A whole bunch of years ago I had a nifty Idea for a windmill design. I'll be describing it in a separate Idea from this one, later, and then add a link here. At the moment the relevant fact is that that old Idea employed sails, much like original Dutch-style windmills had fabric sails on wooden frameworks.

Well, when the wind begins to blow too hard, it is important to "furl" the sails (basically, roll them up), to keep the windmill from rotating too fast (by reducing the total surface area of sail that the wind acts on). In the Age of Sailing Ships, furling the sails was basically done by hand, by folks who climbed up to where the sails were. Dangerous!

Now sails basically come in two types, square-ish and triangular. On a sailboat, the square-ish sails were usually furled from the bottom to the top, and then tied in place. Triangular sails are almost always right-angle triangles, and are either furled horizontally at the vertical mast, pulling the sail fabric toward the mast, or furled vertically at the horizontal boom, pulling the sail fabric down toward the boom.

Nowadays electric motors do the furling, but someone still has to press the button to turn those motors on or off, or to run them in reverse (to unfurl sails after the wind stops blowing too hard).

So, obviously we need an automatic system to furl/unfurl sails, that quickly responds to wind-conditions. This Idea is correct for the Windmill category, and not for sailboats, solely because only windmills incorporate rotary motion as part of their basic functionality, and this Idea depends on that rotary motion.

(Of course you might install a sail-type windmill ON a sailboat, replacing the ordinary sail system with something that powers a propeller, after which this Idea could be relevant to those "sail" boats, too.)

We start by noting that because wind tends to blow harder above tree-top level than near the ground, most windmills are very tall, so that their blades (sometimes called "sails" even today) are high above the ground. That's A Good Thing for This Idea, as you'll see shortly.

Naturally we assume that the type of windmill under discussion here employs actual sails that need to be furled occasionally (existing types "feather"/reorient their blades so they meet a hard wind edge-on instead of face-on).

Now I have to change the subject momentarily, to talk about an ordinary roll-up window shade. The shade/sheet starts wrapped around a roller/rod, much like a furled sail. The roller is attached to a "torsion spring", which is tensed-up as you pull the shade down, and which is able to roll the shade back up again, later. Note that the bottom part of the shade incorporates a stiff ("shaping") rod that keeps the bottom straight and parallel with the top (prevents foldings such as window drapes tend to have), and moves with the shade.

We want something of an opposite of that window-shade system here. We want the unfurled state of each windmill sail to be associated with an untensioned torsion spring. As we furl the sail, the spring tension increases -- if the spring was allowed to loosen, the sail would return to being unfurled.

The overall framework for holding the sail (as if we were discussing a ship's sail) will involve an upper horizontal part associated with the roller/rod, and a lower horizontal part that will be associated with two pulleys. Look at this ASCII sketch:
|O|
|--| (ignore the dashes)
|O|
If the upper "O" is an end-view of the roller/rod, and the lower "O" is a pulley, then we can have a simple looping line (thin rope or equivalent, the vertical bars in the sketch) around the roller/rod and the pulley.

With a pulley associated with each end of the upper roller/rod, we will attach the lower shaping rod to the two moving lines. This keeps the bottom of the sail from flapping in the breeze, and, as we get around to making the upper roller/rod rotate, the lower shaping rod and attached sail smoothly raises or lowers.

Note that verbiage such as "upper rod" and "lower rod" become less relevant when talking about rotating windmill sails! But the basic Idea should carry over satisfactorily.

Next, we need another line wrapped around the roller/rod. If we pulled on this line, it would unwrap, causing the roller to rotate, while simultaneously causing the sail to be furled around the roller, and tensioning the torsion spring.

The unwrapped end of this line will be attached to a free-weight. IT will do the pulling, trying to unwrap the wrapped end....

SO: As the windmill rotates, good old "centrifugal" force causes each sail's free-weight to pull outward from the center of rotation. The torsion spring is now the critical component. We want it to be tough enough to resist the force appled by the free-weight when the windmill rotates slowly.

As the wind picks up, though, the windmill starts to rotate faster. The free-weights pull harder. Now they start to unroll the lines wrapped around the roller/rods. The amount of sail exposed to the wind decreases, and the windmill's rotation becomes speed-limited thereby.

