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poorman Newbie Joined: 10/05/2009 Location: United StatesPosts: 9
Posted: 07:02pm 01 Jun 2009
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So I finally decided on my first project I'm building a very small wind/solar system to power some lights and a fan in my kids tree house. I have about half of what I need (mostly windmill parts) anyways I have a bunch of 4 inch pvc pipe I am planning to try and build some blades out of. My question is all the tutorials and info I have come across says to quarter the pipe before making the blades which I have no problems doing I am just curious if cutting the pipe in thirds making a slightly wider blade would help or hurt harnessing wind power? any suggestions?Do not worry about your difficulties in mathmatics. I can assure you mine are still greater..... Albert Einstein.
niall1 Senior Member Joined: 20/11/2008 Location: IrelandPosts: 331
Posted: 12:32am 02 Jun 2009
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hi Poor man
nice project .....i think this is what is called a conundrum ...more blades equals more torque ...but less speed ...less blades equals a lot less torque ( grunt ) but potential high speed ..also good ...
it all depends on what the alt/motor sweet spot is ( maybe it needs to run fast to charge ....maybe slow
a jigsaw may be your new best friend here ... Edited by niall1 2009-06-03niall
poorman Newbie Joined: 10/05/2009 Location: United StatesPosts: 9
Posted: 01:30am 02 Jun 2009
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I am not really concerned with the number of blades so much as the width of them. It would seem to me (and I'm no genius)seeing as how I plan to use three blades, that instead of the standard method (cutting a pvc pipe into 4 equal sections and having a spare blade) would cutting the pvc into 3 equal sections making the base and tip of the blades a little wider with a little more curve. Will this produce more torque or speed? Or am I off my rocker and this will reduce both?
Do not worry about your difficulties in mathmatics. I can assure you mine are still greater..... Albert Einstein.
MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329
Posted: 03:50am 02 Jun 2009
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Ya know . . cutting plastic pipe sounds easy, but in reality it's anything
but easy.
If you want a really easy method to make blades, do what I do and make
them out of aluminum flat stock. I make my blades 1/8" thick by 2" wide
by 18 inches long each and mount them using steel screws threaded into
the hub in a "Jacobs" style (3 blades; 120-degrees apart). The hub is
made of aluminum also and each of three "tangs" are pre-bent to the
degree of attack. I use 45 degrees for "power" and 15 degrees for
"speed".
I should mention here that all my windmills pump air. I turn the
compressed air into electricity down on the ground in a dry room.
Back to the blade manufacturing: I merely cut them out on the band saw,
round the corners with a flat file and make sure each one weighs the
same. Due to density differences, sometimes one is heavier than the
others, so I just drill little pock marks near the tip to make the weights
the same. Don't drill at the root; you want that part to be strong.
I've had blades like these "sirene" in a gale-force wind (80 knots) and not
break. Aluminum, as it 'stretches' actually becomes stronger (tensile
strength). I usually paint the tips (last 3 inches) white to give the birds a
fighting chance!
Of course, you don't want to get whacked with any blade, plastic or metal,
so be sure to mount them out of range of little boys. That, by the way,
may be quite high!Nothing difficult is ever easy!
Perhaps better stated in the words of Morgan Freeman,
"Where there is no struggle, there is no progress!"
Copeville, Texas
poorman Newbie Joined: 10/05/2009 Location: United StatesPosts: 9
Posted: 04:14am 02 Jun 2009
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I did learn quite abit today about how "EASY" it is to make blades out of pvc. Built a set today and am thinking aluminum stock may be the way for me to go, what kinda cash am I looking at for hub and blades from stock? Do not worry about your difficulties in mathmatics. I can assure you mine are still greater..... Albert Einstein.
AMACK Senior Member Joined: 31/05/2009 Location: AustraliaPosts: 184
Posted: 08:49am 02 Jun 2009
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Poorman I am in the same boat, Have built the gen now need to build the blades. Let me know what design you went with, It may save me a lot of jig saw blades.*Note to self
1. Make it thick
2.Make it heavy.
3.Make it stronger than it should be.
4. Don't rush the first job as the second job will cost more and take mor
poorman Newbie Joined: 10/05/2009 Location: United StatesPosts: 9
Posted: 08:21pm 02 Jun 2009
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AMACK At this point I am still fiddling around I have the three blades made from pvc but dont have the hub built yet. am also going to build a single piece two blade and when I have the time will definitly try the aluminum stock. Being as how this is my first set up I am going small and cheap. As far as saving jig saw blades if you have access to one I think a band saw is easier. If you dont have access to one clamps are your best friend! Clamp down the pvc to whatever you can (steady table being best) cut slowly and if its your first time try to cut just outside the cut line (you will lose your spare blade) this will give you a bit more room for error and you wont lose any size due to sanding and shaping the blade. If all else fails an angle grinder will work but if your not carefull you can really screw up fast (I learned this on my very first attempt). the last thing I would do is use a circular saw, I framed houses for 10 years and am very familiar with this particular tool and if you dont have experience with it dont mess with it it can jump up and bite you before you even know it has jumped. All in all I believe the most important thing is to take your time and allways take the time to make sure safety is first! You cant build the next one if you lose your fingers building the first. Do not worry about your difficulties in mathmatics. I can assure you mine are still greater..... Albert Einstein.
