Merged DDWFTTW in a “Real” Wind

[zooterkin]

The wind ( headwind) is the term 'v'.
The entire point of the claim, and the primary objection to it, is that there is no tailwind above WS, yet it is always insinuated by some other means.
There is no wind power above WS, ddw. That is why boats tack to achieve >WS.

Yes, you're right; if only there was some device that could be perpetually tacking...

The vehicle is effectively tacking the wind. The propeller's blade is presented at an angle to the prevailing wind.

 

[Jack by the hedge]

if it were quite so simple as declaring that the wheel can supply (T*w) power and the prop consumes (T*w³) power, then it would be impossible to push or tow the cart as the power needed to move it would always exceed the power used to move it.

Well, I'm saying it can't.
But the power to tow, comes from the towing vehicle. Not the cart itself.
The towing vehicle will have an engine and fuel. Apples and pears.

It doesn't matter how powerful an engine the towing vehicle has. You state that the cart's wheels can provide T*w power to the prop but the prop consumes T*w³ when turning. So whatever pushed the BB off the line was either powered by magic or you missed something out.

 

[humber]

Yes, you're right; if only there was some device that could be perpetually tacking...

Then someone with an unsupported hypotheses could make that analogy...oh...wait.

 

[humber]

It doesn't matter how powerful an engine the towing vehicle has. You state that the cart's wheels can provide T*w power to the prop but the prop consumes T*w³ when turning. So whatever pushed the BB off the line was either powered by magic or you missed something out.

No. That is not what I said. Spork's submission model has the thrust and generator power rising linearly with cart speed.

I said the load presented by the prop will increase as w^3, but power from the generator increases with w. The gearing ties w directly to the speed of the cart. For a constant torque that is the case.

If the generator is to supply the motor that drives the prop, then to meet the demand, the generator torque must rise as the square of w.
Not possible with the cart as is, but could be made to do so, yet it would still fail.

Prop power = Generator power
Prop power = Tmotor*w^3 = (Tgen*w^2)*w

Gearing will not change the ratio.

Torque is directly related to the wheel drag, so that increases as w^2, and so the square of the cart speed.

Thrust = Prop/V_air so rises with V_cart.

Even the "air lever" fails, because the thrust rises linearly, but the wheel drag is quadratic. Spork's theory is wrong. Such a cart would stall well below WS.
A truck can pull it beyond that.
There is never a "free lunch" with power, and you are seeing the Nth^n attempt to try to do so. It's simple math, JBTH.

ETA:
About that start. Harold Bricer wrote a calculation using calculus, which concluded that a cart in a steady downwind would only reach around 50% of WS. The cart does that a lot, and that can be seen in the Jenkins video where it crawls at 2m/s for a quite a while. That is trial evidence that Harold is right.
When the wind changes from a steady ddw, to a changing offset wind, the cart starts to move. Happens every time, and the NALSA chart shows it.
The NALSA expert Smith, also said that a changing wind could do that. He also said a test of the motor current would say if the wheels were driving the prop above Ws.. The above calculation says it can't be.

 

[humber]

Explain how a tacking sail works, and why a propeller blade can't work the same way.

Explain why elves don't go to the supermarket.
It's up to you to find proof that that props tack, because that is a new claim, and unorthodox.
You will find no references.

 

[Jack by the hedge]

No. That is not what I said.

I said the load presented by the prop will increase as w^3, but power from the generator increases with w. The gearing ties w directly to the speed of the cart.

If power to the cart's wheels rises linearly with its speed and the drag of its propeller rises as speed's third power, then that tells you that it should reach an equilibrium when the prop uses all the available power and none is available for acceleration.

That appears to be all it tells you, though. Got anything else?

 

[Modified]

Explain why elves don't go to the supermarket.
It's up to you to find proof that that props tack, because that is a new claim, and unorthodox.
You will find no references.

Explain how a sail that is forced to move at an angle to the wind by a ship's keel is fundamentally different from a prop blade that is forced to move at an angle to the wind by gearing to a cart's wheels.

 

[CORed]

Doh. There is energy stored in the rubber. You need to wind them up.
When that energy is depleted, no more powered plane...
You can take it as read that Spork will not answer to the math. It's a "vision thing". you see.

Correct. Nonetheless, a rubber band is not an engine, so your assertion that a propeller can only work if driven by an engine is obviously incorrect.

