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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: gnuarm on December 29, 2021, 03:51:59 am ---
Ok, so what is the equation for the power applied to a vehicle to maintain a constant speed into a constant headwind?  Lets simplify the messy bits and assume the force generated by the wind on the vehicle is
 
Fw = Kv * (wind speed + vehicle speed)2

Where Kv is an accumulation of all the factors that relate the force to the relative wind speed. 

So if Fw is the force required to maintain a speed of the vehicle, what is the equation for the power that is exerted on the vehicle to maintain the vehicle speed?

Now, forget wind.  Lets say there is a drag on the vehicle defined by

Fdrag = Kdrag * (vehicle speed)2

What is the power required to maintain the speed of this vehicle?

I bet $50 he won't answer this and ducks the question.  I suppose there's a chance he comes up with something amazingly convoluted.  Probably starts talking about driving the vehicle on a river bottom. 

I really can't believe this guy designs anything.  He must be pulling our legs.

--- End quote ---

It is quite simple. Power needed to counter drag will be

Fw * (wind speed + vehicle speed).

If there is no headwind then

Fdrag * (0 + vehicle speed)

So to give real numbers.
If vehicle speed is 20m/s it will require the same power to maintain speed as if vehicle is at 10m/s with a headwind of 10m/s (ignoring the difference in friction loss inside the vehicle and roiling resistance).

There is only one formula for all cases
0.5 * air density * area * (wind speed - vehicle speed)3

When you go against wind direction the vehicle speed is negative so (wind speed - (-vehicle speed)) thus basically (wind speed + vehicle speed)

gnuarm:

--- Quote from: electrodacus on December 29, 2021, 04:27:37 am ---
--- Quote from: gnuarm on December 29, 2021, 03:51:59 am ---
Ok, so what is the equation for the power applied to a vehicle to maintain a constant speed into a constant headwind?  Lets simplify the messy bits and assume the force generated by the wind on the vehicle is
 
Fw = Kv * (wind speed + vehicle speed)2

Where Kv is an accumulation of all the factors that relate the force to the relative wind speed. 

So if Fw is the force required to maintain a speed of the vehicle, what is the equation for the power that is exerted on the vehicle to maintain the vehicle speed?

Now, forget wind.  Lets say there is a drag on the vehicle defined by

Fdrag = Kdrag * (vehicle speed)2

What is the power required to maintain the speed of this vehicle?

I bet $50 he won't answer this and ducks the question.  I suppose there's a chance he comes up with something amazingly convoluted.  Probably starts talking about driving the vehicle on a river bottom. 

I really can't believe this guy designs anything.  He must be pulling our legs.

--- End quote ---

It is quite simple. Power needed to counter drag will be

Fw * (wind speed + vehicle speed).

If there is no headwind then

Fdrag * (0 + vehicle speed)

So to give real numbers.
If vehicle speed is 20m/s it will require the same power to maintain speed as if vehicle is at 10m/s with a headwind of 10m/s (ignoring the difference in friction loss inside the vehicle and roiling resistance).

There is only one formula for all cases
0.5 * air density * area * (wind speed - vehicle speed)3

When you go against wind direction the vehicle speed is negative so (wind speed - (-vehicle speed)) thus basically (wind speed + vehicle speed)

--- End quote ---

You ignored the rest of my post just as I expected you would.  if you looked at the calculations you would see that the force is only multiplied by the vehicle speed to get the power required to maintain speed.  But you don't want to admit that, so you ignored it.  That was my first prediction, that you would duck the question.

You are hopeless.  You know you are wrong, but refuse to discuss it in any meaningful way.  Silly rabbit.  Trix are for kids. 

Yeah, I do pity anyone depending on you for sound engineering.  I don't believe you even have a technical job.  How may quarters???

electrodacus:

--- Quote from: gnuarm on December 29, 2021, 04:41:39 am ---You ignored the rest of my post just as I expected you would.  if you looked at the calculations you would see that the force is only multiplied by the vehicle speed to get the power required to maintain speed.  But you don't want to admit that, so you ignored it.  That was my first prediction, that you would duck the question.

