How can you

[fcfcfc]

I have to say, I can not get my head around this. I was reading the rather extensive text responses on the "basic 3 phase stator" question. He reports that it is a drag type, vane I guess, and that it stalls out at 20MPH or so... How can you stall a drag machine..??.. Lift aerodynamics no problem, somewhat easy to see, but a drag is a drag. It doesn't get less as the wind gets higher. It keeps getting greater. And the slower the VAWT turns the greater the torque. The whole idea of more being less here escapes me for a drag only machine... The only thing that makes sense to me is that his design is both lift and drag... or somehow his vanes are interfering with each other at a certain amount of "wind slip"

I will sleep on it....

.....Bill

[CmeBREW]

FcFcFc,

    Sorry if I caused confusion. Sometimes it is difficult to explain. It IS only a drag rotor I believe. I think you are referring to this statement:

 "...It does alot of 'trickle charge' (.5 - 5 watts) upto 100rpm, but in the big winds it's like hitting a brick wall around 100-120rpm.  It usually stalls at only 6 watts(.5amp) even in a 20mph wind. "

This is when I tried to put the Smaller prototype rotor on the alternator to ATTEMPT to get more speed (rpm). It failed to do so. IT STALLED , since the alternator is too big for that tiny rotor. It also stalled the bigger rotor very soon after cut-in.(70rmp)    All it could do is a 'trickle charge'. All I meant was, that  even a  big wind gust (20mph or whatever) did not have the power to take the wind rotor in relation to that alternator out of STALL. That is, being HELD BACK (from the stator) from spinning faster)

It can't ever really BEGIN to make power because it was immediately STALLed out right after cut-in.  

I opened up the gap an 1/8" and it is now out of Stall.  

IT is in the Newbie section because I am still learning. It is my first 3-phase alternator and my first attempt to attach a Vawt to an alternator.

Did I use the term "STALL" incorrectly?

[fcfcfc]

Hi: I don't know if you are using it correctly or not. MY idea of stall refers to a lift device when the speed difference between the wind and the airfoil becomes too large. The aerodynamics breaks down and you actually get less force with more wind. Again, I don't know if that is the right way to explain it or not. Basically, the best thing is just to look it up for the exact description of such. You have too remember that when charging batteries, the current can rise allot with even a very small increase in voltage. So, even though you may have thought you were not getting any more in the bigger wind, you may have. Neither rotor of yours is very big though. Usually a VAWT has to be pretty big to start to get "real" power. Mine, when I ever build it, will be 4' x 16' tall, the Helix style... BTW, did you run no load tests on it for RPM vs. wind speed to see how the design does..??.. If one of your posts mentioned this, I apologize...

.....Bill

[fcfcfc]

FYI:

Passive stall control - The blades are mounted to the rotor at a fixed angle but are designed so that the twists in the blades themselves will apply the brakes once the wind becomes too fast. The blades are angled so that winds above a certain speed will cause turbulence on the upwind side of the blade, inducing stall. Simply stated, aerodynamic stall occurs when the blade's angle facing the oncoming wind becomes so steep that it starts to eliminate the force of lift, decreasing the speed of the blades.

[finnsawyer]

I don't know where this "drag" type of VAWT idea came from, but it seems to be a misnomer to me.  How can the air drag on anything?  It's not a bunch of invisible ropes.  In a bucket type machine the air pushes on the concave side of the bucket being driven and slips past the convex side of the bucket moving up wind with a greater force acting on the driven bucket.  There is drag in the normal sense acting on the convex one, but that retarding force is less than the pushing force acting on the concave one.  If someone has a better way to describe the operation of that type of VAWT now is the time to speak up.

Your description of stall for a vane or air foil is correct, but you are leaving out the effect on the drag force that acts to retard to motion of the air foil.  When stall is reached and the attack angle increases above the stall point at 12 to 14 degrees lift decreases rapidly and drag increases greatly.  For an airplane the reduction in lift is catastrophic, not so for a wind turbine.  But the combination of loss of lift and increased drag can have adverse effects on the power output of the turbine.  In my view carving the blades from 2 by 8's or the like guarantees that the blades will be in stall at the design TSR for about the inner half of the radius.    

[fcfcfc]

Hi: I think they use "drag" as a descriptor because drag implies resistance to flow. In any gas or fluid moving there are two pressures involved when a surface is encountered. Skin pressure and forward pressure. As one increases the other decreases. The venturi effect is a good example of these two different pressures at work. Lift on a wing another, as the faster moving flow over the top of the wing gets increased forward velocity and ergo pressure, and the resulting reduced skin pressure causing lift. A rocket nozzle, etc.. I suppose they could call it Push/Pull, but in a way that describes lift designs as well. How about, "Anti lift" or "The other force" ...LOL...

[CmeBREW]

I know "Stall" can come from various factors having to do with the blades.(too small of blades, angles, etc.)  

I don't know if I made a mistake or not.  I thought "stall" could ALSO refer to whatever SOURCE is ultimately causing the blades to "stall."  That is, being HELD BACK (from some source) from reaching a momentum (rpm) of speed and torque for optimal generation of power.

If the term "STALL" is ONLY used in reference to the blades alone, then I apolozise if I misused the term.  I thought the actual CAUSE of the "stall" is the most important thing.  

[wdyasq]

All of you should look up the term "stall" with respect to aerodynamics. It isn't hard to understand, it is hard to explain.

The stall effect can be demonstrated by putting one's hand outside the window of a moving vehicle. Starting with the hand parallel with the road amd tilting the hand slightly one can feel the hand 'lifting'. This lift can be negative or positive. There will be a point where the airflow separates from the flow about the skin and the force back will become great while the lift decreases. The hand has gone into 'stall' at this time. One can notice the small angle where the hand goes from very high 'lift' and not much drag to a lot of drag and not much lift. On a wing or airfoil this is the maximum angle of attack.

Now - relating this to a VAWT. Most use a symmetrical airfoil. Guessing that the maximum AOA (Angle Of Attack) is 15 degrees. a lift type VAWT develops lift power only one time through about 30 degrees of the blade arc. This is only one of the reasons a VAWT has trouble developing power. If one has a two blade "H" style rotor, they get two surges of power that the machinery has to handle each revolution. This is only part of the reasons the ones built by Sandia Labs failed, but one of the major ones.

End of lecture for the present. There is literature out there. It is free. It will be cheaper than recreating the mistakes on your own.

Ron