Wing Sail design

[AleX`G]

I have settled on the idea of making a model with a single wing sail. It will be a semi solid sail which uses the wind to form the foil shape.
I have come up with 2 designs which 1 is better and what could i improve upon.

On type B the leading edge is infront of the pivot point. It would be made solid and would not move with the wind.

The moving portion of B would be made out of foam or bubble wrap or somethign light. It would be a single piece pivoted at a point just behind the mast.

On type A the material wouldnt be fixed to the mast and would be flexible.

Type A has 2 parts that move which are tubes attatched as in the diagram.

Both types would have a tensioner to form the trailing edge.

Sorry for the rubbish diagrams.

 

[frosh]

Hi Alex, Tell us how big you intend the model to be, as the materials to be used will depend largely on size. Load on the wing and weight needs to be considered in the design, hence the type of materials.
I doubt that bubble wrap, is going to be of any use, and the twin tubes in type A also seem dubious to me.
Have you checked other versions of rigid wing sails, (eg. Cogito, the C class catamaran from the U.S.)http://www.sailingscuttlebutt.com/photos/04/cogito726/ and double surface sail cloth sails that have twinned battens to create a wing shape that has thickness, and also changes shape on opposite tacks?
All this is available on the net. This is one example but there are many:
http://www.johnsboatstuff.com/Articles/rigid.htm

 

[AleX`G]

THe sail area is to be 2000cm2 not taking into account the camber. The max height is 90cm for the mast so max sail height would be 88cm by 22cm which would give an AR of 4.
hull length is 70cm min wieght is 2kg 55% of 2kg can be in the keel. no max width hull must be a monohull

I have seen the
http://www.johnsboatstuff.com/Articles/rigid.htm
I thoguht that worked in a simmilar way to type B.
The c class looks great. How does that actually work. is it part rigid part normal sail?

Thanks

 

[tspeer]

For Type B, you will find a very strong turning moment of the leading edge piece about the pivot, tending to rotate it to leeward. You should use a tool like XFOIL to calculate the moments on the leading edge piece and decide where to put the pivot. Especially when you include the tension in the sail, it's not going to be easy to figure out.

I don't get the purpose of the tubes in Type A. Thickness by itself is harmful to maximum lift, and really only useful in preventing separation on the windward side at low angles of attack.

Do some research on the Princeton Sailwing. It's basically along hte lines of what you have in mind.

 

[frosh]

Hi Alex, the Cogito style wing is almost certainly too complex for a model yacht. However it is all rigid in three sections with the clear stuff probably Mylar, and the framing Carbon Fibre composite for minimum weight. There is articulation between the three sections that can be controlled by the crew.
Hence depth of camber is variable, and the shape of wing is highly adustable. I also think that with this wing the upper section of the rear part can twist off in higher wind speeds.
What about constructing the leading 25% in styrene foam and covering with one layer of woven carbon fibre.
The remainder could consist of a double layer of fine sailcloth, also wrapped around the solid leading edge, and supported by carbon fibre battens set in tandem with spacers attached between the pairs.
You would have to find a method to tension the cloth to remove all creases and wrinkles.
You might also need a substantial boom or wing base, and vertical rod rigidly mounted to the base and passing up the length of the wing providing support for the sail battens.
This is just a suggestion, and there will other possibilities also.

 

[AleX`G]

Sounds good so its kind of like a wing mast. Could you tension the sail with a windsurf style boom?
I assume that a 360degree rotating mast would be best for this design.

With the rigid sails like on the cogito would it be possible to have the leading (30-40%) as one symetrical airfoil and another one controled by the servo behind it. Would the sail automatically point into the wind if it was in neutral?
If so then you could adjust the lift by using the flap forming quite a decent airfoil shape.
And still have it hold itself into the wind so the mast swivels freely.

