This is like putting a turbocharger on a sailboat. I love it.
A turbo charger increases fuel consumption though. You can’t just consume more wind.
A wind-powered vehicle that can travel twice as fast as the wind itself
161–170 of 263 posts
Re: A wind-powered vehicle that can travel twice as fast as the wind itself
#162The 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
How does a professor have $10,000 sitting around for a bet like this?? I am a nicely-paid tech worker, and $10,000 wouldn't ruin me, but it would be a major setback for that year.
UC salaries are public[0] and it looks like he made $219k in 2019, which is pretty decent for a professor but yeah $10k would still definitely be a significant setback.
Re: A wind-powered vehicle that can travel twice as fast as the wind itself
#163Earlier quoted context omitted.
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…
> as if it was a plane wing. This is how nearly all sailing works. Excepting the case of sailing directly downwind, the curve of the sail works like a wing, and the keel provides something to "push" against - the effective "lift" (if it were a wing) drives you forward. This is why you can sail into the wind at all...
Obligatory mentioned of the AC72 using rigid wing sails. - https://www.youtube.com/watch?v=hbPTnF6liF8
Re: A wind-powered vehicle that can travel twice as fast as the wind itself
#164I think I have an analogy that actually explains how this works. Imagine one of those people-mover walkways like they have at the airport. Standing next to it on a skateboard, you grab the handrail. Even though the skateboard has energy loss to friction, you go exactly as fast as the handrail. Now imagine you put a little electric generator in the wheels of the skateboard. Now, not only are you moving at the speed of…
This apparently violates conservation of energy as you’re claiming to take energy from one source, put it through some apparatus (i.e two skateboards) to produce more energy without putting anything additional in. Can you account for this?
The people-mover has to expend more energy to push you because you're applying a stronger drag force, so energy is conserved.
Re: A wind-powered vehicle that can travel twice as fast as the wind itself
#165> 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…
Yeah, my first inclination is that since the wind is turning the propeller and the propeller is turning the wheels via a gear system, the speed of the vehicle will be determined by the propeller speed, the gear ratio, and the tire diameter (ignoring friction and air resistance for a moment). The gear ratio is the critical component. It's not like the propeller is a simple sail. I could be completely missing something…
Gear ratio *is* the critical component, specifically prop pitch vs. forward motion, but not exactly for the reason you describe. Xyla Foxlin built a working model and provides a bit more info here:
https://youtu.be/VUgajGv4Aok?t=432
In short the working model she built has approximately a 2:1 ratio between forward wheel motion and propeller pitch. IOW if the propeller pitch is 5" per revolution, the wheels will require 10" of forward travel to spin it one time.
Re: A wind-powered vehicle that can travel twice as fast as the wind itself
#166This is like putting a turbocharger on a sailboat. I love it.
A turbo charger increases fuel consumption though. You can’t just consume more wind.
In this case they are actually "consuming" more wind. A normal sail "consumes" wind by taking moving wind and reducing its speed to 0. This "consumes" wind by taking moving wind and sending it back the other direction, so it creates more thrust per unit wind.
Re: A wind-powered vehicle that can travel twice as fast as the wind itself
#167Earlier quoted context omitted.
A turbo charger increases fuel consumption though. You can’t just consume more wind.
In this case they are actually "consuming" more wind. A normal sail "consumes" wind by taking moving wind and reducing its speed to 0. This "consumes" wind by taking moving wind and sending it back the other direction, so it creates more thrust per unit wind.
Sounds to me like it improves efficiency rather than consumes more
Re: A wind-powered vehicle that can travel twice as fast as the wind itself
#168Earlier quoted context omitted.
In this case they are actually "consuming" more wind. A normal sail "consumes" wind by taking moving wind and reducing its speed to 0. This "consumes" wind by taking moving wind and sending it back the other direction, so it creates more thrust per unit wind.
Sounds to me like it improves efficiency rather than consumes more
Yep, I thought about it a bit more and you're totally right.
Re: A wind-powered vehicle that can travel twice as fast as the wind itself
#169The thing I wonder about stuff like this is that a phenomenon we see in one domain will typically transfer to another domain. For example, the 'hydraulic analogy' [1] for electronic circuits is pretty damn good at least on a macroscopic level. I wonder if there are applications of this phenomenon in other types of physical systems (including electronics).
Re: A wind-powered vehicle that can travel twice as fast as the wind itself
#170Earlier quoted context omitted.
This apparently violates conservation of energy as you’re claiming to take energy from one source, put it through some apparatus (i.e two skateboards) to produce more energy without putting anything additional in. Can you account for this?
The people-mover has to expend more energy to push you because you're applying a stronger drag force, so energy is conserved.
Okay so in this case the people mover is drawing the additional energy. Additional energy is being provided from somewhere i.e a diesel generator somewhere up stream has had to increase her fuel consumption to maintain the power on the network.