 

[CORed]

His explanation will be just word salad. He will never prove his point with vectors. Strange, since he loves math so much.

[qimg]http://img253.imageshack.us/img253/6694/downwindvectorsen3.png[/qimg]

[qimg]http://img811.imageshack.us/img811/4922/propellervectors.png[/qimg]

Probably more like word and math salad, with lots of incorrectly applied formulas, because humber thinks he can prove the sun rises in the west with math.

 

[humber]

Explain how a sail that is forced to move at an angle to the wind by a ship's keel is fundamentally different from a prop blade that is forced to move at an angle to the wind by gearing to a cart's wheels.

Confusion between force and motion. The keel provides a reaction to the lift force generated by motion of the boat when not ddw.
If the prop were to do that to the cart, there would be a force at the shaft to reflect that force. There isn't.

There is no reason to think that explaining a propeller's behavior by analogy with a tacking boat, would not be reflected by explanations of a tacking boat, employing analogy with a propeller.
That is not done, even though many find tacking "counter-intuitive"

 

[humber]

If power to the cart's wheels rises linearly with its speed and the drag of its propeller rises as speed's third power, then that tells you that it should reach an equilibrium when the prop uses all the available power and none is available for acceleration.

That appears to be all it tells you, though. Got anything else?

It mean at the very least, that you would need more force than is available from any known means; turbine, prop, sail.
And that the submission, which is said to be theoretical proof, is flat-out wrong. Like the trial is "proof". Like the TM is "proof".

 

[humber]

Correct. Nonetheless, a rubber band is not an engine, so your assertion that a propeller can only work if driven by an engine is obviously incorrect.

Doh.
Read again Delta V is the acceleration additional velocity.
That is power applied to the shaft.
Don't take ride in a rickshaw. It's a scam. As you know, they can't work because they don't have an "engine".
ETA: And Drela's man-powered plane. All a fake. Is that right?

 

[Jack by the hedge]

It mean at the very least, that you would need more force than is available from any known means; turbine, prop, sail.
And that the submission, which is said to be theoretical proof, is flat-out wrong. Like the trial is "proof". Like the TM is "proof".

That's a non sequitur , trivially disproven by the cart moving away from rest.

 

[A.T.]

The keel provides a reaction to the lift force generated by motion of the boat when not ddw.

The wheels provide a reaction to the lift force of the propeller blades, even if the cart goes ddw.

If the prop were to do that to the cart, there would be a force at the shaft to reflect that force.

There is a torque on the shaft that reflects that force. When lateral movement becomes rotation, the lateral forces become torques.

 

[mender]

Harold Bricer wrote a calculation using calculus, which concluded that a cart in a steady downwind would only reach around 50% of WS.

Proving only that it isn't wise to drink and derive.

 

[mender]

Probably more like word and math salad, with lots of incorrectly applied formulas, because humber thinks he can prove the sun rises in the west with math.

And that he can find many people willing to argue endlessly with him about that.
He's lonely.

 

[humber]

That's a non sequitur , trivially disproven by the cart moving away from rest.

It is not a "non sequitur"
The cart moves away from rest because its driven as a sail, and that is how it works at all speeds.
The theory that the wheels drive the prop as claims, fails in principle.

 

[humber]

The wheels provide a reaction to the lift force of the propeller blades, even if the cart goes ddw.

Well, let me remind you. The wheels drive the prop, so the reaction is at the prop not the wheels.

There is a torque on the shaft that reflects that force. When lateral movement becomes rotation, the lateral forces become torques.

w^3/w = w^2
End.

 

[Jack by the hedge]

It is not a "non sequitur"
The cart moves away from rest because its driven as a sail, and that is how it works at all speeds.
The theory that the wheels drive the prop as claims, fails in principle.

At all speeds up to and beyond windspeed, because the prop is turning and thereby constantly retreating the points of contact with the wind such that they do not exceed windspeed. There is always positive wind pressure on the back of the prop blades.

The wheels do turn the prop. The drive chain from the wheel's axle to the propshaft is always in tension. Or perhaps you have forgotten (again!) that the direction the prop turns as the cart sets off is the reverse direction to the way the wind would turn it if it was freewheeling.

 

[Jack by the hedge]

w^3/w = w^2
End.

So the cart can never move. Yet it moves. What have you forgotten?