Curious result from wind damaged test rig

[MattM]

I've been fashioning test rigs out of sheet metal, which I've already been informed plenty of times is not the material of choice around here.  And I used threaded rod for the pivot, which I also know was too light for the job.  The long story short is the test rig had its pivot rod bend in high winds to the point where the turbine was pointing up in the air at about a 45 degree angle and turned opposite of the wind which made it spin at a higher rate of speed then when it was facing the correct direction.

A = test rig blade design.  I was aiming for hollow aluminum blade with a ten foot diameter, actually ended up closer to 11'.  Basically a two piece construction with heavy aluminum forming a z-shape on the bottom and very thin aluminum cap that slid over and hooked onto the "z".

B = shows basically where the pivot rod bent allowing the turbine to tilt.  The pivot sits atop a 4" water pipe and allows free rotation of the entire turbine.  The tail is drawn out of proportion.  The red arrows show the wind direction that began the counter rotation.  The bent turbine seems to be gathering steam from some kind of ground effect.

C = shows basically the direction of the surfaces that seem to be creating the effect.

What is normally the front of the blade is actually acting like some kind of Lenz vertical wind turbine system, only it only seems to work effectively while in a steep pitch.  Once straightened up it loses a lot of the effect.  I haven't tried it as a pure vawt simply because I do not want to break anything, but tilting it lower to the ground so it is closer to vertical also has a negative impact on its rotation.  One curiosity about it is that it seems to be less prone to slow down when its up to 20-25 degrees off the direction of the wind, whereas that normally tends to really slow down a regular turbine.

The blades are 6.25" wide by 1.5" thick, the dimensions chosen to fit the hub which is designed for mounting blades made from 2x6 boards.  That extra .75" is the front lip of the "z" on the front of the blade.  The original pitch was not optimized in any way, shape, or form; it is merely the slope from corner to corner.  It actually has some 5" wide blade extensions at the root on front and back that taper down to the center of the blade just to increase surface area; it makes it start spinning in lighter breezes.

Going by handheld timing the blades rotate roughly 40% faster when put into the wrong position.  I'm just curious if anyone has seen this kind of effect before?  Its not really acting like what are normally defined as vertical or horizontal wind turbines.  The effect seems more a hybrid of both.

[spinningmagnets]

I've heard of the "Lenz2", shall we call this the MattM?

What voltage are you trying to generate? I've read that slower gens can produce some 12-volt juice.

Is there any way you could roughly estimate the wind-speed/RPM's?

This may be one of the few applications where a "tilt-up" furl might be appropriate compared to the most common and reliable standard furling system (just a thought, I have no actual experience with this).

[MattM]

I'm currently at the pre-generating stage.  Really the idea is to test materials how they hold up in my climate where spring and fall are the most stable wind.  The summer months are relatively dead here and we get the wind in strong bursts, so its not the most optimal place for wind generation.  That doesn't stop me from dreaming.  I can mill a lot of the materials I need, but some I just do not have today.  I'm still relatively young, have a few extra mouths to feed, still paying off the gas guzzlin' suv for the wife, and the wife simply isn't going for me to buy $250 worth of magnets and $50 of magnet wire... yet.  Doesn't sound like much but the other half gets irate when I buy stuff over $100 without her input.

[wooferhound]

Look at what is happening here ...

Lets say you have a set of props and they are pitched at the hub to a 45º angle

Now you take this prop rotor and Tilt it up at a 45 degree angle to the oncoming wind like the picture above labeled B

Now look at the props in relation to the wind. the props on the left are vertical  (high drag) and the props on the right are horizontal (low drag). I could draw a picture if you want. I think this is the effect that you are getting.

There is a story around here about this exact thing, but I can't find it.

[feral air]

It sounds like it was working like an autogyro to me.

It might be worth some more testing so here's a bunch of autogyro blade profiles in case you get an itch.

take it easy