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

[aerohead]

Originally Posted by ennored

That's how I understand it. Traveling at say, 10 MPH, with a 7 MPH tailwind, you have 10 MPH of groundspeed to overcome a 3 MPH headwind.

1) if the 'phenomena' of Rick Cavallero are of aerodynamic origin, then they are governed by the same principles as all aerodynamic phenomena.
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If tested in a laboratory, I believe that you will find that:
A) the vehicle ground velocity never exceeded the wind speed.
B) at sub-critical Reynolds number, laminar boundary layer, all flow across the vehicle was separated.
C) the 'tattle' at the vehicle's nose was being pulled backwards into the low-pressure turbulent wake of the separated flow.
D) the backwards-facing tattle gave the 'appearance' of headwind, when in fact, that never existed.
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Believing that a 'headwind' actually existed, Rick Cavallero's mind made the leap, concluding that he'd done the impossible, re-writing fluid mechanics and thermodynamics.
' Man believes what he wants to believe.'
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If anyone wants to spend a little time studying Sir Issac Newton's second law, pertaining to force/ mass/ velocity/ time/ momentum/ inertia/ impulse, you'll see that this theory of Cavallero's was dead before it was ever mentioned.

[some_other_dave]

Originally Posted by aerohead

The only corollary which applies for 'with-the-wind' would be flying a spinnaker....

But we're not talking about sailing with the wind. And the propeller blades are not turning with the wind--when they turn, they are meeting it at an angle!

-soD

[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.

[aerohead]

Originally Posted by some_other_dave

But we're not talking about sailing with the wind. And the propeller blades are not turning with the wind--when they turn, they are meeting it at an angle!

-soD

1) according to Newtonian physics, the wind from behind is supplying an 'impulse' of the force (F), over a period of time. (F delta-t)
2) F delta-t = ( delta- momentum ) [ delta-p ]
3) Momentum (p) = mass-times-velocity, or p= mv
4) impulse of the force (F) = delta-p/ delta-t
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* the vehicle, with wind from behind, is a crude square-rigger.
* it's aerodynamic drag creates enough force to accelerate the vehicle, from rest V=zero, to some terminal velocity V2.
* while the vehicle is accelerating, it is building momentum as it's mass is being accelerated.
* under the force of the wind, the vehicle's wheel is transmitting power from the road/tire interface, through the wheel bearings, to the differential, to the lower sprocket, to the chain, to the upper sprocket, through the pillow block bearings, to the shaft, to the propeller, to the air, creating a counter-impulse.
* there's a specific, fixed amount of kinetic energy contained in the wind.
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* If we presumed that the vehicle was a 'perfect' sail, and could extract all the available energy from the wind, we would still be losing energy at the tire/ ground interface/ within the tires themselves/ within the wheel bearings, within the differential gears/ at the lower sprocket-to-chain interface/ within every link pivot within the chain/ within the upper chain-to-sprocket interface/ within the two pillow-block bearings-to-jackshaft interface/ and finally at the propeller-to-air interface.
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* Whatever amount of energy is delivered to the vehicle, that amount, less all the powertrain losses, is what is available at the propeller-to-atmosphere coupling.
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a) when the vehicle reaches the air speed, there is no delta-v
b) acceleration is now zero, v= constant, momentum = constant
c) whatever net-momentum exists in the vehicle, it must have a lower amount of net energy than that the surrounding airstream due to aerodynamic slippage, and rolling resistance on dirt ( very high! )
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d) in order for the propeller to push the vehicle beyond the local air velocity, would require zero aerodynamic slippage, zero rolling resistance, zero powertrain losses, and a propeller wing section exhibiting a lift-to-drag ratio at over-unity, since it's being supplied less energy than is available from it's surroundings.
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* All wing sections have a zero-lift angle of attack
* As soon as a wing begins to produce lift, it's also producing drag ( another drain on available energy )
* At maximum lift, all airfoils are producing maximum drag
* All thrusting airfoil sections are 'angled', so, an
'angled' propeller blade cannot be some new, unique quality of Rick Cavallero's system, not seen in other aerodynamic systems.
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Somehow, the phenomenon of the backward's oriented tattle-tale, has convinced observers of a reality which cannot exist in our universe.

[jakobnev]

It seems involving wind and propellers obfuscates the principle too much, let me instead ask:

Can a cart pulled by a rope go faster than the rope?

(Nothing else powers the cart.)

[aerohead]

Originally Posted by jakobnev

It seems involving wind and propellers obfuscates the principle too much, let me instead ask:

Can a cart pulled by a rope go faster than the rope?

(Nothing else powers the cart.)

1) Is the rope inelastic or elastic?
2) Are you measuring rope velocity at the rope/cart connection point, or the prime mover/rope connection point velocity?

[jakobnev]

1) The rope is perfectly inelastic.
2) All motion is relative to the road.

[oil pan 4]

1 build a wind car your self.
2 disprove the observation.
I'm inclined to believe the guy who built the the thing and did the thing.

[aerohead]

Originally Posted by jakobnev

1) The rope is perfectly inelastic.
2) All motion is relative to the road.

Would you please define the road, cart, and any topological or environmental considerations?

[aerohead]

Originally Posted by oil pan 4

1 build a wind car your self.
2 disprove the observation.
I'm inclined to believe the guy who built the the thing and did the thing.

I've already disproved it.
Observation does not establish causality.
His remarkable claim requires the remarkable evidence to back it up.
He can submit his creation for third-party testing.
NASA Ames is the only laboratory large enough to test it.
In the meantime, it's 'cold fusion.'