Author Topic: Stupid things we (ok I ) do  (Read 14218 times)

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Offline rossw

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Re: Stupid things we (ok I ) do
« Reply #30 on: February 23, 2012, 12:27:39 am »
Perhaps something similar is happening on the turbine at very high speeds, instead of drag pushing the rotor off axis the blade are producing lift towards the wind instead of the normal away from wind direction. Essentially it's in equilibrium pulling the turbine forward as much as the wind is trying to push it back.

Both that, and the gyroscopic forces make a degree of sense.

Be pretty easy to tell - if the prop follows the wind quickly, it's more likely the latter explanation. If it wants to stay as it was, then gyroscopic forces seems more likely!

Offline ChrisOlson

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Re: Stupid things we (ok I ) do
« Reply #31 on: February 23, 2012, 06:50:17 am »
I think it has to be aerodynamic forces causing the problem with no furling at high rpm.  Gyroscopes tend to precess.  And the heavier the rotor, and further it is from the yaw axis, the greater the precession force is.  Theoretically this should make a right hand turner/left hand furler (viewed from upwind) tend to precess to the furl side.  But if you calculate the precession force, it is so minute that it is impossible for it to be a factor.

The moment of inertia of a turbine rotor is quite large.  And because of this it will tend to resist changes in its state.  But it will never firmly plant it in the direction of the wind and refuse to move, and even follow the wind when the wind changes direction, as Flux has described.  There is no way that can be described with any of the engineering math I ever learned in college and practical application.

I believe it is purely aerodynamic.  These offset head tail waggers are pretty much unknown in the commercial world of wind power except for a few examples like AWP (designed by Hugh) or Bergey.  And Bergey recognizes that there are times when "excessive power output" can happen with the Excel.  So I dunno.

There was some dude on Fieldlines that had a big grant and a wind tunnel.  He wanted somebody to design a turbine for him with this grant money.  I tried my damnest to get him to let me use that wind tunnel, and he even said he would let me use it.  Except after that, the guy evaporated or something and he forgot all about me and my wind tunnel time I was supposed to get.

If I could've gotten a slot in that wind tunnel I would've had a turbine loaded up in the truck and heading to where ever it is in a matter of a few hours.
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Chris

Offline oztules

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Re: Stupid things we (ok I ) do
« Reply #32 on: February 27, 2012, 07:35:59 pm »
"But it will never firmly plant it in the direction of the wind and refuse to move, and even follow the wind when the wind changes direction, as Flux has described.  There is no way that can be described with any of the engineering math I ever learned in college and practical application."
 
Chris, I had reason to drop in at the larger turbines near town yesterday. I was called to look at a yaw motor (3/4Hp 14:1 reduction box and then more gearing to the head).

That was simply bearings had exploded  (nearly 30 years )and the bits shot into the windings and killed it... not what this is about actually.

What took my attention, was that I had the yaw motor in my hands, but the mill was drifting in and out of cut in 1-5kw.... (panel next to me)but there was no yaw... as I had it.

I thought I was working on the next mills motor, but it was the mill above me (control room at base).

I questioned the owner, who said that provided the wind did not change direction rapidly, the mill would stay directly into the wind and follow it... producing power all the time......... weird science. I didn't believe Flux many moons ago, but have seen it with mine, and now with a biggie ... its true for sure.



...................oztules
Flinders Island...... Australia