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Mess with your minds: A wind powered craft going faster than a tail wind speed.
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electrodacus:

--- Quote from: thm_w on December 15, 2021, 11:35:17 pm ---
--- Quote from: electrodacus on December 15, 2021, 11:28:17 pm ---That calculator does not even have the input data it will need to calculate the correct result as there is no wind direction and no frontal area.

--- End quote ---

Wind direction is toward the rider (head wind, it says if you hover over the box).
Frontal area (Cd*A) is determined by Position of the rider, roughly. Its described on the right hand page.


--- Quote ---tops    0.408, hoods    0.324, drops    0.307, aerobars    0.2914
--- End quote ---

--- End quote ---

Then however made that calculator has the same wrong understanding of physics.  Maybe you can try with some hurricane level winds and see if you can pedal against those as humans can output about 300W so see what the max wind speed is required to stop a human on a bicycle :)
electrodacus:
OK :) I needed to have fun so apparently a human has no problem pedaling upwind at 1km/h with headwind of 230km/h
bdunham7:

--- Quote from: electrodacus on December 15, 2021, 11:18:56 pm ---Sorry to say but that is complete nonsense.  Not quite sure where do you get this sort of intuition.

--- End quote ---

Pro tip:  it isn't intuition!


--- Quote ---Have you ever used a bicycle or pedaled upwind ? It is the same principle as driving on an incline.

--- End quote ---

It's not exactly the same, but let's go with it.  On a uniform incline of θ from horizontal, there will be a constant force of sin(θ) * g * m (mass) downhill.  How much energy does it take to climb the incline a) slowly and b) faster?  Do you agree or not that climbing the incline very slowly can be done with a very small amount of energy?
electrodacus:

--- Quote from: bdunham7 on December 16, 2021, 12:01:54 am ---It's not exactly the same, but let's go with it.  On a uniform incline of θ from horizontal, there will be a constant force of sin(θ) * g * m (mass) downhill.  How much energy does it take to climb the incline a) slowly and b) faster?  Do you agree or not that climbing the incline very slowly can be done with a very small amount of energy?

--- End quote ---

We are talking about two very different things here. Power and energy are not the same thing.
But your analogy is good for you to consider.
How much energy will depend on the distance you need to travel uphill and the weight of the vehicle.
But think a bit more between this analogy and the wind with no wind meaning no gravity tho is not a perfect analogy as you will have gravity as you start to move if it is to compare with wind drag.

In any case all those bicycle calculators are wrong so this is a very widespread problem.
bdunham7:

--- Quote from: electrodacus on December 16, 2021, 12:10:17 am ---We are talking about two very different things here. Power and energy are not the same thing.

--- End quote ---

Have I said they were?  Energy = power * time, it also equals force * distance.  From that you can get that power = force * speed.


--- Quote ---How much energy will depend on the distance you need to travel uphill and the weight of the vehicle.

--- End quote ---

Um, yeah.  So for a given weight, you agree that if I go uphill a certain distance, I've put in a specific amount of energy?  And thus if I do that more slowly, I can use less power but for more time?


--- Quote ---not a perfect analogy as you will have gravity as you start to move if it is to compare with wind drag.

--- End quote ---

The inertial effects are there, but you can make them small by making the vehicle light.  And those effects are there in either the wind or the incline case.


--- Quote ---In any case all those bicycle calculators are wrong so this is a very widespread problem.

--- End quote ---

Really?  'Everyone' is wrong?  How far are  you willing to go with that?  You never doubt yourself even a little?  ::)
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