Brian’s Morning Newsletter

Thursday, October 21st 2010

Good Morning

Posted to the OtherPower forum this morning

I hope this suffices for a BMN this morning, I need a break, badly. Anyway of course I think it is good stuff, info, info, info, right! What could be better?
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We are getting readier for a new set of blades. Kevin Murphy is the designer, I hoped he would post this so you all could ask him questions, alas, it’s me translating.
Concerns:
Load.
New battery load of more than twice the AH rating plus sealed cell over flooded cell has our Other-power book built 10 footer, 2″ disk magnet, 24 volt 50 foot tower (on top on hill) massively under-performing.
Blade length.
Not realizing the critical correlation between blade length and turbine/tower offset I decided to make the third set of CNC blades 6 inches longer, now the turbine isn’t facing the wind properly.

Deep thought and then Action (hopefully, right?).
Kevin said we needed RPM and wind speed data from the mill, but the more he looked, the more it looked like TSR is effectively a “given” and what we need is to set the turbine up with varying loads, and see how it performs at various RPMs.
Then as he worked on the problem of how to get the blades to be more effective aerodynamically something interesting resurfaced, the blade design in the books are pretty much as they say, “tweaked about as good as hand carving needs to get them.”
I am no engineer, never claimed to be, really wish Kevin was explaining this stuff, because frankly, I am more of a “tear it out and change something hopefully radical,” type of guy. I kept asking dumb questions like,” if you did have RPM data and wind speed data how would this affect the model?
“Not as much as better wind would I would hear as an answer.”
Anyway, undeterred by my ignorance, Kevin is forging forth,

I am working more days and hours that ever, my wife is home recovering from surgery on her thumb,
(trapeziectomy with ligament reconstruction and tendon interposition) yeah.

The Day before yesterday I brought home a 10 inch Craftsman table saw

So I am happy

Kevin is still modifying the design, this morning I see this model in my inbox

I see that the blade not being constrained with “hand carving techniques” has double edges, I know he said he was working on a multiple twist profile. Stated in the only terms I know, so pardon the crudeness,  this is also a double curve style blade; convex on top, concave on bottom. Maybe if we’re lucky, people will ask enticing questions of Kevin, and he will reply here.

Like I said, I am the rip it up, and redo it guy. I bought a new saw, on one visit to Santa Fe to take my wife to the hospital there, another time I went to Home Depot, found and scored 9 rough cut Western Red Cedar full dimensional 2″X4″x8′s.
With the saw, and the rough cut cedar in my shop it is my intention to do the lamination here this time, then take the three blanks over to my buddy’s shop and let Kevin do his magic with  the CNC router.

So yeah, our new blades will be Cedar, we’re going back to five foot, to rid this system on the errors associated with randomly changing the TSR and the off-set
The good news is some of the technology I was beginning to feel was way over my head, isn’t, in fact it’s all relative.
The trick, is figuring just how to get our foot in the door of understanding
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Okay, okay, the dawn has broken, such as it was. We had rain coming down in torrents last night, it woke me up. It has to rain pretty damn hard to hear it through the 10 inch thick insulation of our ceiling.

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I don’t know, again, I may have already posted this picture, but I still like it a lot.

Here I am exploring the position of the turbine tail compared to the blades. The tail is supposed to be perpendicular to the blades, except when furling. When furling the blades are pushed back by high winds toward the tail. To me it looks more like the tail is moving while the turbine stays oriented which ever direction it was. One of the wind turbine gurus suggested we add a ribbon to the tower, and perhaps another ribbon to the tail to better observe what is happening.