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

Post by ska » Mon, Aug 09, 2021, 4:52 PM UTC

otherme123 wrote: post #82

marcodiego wrote: post #61

Earlier quoted context omitted.

I really would like a simple explanation of how that is possible. AIUI, when speed is stable, the wheels turning provide power to the propeller. But if the propeller pushes the car, which in turn makes the wheels turn faster making the car faster than the wind itself, what makes it different from perpetual motion machines? I would love a diagram showing how the power flows in this system.

I felt this in a sail boat: when the boat is moving below wind speed, the wind pushes the sail and the boat. At some point, wind and boat equal speeds, so it feels like theres no wind at all except the sail is full. Some well built boats can generate pull (instead of push) in the sail, as if it was a plane wing. The air passing on the convex (forward) side travels faster than the air on the concave, making the pressu…

Post by iamgopal » Mon, Aug 09, 2021, 5:00 PM UTC

Tuna-Fish wrote: post #10

Someone1234 wrote: post #2

The most surprising thing here is that someone on Twitter made a bet, lost the bet, and then actually paid said bet. Playing devil's advocate here a little: The whole machine is very counter-intuitive, and I can see how I myself may disbelieve it if not for the irrefutable demonstration(s)[0]. [0] https://www.youtube.com/watch?v=yCsgoLc_fzI

The small demonstration that made it click for me is from that video: https://www.youtube.com/watch?v=yCsgoLc_fzI&t=812s This is exactly what the blackbird does, only with a propeller pushing air in place of the big wheel, and it's a much clearer and simpler demonstration of the same idea, which you can trivially verify.

Post by yodelshady » Mon, Aug 09, 2021, 5:02 PM UTC

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…

Post by amluto » Mon, Aug 09, 2021, 5:03 PM UTC

mumblemumble wrote: post #51

jrs235 wrote: post #47

Earlier quoted context omitted.

Understandable that it doesn't take much wind for a vehicle well under a pound. But what about one that weighs well over 100 pounds?

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.

Post by munchler » Mon, Aug 09, 2021, 5:12 PM UTC

pkulak wrote: post #113

munchler wrote: post #93

Earlier quoted context omitted.

Here's a simple explanation: Let's assume that the windspeed is 10 km/hr. We all agree that the wind can push this vehicle so that it is now going 10 km/hr downwind, right? From the vehicle's point of view, the wind is now 0 km/hr. But its wheels are turning, which turns the propeller, which behaves like a fan, pushing the vehicle forward in the still air, so that it is now traveling faster than the wind. This isn't…

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.