"Andy Burns" wrote in message
o.uk...


I don't know who NALSA are, other than what is says on their website, but
I'd expect their observer to be able to spot a heavy flywheel, a set of
pedals or batteries and motors hidden within the polysytrene ...

http://www.nalsa.org/DownWind.html

Well they aren't doing it by wind power driving the wheels when they get to
an effective zero wind speed, which they must do.
It has to be done by storing energy or the whole thing is just a joke/fraud.
They can't even claim its the sails (turbine) crossing the wind like a land
yacht as its completely different.
In fact once they pass the wind speed the turbine should reverse as the wind
flow has reversed. I notice it didn't.

"Andy Burns" wrote in message
o.uk...
dennis@home wrote:

maybe its cold fusion? ;-)

There is an explanation of sorts on their website, more or less it's not
the propeller turning the wheels, but the other way round ...

https://docs.google.com/View?docID=0AdRsKX7aaZTPZGRnbjhkajdfMTY0aGRzNWtnaG M&revision=_latest&hgd=1

"The reason the car works is that the propeller is pushing on air that is
moving slower than the speed of the car because there is a tailwind. This
allows energy to flow into the system for propulsion, something that would
be impossible if there were no wind."

Clearly between you, Harry and TNP the details can now be thrashed out for
weeks.


No need its just not true.

dennis@home wrote:

Well they aren't doing it by wind power driving the wheels

They claim to be doing the opposite, driving the propeller from the wheels.

when they get to an effective zero wind speed, which they must do.
It has to be done by storing energy or the whole thing is just a
joke/fraud.

The specific record the NALSA were overseeing does seem *so* tightly
defined and measured as an average over just a 10 second period, that
momentum of the rotating bits might account for it.

During most of the runs they give it a push start, but they do also have
some videos showing that it can get up to the push-start speed just from
the prevailing wind (it's not exactly fast off the line).

An easier claim to "sell" to Joe Public would be over a longer period,
i.e. let it start from zero on the line and reach a final speed that's
faster than the average (or even better the peak) wind speed over the
course.

They can't even claim its the sails (turbine) crossing the
wind like a land yacht as its completely different.
In fact once they pass the wind speed the turbine should reverse as the
wind flow has reversed. I notice it didn't.

They have a picture showing a flag on land blowing in one direction with
the wind, while a streamer on their vehicle blows the opposite way as it
travels past ...

harry wrote:
On 27 Sep, 23:53, The Natural Philosopher
wrote:
harry wrote:
On 27 Sep, 10:12, The Natural Philosopher
wrote:
Gib Bogle wrote:
On 27/09/2010 9:49 p.m., The Natural Philosopher wrote:
Gib Bogle wrote:
On 27/09/2010 8:51 p.m., harry wrote:
On 27 Sep, 02:20, wrote:
On 26 Sep, 19:51, wrote:
ie Complete
********.http://www.youtube.com/watch?v=1IsaM...eature=related
Gravity powered aircraft? As useful as a lead Zeppelin.
Never a mention of friction.
That's just the start of the reasons for infeasibility.
Actually its ultimately not infeasible, just impractical and inefficient.
From a cursory glance (it deserves no more) all it is conceptually,
is a glider
and a balloon. Balloon lifts glider, glider glides to where it has to go.
The energy to turn a lighter than air volume of gas into a smaller
compressed
volume that then acquires sufficient weight to act as a glider, is not
mentioned.
The whole system is claimed to be self-sufficient. As I recall the
compression is powered by the propellers acting as turbines as the plane
glides down. It's perpetual motion.
Oh? I couldn't be arsed to listen that far.
There was one interesting idea that was mooted, that on analysis I
couldn't find a flaw with: A wind powered boat or vehicle that could
sail or drive directly into the wind using a turbine facing the wind to
drive a water prop or wheels..also said to be capable of going faster
than the wind..directly downwind..less sure about that, though.- Hide quoted text -

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^
- Show quoted text -
An ordinary sail boat can sail faster than the wind without the
benifit of strange turbines.
Not directly downwind it cant harry dearest

Go back to your rattle now.- Hide quoted text -

- Show quoted text -

Ah. Making qualifications now are we?.

What part of my original post:-

"..also said to be capable of going faster than the wind..directly
downwind..."

Did you fail to understand?

Or is it reading you have difficulty with.

You are almost as stupid as Drivel.

Andy Burns wrote:
dennis@home wrote:

maybe its cold fusion? ;-)

There is an explanation of sorts on their website, more or less it's not
the propeller turning the wheels, but the other way round ...

https://docs.google.com/View?docID=0AdRsKX7aaZTPZGRnbjhkajdfMTY0aGRzNWtnaG M&revision=_latest&hgd=1


"The reason the car works is that the propeller is pushing on air that
is moving slower than the speed of the car because there is a tailwind.
This allows energy to flow into the system for propulsion, something
that would be impossible if there were no wind."

Clearly between you, Harry and TNP the details can now be thrashed out
for weeks.

Oh no. In this case I am staying out.
I merely mentioned the site: Dennis found it. It will appeal to him.

