Sprung furling

[Capt Slog]

This might be better in the newbie section, but it didn't feel like a newbie type of question.

Has this ever been done?

I hope this is clear enough.  The white circle represents the tower/pivot looking from above.  The black arrows at the bottom are the wind, the zig-zag line is a spring.

I would think the spring would have to be under a little tension at the begining to give the force against the offset.  It would also need some sort of stops and maybe damping.

The reason I ask this is that most of the furl designs I see rely on welding.  I don't have this facility and don't want to pay for it, this seemed like something that could be made with a bolted on hinge and is very adjustable.

[Capt Slog]

I can't see an image in there and have probably got something wrong.  Please have a look at the only entry in my files.

[AbyssUnderground]

Its a .doc file for use in a word processing program.

http://www.otherpower.com/images/scimages/7027/sprung_furling.doc

[Flux]

Yes you can user a spring to replace the gravity component, but you still need an offset to generate the furling force.

As shown it wouldn't work.

You can use a hinge and bolt it on at an angle if you know what you are doing .

You can even work without an offset if you go back to Wheelers original idea with a side vane.

Springs are not without their problems but have been used, it is a question of understanding the forces you are dealing with.

If you search back through my files I am sure there are sketches in there from trying to explain furling to someone who just didn't get the basic idea.

If you are stuck, come back and I will try again to explain it.

Flux

[DanB]

Odds are youll want some parts welded anyhow so I wouldn't give up on that idea.  I think gravity is more reliable than a spring - but springs have been used many times on many machines.  

There is an old posting I made about furling a couple years ago where I mention a spring just to help get the idea across about how it works:

http://www.fieldlines.com/story/2003/7/23/91925/4493

[Norm]

You can make it out of wood like Hiker did....

http://www.fieldlines.com/story/2006/7/21/85027/0260

      ( :>) Norm.

[Capt Slog]

I do understand the usual furling method, I think it was the post that you are refering to that finally sorted it out for me Flux  . But as I said in my post, I think I'd find it hard to build as it requires fixing some sort of peg for the tail hinge at a compound angle.  I can't see anyway of getting that peg secure without recourse to welding

Unless we are talking about different things, I thought had an offset in my drawing.  Isn't the offset the distance between the yaw point and the blade centre?  (The yaw point in my diagram is the white circle = the top of the tower.)

I'm not wanting to put huge blades on this, I can't see me going above 4 feet diameter.

[Capt Slog]

Thank you for posting the link sir.

[Flux]

Sorry, I didn't get the significance of the white circle. Yes you do have the offset.

You can do the gravity furling thing perfectly well without having to use a peg. It's convenient for those who can weld, but you can support the inclined hinge from two brackets, top and bottom. All that matters is that you get the two angles.

They can be combined into a single point at the back if you want although it is simpler to understand if the vertical angle and the horizontal one are kept separate as in the usual Dan style hinge.

The spring will work perfectly well if you find it easier to do, but you need a long spring with some initial pre-load otherwise the force increases with angle too rapidly.

You will have to experiment with spring strength.

Flux

[RP]

The forum here does not support posting Microsoft Word documents.  If you can save the picture as a jpeg or gif, you can post a reply to this story with the new picture for everyone to see.

One thing to consider about springs:  Over the years, I've had to reform the ends of many springs around the house including the dishwasher door, various recliners and several screen doors.  In every case it was the end of the spring that broke and it was annoying every time.  

If your spring breaks it will be at the top of your tower and will probably happen during the worst possible weather you can imagine.  :-)

[Capt Slog]

I'll bear that in mind about the springs, thanks.  But if the springs fail, the turbine will go to fully furled and stop there untill repaired, so in that way it is 'fail safe'

[RP]

If you want to go this route consider a torsion spring setup.  With enough turns in the spring, the overall flexure can be pretty low giving a long life.  Also, the ends of the spring will be "pushing" rather than "pulling" on the wire so they should be under less of a point stress.