Posted by *Ron Rosenfeld* on February 25, 2009, 8:45 pm

On Wed, 25 Feb 2009 11:36:39 -0600, david.williams@bayman.org (David

Williams) wrote:

*>We're all out to lunch. The turbine blades will hit the guy wires. *

*>That's why commercial wind-turbines have unguyed towers. I suppose *

*>there could be guys right down near the bottom of the tower, lower than *

*>the blades go, but they wouldn't be much good. *

Well, that depends on the sizes. Although I agree that the large

commercial turbines, that I've seen, are all on unguyed towers.

My Bergey-XL is on a guyed lattice tower, though. It has a 7m diameter

rotor; it's on a 30m tower, with two sets of three guys -- one at 27 m, and

the second at 14.8m.

--ron

Posted by *Curbie* on February 25, 2009, 8:52 pm

Oh crap, I thought I had it until reading your reply!

I thought (from previous examples), but expanding using your example:

"For example, suppose there are three guys, each at 45 degrees from

horizontal, and at compass bearings 0, 120, and 240 degrees from the

tower. Suppose the wind is blowing from bearing 60 degrees, exerting

500 lbs force on the turbine. The additional downward force produced

by the tensions in the two guys at 0 and 120 degrees will be

500 x sqrt(2), or about 707 lbs, making a total downward force on

the tower base of 1707 lbs. The tensions in those two guys will each

be 500 lbs. The third guy, at 240 degrees bearing, will be slack."

That the additional vertical (downward) force on the mast from a 60

degree windward breeze placing a 500lb horizontal load on the turbine

would add 500lb to the base loading (through the guys and mast) and

707lbs of additional (45 degree) guy tension divided equally between

guys at compass points 0 & 120?

How can guys at compass points 0 & 120 have 707lbs each of tension

without exerting an additional 707 x 2 vertical load on the base?

Thanks for the reply, I'm not trying to argumentive, I'm just confused

now?

Curbie

On Wed, 25 Feb 2009 10:13:40 -0600, david.williams@bayman.org (David

Williams) wrote:

*>For example, suppose *

*>there are three guys, each at 45 degrees from horizontal, and at *

*>compass bearings 0, 120, and 240 degrees from the tower. Suppose the *

*>wind is blowing from bearing 60 degrees, exerting 500 lbs force on the *

*>turbine. The additional downward force produced by the tensions in the *

*>two guys at 0 and 120 degrees will be 500 x sqrt(2), or about 707 lbs, *

*>making a total downward force on the tower base of 1707 lbs. The *

*>tensions in those two guys will each be 500 lbs. The third guy, at 240 *

*>degrees bearing, will be slack. *

Posted by *daestrom* on February 25, 2009, 10:48 pm

*> Oh crap, I thought I had it until reading your reply!*

*> I thought (from previous examples), but expanding using your example:*

*> "For example, suppose there are three guys, each at 45 degrees from*

*> horizontal, and at compass bearings 0, 120, and 240 degrees from the*

*> tower. Suppose the wind is blowing from bearing 60 degrees, exerting*

*> 500 lbs force on the turbine. The additional downward force produced*

*> by the tensions in the two guys at 0 and 120 degrees will be*

*> 500 x sqrt(2), or about 707 lbs, making a total downward force on*

*> the tower base of 1707 lbs. The tensions in those two guys will each*

*> be 500 lbs. The third guy, at 240 degrees bearing, will be slack."*

*> That the additional vertical (downward) force on the mast from a 60*

*> degree windward breeze placing a 500lb horizontal load on the turbine*

*> would add 500lb to the base loading (through the guys and mast) and*

*> 707lbs of additional (45 degree) guy tension divided equally between*

*> guys at compass points 0 & 120?*

*> How can guys at compass points 0 & 120 have 707lbs each of tension*

*> without exerting an additional 707 x 2 vertical load on the base?*

I'm not sure David's numbers are right.

First, looking down from above we have a force acting at 0 degrees and a

force acting at 120 degrees that have to add up to a net force of 500 lbf

acting at 60 degrees (opposite the direction the wind force is acting).

This forms a nice neat equalateral triangle with each leg equal to 500 lbf.

Now, for a guy wire that is 45 from the horizontal to generate a reaction

force of 500 lbf horizontally, it must have 500 lbf / sin(45) of tension 707

lbf. The third guy will be slack.

A tension of 707 lbf in the guy will create 500 lbf in the horizontal

direction from the tower and also 500 lbf downward. With two guys, the

total downward force is double that or 1000 lbf. Add to that the static

load mentioned and you have 2000 lbf total downward.

The issue is that the two guys are pulling 'against' each other horizontally

if you look at it from above, but pulling 'together' downward if you look at

it from the side.

daestrom

P.S. Hopefully I got it right this time, I've worked it out three times and

gotten three different answers :-/

Posted by *Curbie* on March 2, 2009, 10:37 pm

On Sun, 01 Mar 2009 20:51:31 -0600, david.williams@bayman.org (David

Williams) wrote:

*>It's more fun if the wind direction isn't so symmetrical with respect to *

*>the cables. For example, it could be blowing from bearing 90 degrees. *

*>But maybe we'd better not get into that! *

Oh please do!

I'm finally coming to realization that the use of angles in the guys

create new forces which add together on the design elements of tower.

The sharper the angle, the greater the newly created force. I'm still

chasing around the forces in the previous round of examples, but would

like to see an example of wind blowing from bearing 90 degrees.

Thanks.

Curbie

Posted by *ralleyrat* on March 2, 2009, 11:51 pm

*> For guyed towers there are two points of ground contact (support), 1)*

*> the tower base and 2) the guy wire anchors.*

*> Is the loading on the base only vertically downward from weight of the*

*> mast and turbine, or does horizontal forces from wind velocity place*

*> upward forces from the guy anchors that translate into increased*

*> downward forces on the base?*

*> Thanks.*

*> Curbie*

The guy wires add a compression, (or 'down') load to the mast.

Their tension takes side loads to the ground.

Stress on the anchor points is a resultant vector.

Draw the triangles and figure it out.

>We're all out to lunch. The turbine blades will hit the guy wires.>That's why commercial wind-turbines have unguyed towers. I suppose>there could be guys right down near the bottom of the tower, lower than>the blades go, but they wouldn't be much good.