Newton's third law problem.

[fourfathom]

Where the insistence of energy storage being involved here stems from, I can only imagine.

Here's the genesis:
* Because of electro's unwillingness to properly consider frames of reference, he believes that it is impossible for a wind-powered vehicle travel directly downwind FTTW (Faster Than The Wind).
* So, he presumes that energy used for this physically demonstrated FTTW speed has been stored as pressure behind the vehicle while it was travelling slower TTW.
* When presented with simple physical or conceptual models that demonstrate analogous behavior he clings to the "energy storage" model, invoking things like "slip-stick hysteresis". (this does exist in some cases, but is irrelevant here).

So it all goes back to the original propeller/wheel vehicle that violates electro's misunderstood laws of physics.

[electrodacus]

Here's the genesis:
* Because of electro's unwillingness to properly consider frames of reference, he believes that it is impossible for a wind-powered vehicle travel directly downwind FTTW (Faster Than The Wind).
* So, he presumes that energy used for this physically demonstrated FTTW speed has been stored as pressure behind the vehicle while it was travelling slower TTW.
* When presented with simple physical or conceptual models that demonstrate analogous behavior he clings to the "energy storage" model, invoking things like "slip-stick hysteresis". (this does exist in some cases, but is irrelevant here).

So it all goes back to the original propeller/wheel vehicle that violates electro's misunderstood laws of physics.

You're confusing things.

There are two vehicles
a) the direct upwind discussed in this thread as it should be simpler to explain and has analog version using just wheels and this one uses small capacity energy storage and stick slip hysteresis to trigger when energy is being charged and discharged.

b) the direct downwind faster than wind not discussed here that uses a large capacity energy storage called pressure differential and created by the propeller.

The only way wind interacts with any vehicle is through collisions between air particles and vehicle and depending on direction vehicle gains or loses kinetic energy.
That is why the equation for wind power has no variable related to the vehicle design so all wind powered vehicles have access to the same amount of wind power.

WindPower = 0.5 * air density * (area * coefficient of drag) * (wind speed - vehicle speed)³

This above equation is universal for any wind powered vehicle so for direct downwind equation shows there is zero wind power available when vehicle speed equals wind speed.
And for direct upwind discussed in this thread the equation shows the power that winds acts against the vehicle as well as the theoretical max power available to vehicle and so since this two are ideal case equal the vehicle can not move unless it first store energy then uses that stored energy to move a little bit against the wind direction and then repeat this cycle as many times as you want.

So that equation is the only prove I need to show that any vehicle powered only by wind requires energy storage in order to drive faster than wind directly downwind or at any speed directly upwind.
If you want to contradict what I say you will need to provide a wind power equation that matches what is observed and measured in reality.

And my best example of what happens and it is measured in reality was the one about the power needed to overcome drag (same equation) is the same for a vehicle driving at 30m/s with no wind as it is for the same vehicle driving at 10m/s with a 20m/s head wind.

The basic physics law that you try to violate is Newton's third law the subject of this thread and by extension the energy conservation.

[AVGresponding]

Never been sailing? You can tack into the wind, effectively using wind power to propel you in the direction the wind is coming from.

[electrodacus]

Never been sailing? You can tack into the wind, effectively using wind power to propel you in the direction the wind is coming from.

I have never been on a sailboat but I can explain how it works.

A sailboat can not sail directly upwind but it can sail at an angle to gain kinetic energy then rotate to direct upwind and use that kinetic energy to sail for a small amount of time upwind then it will need to change direction again to recharge the kinetic energy.
So it can take advantage of kinetic energy storage if it is allowed to change direction but if that is not allowed it can not sail directly upwind.
A vehicle perpendicular to wind direction will always have access to max wind power no matter the vehicle speed as wind speed relative to vehicle is always the same.

[AndyBeez]

Never been sailing? You can tack into the wind, effectively using wind power to propel you in the direction the wind is coming from.

And if you're using a hydrofoil, you can do it faster than the wind is blowing at you. Wrong but true. Google America's Cup. On the subject of friction reduction, is anyone using the downward force of gravity g in their equations? Does this thing still work in microgravity?

[electrodacus]

And if you're using a hydrofoil, you can do it faster than the wind is blowing at you. Wrong but true. Google America's Cup. On the subject of friction reduction, is anyone using the downward force of gravity g in their equations? Does this thing still work in microgravity?

