"One Man’s Quest to Outrace Wind"

Sailing directly downwind faster than the wind

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Re: "One Man’s Quest to Outrace Wind"

#41  Postby Onyx8 » Mar 06, 2011 9:36 am

How come you didn't directly answer any of my questions?
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Re: "One Man’s Quest to Outrace Wind"

#42  Postby reksio » Mar 06, 2011 9:48 am

Onyx8 wrote:How come you didn't directly answer any of my questions?

See my comments. Some of your questions where irrelevant to the scenario or irrelevant to the question if the car can accelerate at windspeed. Some where too unspecific.
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Re: "One Man’s Quest to Outrace Wind"

#43  Postby reksio » Mar 06, 2011 4:00 pm

The_Metatron wrote:
Once you match wind speed and direction, the relative windspeed is zero.

But the relative ground speed is not zero. Relative to the cart & airmass the ground is moving backwards.
The_Metatron wrote:
This is easy to replicate in still air.

In still air, but on ground that moves backwards. And it was replicated independently by many people:

[youtube]http://www.youtube.com/watch?v=1BRvYZd81AQ[/youtube]

[youtube]http://www.youtube.com/watch?v=MLFb1-GoqNY[/youtube]

[youtube]http://www.youtube.com/watch?v=qIOq5pQ9Tbo[/youtube]

[youtube]http://www.youtube.com/watch?v=9S2HHwfcz9Y[/youtube]

[youtube]http://www.youtube.com/watch?v=Wiiwwz1mtJA[/youtube]

[youtube]http://www.youtube.com/watch?v=o9xnlbKY-qw[/youtube]

The_Metatron wrote:
So, this vehicle should just be able to tear ass around in still air.

The vehicle should be able to accelerate forward in still air, on ground that moves backwards. And it is, just like those small models.
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Re: "One Man’s Quest to Outrace Wind"

#44  Postby Onyx8 » Mar 06, 2011 5:46 pm

spork wrote:Four things to keep in mind:
1) The prop never turns the wheels. The wheels turn the prop

So what starts the wheels turning?


2) Inertia doesn't factor into it. Even exactly at wind speed we can tow a trailer all day long.
Would you mind backing that assertion up?


3) When the vehicle is going directly downwind at wind speed, it feels no wind over it. The "prop" is also going downwind at wind speed. The blades of the prop however are not going directly downwind. The blades are following a spiraling path so they will always feel relative wind even when the cart is going downwind at wind speed - remember their tangential velocity.

Actually they are traveling in a helical path, but nevertheless they are still traveling at exactly the speed of the wind. If it can't 'feel' wind then it can extract no energy from it.


4) When the cart is going the speed of the wind - it feels no wind. But that doesn't mean there is no wind. It simply means there is no relative wind. There's still wind moving over the ground, and that's precisely the energy this vehicle exploits. It leaves a path of slower moving air in its wake - having taken some of its energy.


How does it extract energy from air that is not moving relative to itself? You claim that the wheels turn the prop, so therefore the prop is pushing air, that is the prop is performing work on the air. How do you extract energy from the process of doing work on something?
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Re: "One Man’s Quest to Outrace Wind"

#45  Postby Macdoc » Mar 06, 2011 6:18 pm

Did you actually READ the link about relative wind? :coffee:

Here is the physics and the explanation that is easily translated to this situation as a set of rapid tacking.

but nevertheless they are still traveling at exactly the speed of the wind


no - the blades are not.
Go back to rapid tacking - there is always relative wind.

Only a square rigged set up with the "sail" at right angles to the wind works as you describe. Read the sailing description of how a boat sails faster than the wind and you will understand this.

I do NOT agree the wheels drive the prop except under turntable or treadmill conditions which I consider completely spurious nonsense.
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Re: "One Man’s Quest to Outrace Wind"

#46  Postby reksio » Mar 06, 2011 6:20 pm

Onyx8 wrote:
spork wrote:Four things to keep in mind:
1) The prop never turns the wheels. The wheels turn the prop

So what starts the wheels turning?

Net force on the cart starts it rolling, wheels start turning.

Onyx8 wrote:
spork wrote:
2) Inertia doesn't factor into it. Even exactly at wind speed we can tow a trailer all day long.

Would you mind backing that assertion up?

You cannot use your own inertia to accelerate yourself. When the cart accelerates, all its parts accelerate as well. So the cart in not using any inertia for acceleration.

