pvc prop up and running

[bob golding]

hi all,

after reading all the comments and stories about pipe props i have got one up and running. i couldnt find any cheap pipe so used 41/2" gutttering. got the first one wrong, so reread  everything. by the time i had worked it out the shops were shut so have "borrowed" some guttering from my friends leanto. will replace it monday, honest.:-) my template is 61/2" diameter, and is 30" long from the centre to the tip. the width at tip is 13/4" and the  tip angle is 7 degrees. i have sloped the tip back from the trailing edge towards the leading edge. couldnt find any info on this so  just doing what feels right. i used a rusty handsaw and did the curved bits with a pair of metal shears. cleaned it up with a wirebrush drilled a hole in the middle and fiited it to  my TDM. it has a screwed end on the shaft. just using that  for testing. it took about 2 hours all told and is spinning around as we speak. it took me a while to get my head around the 25 degrees bit. i recomment making a  model first. woofs drawings were a real help once i worked out were the 25 degrees was measured from. will post output data when i get around it it.

cheers

bob golding

[ZooT]

Er uh.......ya' got some pics of this?

I'm "just" getting started with wind genny's and an awful lot of stuff is unclear to me as of yet.

You say you used PVC raingutter?

[Experimental]

       Good morning Bob,

    On racing aircraft, we slope the leading edge, back to the trailing edge, at a thirty degree angle, from the center line -- this is to reduce tip vortex drag ..

    Sounds , just opposite of what you did --- but you are doing something positive, so just keep going !!!

     I just finished a new prop for my generator and set the tips at 30 degrees -- it really runs quiet, and I attribute that to the tip !!???

    It would have been on the forum, but have had troble getting my pics on -- so just skipped the article -- figured it wasen,t much good with out the pics !!

    Keep going with your experiments, and soon we can see a generator attached to the other end !!

    Good day, Bill H......

[Sponge]

http://persistentrealities.com/galleries/thumbnails.php?album=3

I got some plans last year from someone, I might still have those somewhere, if you are interested.

Here are a few pics of my PVC windmill.

(The magnets and stuff was just for testing, they were from my old windmill. The current windmill (this PVC one) hasn't been outside since september, since I cannot find a suitable way to connect the steppermotor shaft (4-6mm?) to the hub... my latest attempt is one hour old, and failed..)

[ghurd]

I have had decent success just press fitting a wooden huh on.

And if the shaft has a hole for a pin, a shallow slot in the hub for the pin helps. A dab of epoxy over 1 end of the pin in the hub holds well, and it can be removed later without 'too much' damage.

I have better luck with shorter faster blades on steppers.

G-

[coldspot]

"I have better luck with shorter faster blades on steppers."

Shorter, I understand.

Faster, Please define.

Two, Three or more?

Shorter, Fatter (More width) Maybe?

[ghurd]

Wow this got long. Hope something in here helps somebody.

Shorter blades of the same design tend to turn at a higher RPM.

Wooferhound and Zubbly collaborated on a PVC blade design. Fast and easy to make.

The dimensions are given only in angles. The blade length and pipe diameter don't seem to matter for the design. (naturally a larger machine should use longer blades and bigger pipe)  But you know that.

I had bad luck changing their design.

With 4" PVC, the blade in front of me has a root width (chord) of 1.75", tip width is 3/4".  This blade happens to be 9" long, but others from 4" pipe go from 6" to 18". They all have the same tip and root chord of 3/4" and 1.75" (determined by the angles on / and the diameter of the pipe).

In the same wind speed...

The Longer blades have more power, but turn slower. Start turning in less wind because they overcome the cogging easier.

The shorter blades turn faster, but have less power. Need more wind to overcome the cogging and start turning.

Blades too long will not be turning fast enough to make charging voltage when they should.

Blades too short won't be turning at all when they should all ready be going fast enough to charge.

There is somewhere when everything gets a nice balance. The blades are long enough to start turning in a wind below where they will make charging voltage, and short (fast) enough to make charging voltage in the low wind.

I make a press fit hub for the stepper, and try different length blades until one works.  Blades are held on the hub with sheet metal screws. 4 'seperate' blades, meaning not one piece. If it can't get going fast enough, try shorter blades.  If it can't get started, try longer blades.

Do this. Really!  Wish I would have done this as the very first thing.

For your stepper try a 4 blade hub and prop, 4" PVC, a set of 8", 10", 12", and 15" (each) blades. (make all 4 sets, you will want them for the next stepper)

Hand held 15" (30" dia) blades can be frightening in a big wind, so be ready.

It is VERY easy to see, feel and hear how everything is working. Or not working.  A few blade changes and you will have a feeling for what is best.

And a much better understanding of "why".

For you next question, a high percentage of my smaller steppers do best with 9 to 11" blades.  Even 1" makes quite a difference.  But make all 4 sets anyway!

G-

[coldspot]

Thank You !!!

Happy Holidays !!!

I was thinking something different, about "faster".

I understand what you've got going.

I don't trust "wood" as a hub and will never use, I'll take the time and effort to find or make from metal.

Have Some Great Days during the HOLIDAYS !!!!