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Science Experiments / Re: Can we go downwind faster than the wind?
« on: 26/06/2021 04:01:42 »My analysis shows that to go faster than the wind,...What does it take to make it move slower than the wind?
For this the advance ratio A must be negative, so you have to get rid of the blue wheel or apply the ruler at the bottom of the blue wheel.
Just to clarify: Above I was answering the question about making it move slower than the wind.
... the bottom wheels must spin in reverse direction than the top.
Well, it depends on which side of the wheel the ruler/belt is interacting with it (see the single spool). But if you stick to:
- top-side for the top wheel
- bottom-side for the bottom wheel
then yes.
The advance ratio A is the ratio of relative velocities, that your gearbox is trying to achieve:
A = air_relative_velocity / ground_relative_velocity
When moving with the air but faster, or against the air, the air_relative_velocity and ground_relative_velocity have the same sign so A > 0. When moving with the air but slower, they have opposite signs so A < 0.
I'm attaching a plot of advance ratio vs. maximal speed. For a gear box with no slippage you can assume the ideal velocity (blue line). With slippage and drag (like the propeller cart) you get something like the red velocity line.To make sense of the diagrams in the table below, you should watch the video on the bottom.
rotor_carts_01.png (209.85 kB . 812x1000 - viewed 5156 times)
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