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catchnthe-)))) Newbie Joined: 03/01/2009 Location: United StatesPosts: 24
Posted: 04:05am 24 Jan 2009
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Hello, I have read this phrase believe me when I say "more than 1 time." Working on a downwind first turbine build."
The article.
"Angle of Attack. The angle between the incident air and the aerofoil chord (line between the leading and trailing edges) is called the Angle of Attack. As a rule of thumb, the highest lift is developed at an angle of attack of about 10 to 12 degrees to the incident air. The point of stall, where the air flow detatches from the lifting side and the lift collapses, occurs at an angle of about 16 degrees. The AA that provides the highest Lift to Drag ratio is the angle of most interest to aeroplane designers, and occurs somewhere between 0 to 4 degrees, depending upon the aerofoil selected.
Wind turbine designers are primarily interested only in the component of the lift that provides torque in the plane of rotation of the turbine, and may select a higher AA to get more lift. The component of lift acting in the same direction as the actual wind only serves to load up the support tower (see Figure 2), so turbine and aeroplane designers have different views on lift."
With this being said... My frame Design is as follows:
2 plate frame, 1/4" x 6" X ? length, lower plate is ATTACHED to Yaw bearing with upper plate hinged in front, ahead of Ametek 30, positioned ahead of Yaw center pole with its shaft pointing to rear, this should (protect seal and front bearing) from the elements..hooked with a love-joy flex coupler connected to a 5/8"o.d. shaft,(a disc for manual braking attached to shaft) with 2 pillow block brg.s ( this will eliminate thrust on generator) shaft then attaches to propeller.
Lower frame has absorber for cushioning and has limit range stop (NOT SURE, AS TO HOW MUCH UP ANGLE TO ALLOW) for upward furl when high wind causes furling for it to return.
This "Angle of attack" I can not grasp this in relation to Horz.level.
Sorry Just a newbee can someone untwist this for me.
Thanks this site is Great.
Chuck S
Edited by catchnthe-)))) 2009-01-25Freedom allows us a lot "Please don't abuse."
Gill Senior Member Joined: 11/11/2006 Location: AustraliaPosts: 669
Posted: 09:19am 24 Jan 2009
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Chuck S,
This doesn't make sense.
I don't understand why you need to grasp Angle of Attack in the horizontal plane?
This is your furled position where you are trying to minimise lift creating further prop speed. By raising your prop towards horizontal, the Angle of Attack is deliberately made erratic, so limiting/reducing the lift as is the intention of furling to limit prop speed.
There is no difference to the basic Angle of Attack effect between side furling and lay back(horizontal) furling. The Angle of Attack is not a design consideration of furling whatever it's type.was working fine... til the smoke got out.
Cheers Gill _Cairns, FNQ
catchnthe-)))) Newbie Joined: 03/01/2009 Location: United StatesPosts: 24
Posted: 08:53pm 25 Jan 2009
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Thanks Gill,
I'd like to say,
The craftsmanship of projects on this site are really overwhelming. The amount of knowledge and information
truly great.
terms in conjunction with wind terminology of turbines can be confusing.
Furling to A side furling turbine is, I understand: A controlled, mechanical force used to reduce pressure onto blades thereby reducing prop speed.
With a measured weight attached to rear with 2 pulley's & cable. once pre-determined wind speed is reached angle of attach will raise prop up ( Maybe it will Not ?) thus pulling against weight and absorber & stopping at predetermined position.
In Our area here we only receive usable wind from S to Sw and north. So the Yaw will not swivel 360 degree only 180.
take care,
Freedom allows us a lot "Please don't abuse."
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 10:37pm 25 Jan 2009
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The bearing that allows wind tracking gives 360 degree movement. The yaw pivot bearing is independent of this and has a controlled[restricted] working region of angles.
Gordon.become more energy aware
Gill Senior Member Joined: 11/11/2006 Location: AustraliaPosts: 669
Posted: 01:12am 26 Jan 2009
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G'day Chuck S,
Firstly I'd have to take issue with [quote]Furling to A side furling turbine is, I understand: A controlled, mechanical force used to reduce pressure onto blades thereby reducing prop speed. [/quote]
I would state (most)furling as an increasing wind force overcoming a preset gravitational force via a mechanical means.
Again, [quote]once pre-determined wind speed is reached angle of attach will raise prop up [/quote] Totally incorrect! I feel you may be confusing prop 'lift' and attributing greater properties to it than is real. The term 'lift' comes from an airfoils use as a wing where the forces created are in an upward direction which lifts the wing. On a yacht the term 'lift' is still used though it is a side trust that is generated. On an aeroplane prop the term 'lift' is still used but the force is forward thrust. On a wind turbines prop 'lift' (& 'drag')is still used as the aerodynamic resultant forces of air flow over the airfoil section as in all the other cases, though this force gives the all important turning moment to the turbine.
Now the amount of 'lift' or in your case maybe we should call it turning moment is controlled by the 'A of A', again this influence effects turning moment only.
Furling is not bought on by rotation movment at all. The prop does NOT spin it's way into furl. You could have instead of a prop just a round fixed sheet of ply and it is the wind force on the ply that overpowers the gravitational force that causes the furling. This is the same for up-wind, down-wind, side-furling or horizontal furling. The mechanics may change but the basic physics do not.
Perhaps a key to your understanding of this is to know that as a prop spins up, it becomes more like a round solid object. The faster it spins the more solid it becomes as an obstacle to the wind. The greater an obstacle it is, the more pressure is exerted on it. The force of this pressure together with the offset from a pivot is the inducement to furl. So we could change the spinning prop for a disc of non spinning wood so long as it has the same 'solidity' and we have the same inducement to furl.
No Prop. No A of A. But an equal furling device. Proving those are not the influences that cause furling.
You'll have to reassess your understanding of the entire process I'm afraid.
On the matter of wind tracking,
It is generally considered not wise to limit yaw.
This is typically the knee jerk response to fears of cable winding around the tower. If your winds are as predictable as you claim then there is not the tangle problem to rectify. If not so stable, then you'll have the windmill head bashing against stops, stressing tower, guys, mounting and furling mechanisms and fatiguing prop mountings and blades. Mills have enough stresses and vibrations as it is. I wouldn't be adding to this many fold. Easier to feed the cable down the centre with a connector on the bottom to take the twist out every month. Edited by Gill 2009-01-27was working fine... til the smoke got out.
Cheers Gill _Cairns, FNQ
catchnthe-)))) Newbie Joined: 03/01/2009 Location: United StatesPosts: 24
Posted: 02:09am 26 Jan 2009
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Thanks Gill,
Your response cleared up a lot in my understanding of terms used here.
I appreciate your taking time to explain.
It remove the cloud "so to speak"
Thanks Again
Chuck SFreedom allows us a lot "Please don't abuse."
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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