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A wind-powered vehicle that can travel twice as fast as the wind itself

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Re: A wind-powered vehicle that can travel twice as fast as the wind itself

#131

Post by namlem »

yodelshady wrote: post #126
michaelt wrote: post #13

> The secret to Blackbird, Cavallaro explained, is that once the wind gets the vehicle going, its wheels start to turn the propeller blades — they're connected to the blades by a chain. As the vehicle speeds up, its wheels turn the propeller faster and faster. The propeller blades, in turn, act as a fan, pushing more air behind the land yacht and thrusting it forward. That's a terrible explanation - no wonder people…

Aye, where do the wheels get the energy from? Actually, more seriously, is there any point where the net torque on the drivetrain is zero? Assuming you're happy that, so long as the wheels are low-friction, that's no difference between "Downwind faster than Wind" and Upwind, and that a single design of craft can do both Downwind and Upwind, then all you need for the "dead air" part is to store energy in a battery, sp…

The energy comes from the air. The air molecules in the wake of the propeller have lower kinetic energy than the rest of the air.

Re: A wind-powered vehicle that can travel twice as fast as the wind itself

#132

Post by blueblisters »

mumblemumble wrote: post #50
Valgrim wrote: post #28

Earlier quoted context omitted.

Then what is spinning the wheels?

Asking what is spinning what is maybe framing it in a way that impedes understanding. A quick summary of the basic forces involved are: The wind pushes the propeller, the propeller pushes the wheels, the wheels push the ground, the ground pushes the wheels, the wheels push the propeller, and the propeller pushes the wind. Or perhaps it's better to say that everything is dynamically interacting with everything else. I…

Perhaps another way to think about it - tailwind. Aircraft can derive energy from the wind even when they're going faster than the wind-speed.

The propeller arrangement is a glider that is being pushed by the wind. The glider is tethered to a cart whose wheels in-turn drives the propeller to become a "powered" glider. Without a tether, the relative speed of the glider with respect to the wind would be zero. With the tether powering the propeller, the relative speed of the glider is greater than zero, which makes the cart go faster than the wind.

Thinking about the "glider" and the tether as two separate systems makes more intuitive sense, imo.

Re: A wind-powered vehicle that can travel twice as fast as the wind itself

#133

Post by [deleted] »

amluto wrote: post #128
mumblemumble wrote: post #51

Earlier quoted context omitted.

The 100 pound vehicle also has a much larger cross section to the wind. And its propeller is further off the ground, so it's getting cleaner wind than the little model version. I can get a boat that weighs more and has less sail area going on less wind than that. And that thing has to be dragged through the water on top of everything else.

In the water, there is no static friction and no velocity-independent friction. If you push a floating boat, it moves.

[deleted]

Re: A wind-powered vehicle that can travel twice as fast as the wind itself

#134

Post by im3w1l »

jfoutz wrote: post #119
mumblemumble wrote: post #50

Earlier quoted context omitted.

Asking what is spinning what is maybe framing it in a way that impedes understanding. A quick summary of the basic forces involved are: The wind pushes the propeller, the propeller pushes the wheels, the wheels push the ground, the ground pushes the wheels, the wheels push the propeller, and the propeller pushes the wind. Or perhaps it's better to say that everything is dynamically interacting with everything else. I…

Sailboats are one I struggled with, especially sailing into the wind. I think my intuition there came from a boat going the same direction as the wind, say, north at 1 meter/sec. now the boat can't go faster than 1 m/sec, but if you turn 45 degrees to the east you can travel sqrt(2) m/sec, because you're still going north at 1/ms and the boat gets pushed along to the east as well. the closer you get to perpendicular…

I think sailing into the wind works because you divide the force of the wind into components twice. Dividing into components first one way and then another lets you pull some tricks.

The first time comes from the sail, you divide the wind into a component flowing along the sail (doing nothing), and one that is perpendicular to it (pushing it)

Then you take the perpendicular-to-the-sail part and divide that into a side-ways (drift) and a forwards component (propulsive). The side ways one is neutralized by the keel.

Btw I kinda wonder if a rotatable keel tuned just right would allow sailing right into the wind...

Re: A wind-powered vehicle that can travel twice as fast as the wind itself

#135

Post by gubby »

I think the key conceptual thing that's difficult to grasp is the propellor's interaction with the wind.

Forgetting the speed of the car vs the wind for a moment, the propellor is arranged so it is trying to push air into the wind (i.e. it is propelling the craft). So, whatever force the wind might impart on a simple flat disc of similar radius to the prop, the force the prop actually experiences is higher than that because it is pushing against the wind.

For me, this realisation that the prop is pushing against the wind, increasing the overall force, unlocked understanding how this craft is possible.

