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prop shape needs to be flat on windward side?
By Norm, Section Diaries Posted on Mon May 12th, 2008 at 02:12:50 PM MST
quick cheap blades

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 !

prop shape needs to be flat on windward side? | 24 comments (24 topical, 0 editorial)

Re: prop shape needs to be flat on windward side? (3.00 / 0) (#1)
by Flux on Mon May 12th, 2008 at 09:04:19 AM MST
(User Info)

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

Re: prop shape needs to be flat on windward side? (3.00 / 0) (#2)
by Norm (peppysue@suite224.net) on Mon May 12th, 2008 at 12:41:58 PM MST
(User Info)

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.
( :>) Norm
[ Parent ]

Re: prop shape needs to be flat on windward side? (3.00 / 0) (#3)
by ghurd on Mon May 12th, 2008 at 01:07:50 PM MST
(User Info)

Whats the yellow plastic from?

Figured you used up all those motors by now!
G-

Re: prop shape needs to be flat on windward side? (3.00 / 0) (#4)
by Norm (peppysue@suite224.net) on Mon May 12th, 2008 at 01:55:55 PM MST
(User Info)

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 !
( :>) Norm
[ Parent ]

Re: prop shape needs to be flat on windward side? (3.00 / 0) (#6)
by ghurd on Mon May 12th, 2008 at 03:12:53 PM MST
(User Info)

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-

[ Parent ]

apology if my enthusiasm has run amuck (3.00 / 0) (#8)
by Norm (peppysue@suite224.net) on Mon May 12th, 2008 at 07:29:52 PM MST
(User Info)

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.
( :>) Norm
[ Parent ]

Re: apology if my enthusiasm has run amuck (3.00 / 0) (#11)
by ghurd on Tue May 13th, 2008 at 07:06:48 AM MST
(User Info)

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-

[ Parent ]

Thanks back to experimenting (3.00 / 0) (#13)
by Norm (peppysue@suite224.net) on Tue May 13th, 2008 at 08:39:13 AM MST
(User Info)

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)
( :>) Norm
[ Parent ]

Re: Thanks back to experimenting (3.00 / 0) (#14)
by ghurd on Tue May 13th, 2008 at 09:27:52 AM MST
(User Info)

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-

[ Parent ]

Re: prop shape needs to be flat on windward side? (3.00 / 0) (#5)
by Ungrounded Lightning Rod on Mon May 12th, 2008 at 02:26:49 PM MST
(User Info)

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.

Re: prop shape needs to be flat on windward side? (3.00 / 0) (#7)
by vawtman (vawtman(at)charter(dot)net) on Mon May 12th, 2008 at 03:53:21 PM MST
(User Info)

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

Re: prop shape needs to be flat on windward side? (3.00 / 0) (#9)
by TomW on Mon May 12th, 2008 at 09:04:08 PM MST
(User Info)

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

If everyone is thinking alike, then somebody isn't thinking.

--George S. Patton
[ Parent ]

Re: prop shape needs to be flat on windward side? (3.00 / 0) (#10)
by Norm (peppysue@suite224.net) on Tue May 13th, 2008 at 04:29:35 AM MST
(User Info)

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.
( :>) Norm

Re: prop shape needs to be flat on windward side? (3.00 / 0) (#12)
by TomW on Tue May 13th, 2008 at 08:21:43 AM MST
(User Info)

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

If everyone is thinking alike, then somebody isn't thinking.

--George S. Patton
[ Parent ]

Re: prop shape needs to be flat on windward side? (3.00 / 0) (#15)
by Stonebrain on Tue May 13th, 2008 at 05:43:56 PM MST
(User Info)

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.

Re: prop shape needs to be flat on windward side? (3.00 / 0) (#16)
by Norm (peppysue@suite224.net) on Tue May 13th, 2008 at 07:44:27 PM MST
(User Info)

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)

( :>) Norm
[ Parent ]

Re: prop shape needs to be flat on windward side? (3.00 / 0) (#17)
by bob g on Thu May 15th, 2008 at 03:02:43 PM MST
(User Info)

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

Re: prop shape needs to be flat on windward side? (3.00 / 0) (#18)
by Norm (peppysue@suite224.net) on Thu May 15th, 2008 at 09:10:59 PM MST
(User Info)

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.
( :>) Norm
[ Parent ]

Re: prop shape needs to be flat on windward side? (3.00 / 0) (#19)
by elvin1949 (elvin1949@yahoo.com) on Thu May 15th, 2008 at 11:48:30 PM MST
(User Info)

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

[ Parent ]

Re: prop shape needs to be flat on windward side? (3.00 / 0) (#20)
by Norm (peppysue@suite224.net) on Sat May 17th, 2008 at 08:26:45 AM MST
(User Info)

Watch it Elvin usually only old timers know about
stuff like custom hand woodworking tools !
BTW liked that Billion thing in the E-Mail !
( :>) Norm
[ Parent ]

Re: prop shape needs to be flat on windward side? (3.00 / 0) (#21)
by spinningmagnets (velmis1450bc(at)aol(dot)com) on Sat May 17th, 2008 at 12:16:27 PM MST
(User Info)

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.

[ Parent ]

Re: prop shape needs to be flat on windward side? (3.00 / 0) (#23)
by elvin1949 (elvin1949@yahoo.com) on Sat May 17th, 2008 at 03:35:25 PM MST
(User Info)

HF sells draw knifes and spokeshaves.
Both good woodworking tools.
later
Elvin

[ Parent ]

Re: prop shape needs to be flat on windward side? (3.00 / 0) (#22)
by elvin1949 (elvin1949@yahoo.com) on Sat May 17th, 2008 at 03:33:01 PM MST
(User Info)

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

[ Parent ]

Re: prop shape needs to be flat on windward side? (3.00 / 0) (#24)
by Dave B on Mon May 19th, 2008 at 02:58:22 AM MST
(User Info) http://www.madbbs.com/users/bruggelog

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.

[ Parent ]

prop shape needs to be flat on windward side? | 24 comments (24 topical, 0 editorial)

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