We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember Tim Lamb
saying something like:

There is an energy input, but I really doubt it could be made large
enough to compress all that air, and afaics, the lifting bodies would be
far too small.
I'd not be surprised if a man-lifter using the idea could be built, but
for larger scale use, probably not.

er.. my understanding was that the energy for compressing the gas comes
from turbines powered by airflow. Unless there is some way to initially
power the pump at altitude, there will be no airflow as the device is at
equilibrium WRT the atmosphere.

The energy input I refer to is the turbine(s), but I can't see it
working from start height without some battery power onboard.
I'd be quite happy to be proved wrong - if it can be made to work on a
small scale it would be a hoot.

On 28 Sep, 11:07, Andy Burns wrote:
dennis@home wrote:
maybe its cold fusion? ;-)

There is an explanation of sorts on their website, more or less it's not
the propeller turning the wheels, but the other way round ...

https://docs.google.com/View?docID=0AdRsKX7aaZTPZGRnbjhkajdfMTY0aGRzN....

"The reason the car works is that the propeller is pushing on air that
is moving slower than the speed of the car because there is a tailwind.
* This allows energy to flow into the system for propulsion, something
that would be impossible if there were no wind."

Clearly between you, Harry and TNP the details can now be thrashed out
for weeks.

So, you might just as well use a sail. Cheaper and more efficient.

On 28 Sep, 10:19, Ronald Raygun wrote:
harry wrote:
On 27 Sep, 21:31, Gib Bogle wrote:
On 28/09/2010 5:51 a.m., harry wrote:

An ordinary sail boat can sail faster than the wind without the
benifit of strange turbines.
It's common *knowledge to anyone with even a slight knowledge of
physics.
http://en.wikipedia.org/wiki/Sailing..._than_the_wind

Yes, I know about sailing. *Did you read the post? *Here, I'll cut out
the appropriate part for you, to make it easier:
"A wind powered boat or vehicle that could sail or drive directly into
the wind using a turbine facing the wind to drive a water prop or wheels"
Do you see the reference to "using a turbine"? *OK, now the question is
this: "Can a WIND TURBINE-POWERED vessel or vehicle go faster than the
wind DIRECTLY DOWNWIND?" *Think about it.
By the way, a sail-driven craft cannot go faster than the wind DIRECTLY
DOWNWIND either. *Get it? *Your slight knowledge of physics should be
adequate to grasp this.- Hide quoted text -

Obviously is soon as it went "as fast as the wind downwind" there
would be no wind (relative to the machine/boat etc). Therefore
impossible.

No, that's a faulty conclusion. *It correctly answers the wrong question.

On 28 Sep, 10:19, Ronald Raygun wrote:
harry wrote:
On 27 Sep, 21:31, Gib Bogle wrote:
On 28/09/2010 5:51 a.m., harry wrote:

An ordinary sail boat can sail faster than the wind without the
benifit of strange turbines.
It's common *knowledge to anyone with even a slight knowledge of
physics.
http://en.wikipedia.org/wiki/Sailing..._than_the_wind

Yes, I know about sailing. *Did you read the post? *Here, I'll cut out
the appropriate part for you, to make it easier:
"A wind powered boat or vehicle that could sail or drive directly into
the wind using a turbine facing the wind to drive a water prop or wheels"
Do you see the reference to "using a turbine"? *OK, now the question is
this: "Can a WIND TURBINE-POWERED vessel or vehicle go faster than the
wind DIRECTLY DOWNWIND?" *Think about it.
By the way, a sail-driven craft cannot go faster than the wind DIRECTLY
DOWNWIND either. *Get it? *Your slight knowledge of physics should be
adequate to grasp this.- Hide quoted text -

Obviously is soon as it went "as fast as the wind downwind" there
would be no wind (relative to the machine/boat etc). Therefore
impossible.

No, that's a faulty conclusion. *It correctly answers the wrong question.

On 27/09/2010 21:33, Gib Bogle wrote:
On 28/09/2010 8:40 a.m., Andy Champ wrote:
On 27/09/2010 10:12, The Natural Philosopher wrote:

There was one interesting idea that was mooted, that on analysis I
couldn't find a flaw with: A wind powered boat or vehicle that could
sail or drive directly into the wind using a turbine facing the wind to
drive a water prop or wheels..also said to be capable of going faster
than the wind..directly downwind..less sure about that, though.



You can go as fast as you like in any direction, provided you have one
thing
moving against another that you can extract energy from.

Typically this is the wind blowing over the water, or the land.

There is no theoretical speed limit; it's just the faster you go the
more the
efficiency of your aerofoils / hydrofoils / wheels matters.

Andy

OK, Einstein, when you are travelling at the same speed as the wind, in
the direction of the wind, what "thing is moving against another",
except for the vessel moving against the water, which creates drag?

Odd, my post from last night seems to have gone missing. Oh well, I
kept a copy...

I ain't Einstein. Luckily this is far easier.

As you so delicately told Harry, you need a turbine. Or some such.

