3 ms·
The way this clicked for me (it took some thought!) was to see it as a lever, or at least an analogue to one. Imagine a lever with the fulcrum on one end, atta
by cfallin 5y ago
The way this clicked for me (it took some thought!) was to see it as a lever, or at least an analogue to one.
Imagine a lever with the fulcrum on one end, attached to the ground. Wind pushes on the middle, and the car is at the other end of the lever. So wind exerts more force with less speed, and the car moves forward with more speed but less force.
That's basically what the linkage and gear ratio between the wheels and propeller do; it's the counterintuitive power flow that makes it so confusing...
- jcims 5y agoI think this is a good intuition about it, and Xyla Foxlin goes into this a bit in her video explaining the build for Veritasium's video. https://youtu.be/VUgajGv4Aok?t=432 https://youtu.be/VUgajGv4Aok?t=432 The essential 'gear' ratio is between forward motion of the vehicle and the propeller pitch (essentially how far the prop would screw through a tub of jello for a given amount of rotation). The vehicle has to move *faster* on the ground than the prop does through the air for this to work at all, and it sounds like it should be roughly twice as fast for it to work on something that is reasonably simple to engineer. So if your prop pitch is 5", your wheel size and gearing should allow the vehicle to move forward approximately 10" for each rotation of the prop. (Note that her video does not explain 'why' this is the case, just that it is a phenomenon that the Blackbird inventors had determined/discovered and is an essential design criteria).
- slowmovintarget 5y agoAnd one of the Veritasium videos: https://www.youtube.com/watch?v=yCsgoLc_fzI https://www.youtube.com/watch?v=yCsgoLc_fzI
- ummonk 5y agoYes exactly. And if you were driving the other way into the wind, you’d flip the lever and use a turbine to extract energy from the wind and push against the ground.