Yes you can because you are allowed to change direction and thus take advantage of the vehicle kinetic energy.
An ideal setup where you sail perpendicular to wind direction can get the vehicle at any speed say 3x the wind speed then all you need to do is change direction to either direct upwind or direct downwind and since there is no friction loss in an ideal set up maintain that 3x speed forever.
In real world you can do the same but you need to repeat the change in direction as the stored kinetic energy will be used up to counter the losses.

[IanB]

And my best example of what happens and it is measured in reality was the one about the power needed to overcome drag (same equation) is the same for a vehicle driving at 30m/s with no wind as it is for the same vehicle driving at 10m/s with a 20m/s head wind.

And by extension a vehicle traveling at 0 m/s with a 30 m/s head wind...

[electrodacus]

And by extension a vehicle traveling at 0 m/s with a 30 m/s head wind...

Exactly right.
There is potential power available just not used by vehicle if it is anchored to earth but if it is not then that power will be accelerating that vehicle in the same direction as the wind.
So after 1ms of this the vehicle speed will no longer be zero but some value that can be calculated based on vehicle weight and friction losses as you calculate the gained kinetic energy and from that you can find out the new vehicle speed.
You will need to integrate as the wind speed relative to vehicle changes as the vehicle speed increases.

[Nominal Animal]

So it all goes back to the original propeller/wheel vehicle that violates electro's misunderstood laws of physics.

I see.  Thanks for letting me know!

This reminds me of the simple thought experiment on conservation of momentum and kinetic energy in elastic collisions.

Let's say you have a spaceship of mass M traveling at velocity V.  There is a projectile of mass m and velocity v on the same trajectory (v > V, both in the same exact direction).  They impact, but elastically, so that neither deforms, they just bounce without any losses.  What are the resulting velocities V' and v'?

Conservation of momentum says that MV + mv = MV' + mv'.  In a perfectly elastic collision, kinetic energy is also conserved, MV^2/2 + mv^2/2 = MV'^2/2 + mv'^2/2.  Solving the system of two equations for V' and v' yields two answers: one is V'=V, v'=v, i.e. no change.  The other is V' = (2mv+MV-mV)/(m+M), v' = (2MV+mv-Mv)/(m+M).  (Feel free to check, e.g. here.)

What happens when the projectile goes twice as fast as the ship, and weighs twice as much as the ship, i.e. m=2M, v=2V?

You work out the math, and out comes the unintuitive but physically correct and easily verifiable (using e.g. an air track) V'=7/3V≃2.333V, v'=4/3V≃1.333V.
In other words, the projectile loses one third of its velocity, and the ship gains four thirds; and the ship will end up traveling faster than the incoming projectile originally was.

If the velocities are a significant fraction of light speed, then one needs to switch to generalized momentum, (Newtonian momentum multiplied by the Lorentz factor γ, p = γmv) and relativistic kinetic energy (E=(1-γ)mc²) that are conserved, but at v<<c, the two yield the same answer to within rounding error.

This also answers the question, "Can you accelerate a spaceship to a velocity higher than at which you can lob boulders at it?", with "Yes.  Just use boulders with more mass than the ship has."

This is also the reason why one wants solar sails to be reflective, and not absorb the photons.  If the solar sail absorbs the photon, the craft gains the momentum of the photon.  However, if the solar sail reflects the photon, the craft gains up to two times the momentum of the original photon, depending on the angle of reflection, with maximum achieved when the photon is reflected back the way it came from.

[electrodacus]

This reminds me of the simple thought experiment on conservation of momentum and kinetic energy in elastic collisions.

Elastic collisions is what you have between the air particles and the vehicle and that is how kinetic energy is transferred from the air molecules to the vehicle.
All the kinetic energy of the air molecule will end up transferred to the vehicle because it will in average bounce back and forth between the air molecule in the back and the vehicle body.

That is how you get to the wind power equation that I always mention as best case wind power available to any wind powered vehicle.
In that equation you have the air density about 1.2kg/m^2 the aerodynamic drag and projected surface area of the vehicle and the vehicle and wind speed.
Nothing else is needed to know what is available in ideal case to accelerate the vehicle.

So wind powered vehicle can be wind powered only in the stationary to wind speed region in the same direction.
You have the max available wind power when wind speed relative to vehicle is highest so stationary or traveling perpendicular to wind direction.
And zero wind power is available for a vehicle with any design traveling at the same speed as wind since air molecules can no longer collide with the vehicle to provide the increase in kinetic energy.

