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Forum Index : Windmills : Tail Pivot Angle

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C-Systems
Newbie

Joined: 09/07/2006
Location: United States
Posts: 3

Posted: 11:50pm 11 Feb 2007

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Glenn,
I was sure glad to see your new page on furling. I tried the formulas, but couldn't seem to get the tail pivot angle right.

It wouldn't come out even when I plugged in the figures from your example.

Maybe someone could explain to a non-engineer like me how it works. Is it "sin of -1 x (turbine moment/tail drag)"? I get negative #'s.

Thanks again for a Great Site!!

Gill

Senior Member

Joined: 11/11/2006
Location: Australia
Posts: 669

Posted: 05:17am 12 Feb 2007

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Hi C-Systems,
Your right Steve the formula is not correct.
I think it should be:

Calculations:

Turbine Thrust = Diameter2 * WindSpeed2 / 24
Turbine Moment = Turbine thrust x Turbine offset
Tail pivot angle = sin-1 ( Turbine Moment / Tail Length/cos45/Tail wt)
Tail Weight = Turbine Moment / Length of tail /Sin ( Pivot angle in degrees ) / Cos(45o)
Tail Length = Turbine Moment / Tail Weight / Sin ( Pivot angle in degrees ) / Cos(45o)

From what I see, to calculate the Tail Moment you have 3 interdependant variables to consider.
The 3 variables are: Pivot Angle, Tail Weight and Tail Length.
In essence you set an arbitary figure for two of these then calculate the third.

In the example, tail weight was set at 20Kg and pivot angle at 20deg, this then allowed the tail length to be calculated.

Juggleing the calculations allow to say, nominate a tail length and a pivot angle and then calculate the weight.
This is the most practical method of field adjusting the furling speed.

Remember that the calculations have been simplified for explaination and are a designers guide only.
Field adjustment should be expected.

Please note the Tail Length diagram is incorrect also. It should be:

This sketch may also be of assistance:

Let us know how you go with that please.

PS. I conclude sin-1 means cosin.Edited by Gill 2007-02-13

was working fine... til the smoke got out.
Cheers Gill _Cairns, FNQ

RossW
Guru

Joined: 25/02/2006
Location: Australia
Posts: 495

Posted: 09:06pm 12 Feb 2007

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Gill said
PS. I conclude sin-1 means cosin.

I think you mean arcsin(), cosine would be the same as sine, but off by 90 degrees.

      -1
   sin

is usually used to convert back to an angle, eg

      -1
   sin ( 0.5 )   is 30 degrees.

not,   sin (-1 * 0.5), which would be -0.0087

C-Systems
Newbie

Joined: 09/07/2006
Location: United States
Posts: 3

Posted: 01:34am 13 Feb 2007

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Hi Gizmo,

Thanks for your prompt response guys.

I've been trying to plug the formulas into a spread sheet, with conversions from U.S. to Metric units. So far so good, but I still could use some help.

I have the tail moment as being: TAIL MOMENT= TAIL LENGTH x TAIL DRAG. It seems logical that the pivot angle should be included though, so what should the working formula look like?

I also agree that nominating a tail length & pivot angle to get the tail weight is more practical.Would the Tail Pivot Angle formula be arcsin(turbine moment/tail lgth/cos(45)/tail weight)/B]?

I tried to get to you on-line, but your site seems to be down. I'll try to get to the forum to see the illustrations you sent me. For some reason they didn't show up, but thanks.

Thanks again for your help. I'll stay in touch.

Steve

"Everything should be made as simple as possible, but not simpler." - Albert Einstein

Gill

Senior Member

Joined: 11/11/2006
Location: Australia
Posts: 669

Posted: 08:41am 13 Feb 2007

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Sorry Gents,
I stand corrected. (Again...)

Hope this sits better with you then.

Tail pivot angle = Arcsin ( Turbine Moment / Tail Length / cos45 / Tail wt )

So lets go again:

Calculations:

Turbine Thrust = Diameter2 * WindSpeed2 / 24
Turbine Moment = Turbine thrust x Turbine offset
Tail pivot angle = Arcsin ( Turbine Moment / Tail Length / Cos45 / Tail wt )
Tail Weight = Turbine Moment / Length of tail / Sin ( Pivot angle in degrees ) / Cos45
Tail Length = Turbine Moment / Tail Weight / Sin ( Pivot angle in degrees ) / Cos45

Sorry I can't edit 'The Page' as we go but perhaps Glenn will pick up on it later when the dust settles.
Edited by Gill 2007-02-15

was working fine... til the smoke got out.
Cheers Gill _Cairns, FNQ

Gizmo

Admin Group

Joined: 05/06/2004
Location: Australia
Posts: 5116

Posted: 10:45am 13 Feb 2007

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Yes I'm lurking in the background. Gill if you could do like you did last time and edit a copy of the furling web page I would really appreciate it. I'm a little tied up trying to keep the web site alive at the moment.

Glenn

The best time to plant a tree was twenty years ago, the second best time is right now.
JAQ

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