Yaw Pivot Orientation

[egreen]

I realized today while working on my 6ft wind turbine that I have the yaw pivot to the right of the blade hub (looking from the front) and the blades have been carved to rotate in a clockwise direction.  After looking at pictures of wind turbines on otherpower.com I recognized that they have the yaw pivot to the left of the blade hub.  Is this going to cause a problem when it come to furling?

[electronbaby]

It will not make a difference as far as furling performance goes. Hugh makes reference to this in his latest manual and actually states that while having the machine furl to the right (opposite from what you have done) that the blades should rotate counter clockwise. This prevents the gyroscopic forces that are put on the blades while furling, from forcing them back and possibly causing them to hit the tower.

If you have made your chassis assembly to furl to the left instead, maybe it is a good idea to allow your blades to spin clockwise. You then would minimize the risk of a tower hit. I cant see any reason why this wont work in reverse...

[egreen]

My blades do rotate in the clockwise direction.  So I guess it'll be okay.  I'm really glad that it doesn't matter which side the yaw pivot is on because I've already welded the frame together.

The gyroscopic force would have to be pretty strong to bend wooden blades back several inches to hit the pole.  I'd think that the blades would break if they bent that far before making contact with the pole.

I have Hugh's "How to build a wind turbine" book... is that the manual that you refered to?  If so I must have missed it.

[scoraigwind]

In my 2005 plans 'how to..' I describe how to furl to the right (looking at the wind turbine from upwind.  that's how I always did it.  the blades turn clockwise, again because that is the way I always have done it.  In this situation, if the wind hits hard and the blades spin up very fast before furling, they do get pushed into the tower by the furling motion.  It's amazing how far back they can bend without breaking (try it)!  But when they do hit the tower they do break.

This is a very rare problem.  If the blades are thick enough it should never happen.  But for safety I have decided to change the habits of a lifetime and furl the left.  Life is an adventure.  It has been hard for me to get my head around the change but I like the extra factor of safety and so far as I know there is no downside to it.

All the designs in my new publication 'A wind turbine recipe book' furl to the left (although you could easily reverse this if you prefer for some reason).  At present this book is only available in metric units but I am working on an inches edition and have set my self the goal of finishing it this year.  Not long to go, yarg.

The new book is better in many ways (and no doubt worse in others) than the old one.  Most notably it is better structured because I wrote it all in one go from scratch whereas the old one is a document that grew organically.  So throughout the 2008 recipe book there are tables of sizes for each of six different machines from 4 foot up to 14 foot diameter.  

It's a really organised piece of work.  I am still polishing it a bit and I put the most significant changes on an upgrade page at http://www.scoraigwind.com/axialplans/recipe%20update/index.htm

That's another little job I will need to catch up with when the new editions come out.  There will be 2 editions - metric and inches - for use with the two sizes of magnet and the two types of tape measure.  I don't personally understand why anyone would work in fractions like 9/16" when they could use 14 mm but I realise that a lot of you do.

Sorry for rabbiting on but it's exciting to me.

[Dave B]

Hugh,

 And to others out there wondering about this. Personal experience has proven that procession (specific gyroscopic forces) is beneficial when set up as you have recently explained. (furl left, blades rotate clockwise as viewed from up wind.) The opposite holds true as mine now furls right with counter clockwise blade rotation as viewed from up wind.

 Many will argue (and have in the past) it makes no difference and for 2 very good reasons. 1) it is not an easy switch to make and 2) if they have not experienced a problem why go to the trouble of such an extensive change.

 I am happy to see you have elected to mention it and the reasoning behind this change. I agree with you 100 % based on experience. Dave Moller and I did some blade testing last year and could not believe a 6' face laminated blade bent 17" at the tip supported at the root before failure. Photos and specs. of this test can be found here at : www.royalfabrication.com

 Thank you again Hugh for posting this information. Side furling is much more controlled and predictable in the more extreme conditions when set up with the above relationships between offset side and blade direction of rotation.  Dave B.  

[Dave B]

Just one more comment on this offset side VS. blade direction of rotation thing. This will probably cause some controversy also but the mystical "blade seeking force" that seems to fight against furling for some will become less of a mystery also when the relationships discussed previously are used with a side furling system. Gyroscopic forces are a very interesting study. I am sure many have seen similar to this (bike wheel precession) http://www.local12.com/mediacenter/local.aspx?videoId=24160@video.wkrc.com&navCatId=179

 Dave B.

[egreen]

Hugh,

Let me see if I have this straight...

If I have the yaw pivot to the right of the blades (looking from upwind) then it will furl left, correct?  If so then that means I'm furling left with a clockwise blade rotation.  So if I understand what you are saying, then because of my ignorance in actually follow the directions in your book that I've unknowingly set the furling up correctly?

[egreen]

I made a typo in my last post and I don't know how to edit it... I should have said "...my ignorance in NOT actually following...".

Sorry!

[scoraigwind]

Both ways will work very well, but the way that I have done it for thirty years until this year is slightly more prone to tower strikes and so yes, my new way and your way are slightly safer.

if:

the alternator and blades are left of the tower centre looked at from upwind and the blades turn clockwise,

 or

  the machine is right of the tower centre and the blade go counter clockwise,

    ...then you are slightly safer than the other options.

The fact that I went thirty years with hardly a single tower strike shows that this is not a big deal (until it happens to you).

[Ungrounded Lightning Rod]

Let's try it another way.

Consider the rotating blades:  When you apply a force to make it yaw, you try to twist the disk of spinning blades.  The gyroscopic effect consists of the reaction to the applied force being "carried a quarter turn" by the spin of the blades.

So the side of the blades you want to push TOWARD the mast is the side that is going UP.  Then, when that push is moved a quarter-turn, the result will be the blades tilt so those at the TOP move toward the mast axis (above the end of the mast) and those at the BOTTOM move away from it.

Of course whatever direction the mill "nods its head" during furling it will do the opposite during UNfurling.  But the "nodding" from furling is stronger than the nodding from unfurling.  (This is because the mills is spinning faster (raising the gyroscopic effect) and the wind gust force causing the furling is unlimited while the tail force causing unfurling is limited by the pivot geometry and generally opposed by some remaining wind force.)  So you design it to be safe for the hard case of furling and let the easier and limited unfurling case be handled by the geometry of the mill.

Thus blades should rotate so they're going down on the mast side of the offset turbine axis.

[egreen]

Thanks for the replies everyone!  I'm glad to see that I accidentally did the correct thing... haha.

Hugh, I look forward to getting a copy of your new book.