The idea is to mount a wing on a Vee-mast that can be pivoted from side to side. When changing tack in this way, effectively the wing is flipped top to bottom, rather than side to side. Therefore it no longer has to be symmetrical and can instead adopt a more efficient profile such as those used on sailplanes. To eliminate problems controlling alpha, the wing has a small controlling foil mounted on a stub, operating like the tailplane of an aircraft, so alpha control is automatic. ...

What you've described is known as a fliptacker. A fliptacker named Wingmill competed for the C Class Catamaran Challenge Trophy. Unsuccessfully, but your aerodynamic control may be more effective than Wingmill's manual control.
http://www.cclass.ca/images_files/image009.jpg

Bernard Smith wrote a book on these craft called "Sailoons and Fliptackers" that was published by the AIAA. It's out of print, but you might be able to cruise the net for a copy.

[ancient kayaker]

Thanks Tom: Now that's what I call a thought-provoking picture, with the crew barely visible far above the water. I wonder if they are trying to right her or are just some pieces of movable ballast left high and dry. If I don't know what I am doing I at least know what it is called, I thought I was first with the fliptacker!

There are quite a few stories about the difficulties of controlling wingsails and the consequences of failure in that department. I should clarify that the control foil is not my idea, there are several successful examples that I am copying. Perhaps I will be (one of) the first to put these two ideas together.

As far as I know, the articulated sailboat concept is genuinely new, I suspect that is because it has no real practical application to boats larger than a kayak. That's rather a lot of innovative ideas to try and marry together all at once (more of a commune); I intend to implement them one or two at a time and also try out a small hand-held version of the flipwing to see how it behaves on it's own.

One thing I always do with sailing rigs for a kayak is incorporate some kind of quick release to dump the rig over the side during that kind of maturing experience. Your picture has reinforced my resolve!

[Munter]

ak - I'm pretty sure you don't right a C-class and keep on sailing. That pic is a moment of disaster just before the wing hits the water and (from memory) disintegrated beyond repair.

[ancient kayaker]

No doubt about it. Gives "flip-tacker" a whole new meaning, doesn't it!

[Munter]

Very true AK. A quick web search reveals a claim from Wingmill's home club (Cabrillo Beach YC) that the capsize was caused (in part) by downwash from a nearby helicopter. What a dissapointing end to such an abitious campaign. They must have felt terribly hard done by after getting the boat all the way to Australia.

The wing on Wingmill appears to have several degrees of freedom -perhaps evem more than appear on most flip-tacker models I've seen. I wonder if that contributed to the difficulty in coping with the helicopter down-wash?

[catsketcher]

If stability is a concern in the kayak then how about a little float? I have gotten right into kayaking in the last couple of years and can't quite see why most kayakers won't consider an outrigger canoe for voyaging. Most kayaks are pretty unsafe machines and yet we like to paddle in them. If you are serious about getting a sail and staying stable I would think that the complexity of a small float and crossbeam setup is far far lower than that of any new rig. The only problem is that it has been done before and proven - for thousands of years by the Pacific islanders. Kayakers tend to be more Eurocentric or more correctly Iceland centric and like to spend lots of time learning how to roll. It is the great mono multi divide raising its head in a different field. I can't see why you can't design out the need to learn how to roll by adding a float! Right now Gary Dierking is using an outrigger to cruise Fiji. He has some great outrigger designs

cheers

Phil

[ancient kayaker]

If stability is a concern in the kayak then how about a little float? I have gotten right into kayaking in the last couple of years and can't quite see why most kayakers won't consider an outrigger canoe for voyaging. Most kayaks are pretty unsafe machines and yet we like to paddle in them. If you are serious about getting a sail and staying stable I would think that the complexity of a small float and crossbeam setup is far far lower than that of any new rig. The only problem is that it has been done before and proven - for thousands of years by the Pacific islanders. Kayakers tend to be more Eurocentric or more correctly Iceland centric and like to spend lots of time learning how to roll. It is the great mono multi divide raising its head in a different field. I can't see why you can't design out the need to learn how to roll by adding a float! Right now Gary Dierking is using an outrigger to cruise Fiji. He has some great outrigger designs

cheers

Phil

I have tried several schemes for sailing canoes and kayaks. It's turning into an informal mini-research project, I suppose. My first canoe sailing rig had a float or ama; it was quite large (7', 2.1 m) and I intended for it to stay in the water full-time. Only about 35 sq ft (3.5 m2), not enough sail really. I sailed with my weight off-center to ensure that. Performance was disappointing. It was a while before I realised how much it was slowing the boat: one day I was moving really fast in a modest breeze and I looked around to figure out why and realised the float was out of the water.

I could have improved the float design but the trick when sailing with floats is, either have a large sail to overcome the extra drag or balance the sail using weight and keep the floats out of the water, then they are only backup in case of a sudden wind change.

Later I tried a sail on a kayak: you can't hike out in a kayak the way you can in a canoe so I needed to balance the sail's heeling moment without using body English. I used a Bruce Foil to do that and it was successful and felt reasonably safe. The kayak I used was quite beamy which helped, but the foil was doing most of the work. Again a very small sail, 15 sq ft/1.5 m2, and a crude plywood foil. I had a lot to learn then. Still do.

Currently I am finishing a small sail boat but when that's done I want to get back to my experiments. This is just one of them. The principle being tested is angling the sail so the sail's thrust vector passes through the boat's center of gravity. At the same time I am trying out the idea of a wingsail with automatic alpha control. I will use the same beamy kayak so I have an extra margin of safety but I believe this will be a stable system when in a steady state: it's the reaction during changes of tack or wind direction I worry about. I have a nice shallow lake to try it out on with a muddy bottom so I am unlikely to hurt myself.

I have been delayed with my boat projects this year, health and family challenges, but I will get there!