Faster than the wind going downwind?

[svetz]

The propeller blades of this cart also have apparent wind

See post #20 for my mental evolution regarding the cart mechanics.

...I rejected their cute illustration of two sailboats on a cylindrical world as a propellor because sailboats on a broad reach still have an apparent windspeed....

Nice set of Newtonian-style vector drawings!
But, I still reject the illustration they used for the reason mentioned, if there's no wind on a boat sail, there can be no force. When the apparent wind is zero, the force is zero. For example, a free-spinning wind turbine mounted on a truck will not spin when the truck speed is moving at the same speed as the wind.

 

[MarkV]

When the apparent wind is zero, the force is zero.

Yes, but the apparent wind is never zero at the propeller blades, just like it is never zero at the sail going diagonally to the wind.

You have to differentiate the apparent wind at the vehicle chassis (which is zero at wind-speed) from the apparent wind at the spinning propeller blades (which can never be zero, if there is true wind). Below is the vector diagram showing the vectors for the propeller blade, when the vehicle reaches windspeed:

For example, a free-spinning wind turbine mounted on a truck will not spin when the truck speed is moving at the same speed as the wind.

But this is not a free-spinning wind turbine. It is propeller that is coupled to the wheels.

 

[svetz]

But this is not a free-spinning wind turbine. It is propeller that is coupled to the wheels.

Yup, came to peace with it in #20 after a whole lot of headbanging. The free-spinning analogy refers to the cylindrical world metaphor and why it's misleading/incorrect.

 

[MarkV]

The free-spinning analogy refers to the cylindrical world metaphor and why it's misleading/incorrect.

The analogy they show is correct, but unfortunately they don't mention the role of the boat's keel which is key here. The keel drives the boat across the wind, just like the wheel drive the propeller blades across the wind.

 

[svetz]

the role of the boat's keel which is key here. The keel drives the boat across the wind, just like the wheel drive the propeller blades across the wind.

When headed directly downwind (which is the only time you can get a zero apparent wind) the only function of the keel is drag as there are no lateral forces. In fact, sailors typically pull the daggerboard up when "running" (a downwind point of sail) to eliminate it.

 

[MarkV]

When headed directly downwind (which is the only time you can get a zero apparent wind) the only function of the keel is drag as there are no lateral forces.

Correct, but in their analogy the boat is not moving directly downwind, but diagonally downwind. This is equivalent to the motion of the propeller blade, which also has a velocity component perpendicular to the wind.

 

[svetz]

... the boat is not moving directly downwind, but diagonally downwind...

Yup, one more reason to discount it since the apparent windspeed > 0. As you can see from #20, I'm not arguing the land vehicle can't go faster than the wind downwind, or how propellors work... just that metaphor breaks down when apparent windspeed = 0. At least I don't see how it supports their case for DDWFTTW.

 

[MarkV]

Yup, one more reason to discount it since the apparent windspeed > 0.

The same is true for the propeller blades of the DDWFTTW cart, so I don't see the reason to discount it. Again, the analogy is not between the boat and the cart. It is between the sail and the propeller blade.

At least I don't see how it supports their case for DDWFTTW.

It demonstrates that DDWFTTW can be achieved if you allow for moving parts, For example like this:

The propeller is also a moving part that allows it in a more continuous and compact manner.

 

[svetz]

...It demonstrates that DDWFTTW can be achieved...

I don't really question DDWFTTW since the explanation in post #20.
Perhaps we're not talking apples to apples, what do you think the boat on the cylindrical world is demonstrating in regards to DDWFTTW?

 

[wholybee]

A high level conceptional overview. We tend to focus of the velocity of the wind. But there is a force applied to the sail/prop/vehicle. Assume any given windspeed, and a sail of a given size. The sail is sized such that a vehicle of a certain mass will travel at the speed of the wind. If we increase the size of the sail, the force is increased, but the velocity is not. It is easy to understand that we can move a heavier vehicle with a larger sail. But there is nothing preventing us from using a larger sail, and converting the extra force that is applied into velocity. Doing so does not break any laws of energy. It is just a question of designing a machine that can convert that extra force into velocity. The propeller adds size to the "sail" allowing the force to push against greater resistance. The gearing from the wheels to the propeller turn that extra force into a greater velocity.