The one I've seen uses wheels and an airscrew - the principle is the
same for a prop. in water and an airscrew.

In order to generate a force against the wind the airscrew, which is not
moving relative to the wind, requires only enough energy to overcome
friction losses and inefficiencies. Polish it enough, and that won't be
much.

Put that force down to the bottom of the vehicle, where it's moving
against the substrate, and you have a force moving through a distance.
From that you can extract substantial amounts of power. Certainly
enough to keep the airscrew spinning in what it sees as still air.

For the numbers, imagine this: Airscrew is generating 1kN of force, and
as the air is still relative to it it requires minor amounts of power only.

The vessel is moving downwind at 1m/s. Half of that kilonewton is used
to shove it through the water; the other half is pushing a prop through
the water. 500 newtons at 1 m/s is half a kilowatt. Not enormous, but
as much as a racing cyclist... OK you won't get it all out of the prop,
and you won't get it all up to the airscrew, but certainly some!

Andy

As to the DDWFTTW vehicle in question:

-- it does not utilize a turbine, it uses a propeller. Several people
have correctly deduced that if it were a turbine, the extractable
power available to the turbine with the vehicle at windspeed would be
exactly zero and thus the vehicle could only attain some fraction of
windspeed.

-- The vehicle has no capabilities of utilizing onboard stored energy
for acceleration -- this was a strict requirement from NALSA (as it
would be with any other good scientist)

-- For record purposes, the NALSA rules impose strict requirements on
the vehicle from the moment it begins to move and not just during a 10
second period as some have surmised. The 10 second period is merely
the length of time that is averaged to come up with the record speed.

On 28 Sep, 16:45, Ronald Raygun wrote:
harry wrote:
On 28 Sep, 10:19, Ronald Raygun wrote:
harry wrote:
On 27 Sep, 21:31, Gib Bogle wrote:

Yes, I know about sailing. *Did you read the post? *Here, I'll cut out
the appropriate part for you, to make it easier:
"A wind powered boat or vehicle that could sail or drive directly into
the wind using a turbine facing the wind to drive a water prop or
wheels" Do you see the reference to "using a turbine"? *OK, now the
question is this: "Can a WIND TURBINE-POWERED vessel or vehicle go
faster than the wind DIRECTLY DOWNWIND?" *Think about it.
By the way, a sail-driven craft cannot go faster than the wind
DIRECTLY DOWNWIND either. *Get it? *Your slight knowledge of physics
should be adequate to grasp this.- Hide quoted text -

Obviously is soon as it went "as fast as the wind downwind" there
would be no wind (relative to the machine/boat etc). Therefore
impossible.

No, that's a faulty conclusion. *It correctly answers the wrong question.

The question was whether it is possible for a boat to sail directly
downwind faster than the wind, powered only by a wind turbine. *That
means whether it is possible for a boat *to sustain* such a speed.

The question you've answered, however, is whether it's possible for the
boat *to reach* that speed, subject to the constraint that it must start
from rest and only ever head directly downwind whilst accelerating.
That's a completely different question, doomed to a negative answer by
the fatal constraints imposed.

Anyway, your answer correctly observes that the relative wind speed
approaches zero as the boat's speed approaches that of the wind, and
so the turbine is faced with the impossible task of extracting power
from a dying wind. *Therefore crossing the barrier of actual wind speed
is going to be impossible in those circumstances, and in practice there
will be a top speed which it is possible to reach but not exceed.

Suppose this practical top speed is about 90% of wind speed, so that a
10% difference or so is enough to provide the power needed to keep up
with water resistance etc.

But if a 10% difference is enough, then travelling at 110% of wind speed
should also be sustainable.

The only problem remaining is how to reach that state to begin with.
Clearly it can't be done subject to the constraint of your scenario,
but it could be done by other means, including by "cheating" and using
stored energy.

I dare say another way would be to use the wind turbine to accelerate
to beyond wind speed by going downwind *but not directly downwind*, and
then quickly turning directly downwind, relying on inertia to lose not
too much speed in the turn.- Hide quoted text -

- Show quoted text -

The speed the boat reaches is determined by the drag through the
water. When the thrust from the sails *= the drag, equilibriibum is
reached and it ceases to accelerate.

Indeed. *Drag increases with speed, but available power (and hence thrust)
reaches a minimum (of zero) at 100% of wind speed. *I postulated that if
equilibrium might be achievable at 90%, that, on the basis that the
relative wind speed is then 10%, equilibrium ought *also* to exist at about
110% when the relative wind speed is also 10% (I appreciate that water drag
at 110% will be a bit more than at 90%, so the difference might need to be
a bit more than 10%).

*The only way to increase the speed in the same conditions is to
increase thrust with a bigger sail.

Or a bigger turbine in this case. *But if doing this on a dead downwind
course, you still can't break the 100% barrier, you will merely push
your equilibrium a bit nearer 100%.

My point, which you may have missed, was that you could exceed 100%
wind speed by making your initial acceleration on a course which is *not*
directly downwind, and where therefore there is no barrier effect at
which relative wind goes to zero. *And then suddenly turn dead downwind
where you should then be able to sustain the 110% you had already
reached earlier.- Hide quoted text -

- Show quoted text -

Nah. The turbine would slow it down. It would be driven by the wind
if going faster.