If the wind blows even harder, then the free-weights pull harder, and the sail area automatically diminishes even more. And of course as the wind slows, the free-weights pull with less force, allowing the sails to automatically unfurl.
-- Vernon, Jan 03 2012

Furling windmill sails http://www.culpeppe...greece-4_1_503.html
Still done, even today. [Vernon, Jan 03 2012]

Sail Turbine Sail_20Turbine
As mentioned near the start of the main text. [Vernon, Jan 04 2012]

Boom Furling Systems http://www.practica...pu60CFUsaQgodwQMfBQ
An overview of existing types [csea, Jan 06 2012]

Windmill Boats https://www.google....sqO4Bg&ved=0CB0QsAQ
In case you want to do automatic furling of your windmill sails, when they actually happen to use sailcloth. [Vernon, Jul 09 2015]

Is there a reason why the following arrangement would not be feasible?:

The main rod, which needs to be rotated in order to furl the sail, has a pinion gear and the supporting structure has a rack-type linear gear. For example in the linked picture, each rod would have a gear inside the central block and the rack(s) would run along the axle, so that as the whole assembly moves towards the building the sails are furled.

You then simply mount a powerful spring against a swashplate type arrangement in order to match the maximum force you want your sails to be subjected to.

Unlike a centrifugal arrangement this would work on static sails as well, assuming it would work at all. I may well have missed something critical, and probably haven't made this nearly verbose enough.
-- mitxela, Jan 04 2012


[mitxela], I don't see in your description the how the force of an intensifying wind becomes a furling force for the sail, or how a lessened wind leads to unfurling.
-- Vernon, Jan 04 2012


// I don't see in your description the how the force of an intensifying wind becomes a furling force for the sail// I think [mixtela] is saying that, as the entire rotor is pushed against the spring by the wind, that axial movement furls the sails.

Why is it not possible to have the sails (or panels thereof) mounted on simple spring hinges so that, as the force of the wind increases, the sails simply fold back?
-- MaxwellBuchanan, Jan 04 2012


[MaxwellBuchanan], a windmill has normal axial movement even when the wind is slow. Why won't that roll up the sails until it jams?

Your spring-hinges notion sounds ok, with the caveat that sails are normally intended to transmit quite a bit of force, which means those springs will need to be quite strong, to NOT let the sails bend over in ordinary breezes.
-- Vernon, Jan 04 2012


To clarify, that axial movement is along the length of the axle, not rotational movement.

Maxwell's hinged panels would work too, but even simpler is to have a variable pitch rotor... which is exactly what modern wind turbines have.
-- mitxela, Jan 04 2012


[mitxela], your words are still not painting a clear picture for me; I still don't see how wind pressure is supposed to do any furling.
-- Vernon, Jan 04 2012


Jeez, your sailing experience was obviously a more positive thing to remember than mine.

Odd commands yelled out harshly meaning to turn this thing one way or another.

Sail changing exercises down inside the hull, too frantic to really understand.

I think I really deserved to have been pushed overboard in Lake Ponchartrain. I'm not sure another first time deck hand could have done better, but I nearly sank that really rich guy's racing yaught by turning that dang whirly pulley the wrong way.
-- Zimmy, Jan 06 2012


The thing is, i'm not sure I get your expanding / collapsing blade idea. If it could be translated to racing ships, I'm all for it. I may still have a scar in my shin from the rope winder thing.
-- Zimmy, Jan 06 2012


[Zimmy], sorry, this Idea is not for ordinary sailboats. There were places in the text where it was relevant to talk about boat-sails, as reference-data, but this Idea is for rotating sails, such as that windmill-link has, or the linked Sail Turbine would have.
-- Vernon, Jan 06 2012


Someday people are going to enshrine and examine [Vernon]'s halfbakery submissions like they do with Newton's notebook and daVinci's sketches. Not sure why, but that's my prediction.
-- RayfordSteele, Jan 06 2012


Or they will be used to insulate buildings, or shade large areas against the effects of global warming.
-- normzone, Jul 10 2015



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