Re: A wind-powered vehicle that can travel twice as fast as the wind itself

#136

Post by twobitshifter »

michaelt wrote: post #13

> The secret to Blackbird, Cavallaro explained, is that once the wind gets the vehicle going, its wheels start to turn the propeller blades — they're connected to the blades by a chain. As the vehicle speeds up, its wheels turn the propeller faster and faster. The propeller blades, in turn, act as a fan, pushing more air behind the land yacht and thrusting it forward. That's a terrible explanation - no wonder people…

It’s really not that complicated - wind speed is not the same as energy. The propellor is a device that pushes against the air to move forward, it takes energy from the wind, produces a force, and the force produces momentum in the vehicle. We know that a stationary turbine can continually take power from the wind. When that wind energy is stored in a battery it can power your car much faster than the wind. This just takes a shorter route and stores the energy in momentum.

See sailboats faster than wind

https://www.kqed.org/science/8503/how-do-these-boats-sail-fa...

> The America’s Cup sailboats are sleek and fast. The AC72, the type of catamaran used in this year’s race, can travel almost three times the speed of the prevailing wind. On June 18th Emirates Team New Zealand recorded a speed of 50.8 mph (44.1 knots), with a wind speed of about 18 mph (15.6 knots).

When sailing directly in line with the wind, the apparent wind in a sail is equal to the actual wind, so there’s no gain. A propellor reshapes the direction of the apparent wind to be in the same direction of the wind.

More interesting is that blackbird can go 2 times as fast as the wind running directly_into_ the wind. That ought to help understand how this is possible.

Re: A wind-powered vehicle that can travel twice as fast as the wind itself

#137

Post by glitchc »

danpalmer wrote: post #110
glitchc wrote: post #98

Earlier quoted context omitted.

It's a sad indictment of the times when people feel that having a million subscribers (read: being popular) is more notable than having a PhD (read: expert training) in a relevant field. It's no wonder anti-vaccine material is so widespread. Someone famous on Youtube said it was bad, it must be true!

Subscribers do so for a reason. In this case not insignificantly because of expert training. I'd suggest that very few YouTubers are popular because they are popular, in fact I think this is fairly rare in general. I think it's more likely that they provide some value to their audiences. I think looking down on "celebrity culture" often fails to account for the types of value that one doesn't value themselves.

Re the first statement, that’s complete horseshit. Celebrity culture is all about being part of a cult following and finding like-minded people. Any correlation to objective fact or basis in reality is purely coincidental, and has no bearing on the quality of the person or the content of the movement being followed.

I totally get that you value Gig Hadid’s opinion on wardrobe whereas I don’t, nor do I judge, to each his/her own. But, to claim that her opinion is more accurate/better/truthful to that of a respected fashion designer or industry expert is inherently flawed. Wearing clothes is not the same as designing them.

Re: A wind-powered vehicle that can travel twice as fast as the wind itself

#138

Post by glitchc »

kube-system wrote: post #118
glitchc wrote: post #98

Earlier quoted context omitted.

It's a sad indictment of the times when people feel that having a million subscribers (read: being popular) is more notable than having a PhD (read: expert training) in a relevant field. It's no wonder anti-vaccine material is so widespread. Someone famous on Youtube said it was bad, it must be true!

I think it's just a simple matter of the relative exclusivity of those accomplishments. If I asked you who Woodrow Wilson was, what would you respond with?

That’s a false dichotomy. Being a president is tangentially related to exceptional intelligence.

A better example would be Brian May (of Queen). No correlation between academic credentials and artistic career. There, if the article were about black holes and May had an opinion, I would expect the reporter to cite his PhD, making it a (potentially) informed opinion.

Re: A wind-powered vehicle that can travel twice as fast as the wind itself

#139

Post by pkulak »

munchler wrote: post #130
pkulak wrote: post #113

Earlier quoted context omitted.

The problem with this explanation, at least to me, is that it doesn't require any wind at all. Why not just give it a push in still air and have to take off into the distance forever? EDIT: I think it's clicking. It's because the air and the ground are moving relative to the craft at different speeds. So if the ground and air were still, there would be no speed difference to draw energy from.

Right. This mechanism doesn’t actually require wind. You get the same effect by placing the vehicle on a treadmill in a windless room: It will move forward on the treadmill.

Well, that's the same as having wind.

Re: A wind-powered vehicle that can travel twice as fast as the wind itself

#140

Post by kube-system »

glitchc wrote: post #138
kube-system wrote: post #118

Earlier quoted context omitted.

I think it's just a simple matter of the relative exclusivity of those accomplishments. If I asked you who Woodrow Wilson was, what would you respond with?

That’s a false dichotomy. Being a president is tangentially related to exceptional intelligence. A better example would be Brian May (of Queen). No correlation between academic credentials and artistic career. There, if the article were about black holes and May had an opinion, I would expect the reporter to cite his PhD, making it a (potentially) informed opinion.

The people who have top YouTube channels also have exceptional intelligence. Maybe less so in logical intelligence or rote memorization, but more so in other intelligences.

> A better example would be Brian May (of Queen). No correlation between academic credentials and artistic career

I am not sure why that example is better -- Muller's academic credentials are very well related to his career. As were Wilson's.

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