Anyway drag and speed relationship is not as simple as that.
Drag is divided into two components.
One is caused by the shape of the object in question and increased
with speed through the fluid. (Gas or liquid). Not linearly either,
it's a square law.
The other is caused by friction with the surface of the object and
decreases with speed.
This means there is a low pont on the combined curve known as mininimu
drag.
So there is and optimum speed that consumes the least power known as
the "best" lift/drag ratio. ie the cruising speed for ships and
aircraft.
There is a picture of the graph here and an explanation.
http://en.wikipedia.org/wiki/Lift-to-drag_ratio#Drag

On 28 Sep, 19:35, (Alan Braggins) wrote:
In article , harry wrote:
On 28 Sep, 11:07, Andy Burns wrote:

There is an explanation of sorts on their website, more or less it's not
the propeller turning the wheels, but the other way round ...
https://docs.google.com/View?docID=0AdRsKX7aaZTPZGRnbjhkajdfMTY0aGRzN...

"The reason the car works is that the propeller is pushing on air that
is moving slower than the speed of the car because there is a tailwind..
* This allows energy to flow into the system for propulsion, something
that would be impossible if there were no wind."

Clearly between you, Harry and TNP the details can now be thrashed out
for weeks.

So, you might just as well use a sail. Cheaper and more efficient.

Apart from the bit where the whole point is to go directly downwind,
faster than the wind, powered by the wind, and a sail can't do that.
Do try and keep up.

http://jalopnik.com/5556198/wind+pow...ernet-naysayer...
seems to be the most appropriately titled article on the subject.

http://blogs.discovermagazine.com/sc...0/06/10/imposs...
has a more suspect title, but does have a good explanation of how it gets
past the wind speed (i.e. through zero relative wind) without relying on
energy storage or switching mode of operation.- Hide quoted text -

- Show quoted text -

http://www.sciencedaily.com/releases...0827104702.htm
Noticable, they are going crosswind.

@harry:
http://www.sciencedaily.com/releases...0827104702.htm
Noticable, they are going crosswind

You are absolutely correct Harry -- in your link with that upwind race
for university students, held it Europe each year, there are no
specific requirement for crosswinds. The races are held head to head
between the competitors and they use whatever wind Mom Nature gives
them on race day.

The Blackbird directly downwind vehicle had no such flexibility. To
set the NALSA (and soon to by published Guiness) record, 18 recording
sensors were placed on the vehicle and the course and during the
record run it was kept within ~3degrees of the wind.

JB

In article , harry wrote:
On 28 Sep, 19:35, (Alan Braggins) wrote:

So, you might just as well use a sail. Cheaper and more efficient.

Apart from the bit where the whole point is to go directly downwind,
faster than the wind, powered by the wind, and a sail can't do that.
Do try and keep up.

http://www.sciencedaily.com/releases...0827104702.htm
Noticable, they are going crosswind.

Noticable if you actually read it, "participating teams were challenged
to drive directly into the wind, without tacking". But I've seen photos
of a wind turbine powered boat doing that years ago.

Sailing downwind faster than the wind is a different challenge (and one
where I'm not convinced you could make a boat efficient enough to do it,
sticking a turbine in the water is going to be more lossy than having
wheels on the ground, and there will be more drag to overcome).
(Well, in one sense you can do it trivially - have a very light wind and
a strong current or tide, and drift. That doesn't really count though.)

@ The Natural Philosopher
Kinetic energy extractable from the air is a function of
the *relative* velocity between the machine extracting
the energy, and the air.

This is true for a device extracting energy through a turbine
mechanism, but not for a device extracting energy from the air using a
propeller.

First, let’s summarize the difference between a prop and a turbine:
In short and simplistic terms, a turbine slows air down relative to
itself, and uses that extracted energy to provide an *output torque*
on the rotor shaft. A propeller requires an *input torque* at its
shaft, and uses that input torque to accelerate air relative to
itself.

One way to highlight the differences in the two mechanisms is to
imagine being on a skateboard on a busy city sidewalk (where for our
purposes everyone is walking the same direction).

If I'm on the skateboard and I just cross my arms and stand still on
the board, I will gradually get pushed down the sidewalk as people
bump into me one by one. I will be extracting energy from each of the
people who contact me - slowing them down just a bit, and obviously I
can never quite reach the speed of those who bump into me. If (though
other means) I manage to attain the speed of the travelers on the
sidewalk, it’s obviously impossible to extract any energy from them at
all. This is the turbine analogy – like the people on the sidewalk,
the air molecules strike the passive blades just as the people strike
the passive skateboarder.

The propeller device works quite different and has a different set of
limitations.