AMACK Senior Member Joined: 31/05/2009 Location: AustraliaPosts: 184
Posted: 09:03am 11 Aug 2009
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Poorman, I went for the PVC pre-formed blades, they work well. I did have a big stuff up with them but that was not the blades it was the operator. They are quiet and work well at low wind speed. I have a AIR X 400watt factory made job and it makes more noise then the home made job. If you can get these blades in the states use them.. I had a go at my own blades and it drove me nuts, one blade easy three blades not so easy. Have a look at the photo's I posted in "MY FIRST WIND GENARATOR COMPLETE". It is all going well now as I got some shorter blades and went at it again.
Andy*Note to self
1. Make it thick
2.Make it heavy.
3.Make it stronger than it should be.
4. Don't rush the first job as the second job will cost more and take mor
MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329
Posted: 03:40am 12 Aug 2009
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Here's a link to a place that sells aluminum and plastic really cheap:
www.onlinemetals.com (US)
I buy a lot of 1" round T-6 aluminum and the hardware store charges me
$39 for what onlinemetals.com charges around $3.50! They will also cut to
order, so you can order maybe 4 blades of 2" by 24" and have one left over
in case you make a boo boo (it happens). By the way, they don't charge for
the cuts, which runs counter to almost all the other places that sell metals.
I have never asked if they ship down under.Nothing difficult is ever easy!
Perhaps better stated in the words of Morgan Freeman,
"Where there is no struggle, there is no progress!"
Copeville, Texas
Pukwudji Newbie Joined: 10/07/2009 Location: United StatesPosts: 20
Posted: 01:11am 25 Aug 2009
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How do you put the airfoil shape on the aluminum sheet? I understand if you don't have a good airfoil shape you lose a lot of efficiency.
Thanks,
Brian-Brian V
Hillsboro, OR (USA)
KF7DUZ
GWatPE Senior Member Joined: 01/09/2006 Location: AustraliaPosts: 2127
Posted: 04:57am 25 Aug 2009
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Does ths answer your question?
Efficiency is difficult to estimate for a flat blade. I use airfoil sections. The flat blades have low form drag, and this may compensate for lower airfoil efficiency.
Gordon.
become more energy aware
MacGyver Guru Joined: 12/05/2009 Location: United StatesPosts: 1329
Posted: 05:46am 25 Aug 2009
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Let me address a couple issues: Blade Design and Method of Attack
First, I fly sail planes and there are two methods to achieve lift. One way
is to shape the wing with under-cut and camber to achieve traditional
"lift". The simplest of this type of design is the Clark "Y".
To get an idea of what a Clark Y is, simply take a standard piece of typing
paper and fold it in half the long way. Next open the page up and make a
1/2" crease down one long edge. Next, fold the side with no crease over
and tuck it into the flap made by the 1/2" crease. Now pinch it here and
there to make it look like a wing. That's basically it.
I used this method to make hollow aluminum blades for my early
windmills. I might mention that if after you find the centerline, you cut
the two long outside edges to form somewhat of a tall trapezoid, when
you fold the 'wing' together, it makes it a "high aspect-ratio" design. If
you fool around with this design, you'll find out you can both mold in a
better airfoil as well as create a 'feathered' blade that will have a steep
pitch at its root and little-to-no pitch at its tip. When these blades spin
about a central axis, they 'pump' air through the length of the blade
section, spoiling the tip vortex.
The other thing I want to address is flight method. A sail plane often has
symmetrical-section wings and stabilizer (stab). So where does the 'lift'
come from?
Angle of attack, that's where.
It's the same for a windmill blades driven by the wind. It can either be
'pulled' through the air stream using its inherent 'lift' or it can simply slip
off the air stream using it angle of presentation.
My flat aluminum blades use the second method. The reason I like this is
because they can be manufactured with half your brain tied behind your
back (thank you Rush Limbaugh). Top that with being super cheap and
it's my kind of race!
I don't give two hoots about efficiency for the most part. We're talking
FREE energy here folks (wind). If I want it to make more power, I just
make my wind-catcher contraption bigger!
I'd better add this: My windmills pump (compress) air, so I'm not worried
about much in the way of being 'slick', looking great or making efficient
use of the wind!Nothing difficult is ever easy!
Perhaps better stated in the words of Morgan Freeman,
"Where there is no struggle, there is no progress!"
Copeville, Texas
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
Print this post
.i think this is what is called a conundrum ...more blades equals more torque ...but less speed ...less blades equals a lot less torque ( grunt ) but potential high speed ..also good ... 
