Car Goes Downwind 2.5 Times Faster Than the Wind

[nechaus]

[youtube]85sc7c2M-Ns[/youtube]
or
[youtube]PCu9wHvamtI[/youtube]

 

[endlessplane]

If you have done 2.5,

The official NALSA ratified dead downwind record is 2.8 x wind-speed.

 

[endlessplane]

...

Yep, directly upwind carts are pretty common. The directly downwind faster than the wind one seems more counter intuitive, despite being the same thing, just with air & ground swapped.

 

[TylerDurden]

Feedback loop does not imply OU, simply energy is directed back to the source. See overheating motors or runaway serial-wound motors.

re 2.5X

john says:
July 18th, 2013 at 5:46 pm
The cart is designed to use the energy in the shear plane that exists between the air and ground when there is wind. By leveraging one against the other, speed can be gained at the expense of force. To achieve 3 times wind speed, they had to sacrifice at least 2/3 (I suspect closer to 3/4) of the propeller’s thrust to the ground to provide the torque to turn the propeller.

However, if you add that force into your analysis, you would still probably conclude that the Blackbird can self propel (at appropriate speeds) with no wind. That is because your analysis seems to be ignoring the effect of the rotor’s rotational velocity relative to its linear velocity through the air. This is actually quite important as it switches from Propeller to turbine when the cart’s linear velocity relative to the air becomes greater than the rotational velocity times the pitch. When this happens, the directions of the forces get reversed. Reversing the forces means they are putting the breaks on the cart which gets added to the breaking of the resistive forces.

The rotational velocity of the rotor times its pitch divided by the ground velocity of the cart is a constant determined by the fixed gear transmission. For simplicity, I’ll call this constant R.

For the DDWFTTW cart, the wheel turns the propeller, so through the transmission, the smaller force of the ground on the wheel must overcome the larger force of the air on the propeller. Since power is at best constant through the transmission, this increase in force must be accompanied by a decrease in velocity. So the DDWFTTW cart must have 0<R<1.

With no wind, the ground velocity is equal to the air velocity. So if the cart is pulled (or pushed) with no wind present, R<1 means the air velocity is greater than the rotational velocity times the pitch and the rotor will act as a turbine, and the force will be a breaking force. When resistive forces (air drag, rolling resistance, etc.) are added, they will only add to that breaking.

A similar analysis with any value of R will show that with no wind the cart will always be in a breaking mode (except for R=1 when there are only resistive forces).

A few added notes:

The Blackbird on the salt flats and the cart on the treadmill are essentially the same system. The only difference is that in one case the Earth (the reference frame from which we tend to view things) is the Blackbirds ground frame, and in the other the Earth is the same as the air frame (different from the cart's ground which is the treadmill). An analysis of the cart in the treadmill reference frame is identical to analysing the Blackbird in the Earth frame, and an analysis of the Blackbird in the air reference frame is identical to analysing the cart on a treadmill in the Earth frame.

A push (or pull) start in no wind cannot replace the wind or the treadmill. The carts are continuously taking energy from the system (the shear interface between ground and air). They are not simply getting a push start. They depend on a continuous supply of energy, and without wind they don't have it.

An over unity device (or greater than unity device) refers to its energy usage. If it ends up with more energy than it started with (if its net power balance is positive) then the final energy divided by the initial energy is "over unity" (greater than 1), and it is an over unity device. If these carts could self accelerate in no wind, they would in fact be over unity devices. At the start neither the air nor the ground has energy, and at the end the air would have some energy, and the cart would have more than it started with.

With wind, the air has energy and the propeller is slowing the air down, thus removing energy from the air and transferring it to the cart. It continues to do so past wind speed and only stops when the cart reaches wind speed divided by (1-R). Since 0<R<1, that is greater than wind speed. For the Blackbird, 2/3<R<1, and I would guess R is close to 3/4. Using that guess, the net thrust would be downwind until the cart reached 4 times wind speed, but would not be able to overcome resistive forces past 3 times wind speed for the conditions they had.