Now imagine me on the same skateboard on the same busy sidewalk, but
instead of simply crossing my arms and passively waiting for
pedestrians to strike me and bump me down the walk to my destination I
quite literally take matters into my own hands – I reach out and push
people backwards while propelling myself forwards. In this scenario,
I can extract *more* energy from each person (I can push back on them
hard enough to bring them to a complete stop, unlike the turbine). I
can also continue to extract energy from people even when I am going
faster than they are as unlike the turbine, I am no longer just
waiting for them to hit me. As I rip down the sidewalk say twice as
fast as everyone else, there’s nothing stopping me from grabbing
everyone I come up on and pushing them backwards to a stop – and
taking all their KE in the process.

So, taking us back to the the assertion quoted at the top of the post
-- one can see that it's a true assertion when applied to a passive
turbine device which *does* rely on the relative motion between air
and machine to extract energy. It's not a true assertion however when
applied to a device which can actively push back on the molecules of
air -- such a device can continue to extract energy from the air even
when it's relative motion is exactly the same as the average speed of
the molecules.

The primary limitation on the propeller device? -- we have to find
the energy somewhere to provide the input torque to turn it. To put
it back in the skateboard example, the energy to power my arms has to
come from somewhere and in this case, it can come from the skateboard
wheels.

If anyone wishes see the math which shows there is ample power
available at the wheels of the skateboard to accomplish this task, I’m
quite happy to walk through it.

ThinAirDesigns wrote:

@ The Natural Philosopher
Kinetic energy extractable from the air is a function of
the *relative* velocity between the machine extracting
the energy, and the air.

This is true for a device extracting energy through a turbine
mechanism, but not for a device extracting energy from the air using a
propeller.

There's something wrong with that assertion.

First, let?s summarize the difference between a prop and a turbine:
In short and simplistic terms, a turbine slows air down relative to
itself, and uses that extracted energy to provide an *output torque*
on the rotor shaft. A propeller requires an *input torque* at its
shaft, and uses that input torque to accelerate air relative to
itself.

Exactly, and this means that unlike the turbine, a propeller does not
*extract* energy from the air, it *imparts* energy to it.

@Ronald Raygun:
Exactly, and this means that unlike the turbine, a
propeller does not *extract* energy from the air, it
*imparts* energy to it.

This is correct -- but only when considering energy relative to the
device itself. In the case of the DDWFTTW vehicle, the propeller
*speed up* the air relative to itself ('cause that's what propellers
do), but is *slows* the air relative to the ground (which is what has
to happen if we want to harvest energy).

Let's go back to the actively engaged skateboarder:

Let's suppose that the pedestrians on the sidewalk are originally
moving at 1ms. Let suppose that that the skateboarder is moving at
2ms. Obviously in this scenario, before the the pedestrians are
'grabbed' by the skateboarder they moving at 1ms relative to the
skateboarder AND 1ms relative to the ground. Once the skateboarder
pushes them backwards, bringing them to a complete stop, there is a
new set of relative numbers. Now, the pedestrian is moving 0ms across
the ground and 2ms relative to the skateboarder.

Pedestrian before contact:
Relative to ground: 1ms
Relative to skateboarder: 1ms

Pedestrian after contact:
Relative to ground: 0ms
Relative to skateboarder: 2ms

So, while the skateboarder *does* speed up the pedestrians (air
molecules) relative to himself, it slows them down relative to the
ground.

No one considers a wind turbine a PM device because we all know that
in it's wake is left a volume of air that has been slowed relative to
the ground. Wind that was going 10mph across the ground before it
encounters the device is slowed and is only going 5mph after it
encounters the device.

The source of the energy from the propeller driven device is
absolutely no different from a physics standpoint -- just as the
skateboarder leaves people in his wake going down the sidewalk slower
than before, the Blackbird leaves a volume of air in it's wake going
across the ground slower than it once was. Wind that was going 10mph
across the ground before encountering the device is not only going
5mph across the ground.

Folks, I apologize for mixing metric and US/Imperial units in my
posts. I was attempting to stick to metric but I tend to
automatically revert to US standards.

I'll try to be more consistent in the future. Thanks for tolerance.

"ThinAirDesigns" wrote in message
...
@ The Natural Philosopher
Kinetic energy extractable from the air is a function of
the *relative* velocity between the machine extracting
the energy, and the air.

This is true for a device extracting energy through a turbine
mechanism, but not for a device extracting energy from the air using a
propeller.

First, let’s summarize the difference between a prop and a turbine:
In short and simplistic terms, a turbine slows air down relative to
itself, and uses that extracted energy to provide an *output torque*
on the rotor shaft. A propeller requires an *input torque* at its
shaft, and uses that input torque to accelerate air relative to
itself.

One way to highlight the differences in the two mechanisms is to
imagine being on a skateboard on a busy city sidewalk (where for our
purposes everyone is walking the same direction).

If I'm on the skateboard and I just cross my arms and stand still on
the board, I will gradually get pushed down the sidewalk as people
bump into me one by one. I will be extracting energy from each of the
people who contact me - slowing them down just a bit, and obviously I
can never quite reach the speed of those who bump into me. If (though
other means) I manage to attain the speed of the travelers on the
sidewalk, it’s obviously impossible to extract any energy from them at
all. This is the turbine analogy – like the people on the sidewalk,
the air molecules strike the passive blades just as the people strike
the passive skateboarder.

