What is furling, what is it used for.

[Valduare]

Hello all i am new to this subject and have been doing quite a bit of research latly. i am intrested to know what the furling i am hearing about on the tails?

[Shadow]

Try this,http://www.fieldlines.com/story/2005/3/9/232440/9997

[MountainMan]

Simple answer: Furling is used to prevent your windmill from self destructing in high winds.  It causes the blades to move out of their normal 90 degree relation to the wind direction to a less efficient angle, which reduces the turning speed and saves the wind mill from spinning itself apart.

jp

[Derodeo]

I'm just starting to educate myself in the realm of wind power generation but I think it's interesting that some blade manufacturers seem to feel that their blade design makes a furling system unnecessary. For example the guy who runs tlgwindpower.com states that his blades loose their efficiency at higher winds speeds and simply slow themselves down thus providing overspeeding protection without a furling system. I can see this as being a very nice feature but is for real??

[Flux]

Yes it may be for real if you keep it small and can live with the noise.

Don't do it on anything over 5ft and don't do it within 2 miles of me and you may be ok.

Things like the old Air 303/403 did just that and they didn't do much to enhance the credibility of wind power.

Flux

[Warrior]

Giant wind turbines (30-60 meters class) are also stall regulated, but I doubt at there slow turning speeds that noise will be a problem.

Warrior

[Flux]

Yes, stall regulation is fine but you need a back up in case you loose the load.

I don't think that was what was implied here. I presume you could include the Proven pitch regulating rotor but again it was not what was being considered.

Flux

[Ungrounded Lightning Rod]

In case it isn't clear from the other posters:

A typical horizontal-axis machine has a blade that is an airfoil and "flys" in the wind - at a tip speed several times the wind speed - getting extra pull from the lift of the air as it goes past the curve of the blade.  It's much like an airplane wing, and JUST like a propellor (except the curved side is on the opposite side of the blade).

Some of these mills are designed so that, when the wind speed is too high (AND the mill is under load) the blades will "stall" - just like an airplane that has been put into too rapid a climb for its current airspeed, or a sailboat "pinching" to closely to the wind.  The airstream detaches from part of the curved backside of the blade and "peels off", trailing a string of vortices downwind.  The lift is reduced, keeping the blade from overspeeding.  (Again:  IF the mill is under load - it will typically still overspeed and perhaps disintegrate, throwing blades heavier than baseball bats across the yard at an appreciable fraction of the speed of sound, if it is NOT loaded.)

The vortices, however, turn an appreciable fraction of that lost energy into sound.  A stalling mill sounds much like a helicopter in rapid flight - for the same reason.  You don't want a stall-regulated mill in your neighborhood if you like peace and quiet - or, if you have neighbors, you still want your mill to be standing next year, all the paint to still be on your car, your barn unburned, ...

Now if you live miles from anyone else and are deaf...

[Derodeo]

Thanks for the good info ULR. If there any problem with having both blades that are designed to stall (supposedly only at very high speed) AND a furling system for umm ... emergencies? Is there a diagram or detailed picture here of a simple side-to-side furling design? I envision being able to have a pivot for furling the tail that is essentially the same as the pivot that holds the generator to the mast (i.e. Randy's workshop "Ametek" Pivot - maybe smaller).