Onyx8 wrote:
spork wrote:
The blades are following a spiraling path so they will always feel relative wind even when the cart is going downwind at wind speed - remember their tangential velocity.

Actually they are traveling in a helical path, but nevertheless they are still traveling at exactly the speed of the wind.

Wrong, you forgot the tangential velocity. At wind speed, the blade velocity vector is the vector sum true_wind + tangential_velocity. Different speed and different direction than the air.

Onyx8 wrote:
spork wrote:4) When the cart is going the speed of the wind - it feels no wind. But that doesn't mean there is no wind. It simply means there is no relative wind. There's still wind moving over the ground, and that's precisely the energy this vehicle exploits. It leaves a path of slower moving air in its wake - having taken some of its energy.

How does it extract energy from air that is not moving relative to itself?

Push it back to slow it down.
Last edited by reksio on Mar 06, 2011 7:23 pm, edited 1 time in total.
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Re: "One Man’s Quest to Outrace Wind"

#47  Postby Macdoc » Mar 06, 2011 6:26 pm

You cannot use your own inertia to accelerate yourself. When the cart accelerates, all its parts accelerate as well. So they are not using any inertia for acceleration.


Inertia does sum the vectors to keep the card in a straight line - which is why I'm interested in the behaviour of a cart on a frictionless surface. Without the lateral hold of the wheels the cart would waggle ( effectively fall off the wind ). Inertia smooths the entire process.
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Re: "One Man’s Quest to Outrace Wind"

#48  Postby reksio » Mar 06, 2011 6:32 pm

Macdoc wrote:
I do NOT agree the wheels drive the prop

Depends how you define "drive". The prop rotates according to the torque from the wheels, so it is at least correct to say, that the wheels "turn" the prop.

Macdoc wrote:
except under turntable or treadmill conditions which I consider completely spurious nonsense.

There is no difference between a cart on the TM and on the ground at wind speed. The wheels turn the prop in both cases.
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Re: "One Man’s Quest to Outrace Wind"

#49  Postby reksio » Mar 06, 2011 6:37 pm

Macdoc wrote:Inertia does sum the vectors

I have no idea what that means
Macdoc wrote:
to keep the card in a straight line

What should push the cart off the straight line?
Macdoc wrote:
Without the lateral hold of the wheels the cart would waggle

Why?
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Re: "One Man’s Quest to Outrace Wind"

#50  Postby Onyx8 » Mar 06, 2011 8:09 pm

reksio wrote:
Onyx8 wrote:
spork wrote:Four things to keep in mind:
1) The prop never turns the wheels. The wheels turn the prop

So what starts the wheels turning?

Net force on the cart starts it rolling, wheels start turning.

What net force? Why are you being so cagey?

Onyx8 wrote:
spork wrote:
2) Inertia doesn't factor into it. Even exactly at wind speed we can tow a trailer all day long.

Would you mind backing that assertion up?

You cannot use your own inertia to accelerate yourself. When the cart accelerates, all its parts accelerate as well. So the cart in not using any inertia for acceleration.

Onyx8 wrote:
spork wrote:
The blades are following a spiraling path so they will always feel relative wind even when the cart is going downwind at wind speed - remember their tangential velocity.

Actually they are traveling in a helical path, but nevertheless they are still traveling at exactly the speed of the wind.

Wrong, you forgot the tangential velocity. At wind speed, the blade velocity vector is the vector sum true_wind + tangential_velocity. Different speed and different direction than the air.

Onyx8 wrote:
spork wrote:4) When the cart is going the speed of the wind - it feels no wind. But that doesn't mean there is no wind. It simply means there is no relative wind. There's still wind moving over the ground, and that's precisely the energy this vehicle exploits. It leaves a path of slower moving air in its wake - having taken some of its energy.

How does it extract energy from air that is not moving relative to itself?

Push it back to slow it down.

Is that an answer?
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Re: "One Man’s Quest to Outrace Wind"

#51  Postby chaggle » Mar 06, 2011 8:42 pm

spork wrote:Four things to keep in mind:
1) The prop never turns the wheels. The wheels turn the prop
2) Inertia doesn't factor into it. Even exactly at wind speed we can tow a trailer all day long.
3) When the vehicle is going directly downwind at wind speed, it feels no wind over it. The "prop" is also going downwind at wind speed. The blades of the prop however are not going directly downwind. The blades are following a spiraling path so they will always feel relative wind even when the cart is going downwind at wind speed - remember their tangential velocity.
4) When the cart is going the speed of the wind - it feels no wind. But that doesn't mean there is no wind. It simply means there is no relative wind. There's still wind moving over the ground, and that's precisely the energy this vehicle exploits. It leaves a path of slower moving air in its wake - having taken some of its energy.