Rick Cavallaro says:
July 18th, 2013 at 7:46 pm
Correct on all counts. The parameter you call R we call VSR (for Vehicle Speed Ratio). And it is in fact around 0.75 for the Blackbird, but can be varied significantly via the variable pitch propeller. That being said, we used a VSR right around 0.75 when our prop pitch was fixed, and used that same value for the design pitch of the prop. Increasing or decreasing the pitch leads to off-design performance which results in a less efficient propeller (at least at the design point).

http://makezine.com/2010/11/04/downwind-faster-than-the-wind-black/


There was another self-proclaimed genius here a while back...

 

[Toorbough ULL-Zeveigh]

oh, he's still very much here.
i can feel the disturbance in the force(dyno).
he's even checked out the biker bar a few times.
care to guess his new user name?

 

[doctorGONZO]

So, if I'm following that assortment of words, it seems you're down to just the point of not understanding how it can harvest energy?

Are you aware that any point you have different speeds, different temperatures etc that this energy difference can be harvested for energy? If so, I'm unclear what argument you're left making.

For, you have often left me doubtful if you have followed my words, so, just one more time is no surprise.

I am not "down " to anything, except in your hopeful imagination.

For is telling the truth, now. For says that , if I accept his own statement that the wind-car is NOT a Over-Unity device, I do not understand how it can harvest energy. A truer word was never spoken. IF IT HARVESTS ENERGY, IT IS OVER-UNITY!

For, you are obviously unaware that momentum and kinetic energy are perfectly related to their observer and his reference frame. LOL. So, " any point you have different speeds, different temperatures etc " is totally dependent on where the observer is, and what is his velocity relative to the system in study. The "believers" have thus far completely failed to explain how any influence of DIFFERENT SPEEDS, DIFFERENT TEMPERATURES, AND ETC can be transmitted by majickes from a wind mass which is being left behind by a car which has been pushed up to a speed equal to that of the wind.

HOW? If the believers have any agenda to convince anybody outside their own little herd, they need to explain in satisfactory detail HOW a unit of energy in the DIFFERENT SPEED, DIFFERENT TEMPERATURE, or ETC migrates to the car mass and accelerates it. All we have been hearing is a deafening silence except for all the Baloney.


" If so, I'm unclear what argument you're left making."

For, I had that figured out a while back, but I cant explain it any more simply.

 

[doctorGONZO]

...

Yep, directly upwind carts are pretty common. The directly downwind faster than the wind one seems more counter intuitive, despite being the same thing, just with air & ground swapped.

You have surprised me. Before, you were only abrasively sarcastic and emotional, but, now, you have said something that has made sense. LOL!

In fact, IN PRINCIPLE, there is no limit to how many times greater than wind-speed a car could go DIRECTLY UPWIND. Except maybe if Special Relativity is true after all.

There are real world practical engineering limits due to real world frictions and possibly other real problems.

But, my friend, DOWNWIND is not just a simple swap. When the car reaches wind speed, the car is then in an envelope of air which is NOT MOVING according to the car's observation of the air around it.

You do not understand that?

 

[doctorGONZO]

Feedback loop does not imply OU, simply energy is directed back to the source. See overheating motors or runaway serial-wound motors.

re 2.5X

john says:
July 18th, 2013 at 5:46 pm
The cart is designed to use the energy in the shear plane that exists between the air and ground when there is wind. By leveraging one against the other, speed can be gained at the expense of force. To achieve 3 times wind speed, they had to sacrifice at least 2/3 (I suspect closer to 3/4) of the propeller’s thrust to the ground to provide the torque to turn the propeller.

However, if you add that force into your analysis, you would still probably conclude that the Blackbird can self propel (at appropriate speeds) with no wind. That is because your analysis seems to be ignoring the effect of the rotor’s rotational velocity relative to its linear velocity through the air. This is actually quite important as it switches from Propeller to turbine when the cart’s linear velocity relative to the air becomes greater than the rotational velocity times the pitch. When this happens, the directions of the forces get reversed. Reversing the forces means they are putting the breaks on the cart which gets added to the breaking of the resistive forces.

The rotational velocity of the rotor times its pitch divided by the ground velocity of the cart is a constant determined by the fixed gear transmission. For simplicity, I’ll call this constant R.

For the DDWFTTW cart, the wheel turns the propeller, so through the transmission, the smaller force of the ground on the wheel must overcome the larger force of the air on the propeller. Since power is at best constant through the transmission, this increase in force must be accompanied by a decrease in velocity. So the DDWFTTW cart must have 0<R<1.

