On Dec 24, 4:25 am, "
[email protected]" <
[email protected]> wrote:
> On Dec 23, 5:23 pm, "[email protected]" <[email protected]> wrote:
> > On Dec 22, 10:54 pm, "[email protected]" <[email protected]> wrote:
> > > > if I have 2 times as much wind my windmill makes 4 times as much
> > > > energy.
>
> > > > Agreed?
>
> > Buteo lineatus said:
> > "If you go twice as fast you get four times as much drag because drag
> > is a velocity-squared effect. "
>
> That is correct.
>
> > I found the 8 times figure on a windmill website I think. I would like
> > to get it right obviously but it's not important for the concept to
> > work. I have this gut feeling that says multiplication tends to
> > exceed adding things up.
>
> The 8 times figure is correct. My previous answer of 4 times was
> based on 4 times the force at the same rpm for the windmill with
> everything else the same. In fact if you adjust the pitch of the
> blades and/or the rpm the windmill can make 8 times the power at twice
> the wind speed. horsepower=torque*rpm/5252
>
> On this page
>
> http://earthsci.org/mineral/energy/wind/wind.html
>
> you will find formulas that contain V^3 or Velocity cubed. So an
> increase from 1 to 2 in wind speed results in 2X2X2=8.
>
>
> > On Dec 23, 5:52 pm, "[email protected]" <[email protected]> wrote:
> > On Dec 22, 10:54 pm, "[email protected]" <[email protected]> wrote:
>
> > > > If I now put up 2 windmills in 1 times the wind.
> > > > Do I also get 4 times as much energy?
>
> > > No. When you double the wind speed you get 4 times the energy because
> > > the formula includes V^2. That is V times V. So if you double your
> > > velocity from 1 to 2 you get 2X2=4 times the energy because of the
> > > change in velocity. When you add a second windmill you have doubled
> > > the surface area which just doubles the force.
>
> > Good,
>
> > Please bare with me for a sec here.. you agree that (roughly
> > speaking):
>
> > 2 times as much windmills gives 2 times as much wind energy
>
> > And
>
> > 2 times as much wind gives 4 times as much wind energy.
>
> 8 times
>
> > Just like:
>
> > 2 times as much frontal surface gives 2 times as much wind energy
> > (drag).
>
> > And
>
> > 2 times as much speed gives 4 times as much wind energy (drag).
>
> 4 times the force times twice the distance gives 8 times the energy,
> same as the windmill.
>
> > In the context of:
>
> > 2 times as much sail area gives 2 times as much wind energy.
>
> > And
>
> > 2 times as much wind speed gives 4 times as much wind energy.
>
> > We note that propeller ships capable of "sailing" directly up the wind
> > already exist. The combination of sailing and windmilling technologies
> > thus allow for aerodynamic drag to be a means of propulsion's. If
> > there is more wind this kind of vessel accelerates UP the wind faster.
>
> Are you saying the ship's propeller is powered by a windmill?
> Something like this 
>
> http://i.treehugger.com/images/2007-2-21/Windmill-Sailboat.jpg
>
Yes, I should probably ask if you have objection against this kind of
devices? ^_^ There are at least 4 credible sounding and looking people
who claim to have build working prototypes rolling up the wind. There
are also patents describing the effect. But to be really honest I feel
I should accept that normal sailing close to the wind under is closer
towards sailing up the wind as out of it. Then have hundreds of
millions of examples.
Those last few degrees don't seem like a big deal to me. The
amplification of wind is a well known effect.
But keep in mind: any further drag may decrease speed with a negative
value.
Drag = good
> That link I provided
> above says, "Windmills are NOT efficient. At the very most, a
> windmill can extract only 16/27ths of the kinetic energy from the
> wind. This is called the Betz Limit and it can be mathematically
> proven through calculus. Most of today's windmills extract about 30
> percent of the wind's energy."
Yes the other 70% of the drag is lost.
That doesn't mean it suffers it, it blows though the mill.
> With the land based vehicle even a small amount of power can be used
> to slowly creep up wind.[..]And for the land based vehicle, as soon as
> you try to go faster by supplying energy from another source, the
> added drag will sap off more energy than is gained by the increased
> wind speed at the windmill.
>
"added drag"? I agree drag goes up but added to what? The drag is
negative. So I think we can agree the drag does negative work.
right?
> I see that Ben C gave the same advice in the "Vortex ram" thread.
>
> http://groups.google.com/group/sci.energy/msg/d91dc72297d6d5e1
>
Yes good post, but a ram is still far away. :-(
> > If drag can evidently be engineered to be a positive ingredient I ask
> > you start wondering what happens when we accelerate into the wind
> > (using an engine).
