I dunno. Someone posted an interesting site a while back about why an
all-powerful God who makes miracle cures each minute of each day has never
regrown a severed limb. I had my (sadly dying) evangelic cousin tackle that
and she responded "there have been cases of fingertip regeneration." If
there is a God, he/she/it seems strangely limited to effecting cures that
random chance could just as easily explain. The fact that there are so many
different versions of God tends to prove that there isn't any true one. A
"true" God should have been revealed a long, long time ago but just the
reverse is happening - religions split all the time, splintering even
further the concept of one all-knowing God.
That's just not true. There were 200,000 witnesses to God's revelation at
Sinai (plus countless women, children, slaves, and asses). And an unbroken
oral tradition retelling the tale to subsequent generations. As such, that
fact is as acceptable and believable as a news story in the New York Times.
That's certainly not what polling data indicates...while historic
organized denominations (of all stripes) are losing market share to the
nondenominational and that ilk, individuals indicate a personal belief
at roughly 70% overall US population. Down some, but not "most" on the
side of no belief or belief in none by any stretch.
[No value judgment implied either way, simply observation...]
Actually, the Cheney-instigated invasion of Iraq (neglecting the REAL
target, Osama's refuge in Afghanistan) was to put down that insolent
rascal of a Saddam Hussein who actually thought he could bust the
sacrosanct US.-Saudi oil relationship and replace it with his cartel.
Tsk, tsk! And then to have the chutzpah to plan denominating his oil
in Euros instead of the sacred Dollar! Man's gotta go...
Uh, we invaded Afghanistan before we invaded Iraq.
It was never the policy of the Bush administration to kill or capture Osama
Don't get me wrong, if OBL HAD been captured or killed, that would have been
a plus, but the stated goals of the Bush adminstration was to disrupt or
destroy the ability of terrorists to train, have sanctuary, get financing,
recruit, or organize. These goals were substantially achieved.
When you look at an ordinary fan, it has large blades that occupy a
significant portion of the cross-sectional swept area.
When you look at a wind turbine, the blades are very thin, occupying a
very minimal amount of swept area, allowing much of the wind energy to
flow right through or between the blades.
If a fan has fan blades that are designed to *efficiently move air*,
then why won't that same basic blade design also be *efficiently moved
by air* ?
The cross-sectional area of a plane's propellers are a hindrance (drag)
to forward motion. So while a fatter blade can provide more thrust at
a lower rpm or with a lower swept area, a fatter blade will present more
drag to counter a plane's forward movement. The slower a plane is
designed to fly, the slower a plane's engine is designed to operate, the
more sense it makes to use a fatter blade, or more blades (3 or 4 vs 2).
A helicopter develops lift because it's blades are really air foils that
just like wings develop a low pressure area on their upper surface as
they are moved forward (ie - as they are rotated).
When you look at the constraints of a typical house fan (low speed,
inefficient motor, small design envelope or package) what you get are
wide, fat blades. If wide fat blades are best at being turned by motors
of low power to generate a breeze that consumers demand out of a small
package size, then I'd have to assume that wide, fat blades would also
be most easily and efficiently rotated by a breeze or flow of air
passing through them.
If it doesn't take much motor force or motor power to turn wide/fat
blades to generate an acceptible air flow, then the converse must also
be true - that wide/fat blades are more easily turned by a given breeze
vs long/narrow blades.
The energy potential in a wind field is measured in terms of the swept
area of the blades.
So how can you capture a respectible fraction of this energy by using
thin blades that "see" or experience only a small fraction of this swept
area, vs using fatter blades that expose themselves to a greater
percentage of this wind field?
jamesgangnc used improper usenet mesage composition style by
A typical air foil is an airplane wing. The "foil" is cross-sectional
profile - curved upper surface, flat lower surface. The foil is what
gets you life when it's moved forward through the air. You create a
low-pressure area on the upper surface.
I can move air with flat blade angled at 45 degrees. The blade doesn't
need a foil-shaped cross section - instead it can be flat. When a flat
blade is angled (any angle other than 0) and rotated, it is pushing air
out of the way as it turns.
Similarly, wind that wants to move past the blade must push it aside,
and in doing so it will rotate the hub. The more surface area you
present to the wind (ie the wider the blade) the more rotational force
you transmit to the hub.
Maybe it's all a scam. Maybe wind turbines don't need to cost a few
million each, and be hundreds of feet tall with blades made from exotic
materials and methods.
Explain what's wrong with my concept.
How much cross-sectional area is occupied by the blades in a water
turbine as water flows past them in a hydro-electric station?
harry used improper usenet message composition style by full-quoting:
If a conventional airplane wing is a foil, and if a flat plate can be a
foil, then fuck, everything and anything can be a foil according to
you. So where does that get us?
No matter which way you cut it, you're still left with capturing a
lateral force (ie = wind pressure) and convert it into rotational
energy. A flat blade angled at 45 degrees will probably get you the
most torque and rotational speed out of a given breeze of air (but it's
totally possible that optimal blade angle is a function of RPM), and the
more surface area your blade has, the more of that wind energy it can
convert into rotational energy.
If you look at the old stereotypical "prairie" style windmills, that's
how they are. A disk with pie-shaped blades angled at 45 degrees,
facing directly into the wind with the help of a fin.
All that surface area catches a lot of wind, but it also creates a lot
of aerodynamic drag which makes it require higher wind speeds to turn.
The air pushing through the "fan" creates rotational energy, but the
air AROUND the fan is creating drag as the tips of the blades contact
The reality is that what makes a good propeller or helicopter rotor
also makes a good windmill blade. Maximum lift with minimum drag. THAT
is why we have thin blades. The cross-section of a modern wind turbine
blade is a high lift, low drag airfoil that will catch air and turn
the rotor at far lower wind speeds than a solid disk of 45 degree flat
I believe that drag is a function of the surface area of either the
front or rear (or maybe both) trailing edges of the blade.
Which if you look at the ratio of blade area to frontal or trailing edge
area, the conventional long thin blades have a horrible ratio.
Those blades are operating in a wind-speed regime that far exceeds the
design profile of capturing low-speed terrestrial wind currents. So
again I don't know why airplane propeller blades (or in general the
long, thin blades) are being thought of as the most optimal to capture
energy from 5 to 25 mph wind currents.
Look at the cross-sectional area of a jet turbine. Lots of surface area
there. Ever sit on a jet parked at the gate and watch it's turbine
rotate as it catches the calm breeze wafting by?
I think that in the future your going to see more of these helical-based
"Helical structured wind turbines are the future of wind mill
technology. These amazingly unique looking twists and turns
will replace those long and boring blades which represent the
conventional image of a windmill. These new and sleek looking
windmills are designed much like the old ones when it comes to
converting their circular motion in to mechanical work, but it
is the structural design that makes them unique and special.
In fact, they logically should function better than the traditional
windmills as the helical structures seems to not just utilize the
energy of the wind, but maximize it by containing the wind."
On 7/21/2011 1:29 PM, email@example.com wrote:
Have you seen the eight bladed props on the Airbus A400M Military
transport plane? The propellers look quite a bit different from
what you'd expect to see on a turboprop engine. I remember seeing
pictures of NASA developing such a prop years ago.
On 7/21/2011 1:29 PM, firstname.lastname@example.org wrote:
None I've seen were actually flat, though. All ours had a curve built
into the blades; steeper front attack angle than rear. Dated from
roughly 1910 on thru the 20's...
The old Delco Windcharger (mid-1910s when ours installed; not sure when
they were actually introduced) did have a three-bladed hub; not quite so
aerodynamic as current but certainly reminiscent.
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