With no wind, the ground velocity is equal to the air velocity. So if the cart is pulled (or pushed) with no wind present, R<1 means the air velocity is greater than the rotational velocity times the pitch and the rotor will act as a turbine, and the force will be a breaking force. When resistive forces (air drag, rolling resistance, etc.) are added, they will only add to that breaking.

A similar analysis with any value of R will show that with no wind the cart will always be in a breaking mode (except for R=1 when there are only resistive forces).

A few added notes:

The Blackbird on the salt flats and the cart on the treadmill are essentially the same system. The only difference is that in one case the Earth (the reference frame from which we tend to view things) is the Blackbirds ground frame, and in the other the Earth is the same as the air frame (different from the cart's ground which is the treadmill). An analysis of the cart in the treadmill reference frame is identical to analysing the Blackbird in the Earth frame, and an analysis of the Blackbird in the air reference frame is identical to analysing the cart on a treadmill in the Earth frame.

A push (or pull) start in no wind cannot replace the wind or the treadmill. The carts are continuously taking energy from the system (the shear interface between ground and air). They are not simply getting a push start. They depend on a continuous supply of energy, and without wind they don't have it.

An over unity device (or greater than unity device) refers to its energy usage. If it ends up with more energy than it started with (if its net power balance is positive) then the final energy divided by the initial energy is "over unity" (greater than 1), and it is an over unity device. If these carts could self accelerate in no wind, they would in fact be over unity devices. At the start neither the air nor the ground has energy, and at the end the air would have some energy, and the cart would have more than it started with.

With wind, the air has energy and the propeller is slowing the air down, thus removing energy from the air and transferring it to the cart. It continues to do so past wind speed and only stops when the cart reaches wind speed divided by (1-R). Since 0<R<1, that is greater than wind speed. For the Blackbird, 2/3<R<1, and I would guess R is close to 3/4. Using that guess, the net thrust would be downwind until the cart reached 4 times wind speed, but would not be able to overcome resistive forces past 3 times wind speed for the conditions they had.

Rick Cavallaro says:
July 18th, 2013 at 7:46 pm
Correct on all counts. The parameter you call R we call VSR (for Vehicle Speed Ratio). And it is in fact around 0.75 for the Blackbird, but can be varied significantly via the variable pitch propeller. That being said, we used a VSR right around 0.75 when our prop pitch was fixed, and used that same value for the design pitch of the prop. Increasing or decreasing the pitch leads to off-design performance which results in a less efficient propeller (at least at the design point).

http://makezine.com/2010/11/04/downwind-faster-than-the-wind-black/


There was another self-proclaimed genius here a while back...

The cart is designed to use the energy in the shear plane that exists between the air and ground when there is wind. By leveraging one against the other, speed can be gained at the expense of force. To achieve 3 times wind speed, they had to sacrifice at least 2/3 (I suspect closer to 3/4) of the propeller’s thrust to the ground to provide the torque to turn the propeller.

This is one of the biggest piles of Baloney yet. Tyler has completely failed to give a rigorous derivation of any of his numbers or factors.

"(I suspect closer to 3/4)"

I suspect.

 

[doctorGONZO]

If you have done 2.5,

The official NALSA ratified dead downwind record is 2.8 x wind-speed.

Well I have to ask you, HOW LONG WAS THE 2.8 sustained? An hour? 1.98 nanoseconds?

 

[doctorGONZO]

Anyone who is sincerely interested in all this Baloney and is not just trying to scam a chump and is not just jerking themself off on late night internet should look up Gyrobus, used in Switzerland and other nations decades ago. The bus used a flywheel that activated a generator that activated electric motors that turned the wheels.

 

[doctorGONZO]

Actually, in PRINCIPLE, there is no limit to how fast the flash peak speed can be when the car is draining the prop of its kinetic energy and accelerating past wind speed DOWNWIND.

In real world reality there are a myriad of engineering practical problems that will, by frictions, et al, severely limit the peak flash speed.

The trick is to make the prop have a high Radius Of Gyration, or, depending on your persuasion, Moment Of Inertia, so that it can power the prop thrust a long enough time to push the car up to a faster speed after it has reached Wind Speed. The prop must be heavy, maybe being full of lead, or, even lead acid batteries.