The propeller device works quite different and has a different set of
limitations.

Now imagine me on the same skateboard on the same busy sidewalk, but
instead of simply crossing my arms and passively waiting for
pedestrians to strike me and bump me down the walk to my destination I
quite literally take matters into my own hands – I reach out and push
people backwards while propelling myself forwards. In this scenario,
I can extract *more* energy from each person (I can push back on them
hard enough to bring them to a complete stop, unlike the turbine). I
can also continue to extract energy from people even when I am going
faster than they are as unlike the turbine, I am no longer just
waiting for them to hit me. As I rip down the sidewalk say twice as
fast as everyone else, there’s nothing stopping me from grabbing
everyone I come up on and pushing them backwards to a stop – and
taking all their KE in the process.

Now do that without the chemical energy being used by your muscles!


So, taking us back to the the assertion quoted at the top of the post
-- one can see that it's a true assertion when applied to a passive
turbine device which *does* rely on the relative motion between air
and machine to extract energy. It's not a true assertion however when
applied to a device which can actively push back on the molecules of
air -- such a device can continue to extract energy from the air even
when it's relative motion is exactly the same as the average speed of
the molecules.

Rubbish. It is the air that is gaining energy as you are pushing it.
Any attempt to move air by the propeller must use energy by definition.


The primary limitation on the propeller device? -- we have to find
the energy somewhere to provide the input torque to turn it. To put
it back in the skateboard example, the energy to power my arms has to
come from somewhere and in this case, it can come from the skateboard
wheels.

Nice set of brakes there.


If anyone wishes see the math which shows there is ample power
available at the wheels of the skateboard to accomplish this task, I’m
quite happy to walk through it.

Go on then.

@"dennis@home"
Now do that without the chemical energy
being used by your muscles!

That's absolutely correct Dennis - and why I stated:

"To put it back in the skateboard example, the energy to power my arms
has to
come from somewhere ..."

Rubbish.
snip
Any attempt to move air by the propeller
must use energy by definition.

You are again correct -- by definition, a propeller *does work on the
air*(but only relative to itself) and it must be provided an input
torque on it's shaft to do to so. But it's not rubbish in any way to
assert that a propeller can be used to slow the wind down relative to
the ground even when it's traveling at the speed of the wind -- and
that's what the paragraph that you 'Rubbished" said.

Nice set of brakes there.

And again, correct -- to extract any energy from the rotation of the
wheels, there will of course be a resultant braking force. This
braking force can be calculated as can the thrust of the propeller.
Only if the thrust is equal to or greater than the braking force can
any given speed be maintained or accelerated from.

Go on then.

I will do so, but give me a bit to put a post together. I'm off to
lunch at the moment.

On 29/09/2010 20:04, ThinAirDesigns wrote:

I will do so, but give me a bit to put a post together. I'm off to
lunch at the moment.

Feel free to be rude about my post from yesterday. I did drop some
(metric!) numbers in there.

Andy

Alrighty -- following is a simple energy/force analysis for a small
propeller equipped DDWFTTW vehicle. In this analysis, we show that
in a 27.5ftsec wind, and with the vehicle traveling over the ground at
55ft/sec, the retardant force on the wheels needed to drive the
propeller is less than the propeller needs to keep the vehicle at that
speed.

A:
1.0 HP = 550 foot-pounds per second
(http://en.wikipedia.org/wiki/Horsepower)
This means that @55ft/sec, 10lbs of force exerted on our chassis will
allow us to harvest 1.0hp from our wheels with a lossless generator
(we'll deal with losses below)

B:
1/2HP = 275 foot-pounds per second
This means that at 27.5ft/sec, 10lbs of force can be produced by a
lossless propeller consuming 1/2hp. (we'll deal with losses below)

C:
If the wind is blowing at 27.5ft/sec and our vehicle is traveling DDW
at 2x the speed of the wind, the vehicle is traveling over the ground
at 55ft/sec and through the air at only 27.5ft/sec.

D:
Through the establishment of "A", we know we can pull 1.0 HP from the
wheels of the vehicle if it's propelled by 10lbs of force, and through
the establishement of "B" we can see that the propeller in the
relative tailwind only needs 1/2HP input to produce that same 10lbs of
force.

E:
We subtract the 1/2hp that the prop needs to produce its 10lbs of
thrust from the 1.0hp that the wheels can produce from that same 10lbs
and you have 0.5hp left over for the system losses.(told you we would
get to losses).

In the real world we don't have lossless components of course. If you
consider an 85% efficient propeller (easy to achieve) and an 85% drive
train (even easier to achieve) we've still got nearly 1/4 HP left over
for the Crr of the tires (very low for high pressure bike tires) and
aero drag (which is also very low as our relative headwind is slight).

Do the same calcs on a no wind day and it's easy to see that the
wheels still produce 1.0HP at 55ft/sec, but now the propeller is force
to do work at 55ft/sec rather than 27.5ft/sec and it now takes a full
1.0HP at the prop to produce the 10lbs of force. This of course means
that there is nothing left for losses and since there are *always*
losses, the vehicle simply can’t motivate itself when there is no
wind.

