"Faster than the wind," impossible they say but the Blackbird settles the debate

[RedDevil]

There is no sound of importance in that video.
Neither is there a trick, motor, spring, inclination or whatnot.

My mother was a professional sewing class teacher and I used to play around with the metal sewing machine thread spools, intrigued by how you can make a spool wind up itself by rolling it over a flat surface while just pulling the end of the wire, and how it would indeed move faster than the wire.

I actually pulled it at an angle because you want the wire pulled tight on the spool.
By increasing and decreasing the angle you could even make it roll back and forth.

If the sine of the angle of the wire is equal to the difference between the spool flanges and the core (like if the direction of the wire if extended to the surface would be right between the flanges) then the spool won't turn either way but be dragged over the table if you pull hard enough.



Green: the spool rolls to the right, rolling up the thread.
Red: the spool rolls to the left, unwinding itself.
Blue: the spool drags over the table neither winding up nor unwinding.

The propeller car is even simpler than this because there's no thread, no spool and no angry mom.

[aerohead]

Originally Posted by some_other_dave

No, it is not. You are starting from this assumption, and so you go wrong from the beginning.

It is not a square-rigger, it is much more like a modern sailboat with triangular sails. Which can and do sail faster than the wind speed. And the sails (the propeller blades) meet the wind at an angle.

-soD

1) Okay.
2) So, the vehicle has no wind energy capture capability except for the blades?
3) And the blades power the wheels to actually propel Blackbird?
4) And without any change to their configuration, the energy-capturing 'turbine' blades somehow become a perfect, thrust-producing propeller?
5) And simultaneously, the perfect 'propeller' is also a perfect 'turbine', and not only maintains velocity, but increases velocity, due to the airfoil profile, with no momentum added to the system?
6) As, the cart is exceeding the local air velocity?
7) The Universe makes special physics for Rick Cavallero, but no other?

[aerohead]

Originally Posted by RedDevil

No amount of proof will ever convince anyone who does not understand the principle.
And those wo do understand the principle know it should work, and proof is just confirmation.
So please try to understand the principle. It is a real Aha! moment when you see it.

I'll try to explain with a stepwise approach.

Fact - You cannot blow a sail with the wind past wind speed.
But if you take a very long boat and you put the mast on a cart inside the boat and you push that cart towards the stern, then the boat would move faster than if the sail was fixed. The boat would move faster than the wind if you push hard enough.
I think you can agree that would work.

Instead of a sail we use a propeller. Instead of a boat we use a car.
If we motorize the propeller to push against the wind, of course we could move faster than the wind.
With our motorized cart, the force that drives the car forward is the forward pressure on the propeller that transfers through the axle bearings. All obvious, right?

Now comes the tricky part.
We set the motor speed such that the propeller turns against the wind but slightly slower that the wind speed.
The car will speed up beyond the wind speed, as the wind is still pushing against the propeller as its surface moves slower than the wind.
Even though the propeller forces the air backwards compared to the car, it still moves forward compared to the ground - but slower than the wind, while the car moves faster than the wind.
The wind still pushes against the propeller so the car still accelerates.

Because the car still accelerates in those conditions we might tap some of that energy to drive the propeller. The force needed to do so is less than the forward force on the propeller, as long as the propeller pushes the air backwards ar a slower speed than the car is moving.
We don't need the motor after all as long as the overall friction is less than the difference between the forward force on the propeller and the driving force turning it against the wind.

It is the gearing that makes it possible.
Likewise when you have a big sail and a system of pulleys to rile in the boom. If you let go of the rope the wind will catch the sail and the rope end will speed up way past the wind speed.
Here the sail is a propeller, the pulleys are the gearing and the rope end is the car.

As for proof, the wind vane on the car is all you need.
Of course the wind speed is lower close to the ground, but it is enduring quite a strong virtual headwind; much more than you'd expect.
There is a headwind even right in front of the propeller; in fact the headwind there should be even slightly stronger as the propeller slows the wind speed down, so it is a higher headwind relative to the car.

1) I'll presume that you meant to say that the 'long boat' was already in motion?
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2) And then, the mast and sail is immediately transferred to the cart, at the bow of the boat?
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3) Whoever is 'pushing' the cart towards the stern, is 'adding' external power to the system, which doesn't exist aerodynamically.
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4) The 'pusher's' legs are applying tractive power through the deck interface, to the boat.
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5) The aerodynamic power, plus the human's metabolic power, together, is exceeding the original net power available from the ambient aerodynamic environment.
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6) Remove the human horsepower from the equation and the whole thing falls apart.

[aerohead]

Originally Posted by RedDevil

It is frustrating to see how you miss it. I really did not expect that.

You're so convinced it cannot work that you can't bring yourself to studying it in detail.

If you set the blades of the propeller flat, so the wheels make it spin but it does not push the air forward or backward compared to the car, do you agree that the wind will push the car forward, albeit not as fast as the wind?

Now if you alter the angle of the blades so that it pushes slightly against the wind, do you agree that would only increase the pressure on the blades leading to an even greater forward force, although a part of that is needed to overcome the resistance of moving the blades against the wind?

A sailboat cannot sail straight against the wind because its mast does not move relative to the boat. But propeller blades do move and that has the same effect as a sail boat tacking back and forth to end up in a position that is straight against the wind from the starting point.