 

[endlessplane]

I do not understand how it can harvest energy.

By reducing the velocity difference between air & ground (a.k.a true wind).

So, " any point you have different speeds, different temperatures etc " is totally dependent on where the observer is, and what is his velocity relative to the system in study.

Nope. The velocity difference between air & ground is frame invariant. No matter how fast you move relative to air & ground, you always see the same velocity difference between them.

 

[endlessplane]

But, my friend, DOWNWIND is not just a simple swap.

Yes it is.

When the car reaches wind speed, the car is then in an envelope of air which is NOT MOVING according to the car's observation of the air around it.

UPWIND: When the cart starts rolling, the GROUND is initially at rest relative to the cart, while the AIR moves back fast relative to the cart.

DOWNWIND: When the cart passes wind speed, the AIR is initially at rest relative to the cart, while the GROUND moves back fast relative to the cart.

As you see the two cases are symmetrical, just with GROUND & AIR swapped.

 

[liveforphysics]

If you have done 2.5,

The official NALSA ratified dead downwind record is 2.8 x wind-speed.

Well I have to ask you, HOW LONG WAS THE 2.8 sustained? An hour? 1.98 nanoseconds?

It is unrelated to stored rotational kinetic energy. The system can travel at 2.x wind speed down-wind indefinitely as long as the wind holds and the vehicle has a surface to travel upon.

 

[endlessplane]

Actually, in PRINCIPLE, there is no limit to how fast the flash peak speed can be when the car is draining the prop of its kinetic energy and accelerating past wind speed DOWNWIND.

No, that is not how it works. The cart is not using any internally stored energy for propulsion. That would violate NALSAs rules for sail-craft:
http://www.nalsa.org/BlackBirdDDWSR/Observers%20ReportNALSA%20C4BlackbirdJuly2and%2032010.pdf

S2: We found no evidence of any energy storage devices. There has been some discussion on www
discussion groups that the rotating propeller constitutes a form of stored energy that might be converted to
propulsion by slowing it down or changing its pitch. Since the propeller is connected to the wheels with a
constant ratio connection slowing the propeller to harvest some of its rotational energy also slows the
craft. The fact that the craft is required to accelerate during the measurement means, for a fixed gear ratio
craft, that rotational energy is being added to the propeller to speed it up during the measurement period
rather than the other way around.

Well I have to ask you, HOW LONG WAS THE 2.8 sustained?

Since it doesn't use internally stored energy for propulsion, even a few seconds prove steady state.

 

[bobc]

'fraid I'm with the sceptics here - upwind no problem, the observer on the car sees a stronger wind; but directly downwind - at 1.0 x the wind speed the observer on the car sees no wind at all - how do you harvest something from nothing?
Note the (absolutely marvellous) americas cup racers last year: they went faster than the wind downwind, but effectively by 'tacking' downwind. not by going straight, directly downwind.
Faster than the wind upwind - I have absolutely no problem with this, & all the force vector baloney with the rotor blades spinning etc. holds water in that case

 

[endlessplane]

but directly downwind - at 1.0 x the wind speed the observer on the car sees no wind at all

Wrong, he still sees the same true wind (velocity difference between air & ground). You can extract energy from this velocity difference.

Note the (absolutely marvellous) americas cup racers last year: they went faster than the wind downwind, but effectively by 'tacking' downwind. not by going straight, directly downwind.

The propeller blades are also not moving directly downwind. They are moving on a continuous helical tack (broad reach). This is visualized here:

[youtube]UGRFb8yNtBo[/youtube]

Faster than the wind upwind - I have absolutely no problem with this, & all the force vector baloney with the rotor blades spinning etc. holds water in that case

The vectors for directly downwind faster than wind work out fine as well:

 

[TylerDurden]

at 1.0 x the wind speed the observer on the car sees no wind at all - how do you harvest something from nothing?

The "car" is at stasis, but the thrust of the prop is not, it exerts positive pressure against the wind.

The system uses mechanical advantage by gearing the prop rotation less than the wheels. If the torque (generated) at the wheels is greater than the torque required to turn the prop, thrust is generated.

 

[doctorGONZO]

at 1.0 x the wind speed the observer on the car sees no wind at all - how do you harvest something from nothing?