You are hopeless.  You know you are wrong, but refuse to discuss it in any meaningful way.  Silly rabbit.  Trix are for kids. 

Yeah, I do pity anyone depending on you for sound engineering.  I don't believe you even have a technical job.  How may quarters???

--- End quote ---

:) So I correct your mistake and you are saying that I ignored your post ?
You should do a test and see that your assumption is wrong.
You just believe the same absurd thing that those people that designed those online bicycle calculators.
Like 300W is plenty to bike at 1km/h against a 230km/h head wind.  People that say that is a possibility are just clueless.   

IanB:
OK, we are making progress here. We have established that university professors are getting it wrong. We have established that Wikipedia is getting it wrong. We have established that the bicycle power calculators are getting it wrong.

What now remains is to figure out where the physics textbooks are getting it wrong, then we can have them recalled and pulped, and replaced with corrected versions. It is astonishing how the whole world has been getting this wrong for so long.


--- Quote from: electrodacus on August 29, 2021, 05:14:49 am ---Unfortunately there are enough people that do not understand what conservation of energy really means and so with that there is a bad understanding of how the world works.
It seems the education system is failing in this regards.  I say this seeing university level physics professors getting this wrong.
--- End quote ---


--- Quote from: electrodacus on December 27, 2021, 01:10:09 am ---See this link and scroll down to air drag https://en.wikipedia.org/wiki/Bicycle_performance
You will find two equations

This is the same that I use for max wind power available.
And this

That is incorrect (you can not always expect much from wikipedia).
--- End quote ---


--- Quote from: electrodacus on December 27, 2021, 06:53:55 pm ---Here again the wrong formula https://en.wikipedia.org/wiki/Drag_(physics)


They add vehicle speed and wind speed for force part of the equation but not for the power part ?
How will that make any sense unless people just understand force but have no clue what power is.
That last therm also need to be vo+vw then result will be correct.

This can be tested relatively easy why is this not done at universities ? If they did this test they will realize their formula is just wrong and use the correct one.
--- End quote ---


--- Quote from: electrodacus on December 28, 2021, 08:50:26 pm ---There will always be people that do not understand some parts of physics and I will not get bothered by this particular problem if it was not such a wide spread misinformation involving science communicators and university professors.

--- End quote ---


--- Quote from: electrodacus on December 29, 2021, 04:50:01 am ---You just believe the same absurd thing that those people that designed those online bicycle calculators.
Like 300W is plenty to bike at 1km/h against a 230km/h head wind.  People that say that is a possibility are just clueless.

--- End quote ---

electrodacus:

--- Quote from: IanB on December 29, 2021, 05:57:44 am ---OK, we are making progress here. We have established that university professors are getting it wrong. We have established that Wikipedia is getting it wrong. We have established that the bicycle power calculators are getting it wrong.

What now remains is to figure out where the physics textbooks are getting it wrong, then we can have them recalled and pulped, and replaced with corrected versions. It is astonishing how the whole world has been getting this wrong for so long.

--- End quote ---

I had not seen any university professor getting this exact equation wrong but it looks like some just do not know the equation at all or think it is not relevant here while it clearly is.
Wikipedia and the few online bicycle calculators I checked (at least 3) all got this wrong.

What other proof do you want other than the correct equation next to wrong equation on Wikipedia presented as being the same thing but provide different results.
And also for the bicycle calculators what else will you want as proof other than to get the result that 300W is enough to bike at 1km/h against a 230km/h head wind.
I mean most any person can put out 300W at least for a few seconds and all you need is get some strong wind 80 to 100km/h is enough (no chance to ever see 230km/h) and try to pedal against that wind even for a minute at 1km/h
Even the 80km/h will require 3kW and not sure if anyone in the world can manage that.

I already posted this as evidence for those that never experienced high wind speeds and those are professionals in way better shape than most of us and they where not able to bike against 80km/h headwind that is about 60x milder (lower power) than a 230km/h wind


So how can anyone seeing this video say the online bike calculator is providing an accurate result ?

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