1) In # 37 ( permalink ), some other dave states that it is the 'triangular
sails- propeller blades' that are responsible for Blackbird's motion.
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2) The wheels cannot power the propeller if the propeller is the sole source of power for the wheels.
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3) If you examine turbine blades and propeller blades, you may find that their airfoil geometries are 'reversed.'
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4) In a bonafide powerplant failure during flight, in a variable-pitch propeller aircraft, the aircraft checklist instructs the pilot to 'de-pitch' the prop, in order
to reduce prop-drag, thereby increasing glide radius for a dead-stick landing.
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5) The 'Blackbird' propeller analogy implies that, in a flight emergency, the pilot would merely 'reverse' the propeller ( like a Lockheed C-130 Hercules ), and the free-wheeling reversed propeller would now be capable of maintaining enough thrust for level flight.
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6) The 'masts' which hold the aircraft propeller are free to move in relation to the aircraft fuselage.

[aerohead]

My experience with spools is that, the attachment point aligns with the applied tensor, and either lifts off the surface, or drags along the surface in the direction of the force vector.

[jakobnev]

Can you provide a transcript of what the presenter was saying?

Nothing was said, it was all about the visuals.

1) Did you notice that the pull-string shortens during the presentation.
2) The string is being wound around a spool within the 'cart'.
3) If there is a spring-powered clock-drive, or battery-powered- motor-spool within the 'cart', this power , added to the 'system', is what's responsible for the phenomena you are experiencing, as the string continuously winds itself onto the spool.

This is all that is inside, a magic bog roll core:


No batteries, no springs, no antenna to receive power from a Tesla coil.

4) A parlor trick.
5) A visual distraction from the actual dynamics.

I'd have to disagree, I think it illuminates the principle at play with surgical precision.

The diameter of the bog roll is smaller than the diameter of the wheels, so with the same torque it can pull the cart forward with greater force than the wheels pull it backwards.

Another way of looking at it is that the relative motion of the cart and string is slower that the relative motion of the cart and floor, so the same power can provide a greater force.

[aerohead]

The 'rope' was misrepresented from the beginning.
It's my fault that I didn't insist on a full disclosure including all views of the cart before I opened my mouth.
I presumed intellectual honesty. I was incorrect.

[RedDevil]

Originally Posted by aerohead

1) In # 37 ( permalink ), some other dave states that it is the 'triangular
sails- propeller blades' that are responsible for Blackbird's motion.
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2) The wheels cannot power the propeller if the propeller is the sole source of power for the wheels.
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3) If you examine turbine blades and propeller blades, you may find that their airfoil geometries are 'reversed.'
--------------------------------------------------------------------------------------
4) In a bonafide powerplant failure during flight, in a variable-pitch propeller aircraft, the aircraft checklist instructs the pilot to 'de-pitch' the prop, in order
to reduce prop-drag, thereby increasing glide radius for a dead-stick landing.
-------------------------------------------------------------------------------------
5) The 'Blackbird' propeller analogy implies that, in a flight emergency, the pilot would merely 'reverse' the propeller ( like a Lockheed C-130 Hercules ), and the free-wheeling reversed propeller would now be capable of maintaining enough thrust for level flight.
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6) The 'masts' which hold the aircraft propeller are free to move in relation to the aircraft fuselage.

None of this addresses what was in the post you replied to.
But I'll reply to yours point for point. The first two hit the essence.

... it is the 'triangular sails- propeller blades' that are responsible for Blackbird's motion.

Yes, but you have to understand in what way they are responsible.

The car is moving faster than the wind, but as the propeller spins backwards the surface of the blades is moving slower than the wind.
So the wind pushes against the blades, forcing the car forward.
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2) The wheels cannot power the propeller if the propeller is the sole source of power for the wheels.

The forward vector of the force on the blades powers the car forward, the sideways vector works against the gears that push the propeller against the wind. If the gearing is set so that the surface of the blades still moves forward, albeit slower than the car and of course slower than the wind, the force fighting the rotation is less than the forward pull on the blades.

The forces would be equal if the propeller would force the air backwards at the same speed as the car is moving.
The optimal setting is just slightly less than that; the friction in the system determines how much less it needs to be to function.
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3) If you examine turbine blades and propeller blades, you may find that their airfoil geometries are 'reversed.'

This is not a turbine. The propeller does not harvest energy through rotation, but through forward pull.
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4) In a bonafide powerplant failure during flight, in a variable-pitch propeller aircraft, the aircraft checklist instructs the pilot to 'de-pitch' the prop, in order
to reduce prop-drag, thereby increasing glide radius for a dead-stick landing.

A powerless plane has no surface that moves with a different speed to the wind to do anything with, what renders their propellers useless. Putting them in vane position is the only sensible thing to do in that scenario.
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5) The 'Blackbird' propeller analogy implies that, in a flight emergency, the pilot would merely 'reverse' the propeller ( like a Lockheed C-130 Hercules ), and the free-wheeling reversed propeller would now be capable of maintaining enough thrust for level flight.

Second flight analogy, but again if you have no fixed surface moving at a different speed than the wind you have no source of power.
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6) The 'masts' which hold the aircraft propeller are free to move in relation to the aircraft fuselage.

Third flight analogy. It is a flight away from the core mechanism at work.

[RedDevil]

https://www.youtube.com/watch?v=VAK4sGivEx4

Note how the wheels move faster than the rope.
The force on the wheels is equal to the pull on the rope. The axle is the 'gearing' that works against the motion, but the resulting rope movement is still forward.

I think it is clear there's no trickery involved. The experiment does not look that difficult to replicate anyway.

[Piotrsko]

From the articles I have read, there are two camps regarding this vehicle: those that understand the math and theory and those like myself that can't. Just can't wrap my thoughts around how it works. No shame to be in either position.

Do I believe it works? Kinda, but it is a you tube video so I automatically distrust it's veracity. If it works, it should be repeatable by someone like myself without requiring fancy and obscure techniques, otherwise it doesn't work as advertised which is what I believe to be the actual base argument. Sagan's law: extraordinary claims require extraordinary proof.