The "car" is at stasis, but the thrust of the prop is not, it exerts positive pressure against the wind.

The system uses mechanical advantage by gearing the prop rotation less than the wheels. If the torque (generated) at the wheels is greater than the torque required to turn the prop, thrust is generated.

TYLER, You obviously known less than ZERO about basic simple Newtonian Physics. A prop DOES NOT PUSH AGAINST THE WIND. It simply pushes against air molecules within its striking range. And the equal and opposite reaction is to find itself pushed in the opposite direction than where it pushed the air molecule.

Increasingly, the "believers" are seeming to be immature juvenile ignorant hoaxers who are just having a lark by trying to flummox honest scientists.


Tyler, little darling, the question was "How do you HARVEST something from nothing?" The subject is that the car is supposedly absorbing kinetic energy from a mass of air which is stationary with respect to the car. Little darling Tyler, if the car is HARVESTING ENERGY, it must be the one that is getting pushed. What the prop is "pushing against" is a perfect non-sequiter.

HOW IS AIR THAT IS STATIONARY WITH RESPECT TO THE CAR, PUSHING AGAINST THE CAR?

A clue for you, Sherlock, IT CANNOT DO IT!

 

[doctorGONZO]

I just want to say, If I wanted to do such a thing, I absolutely positively know how to hide enough batteries and electric propulsion device in the car as illustrated so that only a totally demolished tear-down would reveal such a thing. And the car would go like hell.

I am smart, really, but am not the only smart fellow around. My hooligan detractors would say that anything I can do, somebody else could already have done it too. Right, critics?

Maybe anything I can do to hide propulsion in such a car has already been done.

Was a total demolition tear-down done on any of these miraculous runs?

 

[endlessplane]

"How do you HARVEST something from nothing?"

That has been answered already: You harvest energy from the velocity difference between air & ground. That velocity difference is non-zero regardless of the reference frame.

HOW IS AIR THAT IS STATIONARY WITH RESPECT TO THE CAR, PUSHING AGAINST THE CAR?

You have just answered that yourself:

[The propeller] simply pushes against air molecules within its striking range. And the equal and opposite reaction is to find itself pushed in the opposite direction than where it pushed the air molecule.

The subject is that the car is supposedly absorbing kinetic energy from a mass of air which is stationary with respect to the car.

In frame of the ground, the propeller removes kinetic energy from the air.
In frame of the car, the propeller adds kinetic energy to the air.

 

[endlessplane]

I am smart, ...

Smart are the high school kids who passed this semifinal exam for the International Physics Olympiad:
http://www.aapt.org/physicsteam/2013/upload/E3-1-7-solutions.pdf

Question B1 on page 11 deals with directly down & up wind faster than the wind. The solution on page 12 says:

Both modes are possible as claimed.

 

[bobc]

Fascinating - the good news is that around 1.0x windspeed directly downwind you need VERY little actual power
OK rethink - where I've been going wrong is to think of that big whirly thing as a "prop" or a "windmill". It can be either.
at 1.0x downwind, it is a prop operating in still air, taking energy from the wheels and supplying it back to the still air through the prop. Energy is force x distance, the same force means MUCH more energy from the wheels than is needed for the prop to work in still air.
Sorry if someone already said that 4 pages ago, but I guess i had to work it out for myself

 

[endlessplane]

I stand by "nothing can possibly work at 1.0x windspeed directly downwind"

But you have no problem with starting directly upwind?

- When the cart starts rolling upwind, the GROUND is initially at rest relative to the cart, while the AIR moves back fast relative to the cart.

- When the cart passes wind speed downwind, the AIR is initially at rest relative to the cart, while the GROUND moves back fast relative to the cart.

As you see the two cases are symmetrical, just with GROUND & AIR swapped. Why should acceleration with zero airspeed be impossible, if acceleration with zero groundspeed is possible?

You actually want the prop to reverse as you go through,

You don't have to change anything about the prop as you pass windspeed going downwind. Here is the BB-prototype with a fixed propeller pitch and a fixed ratio transmission, accelerating from rest to above 2x windspeed. Watch at 3:00min:

[youtube]EEuAqq8FINw[/youtube]

 

[bobc]

worked it out