blade progress - 2 (heavy pics)

[kitestrings]

Greetings,

Here's a few more pics of our blade progress.  The blade paint rack worked very well.  I just used a carriage bolts on the root end and a nylon acorn nut on the tip end.  Threading them up snug allows you to rotate, but hold them in any position.  I wish I'd thought of using it for sanding.

I can't take credit for the paint job.  That was my high school friend and autobody guru across town.  He genrerally follow this outline, except for using what I understand to be comparitively much harder one-part polyurethane top coat (which wasn't available when this was written):

http://homepower.com/article/?file=HP100_pg138_QandA_6

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Here's a couple picks of the wind farm viewed from my yard.  They're trying to compete I think .

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~kitestrings

[fabricator]

Those look heavy on root and light on airfoil.

[birdhouse]

fab-  i agree.  my blades look kinda similar.  very heavy and thick at root, though my airfoil does begin much closer to the root.  makes for very robust blades that don't flex much.

just that beautiful paint job alone must make them produce an extra 100w!   

seriously though.  nice work!  looking forward to seeing the juice they make!

adam

[kitestrings]

Yes, and there are some admitted tade-offs; flexibilty vs. unsupported end grain at the root for one.  Viewed from the back of the blade it is a bit deceiving (because they're so wide).  The cut/drop is pretty deep right off the say 2nd & 3rd stations.  It is abpout 15-20 degrees as I recall.  You can see it better here:
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Still, Neilho (my partner on this project) & I have been having quite a bit of discussion about the root end treatment.  They are one piece stock, with some knots, imperfections and drying checks, etc.  I think with the next (laminated) set I might feel braver about taking them down more.

~kitestrings

[kitestrings]

Adam,

my blades look kinda similar.

So how do they perform for you?

[birdhouse]

kitestrings-
i don't really know....     my mill is a 8.5' dia based on a servo motor on a 70' tower up at my ranch.  i haven't been up there a lot as of late.  i do know the blades "spool" up awful quickly when i can barely feel an wind at ground level.  the most i've seen out of it is 150watts, again with almost no detectable wind at ground level.  so i guess they work well??

i do know they are incredibly difficult to flex the tips towards the tower.  mine were 3" thick at the root with a high max (corner to corner) angle there.  this may make them start up more quickly, but i don't know that that really matters as there is little power in those wind levels anyways... 

my next project with the mill is hooking up a doc wattson through a shunt so i can gauge performance in a more specific manner. 

adam

[fabricator]

With those output numbers you won't need the external shunt.

[birdhouse]

fab-
yea, i hear ya.  i've yet to witness it in any thing more aggressive than a slight breeze though.  plus, i find it really odd to use nice thick tranmission lines to minimize voltage drop, then wire nut them to some dinky wires coming out of a dinky meter.  i'd just feel better having the nice thick lugs on a shunt to attach my wiring to.  attaching a #3 to a #12?? just doesn't float well with me. 

maybe it's over board, but then hey, it'll be set to go when i build a bigger mill! 

adam

[fabricator]

True enough, I added the external shunt to mine, but mine has seen 70 amps for short periods.

[birdhouse]

fab-
not trying to bust your genny's, but i, as well as many would love to see a write up (with pics ideally) on how to hook the shunt to the doc wattson.  if you'd be so kind, maybe someone could make it a sticky in the "controls" section.  actually, this goes out to anyone who has the time to explain this in an in depth way.  

i've got them both ordered from power werx, but not quite sure what i'll do once they show up at my doorstep.  

if not, no worries.  i'm sure i'll figure it out once i crack the case on the wattson.  

done hijacking now.  sorry.
adam

[kitestrings]

adam, fab,

It's all good discussion.  Besides, I frequently find have to leave the room and come back in to remember what the original topic was .

If I were wiring a DocW, or similar gadget, I'd use the shunt too.  Not only is the wire dinky, but take a look at the internal components and connections, and this pretty quickly becomes the weak link.

Regarding blades, I frequently see examples here where (IMHO) the inner ~third of the blade has an airfoil that is pretty compromised from theoretical.  I assume this is due to 1) the limits of the thickness of the stock used, and 2) a general consensus that the amount of power there is relatively small.  I haven't ever seen start up torque to be much of an issue - perhaps even less so with an axial, where cogging is not an issue.  I once carved a two-blade'r/wind-spinner on a picnic table, with no plans (or expectations).  It started in a mild fart of wind.

I'm not criticizing, because mine are far from proven, but here's what I'd question:  As you move toward the inner stations, in theory, the angle and cord length increase, but there is also more material below the cord line, which makes the enter section thicker and 'blunter' for lack of a better term.  Many seem to just ignore this - the trailing edge becomes a straighline approximation rather than a curve.
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I know little of aerodynamic theory, but I've been led to believe that the 'backside' (low pressure side?) profile is much less critical than the angle of the airfoil and bringing it to a thin clean trailing edge.  Some of Hugh's blades seem to attest to this, where the rounded portion of the leading edge is very blunt (almost triangular).  Some of the blades I've seen appear to have an accurate profile, but are much shallower pitch - again likely limited by the stock.

Notice how much of the rounded portion of the airfoil is really pretty much parallel with the edge of the stock (moving say from the trailing edge toward the 'nose'.
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Just some thoughts, I welcome others, ~k