So the vehicle is moving faster than the wind? In that case the wind "in its wake" hasn't reached it yet. How can it have taken some of its energy?
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Re: "One Man’s Quest to Outrace Wind"

#52  Postby Onyx8 » Mar 06, 2011 8:48 pm

I think I understand why these threads go on forever. Questions are avoided, the answers are needlessly complicated with unnecessary details, arguments by analogy are rife while ignoring observations like chaggle just made.

It is just a perpetual motion machine, what is not to like?
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Re: "One Man’s Quest to Outrace Wind"

#53  Postby reksio » Mar 06, 2011 9:22 pm

chaggle wrote:So the vehicle is moving faster than the wind? In that case the wind "in its wake" hasn't reached it yet.

The air in the wake has already passed trough the propeller circle.

chaggle wrote:SHow can it have taken some of its energy?

By accelerating it backwards, and thus slowing it down relative to the ground.
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Re: "One Man’s Quest to Outrace Wind"

#54  Postby Onyx8 » Mar 06, 2011 9:25 pm

See?
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Re: "One Man’s Quest to Outrace Wind"

#55  Postby reksio » Mar 06, 2011 9:48 pm

Onyx8 wrote:ignoring observations like chaggle just made.

chaggle's "observation" is just a misconception about what "wind" is. Wind means that the entire air mass in the area is moving relative to the ground. The wind doesn't have to "reach the vehicle" as chaggle puts it, because the vehicle is always immersed in air that moves relative to the ground (a.k.a. wind).
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Re: "One Man’s Quest to Outrace Wind"

#56  Postby jaydot » Mar 06, 2011 10:46 pm

i love it when people say "it can't be done." and some clever chap comes along and shows that it can. heavier-than-air machines were once considered an impissibolity - until those pesky wright brothers came along.

keep going, spork, et al. you'll show 'em. :)
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Re: "One Man’s Quest to Outrace Wind"

#57  Postby reksio » Mar 06, 2011 11:14 pm

jaydot wrote:i love it when people say "it can't be done." and some clever chap comes along and shows that it can.

I love it even more when people say "it can't be done." after it has been done.
jaydot wrote:
heavier-than-air machines were once considered an impissibolity - until those pesky wright brothers came along.

That was allegedly Lord Kelvin, just a couple of years before the Wright's . He made many wrong predictions, so it might be just a joke by someone, that got quoted, requoted and became accepted as real.
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Re: "One Man’s Quest to Outrace Wind"

#58  Postby Oldskeptic » Mar 06, 2011 11:54 pm

While I am having an extremely hard time trying to understand how Black Bird can go 2.8 times faster down wind than the wind I'm fairly certain that it did. The videos didn't quite convince me but I find this http://www.nalsa.org/BlackBirdDDWSR/Obs ... 032010.pdf to be very persuasive.

It seems to me that it is time for nay sayers to show how the experiment/tests are flawed, rather than just repeating that their common sense tells them it can't be so.

I understand high skepticism of the proposal while it is only on paper, but not after the results of a practical demonstration are in. It seems counter intuitive, but many things that have now been proven did in the beginning.

Every part of my common sense tells me that this can't happen, but my skepticism runs into a wall when reality shows my common sense to be somewhat unreliable.
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Re: "One Man’s Quest to Outrace Wind"

#59  Postby Onyx8 » Mar 07, 2011 12:17 am

That's fine, I'm skeptical and could be wrong, it's happened before. It just seems to me that honest questions get avoided, misinterpreted, or not answered, often things seem to be intentionally complicated in an apparent attempt to obfuscate.

When the ribbons are hanging straight down where does the energy come from to accelerate the vehicle?

If this is a natural thing for a spinning propellor then why do we not see this in everyday life, for instance if I manually spin a propellor why doesn't it access this energy source and continue spinning indefinitely?
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Re: "One Man’s Quest to Outrace Wind"

#60  Postby CdesignProponentsist » Mar 07, 2011 12:39 am

chaggle wrote:So the vehicle is moving faster than the wind? In that case the wind "in its wake" hasn't reached it yet. How can it have taken some of its energy?


From the frame of reference of the vehicle the wind behind it is moving faster. But from the ground frame of reference it has slowed the wind behind it.
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