To quote me quoting an ancient rocker "There aint 'alf been some clever bastards."
This method of furling requires no springs, is very reliable, and by all accounts works a treat.
It furls the turbine by lifting the vane upwards, towards the wind if the wind is too strong. I like it already.
Whoever came up with this was, without question, a genius.
First we start with a pole to mount everything on.
Its basically a sleeve welded at an angle to a plate.
We attach this thing to the top of the pole via a bearing so it can spin around freely.
This is what we will now stick our turbine and wind vane to.
Note that the sleeve is on an angle. It's very important.
Then we stick the two bits together by slotting the shaft into the sleeve and attach our turbine.
Note that the turbine and the vane are off centre on either side of the pole.
This offset is also very important
When the wind blows onto the turbine, the force is one that tries to pivot the turbine around the pole and to the left.
Because the vane is always blown downwind, there is a tendency that the two try to meet.
The stronger the wind, the stronger this tendency.
This is a good thing because we want the blades to point away from the wind a bit as the wind gets too strong. Auto furling is the desired outcome after all.
But the reason they don't just give in to their desire to meet is the clever bit.
The reason they don't meet is to do with the angle of the sleeve on the pole cap. In order for the tail to swing to the right, it also has to move up because of the angle of the sleeve. This means that the weight of the tail sets the tension rather than some kind of spring. The weight of the tail resists the tendency to arc up and to the right. By setting the weight of the tail, we determine at which wind speed the device starts to furl. Gravity is very reliable. Things like springs, not so reliable.
Remember, throughout this thing adjusting itself, and setting how much of the turbine is presenting to the wind, the device is still tracking the wind. The vane still does its job and continues to follow where ever the whim of the wind takes it. When I talk of the vane arcing up and to the right, it's only moving to the right relative to the turbine. It's following the wind, always pointing downwind, and is taking the turbine with it.
Relative to the universe everything rotates together on the pole as the device tracks the wind, as decided by the vane.
Relative to the wind, the turbine is presented at a different angle depending on the wind speed.
The tail still serves as a vane and maintains the turbines aspect into the wind, but it folds a little as the wind gets too strong.
The vane is in its maximum straight position and is sitting flat to the horizon.
Flatish in my diagram.
When the wind becomes a little too strong we want to turn the turbine slightly away from the wind to collect a little less power. This way we still get energy from the wind but we reduce just how much we collect. After all, there is now a bit too much energy in the wind, so we shouldn't be greedy and risk damage to our turbine.
The vane still points downwind, but it has folded toward the turbine... or the turbine has folded toward the vane, depending on how you look at it.
The vane has also lifted a little. It's weight is now coming into play. As the vane rotates toward the turbine it also has to rise up as a result of the angle of the sleeve, and the shaft that sits within it that's attached to the vane.
The weight of the vane wants straight, the wind wants folded.
|front / side view|
Remember the wind is coming from the left and meeting the auto adjusted blade at a 45 degree angle at this particular wind strength. The vane is pointing downwind but we can see the wind strength has overcome the vane's weight.
If the vane were to move down like gravity wants it to, it can do so, but it will stay down wind. Due to the angle of the sleeve, it must also turn the turbine back into the wind. It can only do that if the wind slows down a bit.
If all the constructed angles are correct on the sleeve and the vane shaft, we should see our turbine still generating electricity, or doing whatever it's supposed to be doing, regardless of the wind strength. If it's all designed properly it should be safe without having to lock it all down in a gale to protect it from burning out the generator, or spinning so fast that the whole thing breaks apart and scatters it's bits to the horizon.
Those angles are really important. I don't know what they should be yet. But I'm pretty sure they would have to be spot on to furl at the correct wind speed, and unfurl at the other correct wind speed. Given the correct wind speeds would be different for different wind turbines, There is a reasonable chance the angles of the sleeve might need to be designed to suit. It's also possible that one angle fits all.
I'll find out before I start building one.
I'll even let you know.
What all this enables us to do is create a turbine that can work in lower winds, but that can still survive higher winds. We could just make a wind turbine so it was safe from high winds by fixing the vane so it presented the blades almost side on to the wind, as in the last picture, but that would not catch enough wind to be of any use in light winds.
It seems wind turbine design is always a compromise between getting the most out of light winds, and still being upright to cash in on those times when the winds are strong. This automatic furling mechanism goes some way towards having the best of both worlds.
From what I've read so far, this looks like the furling method I would employ.