Quote:
Originally Posted by RedDevil
related to THE CAR. the plank will move in the same direction as the car related to THE GROUND at half the speed of the car. Just like in Veritasum's video.
The whole point of that demo is to prove that you can make an object move faster than the speed of the two media it interacts with.
I don't know where it says that, but I would agree to it if you replace 'body' with 'propeller'. Als long as the car moves slower than the wind the minimal drag on the body helps a bit though.
Exactly! The car does not break the law of conservation of energy (thermodynamics are not relevant here, but not violated either).
If anything, it makes clever use of it.
There are two media at work here: the wind and the ground.
The wind pushes against the propeller, the ground pushes against the wheels.
The forward force on the propeller and the wheels are roughly equal.
But the distance the wheels move over the ground is larger than the distance the propeller moves the air relative to the car. And energy is force times distance.
So the energy needed to spin the propeller to withstand that force is less than the energy obtained by pushing the wheels over the ground with that same force. No broken laws, just a well used one.
Ground speed and air speed are equal in a windstill. The car obviously has no power source then. I think you meant to say something else, but I'm not guessing.Indeed.Negative to the car you mean? Because that is exactly what we try to achieve.
There's no such thing as negative wind speed compared to the ground.
There's no such thing as negative wind speed compared to the surface of the propeller blades.
Obviously the wind needs to keep pushing against the propeller. It has to turn to allow for that.
Again, energy is force times distance. And as the propeller is forcing the air backwards slower than the wheels move over the ground, it needs less energy to do so than the wheels provide from the same force.No need for tacking if you rotate around an axle for an 'infinite tack'. The propeller is nothing but two sails on an axle.
As for lift to drag ratio, that can go all the way to 60:1. Seems adequate.
Ha! What would anyone have to do to convince you?
When building the damn thing, having sceptics inspect it, having an official registration of a record 2.8 times wind speed and all, and winning a 10,000 dollar bet with an UCLA professor does not even convince you?
No proof will ever be good enough for you, because the only thing you'd do with it is trying to debunk it.
Because deep in your heart you KNOW it cannot work.
Because you make a mistake in interpreting its physics, but you cannot admit that somehow. |
1) the little model is not air driven.
2) the little model does not mimic El Mirage Dry Lake conditions
3) it's Rick Cavallero who says in the vodeo that it's the body of Blackbird which is reacting to the wind impulse to move it ( disregarding the propeller thrust )
4) we know from Hoerner that, Blackbird's drag will be over 3X higher with the wind from behind, than from the front, so it is a 'square-rigger sail' so to speak.
5) the Second Law of Thermodynamics is operating at:
* wind-to-body aerodynamic coupling surface friction
* flow separation induced turbulence viscous shearing forces.
* dirt ground-to-tire tread interface
* internal hysteresis loss and heating within the tires
* all wheel bearings
* all gears
* all sprockets
* all power transfers from component to component
* all other bearings
* within every chain link swivel
* at the propeller-to-atmosphere coupling heating
( if you had the proper infrared imaging equipment, you'd see Blackbird raising the temperature of the air around it at all contact points, and within all it mechanical components ) That's all 'entropy'
6) the tires resist rolling on the dirt as a function of their coefficient of rolling force ( which must be quantified for dirt )
7) along with the body, the air flow impacts the thrusting face of the propeller.
8) I'm uncertain how you could quantify what the forces would be on the propeller and wheels.
9) the distance the wheels travel will be whatever it is.
10) the distance the slipstream moves through the propeller disc will be a function of its diameter and nominal pitch, along its axis of rotation as if it were moving along a helix of slope equal to it's blade angle. Which would need to well exceed the ground velocity in order for Blackbird to exceed the local wind velocity at the prop.
11) we don't want to confuse gross available energy with net useful energy. Blackbird lives on the margin.
12) do you have the propeller specifications for Blackbird?
13) do you have the aerodynamic 'push' data for blackbird?
14) yes, when airspeed and ground speed are equal, there is no more impulse, and momentum is constant.
15) if the car is exceeding the windspeed, it has a negative impulse acting on it, it's running away from its energy source, while for the first time, experiencing positive aerodynamic drag.
16) impulse from the rear was experienced from a 'tailwind' up until the point where air velocity nulls, at zero apparent air velocity, measured only at the car.
17) if the ground speed of the car exceeds wind speed, its now in a headwind, while the ground is always experiencing some true wind.
18) the car is in an ocean of moving air, like a commercial airliner in the Jet Stream, going supersonic by ground measurement, however, only 600-mph by pitot tube/ manometer aboard the plane ).
19) the ground just experiences, from a fixed position, whatever the wind is doing.
20) there would be a point where the propeller experienced zero wind speed, however we'd need to know everything about the prop. to calculate that.
21) the wind will just blow.
22) if the propeller is turning, and it has a certain degree of slipstream coming off it, it will be acted upon by the wind, even if exceeding the wind speed.
23 ) I'd prefer we use 'power' rather than energy.
24) Blackbird will have a ROAD LOAD Horsepower requirement under any given set of circumstances.
25) this power is associated only with aerodynamic drag and rolling resistance.
26) if the propeller can impart horsepower to the atmosphere in excess of the road load, it will continue to accelerate. That's neve been in question.
27) everyone ( I believe ) accepts that the propeller is 'tacking' around its shaft and capable of imparting thrust.
28) given a true wind speed spectra, a terminal ground velocity at that specific wind velocity, and all the necessary particulars of Blackbird, things will be what they are. I'm happy just to have the facts, without all the drama.
And it's the shortcomings of the video presentation which appears to have created all the controversy.
The treadmill tests proved nothing.
The test at El Mirage is lacking in information.
The $10,000 bet means nothing to me.
I'm just asking for algebra. I want the left side of the = sign to match the right side.