For clarity, I would like to add two words to the first paragraph in
my last post. I have wrapped these two words in *** to highlight the
edit.

-----------------

Alrighty -- following is a simple energy/force analysis for a small
propeller equipped DDWFTTW vehicle. In this analysis, we show that
in a 27.5ftsec wind, and with the vehicle traveling ***directly
downwind*** over the ground at 55ft/sec, the retardant force on the
wheels needed to drive the propeller is less than the propeller needs
to keep the vehicle at that speed.

-----------------

On Sep 29, 4:25*pm, ThinAirDesigns said:

In this analysis, we show that
in a 27.5ftsec wind, and with the vehicle traveling ***directly
downwind*** over the ground at 55ft/sec, the retardant force on the
wheels needed to drive the propeller is less than the propeller needs
to keep the vehicle at that speed.


[cough]bull****[/cough]

In article , Rick Cavallaro wrote:
On Sep 29, 4:25*pm, ThinAirDesigns said:

In this analysis, we show that
in a 27.5ftsec wind, and with the vehicle traveling ***directly
downwind*** over the ground at 55ft/sec, the retardant force on the
wheels needed to drive the propeller is less than the propeller needs
to keep the vehicle at that speed.

[cough]bull****[/cough]

So on the one hand we have someone who's actually built the thing and shown
that it works doing an analysis of it working, and on the other hand we have
a random usenet poster saying it's bull**** for no reason. Who to believe....

On Sep 30, 12:45*am (Alan Braggins) wrote:

So on the one hand we have someone who's actually built the thing and shown
that it works doing an analysis of it working, and on the other hand we have
a random usenet poster saying it's bull**** for no reason. Who to believe.....

Hmmm... tough call - particularly in light of the fact that I
designed, built, and drove it.

ThinAirDesigns wrote:

We subtract the 1/2hp that the prop needs to produce its 10lbs of
thrust from the 1.0hp that the wheels can produce from that same 10lbs
and you have 0.5hp left over for the system losses.

Thanks for the numbers and your skateboarder examples, I think I can
grasp it now, but I'd hate to have to explain it down the pub from
scratch ...

"Andy Burns" wrote in message
o.uk...
ThinAirDesigns wrote:

We subtract the 1/2hp that the prop needs to produce its 10lbs of
thrust from the 1.0hp that the wheels can produce from that same 10lbs
and you have 0.5hp left over for the system losses.

Thanks for the numbers and your skateboarder examples, I think I can grasp
it now, but I'd hate to have to explain it down the pub from scratch ...

You won't explain it from that description as its rubbish.

I can imagine it being done by moving the sail (propeller blades) in such
away that they are effectively tacking across the wind as they would on a
land yacht going sideways but that isn't what is being claimed here.
They are claiming they can develop thrust by removing energy from the
vehicle and that gives the vehicle more energy to make it faster, which is
just daft.

dennis@home wrote:

You won't explain it from that description as its rubbish.
They are claiming they can develop thrust by removing energy from the
vehicle and that gives the vehicle more energy to make it faster

No, they are claiming they can develop thrust by removing energy from
the wind by slowing it down as it passes through their propeller, the
reaction pushes the vehicle forwards, which spins the wheels, which
spins the propeller ... I think!

"Andy Burns" wrote in message
o.uk...
dennis@home wrote:

You won't explain it from that description as its rubbish.
They are claiming they can develop thrust by removing energy from the
vehicle and that gives the vehicle more energy to make it faster

No, they are claiming they can develop thrust by removing energy from the
wind by slowing it down as it passes through their propeller, the reaction
pushes the vehicle forwards, which spins the wheels, which spins the
propeller ... I think!


The vehicle is going faster than the wind, so the air that passes through is
not the wind, it is the wind - the vehicle speed which is some negative
value as the vehicle is going faster than the wind.

How do extract energy from the wind when they are effectively going into the
wind *they* are generating by moving the vehicle to make the vehicle gain
energy and go faster?

This is in the same area as the numpties that think they can run a car on
water by splitting it into hydrogen and burning it by using the "spare"
power in the alternator. You can even see videos of them doing it (but none
without the batteries being connected).

On Sep 30, 2:50*am, "dennis@home" wrote

You won't explain it from that description as its rubbish.

I'm sure it looks that way to someone that can't understand it.


I can imagine it being done by moving the sail (propeller blades) in such
away that they are effectively tacking across the wind as they would on a
land yacht going sideways but that isn't what is being claimed here.

Of course it is. Can you honestly not see how our "sails" (i.e. prop
blades) are going sideways due to the rotation of the prop, as the
vehicle itself goes straight downwind?

They are claiming they can develop thrust by removing energy from the
vehicle...

Wrong

On Sep 30, 3:31*am, "dennis@home" wrote:

This is in the same area as the numpties that think they can run a car on
water by splitting it into hydrogen and burning it by using the "spare"
power in the alternator. You can even see videos of them doing it (but none
without the batteries being connected).

