I think this explains it conceptually best: https://www.youtube.com/watch?v=k-trDF8Yldc I'm surprised people have such trouble with this.
Yeah, this was exactly the mental model I used to simplify it. Nice to see it in action.
A wind-powered vehicle that can travel twice as fast as the wind itself
221–230 of 263 posts
Re: A wind-powered vehicle that can travel twice as fast as the wind itself
#222I think this explains it conceptually best: https://www.youtube.com/watch?v=k-trDF8Yldc I'm surprised people have such trouble with this.
Yeah, this was exactly the mental model I used to simplify it. Nice to see it in action.
I bet your mental model didn't have all the stuffies, though.
Re: A wind-powered vehicle that can travel twice as fast as the wind itself
#223Earlier quoted context omitted.
You are mistaken. It has been achieved, and the fastest race boats today do it routinely. This is one of the reasons you don't see spinnakers on boats like the America's Cup AC72s, AC50s, F50s, huge open class trimarans, etc. I'm not sure the first boat to achieve it, but it wouldn't be surprising if it was done during the Clipper era. Those boats held 24 hour records from 1860 something all thee way to the 1980s, wh…
I think we just have different definitions. It's about the "Directly" You need a propeller to go Directly Downwind Faster Than The Wind as far as I know. I think on water it has to be very large. I expect there are other ways other than a propeller but haven't seen them. A half way definition (This isn't DDWFTTW to me either), I'd like to know if an America's Cup boat could beat a balloon? So it would be allowed off…
I know what you meant. You are mistaken. Look at the 180 degree data on the polars for AC72 or Bank Populaire. They're more efficient at a broad reach, but they can do it a few knots faster than the wind.
Re: A wind-powered vehicle that can travel twice as fast as the wind itself
#224Earlier quoted context omitted.
I think we just have different definitions. It's about the "Directly" You need a propeller to go Directly Downwind Faster Than The Wind as far as I know. I think on water it has to be very large. I expect there are other ways other than a propeller but haven't seen them. A half way definition (This isn't DDWFTTW to me either), I'd like to know if an America's Cup boat could beat a balloon? So it would be allowed off…
I know what you meant. You are mistaken. Look at the 180 degree data on the polars for AC72 or Bank Populaire. They're more efficient at a broad reach, but they can do it a few knots faster than the wind.
Why does the Blackbird use a propeller, why not a simple high-performance land sail boat like the Greenbird, a design that fits with the original idea from the sailing community?
There is nothing online that says a sail boat can go DDWFTTW. DDWFTTW is at least a 4 decades old term in the sailing community looking at magazines.
Here's a design from 1985 using a propeller https://issuu.com/latitude38/docs/latitude3894apunse/162
Sorry, you are mistaken.
Re: A wind-powered vehicle that can travel twice as fast as the wind itself
#225> 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…
Gravity. Without it the wheels wont have sufficient friction to generate torque
Re: A wind-powered vehicle that can travel twice as fast as the wind itself
#226Earlier quoted context omitted.
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…
Gravity. Without it the wheels wont have sufficient friction to generate torque
> Gravity
I'm sorry but you're either answering a different question than "where do the wheels get their energy from" or extremely confused.
We're on a flat plane normal to the direction gravity acts, so I'm going to let you go out and work out how much energy gravity can provide there.
Re: A wind-powered vehicle that can travel twice as fast as the wind itself
#227Derek from Veritasium asked Xyla Foxlin to build a functional model, and she goes through the trials and tribulations of that in quite a bit of detail in her video here: https://youtu.be/VUgajGv4Aok There's a key aspect discussed in 7:10 relating to the ratio of the propeller pitch to the vehicle forward motion that is necessary for this to work. (Xyla's channel is a great follow overall btw)
Xyla channel is definitely worth a look.
But she is somewhat rubbing me the wrong way (no pun intented) ... I am not sure if she had a channel before this one, but she basically appears out of nowhere with a perfect brand image: https://www.youtube.com/watch?v=3B9XYJJY6IQ
From the get go she is connected into the wider content creation sphere. Appearing in videos from Veritasium, BPS.space, Dolphin Labs, probably some more.
She is every nerds wet dream ... smart, creative and good looking with a overly happy attitude.
I don't want to talk bad about her ... It's just too perfect for me not to be somewhat suspicious.
Re: A wind-powered vehicle that can travel twice as fast as the wind itself
#228Earlier quoted context omitted.
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…
Ok I have taken college level mechanics (after physics 1-2) and I have no idea what you’re saying.
With due respect to you, and assuming you passed, that's pretty damning of whatever college you went to. I'd want a refund.
The definitions of kinetic energy and momentum and some basic differentiation, that should all be thoroughly covered.
Re: A wind-powered vehicle that can travel twice as fast as the wind itself
#229Earlier quoted context omitted.
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. [0] https://ucannualwage.ucop.edu/wage/
pretty decent for an incompetent professor in my opinion
oh c'mon now! Your insult is just outrageous. You're insulting a person who had the guts to make very valid questions and observations. Since when is questioning incompetence? Are you a man whose intuition is always right?
Re: A wind-powered vehicle that can travel twice as fast as the wind itself
#230Earlier quoted context omitted.
Gravity. Without it the wheels wont have sufficient friction to generate torque
> Gravity I'm sorry but you're either answering a different question than "where do the wheels get their energy from" or extremely confused. We're on a flat plane normal to the direction gravity acts, so I'm going to let you go out and work out how much energy gravity can provide there.
You 're right, gravity provides the force of friction but not energy. The energy is from the pressure of the wind, the device just makes better use of it compared to a fan-less cart.