Vehicle can take energy from the wheel but that will result in a proportional reduction in vehicle kinetic energy so speed and appling that energy extracted at the wheel to another wheel or propeller or any other form of propulsion can not give a net gain even in ideal case.
Thus the only option to exceed wind speed directly down wind or drive directly upwind is to use energy storage.
Exceeding wind speed at an angle to wind direction is possible because there is still wind relative to vehicle and the only limitation when perpendicular to wind direction are the frictional losses.     

[Nominal Animal]

Elastic collisions is what you have between the air particles and the vehicle and that is how kinetic energy is transferred from the air molecules to the vehicle.

Only if the vehicle is basically a stiff box, and has no mechanism at all.

Consider autogyro.  If what you claimed was correct, it could not fly.  Yet, it does. Lift is provided by freely rotating rotor blades, due to a pressure differential between different sides of the blade.  The rotation of the blades is caused by perpendicular airflow below the rotor, generated by a fore or aft propeller engine.

Things like airfoils (aeroplane wings, wings in vertical wind turbines, etc.) are not elastic collisions, as the pressure varies around the airflow.  Air is a compressible fluid, and has properties which can be exploited in a mechanism, for example via by conversion between different forms of energy (which means it behaves non-elastically).  Linear momentum is not conserved, but kinetic energy is, if and only if we include temperature (thermal energy) as part of the kinetic energy.

A particular example of conversion between different forms of energy in a compressible fluid (air) is de Laval nozzle in supersonic engines, converting thermal energy to kinetic energy.

The maximum speed a vehicle can attain depends on the losses.  To simplify, the power (energy transferred or converted per unit time) used matches the power lost, when the vehicle travels at its maximum velocity.  However, the losses can be made arbitrarily small.  (As an example, if you dimple your car's surface like a golfball, you'll reduce aerodynamic drag significantly, and increase fuel efficiency, as demonstrated famously by MythBusters.)  So, it is just a question of how to harvest energy from the wind, using a platform traveling downwind at velocities below and above the windspeed.  It is just an engineering problem, really, hiding inside a scenario that seems counterintuitive to most people.

[electrodacus]

The maximum speed a vehicle can attain depends on the losses. 

Only true for a vehicle traveling perpendicular to wind direction.
For particular cases of interest here:
Direct downwind limit is wind speed.
Direct upwind limit is zero.
Both direct downwind faster than wind and direct upwind is possible using energy storage.

For direct downwind as soon as you are above wind speed there is no longer any wind power available so you can drive above that speed only for as long as the stored energy permits.
For direct upwind wind the same is true is just that due to fast cycles of charge and discharge effect is not visible in most cases without slow motion video.
 

To simplify, the power (energy transferred or converted per unit time) used matches the power lost, when the vehicle travels at its maximum velocity.  However, the losses can be made arbitrarily small.  (As an example, if you dimple your car's surface like a golfball, you'll reduce aerodynamic drag significantly, and increase fuel efficiency, as demonstrated famously by MythBusters.)  So, it is just a question of how to harvest energy from the wind, using a platform traveling downwind at velocities below and above the windspeed.  It is just an engineering problem, really, hiding inside a scenario that seems counterintuitive to most people.

The only way the vehicle is powered by wind is by air particles colliding and providing their kinetic energy to vehicle.

So to get a real world example we can take a Tesla model 3
First google search say Cd = 0.23 and frontal area 2.22m²
So if vehicle is stationary with the front facing the wind (so upwind) and wind speed is say a constant 30m/s (maybe a wind tunnel or something that can provide this perfectly constant air flow).

Then vehicle will experience a wind power trying to push vehicle backwards of
P_w  = 0.5 * 1.2 * 0.23 * 2.22 * 30³ = 8272W
So this is both the power that wind wants to accelerate the vehicle backwards (as front faces the wind) so the max theoretical available wind power and the power the vehicle will need if it wants to stay in place without the brakes engaged.
So if the vehicle wants to drive at 1m/s upwind it will need the following amount of power
P = 0.5 * 1.2 * 0.23 * 2.22 * (30+1)³ = 9127W

Hope you see that it is impossible for a vehicle even ideal one with no friction losses to drive upwind at any speed as power out can not be higher than power in.