You can see us doing this without batteries attached. Moreover, we've
posted detailed build videos on YouTube so you can build your own
working model for about $40 and prove it to yourself. Do the
perpetual motion nuts do that?

How do you think we managed to fool the aero departments at Stanford
and SJSU? How did we manage to fool the official observers from the
North American Land Sailing Association?

Perhaps it's time you consider that you simply have to try harder to
understand what's being claimed and how it works. There's no magic
(and no free energy) here.

"Rick Cavallaro" wrote in message
...
On Sep 30, 2:50 am, "dennis@home" wrote

You won't explain it from that description as its rubbish.

I'm sure it looks that way to someone that can't understand it.


I can imagine it being done by moving the sail (propeller blades) in such
away that they are effectively tacking across the wind as they would on a
land yacht going sideways but that isn't what is being claimed here.

Of course it is. Can you honestly not see how our "sails" (i.e. prop
blades) are going sideways due to the rotation of the prop, as the
vehicle itself goes straight downwind?

Yes, but that is not enough, but you jumped on it without actually
understanding what I said or how it works.
Draw a vector diagram and you can work it out for yourself.


They are claiming they can develop thrust by removing energy from the
vehicle...

Wrong

Well its been claimed you accelerate the wind in a negative direction using
energy from the vehicle

Let me know when you publish detailed plans and someone duplicates it.

In article , Rick Cavallaro wrote:
On Sep 30, 12:45*am (Alan Braggins) wrote:

So on the one hand we have someone who's actually built the thing and shown
that it works doing an analysis of it working, and on the other hand we have
a random usenet poster saying it's bull**** for no reason. Who to believe....

Hmmm... tough call - particularly in light of the fact that I
designed, built, and drove it.

My apologies, I misinterpreted your "bull****" comment as being yet another
one of the people saying that since they couldn't immediately see how it
worked, then it couldn't possibly work. I recognised the ThinAirDesigns
name, but hadn't looked at the Team page.

Care to expand on your comment?

"Rick Cavallaro" wrote in message
...
On Sep 30, 3:31 am, "dennis@home" wrote:

This is in the same area as the numpties that think they can run a car on
water by splitting it into hydrogen and burning it by using the "spare"
power in the alternator. You can even see videos of them doing it (but
none
without the batteries being connected).

You can see us doing this without batteries attached. Moreover, we've
posted detailed build videos on YouTube so you can build your own
working model for about $40 and prove it to yourself. Do the
perpetual motion nuts do that?

How do you think we managed to fool the aero departments at Stanford
and SJSU? How did we manage to fool the official observers from the
North American Land Sailing Association?

Perhaps it's time you consider that you simply have to try harder to
understand what's being claimed and how it works. There's no magic
(and no free energy) here.


Have you seen the cr@p in this video?
http://www.youtube.com/watch?v=xHsXc...eature=related

The statement that a cart on a treadmill in still air is the same as a
moving cart on road in the wind is just wrong.
Any fool can take energy from an electrically powered conveyor belt to move
the opposite way it just depends on friction. The energy comes from the
electric motor.

The claim is you can take energy from the apparent wind and accelerate the
cart into the apparent wind.
If you can do this then you should be able to go out on a still day, push
the cart to create an apparent wind and then go from that. If you do that
then that would be pretty difficult to deny. I won't hold my breath.

@Alan Braggins

My apologies,

Care to expand on your comment?

No apologies necessary Alan -- Rick's a smart ass.

@dennis@home
They are claiming they can develop thrust by removing
energy from the vehicle and that gives the vehicle more
energy to make it faster, which is just daft.

That would be daft if only we were claiming that.

The claim is clear -- the wind across the ground is slowed and this
energy must go somewhere. We use it to propel the vehicle.

A: I have shown that a mechanism exists (prop) which can slow the air
relative to the ground even when at or above windspeed (see
skateboarder examples)

B; I have shown through simple force/energy calculations that there
is more than enough energy at the wheels to power said prop.

If you can point out specifically where you found the flaw in either
of the above, we'll chat about it.

@Andy Burns
No, they are claiming they can develop thrust by removing energy from
the wind by slowing it down as it passes through their propeller, the
reaction pushes the vehicle forwards, which spins the wheels, which
spins the propeller ... I think!

Hi Andy,

Actually, the propeller never spins the wheels (it can't -- it's a
propeller and thus doesn't produce an output torque).

Initially the wind merely starts blows the vehicle downwind. Once the
vehicle is moving the wheels provide the input torque to turn the
propeller. The propeller takes wind that was moving at say 10mph
across the ground and pushes back on it until it is only moving say
5mph across the ground. The energy removed from the wind when it is
slowed is the energy powering the vehicle.

@dennis@home
Well its been claimed you accelerate the wind in a
negative direction using energy from the vehicle.

That's never been claimed by us and we're the only ones I care to
defend.

Let me know when you publish detailed plans
and someone duplicates it.

You're a year or two too late. We published build videos way back and
near a dozen independent parties have already duplicated results.
Look it up.