>
> > If there is no wind and we accelerate from 10 to 20 we suffer 4 times
> > as much drag.
>
> > If the wind is 10 mph and we accelerate from 10 to 20 we also suffer 4
> > times as much drag.
>
> Not really. Traveling at 10 with a 10 headwind means we start with a
> 20 mph wind. Traveling at 20 with a 10 headwind means a 30 mph wind.
> 30 is only 1.5X20 so the drag would force would be 1.5X1.5=2.25 times
> as great.
>
how sloppy.
The point is that a negative aerodynamic profile creates more
propulsion if there is more drag. Just like a normal aerodynamic
profile takes away propulsion.
So even when it's not very efficient at low speeds it's output goes up
the faster it goes. As that little percentage of negative drag
accumulates just as much as normal drag does.
> > This 4 times includes the wind does it not?
>
> > energy content of the combination of drag and wind exceeds the sum of
> > it's parts?
>
> > yes?
>
> Not sure what you are trying to say here. If it is that 30X30 is
> greater than 10X10+20X20 then yes.
>
Say we push a windmill on a kart.
It's rotor spins free, most of it's drag disappears slowly.
We use it's coupling and the demanded force to roll the mill goes up
the moment we start to extract kinetic energy from the propellers.
We use this kinetic energy to move the kart again.
Now the energy is getting pumped in a circle but it's not even going
to be 100% efficient.
In an ideal configuration the end result would roll just as fast with
the prop attached to the gearing as it would spinning free. A few
meters, then it stops.
But we don't have an ideal configuration. We have much much losses in
our conversion processes. We do keep it kinetic so the losses don't
grow to insane levels like turning fire from coal into electricity and
using the electricity to charge your electric car in order to drive
around enormous battery collections. But losses there will be.
It's also not a closed system, the wind is blowing exponentially, it
becomes stronger the faster you travel into it.
The closed loop assembly would have the opposing wind force at it's
disposal at all speeds.
The incoming drag is always 1 wind speed faster as it should be.
The faster we travel the bigger it becomes.
At 0 mph the 5 mph wind doesn't do much useful work.
At 100 mph the 5 mph wind does loads of work.
At least thats what it seems like to me.
Sure you have to overcome the drag but we had agreed on a negative
figure.
> >http://gabydewilde.googlepages.com/wheel-cover-turbine
> > gabydewilde - wheel cover turbine
>
> > When most of the bike has a reasonable aerodynamic shape the propeller
> > can easily suffer more drag as the rest of the bike.
>
> > Going down the wind one could use the prop to propel the bike again
> > but that aside.
>
> > It seems one may obtain the full wind energy at all speeds multiplied
> > by the speed they are moving up the wind at.
>
> > Yes or no?
>
> Again I am not sure exactly what you are trying to say, but given the
> 30% efficiency above I would say that you are only going to get 1 hp
> back from the windmill for every 3 hp that you put into overcoming its
> drag. So it looks like a losing proposition to try pushing it any
> faster than the wind drive alone can propel it.
>
> Bruce
I think the 30% relates to the energy available in the square meters?
If no energy is taken then there is no drag either?
The fact that various working models have been made does not leave
room for contradicting assumptions. Moving up the wind does not remove
or decrease the wind. The increase in drag cant possibly have
negative effects on the prop.
I don't have access to those fancy science journals and I doubt I
could understand much of what goes written there. If some one claim to
have build various boats and have pictures of those then thats the
evidence for me.
It's not proof, but normally I need only one of those claims to go 'n
try figure out what the invention was. One clue is enough for me. But
under this topic there is math, pictures and there are patents. A
paper that mathematically disproves heavier than air flying apparatus
wouldn't mean anything to me. I would say the emperor is neked. lol
The boats and toys worked. End of story.
I think a wheel turbine can consume a large percentage of the frontal
area.
Imagine a spiral of flat spokes, like U shaped rotor blades stacked
all the way around the wheel but with the center missing.
Air from the conical inlet tubes is injected into the center (or just
below it).
The inlet tube may be concaved and textured in order to vortex the air
a bit in the direction the wheel is spinning in. Giving the tubes an
in inwards spiral shape will also increase the speed of the flow (make
more drag)
The air is then collected again in the outer ring of the turbine and
directed to the back of the ride.
The length of the vehicle determines how fast we can vortex the air
before injecting it into the turbine.
It can do so without increasing the frontal surface.
http://gabydewilde.googlepages.com/wheel-cover-turbine
gabydewilde - wheel cover turbine
