...although my furling is set up well when there is less turbulance and straight on increases in wind speed completely furling it between 25 -30 MPH there are "freak" wind scenarios with extreme winds and turbulance with my system. It has to do with yawing direction being in or out of sync with the furled tail.
Always one of my favourite puzzles. It's something I never get bored of watching on mine.
Others may have better ideas for dealing with dynamic effects, but my suggestion is to "damp" the response. If the tail could be made to fold up easily, but the unfolding was slowed down, then you might have a system that prevents gusts, from any direction, from speeding up the rotor by making the tail momentarily unfold.
When the gust isn't abrupt, the furling mechanism doesn't get far from static equilibrium. The mill will furl consistently and the RPM won't rise too high.
The rotor and the tail have different inertias, and different forces making them move. If the gust makes the wind change direction abruptly, it can both reduce the thrust on the rotor (a force that causes furling), and push the tail out. It could just as easily come from the other direction and encourage the tail to fold up, too. One direction is safe for the windmill, the other can promote overspeeding.
A simple damper could make a tail move this way, but it would be hard to size up and fit a damper to the hub of a windmill. Making it work in one direction only also wouldn't be easy. Also a concern: What would happen if the damper froze up?
Still, I can't stop thinking about it.
There are speed gusts, directional gusts, and combinations of the two. The rate of change is also a factor. Observing abrupt gusting at the top of an 80' tower - I cannot imagine the pounding your house got!
For example, if the gust made the wind direction change instantaneously by 30 degrees counter-clockwise (looking down on the tower), then the angle of attack of each blades changes differently. The blade turning toward the wind change (say it's the top blade, for a clock-wise turning prop) will see increased wind speed and decreased angle of attack. Expect a small increase in thrust load, but the change in direction undermines that blade's contribution to the torque of the rotor. The opposite happens to the blade passing the bottom; decreased wind speed and increased angle of attack. There is more drag at increased angle of attack, which now also undermines the torque. Blades pointed horizontally at that moment see a flow along their span which is of no use to them. The rotor slows down and it won't speed up again until the gust can make the tail turn the mill around to face the new wind direction.
The tail, though, is a dynamic system in itself. It's a balance between gravity that prevents it from hinging, and a "lift" load that can overcome the gravity component when the wind is strong enough. Once the tail lifts, the angle of furling is affected by the rate of yawing rotation. Either a gust can slam the tail down, or pick it up farther than it would normally go if it had just been blowing steadily that way.
Obviously, I like to spend time thinking about this, but I never reach a conclusion!
