prop shape needs to be flat on windward side?

[Norm]

Trying to make some quick cheap blades....but

with me not so quick.....well anyway I'm mostly

just wanting to know does the windward side of

the blade really have to be pretty flat? does it

affect performance to a large degree?

 







Waddaya think? the dowel stub goes in the hub and

pitch of the blade can be adjusted....the cardboard stretcher will be made from that

clipboard 3 blades to spin one of those little

Rubber Tire stepper motors of Ghurd's

(cute little motors BTW), about 200 -300 rpm will

charge a few AA NiCads !

[Flux]

No it doesn't have to be flat, in fact I can't think of an aerofoil that is truly flat Although ClarkY is nearly so.

Flat is nice and easy for hand carving and works well enough. The front face can be convex or concave depending on the choice of aerofoil. If you use other than flat you will need different angles from those commonly used. Concave front faces are associated with high lift sections and may be good in low wind. Most of the larger commercial machines use convex front faces for greater structural strength with spars up the middle.

Symmetrical shapes work ok if you choose the correct pitch angle, but you will have to experiment.

Flux

[Norm]

Symmetrical shapes work ok if you choose the correct pitch angle, but you will have to experiment.

Which should be easy enough with each blade being

on a dowel rod....just have to twist all of them

at various angles until I get the happy medium.

Thanks for being so thourgh in explaining Flux.

Helped make my day.

[ghurd]

Whats the yellow plastic from?

Figured you used up all those motors by now!

G-

[Norm]

Yellow plastic from folders (office supplies

at Dollar General) enough for 2 blades 48 cents

figure dowel rod ....foamboard...hot glue, duct tape

complete windmillwith RT stepper about $2.50 + labor $5...

( I work cheap !)LOL

I may just use a lot of these RT steppers up if

I get these blades working....gotta find out the

angle.

Love those little RT steppers !!

Just to accidentally bump against the prop

and a LED lights up is amazing !

[Ungrounded Lightning Rod]

For a wind-facing horizontal-axis machine you want the blade airfoil to generate lift that pulls the blade both rotationward and downwind.  This efficiently decelerates the wind and uses the resulting power to spin the axle.

While you can generate lift with a symmetric airfoil by picking an appropriate angle-of-attack, efficient designs tend to be more like an airplane wing - strongly curved on the liftward (downwind and forward) side, nearly flat on the anti-liftward (upwind) side.  If I understand it correctly:  This builds in a tendency to bend the passing airflow in the appropriate direction and keep it "attached" to the surface for a broader range of angles-of-attack.

[ghurd]

Mr. Flux can jump in again if he wants.

I am going to butcher this.

Those steppers have a maximum current.

Meaning faster won't make more amps.

The higher speed makes higher HZ (faster AC), and

that makes high resistance in this case.

At some RPM point, the inductance becomes so great,

the amps will not increase.

And for the RT Stepper motors,

that RPM ain't as high as you might think!

Meaning a steep pitch angle would be my first bet.

Those "RT Steppers" are almost all gone.

I figured I'd never be rid of them!

BTW, RT Steppers are not for sale.

G-

[vawtman]

Hi Norm

 That would be a great classroom project for young kids and i think you would be a great teacher with your nice personality.

 Next thing you know we"ll have 5th graders asking questions here.

 OOps, maybe not a good idea :v%

 Mark

[Norm]

Well sometimes I run mouth before engaging brain

bad habit of mine....wouldn't want anyone to go

swamping you with inquiries about the RT stepper

and I imagine it isn't all that unique just that

a stepper motor when hooked up properly to some

white LEDs are quite impressive.....to young

people...as they barely turn it and it lights up!

  Hope I didn't mislead anyone into thinking that

you can charge really big batteries with one of these

....if they can charge up 10 AA NiCads in

parallel in a 5MPH breeze and it takes all day

or all week just as long as it works.

   So Ghurd please accept my apology if I got

off on the wrong foot with you.

[TomW]

Mark;

 Next thing you know we"ll have 5th graders asking questions here.

From some of the posts I think we already have that.

Fact is none of us is hatched knowing this stuff.

Tom

[Norm]

Tom...you mean 'Are you smarter than a fifth

grader?' Heck No !....I wasn't as smart as a

fifth grader when I was a sixth grader, they just moved me cause I was in the way.

[ghurd]

No, not needed Norm.  

