31–40 of 263 posts
The treadmill demos made me think of another counterintuitive possibility that I wondered if anyone had pulled off: sailing a boat indirectly up a river in no (bank relative) wind. Turns out, it has been done: https://www.youtube.com/watch?v=q2il8Fagbyk
Can it be done with solar sails?
The treadmill demos made me think of another counterintuitive possibility that I wondered if anyone had pulled off: sailing a boat indirectly up a river in no (bank relative) wind. Turns out, it has been done: https://www.youtube.com/watch?v=q2il8Fagbyk
Can it be done with solar sails?
"A popular YouTuber filmed himself driving a wind-powered vehicle downwind faster than the wind itself. [...] Muller, the creator of the Veritasium YouTube channel, likes to break down funky science concepts for his 9.5 million subscribers." The "popular YouTuber" is Derek Muller, who studied Engineering Physics and has a PhD in Physics Education Research... It's so frustrating to see how the writer tried so hard to…
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
It's not at all counterintuitive. It's just poorly explained. Energy is 1/2mv^2, and momentum (related to force) is mv. Anytime you have different speeds, you can arbitrage. If I am pushing against still air, I can generate nearly-infinite force for arbitrarily little energy. That's why you use wings instead of pointing jet engines downwards. You push a lot of air by a little bit (lots of mv, not a lot of 1/2mv^2, si…
Is this similar to sailing? Where the lift generated by wind passing over the curved sail or prop blade produces more lift allowing the boat or car to go faster than the wind speed.
> 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…
You're right that it falls far short, but it corrects one of the fundamental misunderstandings many people have about the vehicle: the wind does not spin the propeller, the wheels do.
Edit: FYI in the video he does sort of cover his claim even if it got started by a non wind force by stating the vehicle can maintain a speed faster than the wind pushing it. But I'm still curious, was a non wind force needed in the desert to get it started?
Is this similar to sailing? Where the lift generated by wind passing over the curved sail or prop blade produces more lift allowing the boat or car to go faster than the wind speed.
To extend the analogy further, I think that the wheel-and-chain mechanism ends up functioning analogously to the boat's keel.
Earlier quoted context omitted.
> Downwind, when the vehicle is traveling faster than the windspeed, the ground is the fastest-moving medium relative to the vehicle, so the wheels harvest the power and impart it to the rotor, which propels the vehicle. So the wind pushes the vehicle faster than wind speed to start with? How?
The angle of attack of the propeller blades and the gearing relative to the wheels cause the blades to be seen by the wind as moving upwind relative to the ground. Alternatively, think of it as merely harvesting energy from the velocity difference between the ground and the air. It's connected to the ground by wheels, and to the air by a big prop. It doesn't matter how fast the vehicle itself is moving as long as the…
But if those values are fixed, as with Blackbird, then you are of course limited to a top speed that is some constant multiple of wind speed.