Ran out of pvc pipe

[opo]

After several monts of learning and experimenting with my motor conversion mill and about 8  pvc blades lost I decided it is time for me to start playing with wood blades.

I decided to go with constant pitch blades. I started with a piece of 2"x6"x2' , made a diagonal cut along the length to obtain two triangular prisms: base=6" height=2"

2' long. Next the right angle was removed with another cut along the lenght so that the thickest part of the blade was about 2/3 of the final chord. So a piece of 2x6 produces 2 identical blades.

Another piece produced two more. I then picked three of them so that they balanced easier. Sanded the roughness out of them and rounded the corners a little bit.

Now Im having second thoughts. The blades look too wide to me now. My idea was to make slow blades, but now I think I over did it. I havent put them on te mill yet.

The mill cuts in at about 220 rpm for 12v by the way. And in strong winds produces more than 100 watts (my cheap multimmeter is only 10A) with pvc blades 1.4m dia.

What do you guys think?

Octavio

[opo]

Forgot to mention that the intended pitch slope is 1/3.

I hope I explained myself.

Opo

[taylorp035]

With a cut in of 220 rpm for 12v, you could get away with a slightly larger diameter for more torque.  Your pvc blades come out to ~54 inches, and they seem to operate decently for you.  I would go with a 60" set with an airfoil + a 5-10 degree tip + a 1/3 root.  Basically, it depends on how handy you are and what tools you have. If you have enough tools, I would make a blade similar to most of the pictures on otherpower.com, because a true airfoil pays off big time in higher winds.  

I once made flat blades, like you described, and I found them to be way too heavy and very slow in high winds.

You can check out my youtube channel here as there are about 10 videos there, all showing different things:

http://www.youtube.com/my_videos

If I were to make flat blades that were also straight with no twist, I would make the angle closer to 10 degrees (1/6 slope ).

Keep us updated!

[opo]

Thanks Taylor,

My blades are not intended to be flat. They have no twist and the chord is also constant. They have an "airfoil" shape: imagine a 2" x 6" x 2' long piece of wood. It has two 2" x 6" faces, looking at one of them trace one diagonal, now you have two identical right triangles. Cut the piece of wood along this diagonal. You end-up with two "airfoils" 2' long. Of course leaving the right angle as is does not look like an airfoil. So divide the chord into 3 sections, trace a vertical line 1/3 of the way and you get a point in the wood from which to trace a line to the leading edge of the blade. Now you cut the wood all the way along this line.

The shape of the airfoil is still a triangle which can be rounded of by sanding. So I ended up with two pieces of wood that are not flat but not a true airfoil either.

As far as tools, I don't have many for wood working. The cuts are straight forward for the guy at the carpentry shop (they still look funny at you). I'll try to post a diagram or picture latter.

As far as length, I started first with 4'(1.2m) diameter pvc blades and every time I had a failure I replaced them by slightly longer blades. The conversion seemed to like longer pvc blades. Since I don't have any experience with wood blades I decided to start small first because I don't have a furling mechanism yet (pvc blades allows you not to have that I think, or maybe that's why they failed).

Cheers  

[opo]

Hi guys,

Here is a diagram of the cuts into the 2"x6"x2' piece of wood. Three cuts total: one on the main diagonal and two more to eliminate the right angles.

 <IMG="http://www.fieldlines.com/images/scimages/13042/woodblade.jpg"><IMG>

or

http://www.fieldlines.com/images/scimages/13042/woodblade.jpg

The outside box is th 2"x6" face of the wood plank. The cuts run all the way into the 2' length of the wood. The brown triangles are the actual "airfoils". Of course after sanding this edges are rounded of a little bit.

I hope this clarifies my explanation.

Octavio

[ghurd]

I think the trailing edge should be sharp (not sanded to round off a bit).

And I think the 'back' of the blade should be sanded more than a bit.

Possibly sanded a bit near the root, and quite a bit more near the tip.

But I think it will work.

G-

[taylorp035]

The picture helps a lot.  As ghurd said, make the airfoil smooth, but don't sand the trailing edge.  I am sure these will perform better than you pvc blades.  Post a pic of the final blades when you are done!

[opo]

Thanks G and T,

I will follow your advice: no trailing edge rounding and gradual sanding of the hump so it is thinner at the tip.

Salud,

Opo

[TomW]

[opo]

Thanks Tom. Could you please post airfoil, rotor, hub and blademount for me?

Thanks again

[adaml]

Keep at it Opo.  Can remember starting with PVC and being afraid of taking the plunge with wood.

I think I looked on Hugh Piggot site and followed the pictures and instructions there. They didn't turn out too bad nor too good but still out performed the pvc.  I think it is a case of practice makes perfect (or as close as one can get!)  Your plan sounds about right from my experience anyways.

I think there are some pictures in my files of my attempts that you might find amusing.

[opo]

Ok,

Here are some pics of the intended setup.

First, the rough airfoil

The completed rotor follows

A close up of the hub follows. I'll reinforce the root of the blades with a piece of sheet metal

Finally a close up of how the blades are placed in relation to the hub for clockwise rotation

I'm experimenting with diferent paint leftovers for the final finish that's why some blades look blackish/whiteish.

Cheers

Octavio

[TomW]

[opo]

Thanks for your encouragement Adam,

I can follow Hugh's instructions, and actually started work on one of his 4' blade design it is going very slow, there is a lot of wood to be removed and I don't have tools/experience. The blade looks like it will rock & roll. I'll use it in a future axial-flux project.

Cheers,

Octavio

[taylorp035]

I like it!  Those should have a lot of rotational energy stored in them, so your power output won't be quite so "peaky".

[opo]

Blades are spinning and  made ghurds controller chirp as the wind speed increases: it goes from 2 chirps per sec to almost continuos. I never saw that with previus blades.

Thanks for all your help and encouragement.

[ghurd]

Blades are spinning and  made ghurds controller chirp as the wind speed increases: it goes from 2 chirps per sec to almost continuos. I never saw that with previus blades.

Thanks for all your help and encouragement.

That is good news about the blades!

The bad news is you need more dump load.  Add another fet and load.  Possibly 2 fets and 2 loads!

G-

[opo]

Thanks for the heads up. Is there any equivalent fet to the zn you provide in your kit?

I never imagined the diference in performance of these poorly designed blades with respect to pvc blades would be so abismal.

I did observed that the rotor does not stop so often, start earlier and follows wind speed increase almost instantly, it is very quiet. The turbine as a whole is also quieter as in smoother.

I'll be keeping watch on it.

Opo

[ghurd]

Can add the extra fets and loads to the existing controller.

There is nothing Exactly equivalent to the ZM.
Other things can be made to work, but all the values change.  Others are not as predicable either, even from parts with the same number and manufacturer.

The in route package has an extra ZM.
G-