 

[MarkV]

what do you think the boat on the cylindrical world is demonstrating in regards to DDWFTTW?

Look the vector diagrams in post #25. It's the same aerodynamics.

 

[svetz]

Look the vector diagrams in post #25. It's the same aerodynamics.

We're still not talking the same thing, that's okay. I believe there are no aerodynamics when the apparent wind speed is 0 which I think you agree with.

A high level conceptional overview.

The bit with the size of the sail could be confusing as once you go faster than wind-speed, in parallel to the wind, bigger would be more drag. Also, no sail on the vehicle which might also confuse some. But it sounds like you have it, if not 100% sure see post #20.

 

[MarkV]

I believe there are no aerodynamics when the apparent wind speed is 0 which I think you agree with.

Yes, but it's irrelevant. The apparent wind at the propeller blades can never be zero with this setup

Also, no sail on the vehicle which might also confuse some.

The propeller blades are the analogue to the sail.

 

[upnorthandpersonal]

Follow up video.

 

[svetz]

Best quote, "In my defense, I didn't present the information good enough in the first video". Makes me feel a whole lot better that I wasn't the only one that had a hard time believing it. That video bothered me for a week.

When I first saw the video I was saying the same things as the professor and found the same faults with the treadmill model. The stab at a force analysis in #20 doesn't quite match up with 12:14 (no infinite force problem), but I'd say the video has a better rendition.

Loved the Fox model, ~15:00 she's handling it on the treadmill that blows the arguments in the OP about the model out of the water.

 

[Diysolar123]

Follow up video.

it was nice of them to follow up with a more complete proof for those who thought it could never be...

and kudos for the professor for betting the $10000 (thats a bold strategy cotton) and then actually paying the bet when he was shown he was wrong as the vehicle could travel as fast as stated!!
heavy betters are always interesting people...

 

[Supervstech]

Another video going into glorious detail on the issues.

16:30 has a bonus example that further explains it.

 

[Ribbit74]

It’s 100% real. Physics can be counter-intuitive; you have to learn to trust the math. In order to trust the math you have to learn the math.

A simpler example of this from my school days: put a helium balloon in your car, resting on the ceiling. Drive for a bit and then slam on the brakes - which way does the balloon go, toward the front or toward the rear? This one has less math involved so it’s easier to explain, though counter-intuitive for many people at first.

The more important question about the thread topic though: of the people that voted “fake,” how many would change their vote after seeing the explanations?

 

[time2roll]

Did the engineer ever get to ride in the contraption at greater than wind speed?

 

[chrisski]

I wonder if the wind speeds at height of 10 to 15 feet are stronger than the wind speeds at the ground?

 

[rmaddy]

I wonder if the wind speeds at height of 10 to 15 feet are stronger than the wind speeds at the ground?

See the video in post #39 (and #41). This was addressed in that video. In short, yes, it's common for winds to be slightly higher speeds further from the ground but not enough to negate the results they had. The video covers it in much more detail.

 

[chrisski]

See the video in post #39 (and #41). This was addressed in that video. In short, yes, it's common for winds to be slightly higher speeds further from the ground but not enough to negate the results they had. The video covers it in much more detail.

Well, I’m busted. I did not read through all three pages. At three pages there’s probabaly nothing I can contribute that has not already been said.?

 

[MarkV]

I wonder if the wind speeds at height of 10 to 15 feet are stronger than the wind speeds at the ground?

Here the video with higher placed telltales:

For the record of 2.8 x windspeed NALSA measured the wind at the height of the propeller hub.

 

[chrisski]

For the record of 2.8 x windspeed NALSA measured the wind at the height of the propeller hub.

For all those who thought a perpetual motion could not be created.

 

[upnorthandpersonal]

For all those who thought a perpetual motion could not be created.

Of course, it's not perpetual motion. It obeys the laws of thermodynamics.