Like three sheets to the wind.
Explain this? Vehicle travels faster than the wind. My head hurts trying to figure this out.
- Thread starter WobblyElvis
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Jacques Cousteau built one.
OVERKILL
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It's a compounding of the two forces, and yes, absolutely requires wind, and there will be a limit as well. Basically you have:
wind->motion
wind motion--><thrust
wind motion---><-thrust
wind motion---><--thrust
The wind gets it moving with the prop basically acting like a sail and the wheels turn the prop and eventually the prop starts to move enough air to create thrust and that thrust pushes against the wind, compounding the force so that the net overall speed is faster than the wind speed.
Requirements of course are excellent aerodynamics and very light weight.
The energy in wind should not be thought of in terms like mph.A sailboats best point of sail is a beam reach(until hurricanes) ie across the wind, almost always exceeding wind speed, the area of energy capture (sail area)is more important then wind speed.
The propellor blades are moving perpendicular to the wind, just like tiny rotating sailboat sails moving perpendicular to the wind and pushing the boat faster than the wind.
Years ago a local inventor made a similar model. It would travel directly into the wind and had people scratching their heads.
Years ago a local inventor made a similar model. It would travel directly into the wind and had people scratching their heads.
Wait how did his work?
If you could combine a few designs and get them to work happy together maybe you could build a wind powered tricycle that can go any direction
Call me a flat earther if you like but I still don't get it. I look at this situation in terms of energy. There is one source of energy, the wind as it acts on the structure of the vehicle.
The wind pushes the vehicle up to the speed of the wind at best. If energy is removed from the wheels contact with the ground, and applied to the propeller, it can only add forward momentum [energy] to the vehicle up to that which was removed by the wheels. If this energy is applied in any way to move the vehicle forward, the laws of physics demand that no net gain is possible. It doesn't matter how this energy is applied to forward motion [propeller or whatever] it cannot apply more energy to forward motion than is supplied by the wheels contact with the ground.
Once this vehicle matches the speed of the wind, there is no energy input to the vehicle.
If this vehicle worked, it would be capable of unlimited speed.
The wind pushes the vehicle up to the speed of the wind at best. If energy is removed from the wheels contact with the ground, and applied to the propeller, it can only add forward momentum [energy] to the vehicle up to that which was removed by the wheels. If this energy is applied in any way to move the vehicle forward, the laws of physics demand that no net gain is possible. It doesn't matter how this energy is applied to forward motion [propeller or whatever] it cannot apply more energy to forward motion than is supplied by the wheels contact with the ground.
Once this vehicle matches the speed of the wind, there is no energy input to the vehicle.
If this vehicle worked, it would be capable of unlimited speed.
limited when it's aerodynamic drag (+internal friction of the mechanicals) is higher than the force applied by the wind to the propeller. Aerodynamic drag isn't linear, but quadratic, so it hits a limit based on these forces.
Think of the propeller blades as sails. Since they move backwards relative to the wind, the wind pushed forward on the propeller blades even though the vehicle is going faster than the wind. Also the propeller doesn't have a steep pitch so even though the wind is pushing on the flat side of the propeller it spins easily
Basically the sail is always going slower than the wind even though it doesn't look like it
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You have to think of it as a positive feedback loop.
1. Starting from a stop. Blades not turning. Wind simply hits the craft and pushes it forward slightly.
2. Wheels turn. They drive a motion to the prop counter to the wind, pushing against the wind.
3. The vehicle accelerates. The wheels pick up speed, turning the prop faster, which further pushes against the wind and drives the vehicle forward.
From the perspective of the wind, the more it pushes against this vehicle, the more the vehicle pushes back. The vehicle can travel faster than the wind because it is capturing a continuous flow of energy.
If it a simple positive feedback loop, it would be a perpetual motion machine. But it's not.
There is no net gain. The prop is geared to and powered by the wheels. So power at the prop is equal to power at the wheels, minus losses. The wind pushes on the cart, powering the wheels, and the wheels transfer some of that power to the prop.
Now here is the kicker. The entire thing depends on this: the wheels are moving relative to the ground faster than the prop moves relative to the wind. This is because the cart is moving downwind. Suppose the wind is 15 mph, so when the wheels move 20 mph relative to the ground, the prop moves only 5 mph relative to the wind.
First assume for simplicity the wheel+prop is 100 efficient. Since power is thrust * speed, and the prop moves 1/4 as fast through the air as the wheels do on the ground, the prop has 4 times as much thrust as the wheels. Now you can see that even if it loses half the power through inefficiency, the prop still has twice the thrust as the wheels. That means it's pulling the cart forward.
From an energy conservation perspective, the cart is using the energy of the moving airmass, and also taking advantage of the difference in speed between ground & air and using gearing or leverage to turn that into extra thrust. The energy it consumes should slightly slow down the airmass it moves through, from both the cart itself and the propeller pushing back on it.
The treadmill doesn't illustrate how it gets started, but it does illustrate how it can move downwind faster than the wind. From a reference frame perspective, a treadmill moving at a constant speed under a stationary air mass, is the same as an air mass moving at the same constant speed over stationary land. So the experimental cart on the treadmill simulates that.
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You’re misinterpreting me slightly here. It’s certainly not perpetual motion. It is, however, a positive feedback loop, up to the point where equilibrium is met. I left that part out for the sake of brevity.
Yes, this is consistent with what I’ve been saying.
Agreed.
I am still not convinced. I've noticed the professor settled his bet in the video but holds some reservations about the experiments validity. I would agree with him. His idea that the wind speed down closer to the ground is much lower that up where the propeller is could explain a lot of things.
When travelling at wind speed "blackbird" is in a state of equilibrium. [very close]
The propeller robbing power from the wheels cannot produce more forward thrust than it receives. It does matter that the vehicle is subject to only a small headwind.
That's my story and I'm sticking to it.
When travelling at wind speed "blackbird" is in a state of equilibrium. [very close]
The propeller robbing power from the wheels cannot produce more forward thrust than it receives. It does matter that the vehicle is subject to only a small headwind.
That's my story and I'm sticking to it.
True, and in this case it doesn't. It produces a small forward thrust, which is less than the power it receives from the wheels. It doesn't take 100% efficiency, it only takes something greater than 0.
Ponder this: it's well known that sailboats can move downwind faster than the wind.
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A bowling ball can accelerate a bowling pin faster than it was moving. In an open system where masses are unequal and energy is conserved, velocity can vary.
OVERKILL
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Yes, it illustrates that part of it, but there's no wind being pushed against with the treadmill, it's a static column of air. In this scenario, you are introducing energy through the treadmill, to spin the wheels and create the thrust from the prop to go faster than the treadmill itself (mechanical advantage, which he also demonstrates with the 2x4), whereas in the actual vehicle, the ability to move faster than the wind is from the compounding effect of the thrust from the propeller moving against the wind that is pushing it because that's the source of energy in that scenario (the wind).
the relative motion between the ground and the wind is what makes it work. whether its the ground or the wind that's moving doesn't matter.
also these vehicles can drive into the wind and they race them in Norway
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It comes down to the process of acceleration. There are several phases:
1. Initial traditional sail-like push
2. Positive feedback acceleration before reaching wind speed
3. Acceleration beyond wind speed due to continued differential leverage between ground and air
4. Equilibrium at some velocity
The treadmill starts at 3.
1. Initial traditional sail-like push
2. Positive feedback acceleration before reaching wind speed
3. Acceleration beyond wind speed due to continued differential leverage between ground and air
4. Equilibrium at some velocity
The treadmill starts at 3.