Mine didn't come out right, at all.

Partly avoiding the "I want to go off grid with an RT".

Mostly, I meant they don't have to go too fast

before the amps peak out.  I can't remember how

fast...

Seems like output at 600 and 1200 RPM wasn't much different.

So maybe start with a steep angle.

The little buggers impress me.

I used them for 12V.  Slow, but it worked.

Kept a 12V 7AH enough to charge my cell phone. :-)

G-

[TomW]

Yeah, Norm.

Lead, follow or get out of the way..

At least you "get" that you won't be going off grid with these small turbines. Funny how many don't.

Personally, I think you have entirely too much fun and expect the Government to impose a "Sin Tax" on the activity and it will all be your fault!

Tom

[Norm]

Trying to find something that works and getting it to work better and looks good too...yet easy to make....these yellow blades will sure look pretty flying in the breeze !

  Well what would you rate one of these at?

a couple of watts? Under ideal conditions...

a close rival to a small solar panel?

 (Trying to keep in mind there are probably other

steppers out there that are maybe just as good

or better than these ...Was just my first introduction to steppers) to be continued)

[ghurd]

Hehe.  At 12V it was 35~40ma.  So about 1/2W.

They did a lot better amps at lower volts, but still about 1/2 or 2/3 watts.

If you are looking for 6V, I might have something better,  

If I didn't lose it.  Couple hundred ma at 6V, but won't hit 12V.

No fancy tire on it.

G-

[Stonebrain]

If you take a symmetrical airfoil,naca 0020 or so,the sides are ..kind of..

flat from the thickest part to the trailing edge.What counts is the angle,more than the exact shape.If I look at your yellow thing(don't forget to drink your coffee),I would say it's not so bad.



naca 0020(the lowest one)The upper is the same,but the chord bended on a circle.

[Norm]

Yes the yellow thing is more like the bottom one

Had all three made today....got a couple of brief

6mph gust...just a glimpse that it might work.

  I think it's too large going to shorten the rods

so it will be 30inches from 36inches estimated

about 120 rpm (no load) ....need more research

( that's spelled more wind) they so seem to work

well....but maybe not good enough...fun nevertheless

(about 8 cups coffee later)

[bob g]

some years ago nasa iirc had a simulator so one could generate different

profiles and then test them showing the pressure points (or lack thereof)

what is interesting is when you increase camber you move the low pressure region forward and the high pressure rearward, thus increasing the speed of the blade

and the power.

the problem is hand carving a concave windward side to a piece of wood

far easier to leave it flat on the windward side, and do a convex profile on the back

i made up some cambered fiberglass blades and did some simple windflow tests with

a smoke trail from my cigar, what the simulator illustrated i could then see quite clearly.

most if not all the commercial profiles are cambered to some extent, some dramatically so.

i would really like to see someone carve a set of heavily cambered blades

even if it were a small set to compare real world against the more standard clarkY

and other flat sided blades.

maybe one day

bob g

[Norm]

the problem is hand carving a concave windward side to a piece of wood



Bob....No problem there...you just make a hand

tool ...scraper blade from an old handsaw grind the

tool to whatever radius you want.

[elvin1949]

Norm

 You took the words right out of my mouth.

I make scrapers all the time for different things when working with wood.

later

Elvin

[Norm]

Watch it Elvin usually only old timers know about

stuff like custom hand woodworking tools !

  BTW liked that Billion thing in the E-Mail !

[spinningmagnets]

A useful search term is "draw knife"

http://www.endtimesreport.com/pictures/draw_knife.jpg

You could make one with a perfect size of handles and frame for your size of projects, and make the blades separate, so they could be changed to different shapes, or easily replaced when sharpening wears them down too low.

[elvin1949]

Norm

 I thought you would.My sister is always sending me junk.Most of the time i through it away.

 Have fun

later

Elvin

[elvin1949]

 HF sells draw knifes and spokeshaves.

Both good woodworking tools.

 later

Elvin

[Dave B]

Hi Bob,

  Take a look here at http://www.royalfabrication.com/index.htm  That's me standing next to my 18' hybrid Wincharger. Dave Moller carves these Gottigen 222 profile blades on his custom carving machine and like one would expect, they really perform. No twist, no taper, constant pitch very similar to the Bergey machines. It's no coincidence a blade profile similar to that used for decades continues to run on the most popular commercial machine today. Dave B.