 

[frosh]

Hi Alex, what you suggested I think was essentially two rigid wings, one-third as the fore wing, and two-thirds as the aft wing, the two being articulated.
This would work quite well but they would likely be symmetrical sections.
Is so, they could be shaped from styrene foam and laminated with one layer woven carbon fibre. You would probably want to use three stays attached to the leading edge of the fore wing about 30% down from the mast head. Also a small metal rod mounted at the base of the fore wing fairly close to the leading edge would allow the fore wing to align with the apparent wind.
The aft wing would be sheeted in by RC servo so that the leeward side of the combined wings made a smooth aerodynamic shape like that of the upper surface of a glider's wing. The small sharp angle created on the windward side which would represent the air flow transition from fore to aft wing is not that critical, as long as the shape on the leeward side has no bumps or angles or large gaps.
The boom on which the clew of the aft wing would mount, could rotate around the same rod that the fore wing is mounted on.
I also think that you are planning to use a rectangular plan shape.
I would taper the wings so that the chord is not 22cm everywhere, but perhaps 28cm at the base, going to around 14 cm at the head. Of course the thickness of the aerofoils also need to taper in proportion to the chord taper.

 

[AleX`G]

So the whole wing would rotate freely with the wind. Then you can adjust the shape by sheeting in the second wing. As long as it only uses one servo to operate its fine.
would you have to tack downwind?

Would you want the fore wing pivot point
(were its attatched to the deck)
to be as far forward as possible so it is easier for it to ratate with the wind.
I could probably fit the servo actually in the sail but it might be better performace wise to have it in the hull. As that would make the sail as light as possible.

I was thinking of usuing aluminium sheets to make ribs for the wings then wrap them in something.
Could you mould carbon fibre around a clay mould. To form a hollow wing section which would be ultra light.

Thanks for the help

AleX

 

[frosh]

Alex, re tacking downwind, I don't a lot about model boats but small racing dinghies and catamarans make better VMG normally by tacking rather than running dead, except for slower dinghies that don't go that quick even with apparent wind on the beam. A rigid wing sail really should be sailed so that it produces lift not pure drag therefore tacking downwind is theoretically better.

Pivot should be as far forward as possible and front wing should not need a servo but weathercock accurately with apparent wind. The servo should drive the boom to which rear wing is attached to, and should be situated as low as possible.

Thin marine ply (around 2mm) would be easier to work with and much lighter than aluminium for ribs.

I have doubts about using a clay mold, as I dont know how precise you could manufacture a wing shape. Also you would have to work out how to release the carbon skin from the mold, without damage to the carbon which believe me will be very fragile. Thats why I suggested the polystyrene form onto which to laminate the carbon. Don't worry about the weight of the wings in polystyrene and one layer of about 80 g.s.m. woven carbon, they will be very light.

 

[AleX`G]

What about the thickness of the airofoils. Would both be the same thickness or the aft one thinner.

Also would you attatch the aft wing to the fore wing like a flap on a plane were they are not actually seperated or leave a gap .

Thanks

 

[frosh]

I refer you to the aerodynamic work of Tom Speer and the diagram is self explanatory. You will see that the relative thickness is larger on the leading wing. Using the code designations you can find a lot more detail on the foil shapes on the net.
The rear wing should be hinged to the front one with the least possible gap.
If you look carefully at the diagram of the sections of the two wings you will see that the leeward edge of the two wings appears very much like the leeward edge of one single larger wing. This is what you are aiming to achieve.
http://www.tspeer.com/RigidRigs/50flap/S901fa20.htm

 

[frosh]

Thin rubber fairings might work. The theory of it is good but you would have to check it out in practice. The air flow needs to be especially non-turbulent over the entire leeward surface of the wing pair. Any fairing should be recessed so the final surface is flush with the rest of the wing surface
It might be more trouble than it is worth. Depends how much effort is enough; and that is entirely up to you.

 

[AleX`G]

Have just read this article about reynolds numbers
here

Could spell doom to my project as the windspeed would need to be about 15mph to make a wing worthwhile.
And for that id have to extend the chord length to at least 0.35m which would leave me with a sail 57cm high.

But it also says as long as the area is the same a wing will be more efficient even thought it has a very low aspect ratio. because wind shear is not noticed so much on models because of thier tiny size.

 

[frosh]

Alex, I agree that in lighter winds a rigid wing sail will not outperform a conventional sail. However disagree with the aspect ratio needing to be low. Have you allowed for a taper in the chord length as you go up?

 

[AleX`G]

I could have the masts swapable so i could have a conventional sail in light conditions and a solid sail for high wind speeds.

I think a sail shape like maquires innovation would work well. It has a low apect ratio and would give a better reynolds number for moderate wind conditions. And also have less of a heeling force.

http://www.macquarie.com.au/speedsailing/gallery.htm

PS: a newb question here. How do you go about working out the center of effort.