[fourfathom]

[...]
Direct upwind limit is zero.
Both direct downwind faster than wind and direct upwind is possible using energy storage.

For direct downwind as soon as you are above wind speed there is no longer any wind power available so you can drive above that speed only for as long as the stored energy permits.
For direct upwind wind the same is true is just that due to fast cycles of charge and discharge effect is not visible in most cases without slow motion video.

Hope you see that it is impossible for a vehicle even ideal one with no friction losses to drive upwind at any speed as power out can not be higher than power in.

And with this you have completely lost the plot.  Direct upwind is possible, has been demonstrated in the real world, and requires no energy storage, no "charge and discharge cycle".  You have not learned a thing from these tedious discussions.

[electrodacus]

And with this you have completely lost the plot.  Direct upwind is possible, has been demonstrated in the real world, and requires no energy storage, no "charge and discharge cycle".  You have not learned a thing from these tedious discussions.

Of course direct upwind is possible using energy storage.
The explanation of how it works is wrong nobody is denying the experiments.

[IanB]

Of course direct upwind is possible using energy storage.
The explanation of how it works is wrong nobody is denying the experiments.

And if you average the upwind movement over thousands or millions of cycles, then at the limit it becomes continuous upwind movement, which can last forever, without stopping.

[electrodacus]

And if you average the upwind movement over thousands or millions of cycles, then at the limit it becomes continuous upwind movement, which can last forever, without stopping.

It is never a continues upwind movement even if it will look like that the same way as a youtube video looks continues to you even if is just 30 or 60 separate frames.
The point is that power that wind pushes against the vehicle even if you capture all of that at 100% efficiency is not enough to advance against wind direction so you need to wait while you charge a small energy storage device then use that stored energy to advance a tiny amount against the wind direction.
When you sail upwind this cycles are much larger so that you can actually see them as you actually drive at an angle where you can using directly wind power then when you picked up enough speed (so increased the vehicle kinetic energy) you can rotate even direct upwind and you will advance in that direction while the speed and thus kinetic energy drops.

Direct down wind will also be visible if you did the test for long enough to see how acceleration rate drops as stored energy is used up then see how vehicle slows down all the way below wind speed where you can recharge and start the cycle again.

[fourfathom]

And if you average the upwind movement over thousands or millions of cycles, then at the limit it becomes continuous upwind movement, which can last forever, without stopping.

It is never a continues upwind movement even if it will look like that the same way as a youtube video looks continues to you even if is just 30 or 60 separate frames.
The point is that power that wind pushes against the vehicle even if you capture all of that at 100% efficiency is not enough to advance against wind direction so you need to wait while you charge a small energy storage device then use that stored energy to advance a tiny amount against the wind direction.

And yet, the net motion is still upwind.  How can this possibly be happening, given your "stored energy" theory??? (hint: You are wrong.)

[bdunham7]

You have not learned a thing from these tedious discussions.

Apparently some of us haven't either....

[electrodacus]

And yet, the net motion is still upwind.  How can this possibly be happening, given your "stored energy" theory??? (hint: You are wrong.)

If you are not moving wait for 1 minute to charge your energy storage then move at any low speed upwind for even a second will you not have an average upwind speed higher than zero ?

[fourfathom]

You have not learned a thing from these tedious discussions.

Apparently some of us haven't either....

You're right.  Although I can quit anytime I like... (he said)

[james_s]

You guys are arguing with either a troll or an idiot, possibly both.

[PlainName]

The only way the vehicle is powered by wind is by air particles colliding and providing their kinetic energy to vehicle.

Wrong. You'll never get how it works whilst you persist on thinking this.

[AndyBeez]

You guys are arguing with either a troll or an idiot, possibly both.

Harsh dude

Maybe these wikis will help OP:

https://en.m.wikipedia.org/wiki/Fluid_dynamics

https://en.m.wikipedia.org/wiki/Radiation_pressure

https://en.m.wikipedia.org/wiki/Yarkovsky_effect

[electrodacus]

You guys are arguing with either a troll or an idiot, possibly both.

I wish I was a troll then I will have enjoyed this.

[electrodacus]

The only way the vehicle is powered by wind is by air particles colliding and providing their kinetic energy to vehicle.

Wrong. You'll never get how it works whilst you persist on thinking this.

Please enlighten me.
How do air particle transfer energy to vehicle if not through collision ?

And as you claim to know how it works please also provide the equation describing the amount of wind power available to vehicle.