Author Topic: Mess with your minds: A wind powered craft going faster than a tail wind speed.  (Read 147415 times)

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Offline IanB

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Not according to this: https://www.omnicalculator.com/sports/cycling-wattage
Its ~10W at 1km/h vs ~300W at 36km/h

That's a nice calculator. A screen grab is attached below.
 

Offline electrodacus

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The relative wind speed produces, as you say, the same force.  That force, multiplied by the speed of the bicycle, is the power required.  The power required is not the same in each case.


Sorry to say but that is complete nonsense.  Not quite sure where do you get this sort of intuition.
A bicycle as far as I know without the brakes applied will roll backwards (unless you have some sort of special bicycle that will not allow that).
So just sitting still not pedaling you will act like a 0.5m^2 sail (may be less depending on your position on the bike but we will use this round number).
A sail of that size in 35km/h = 9.72m/s will provide an equivalent power of 0.5 * 1.2 * 0.5 * 9.72^3 = 275.5W
So if you want to drive upwind at 1km/h in a 35km/h headwind you will need to provide 0.5 * 1.2 * 0.5 * 10^3 = 300W
Bicycles are fairly efficient so if you ignore the rolling resistance and small frictions between pedals and wheels you need to provide 300W to maintain 1km/h with a constant 35km/h headwind.

Have you ever used a bicycle or pedaled upwind ? It is the same principle as driving on an incline. Maybe it is not that windy where you live.
How about ever being in a river and trying to move upstreem vs downstreem.  Curious if any of you ever left the house :)

Offline electrodacus

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That's a nice calculator. A screen grab is attached below.

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.

Offline thm_w

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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.

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.

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tops    0.408, hoods    0.324, drops    0.307, aerobars    0.2914
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Online BrianHGTopic starter

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You need 300W to cycle at 36km/h with no wind and also 300W to cycle at 1km/h with a 35km/h head wind.

Not according to this: https://www.omnicalculator.com/sports/cycling-wattage
Its ~10W at 1km/h vs ~300W at 36km/h
Most of that excess power difference is due to rubber tires on asphalt which is really affected by tire pressure.
I know that over-inflated 125psi high pressure narrow racing tires take half the effort compared having the same tires inflated to 80psi.  Even worse compared to fat underinflated mountain-bike tires.

Like a train, if your bike had metal wheels driving on a flat steel beam, then wind preasure would be more dominating.

Also, the wattage in that calculator, it that the human muscle exertion's calorie burn, or torque at the pedals?

Yes, the wind is still a major factor as it also pushes on every moving surface.
 

Offline electrodacus

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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.

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

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 :)

Offline electrodacus

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OK :) I needed to have fun so apparently a human has no problem pedaling upwind at 1km/h with headwind of 230km/h
1350599-0

Online bdunham7

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Sorry to say but that is complete nonsense.  Not quite sure where do you get this sort of intuition.

Pro tip:  it isn't intuition!

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

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?
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline electrodacus

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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?

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.
« Last Edit: December 16, 2021, 12:12:05 am by electrodacus »
 

Online bdunham7

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We are talking about two very different things here. Power and energy are not the same thing.

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

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

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?

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

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.

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

Really?  'Everyone' is wrong?  How far are  you willing to go with that?  You never doubt yourself even a little?  ::)
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 
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Offline thm_w

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Most of that excess power difference is due to rubber tires on asphalt which is really affected by tire pressure.
I know that over-inflated 125psi high pressure narrow racing tires take half the effort compared having the same tires inflated to 80psi.  Even worse compared to fat underinflated mountain-bike tires.

Like a train, if your bike had metal wheels driving on a flat steel beam, then wind preasure would be more dominating.

Definitely not half the effort for slightly higher inflated tires.
The difference in rolling resistance for 100 vs 120psi on GP5000 tires at 29km/h is ~0.7W: https://www.bicyclerollingresistance.com/road-bike-reviews/continental-grand-prix-5000-2018
So 80 vs 125psi would be ~3W at most (10-13W total).

Sure fat mountainbike tires will be worse, but, calculator is not using them.


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Also, the wattage in that calculator, it that the human muscle exertion's calorie burn, or torque at the pedals?

When we talk about wattage on a bike, its power going into the pedals, not humans actual watt output, which would be much higher and vary depending on the individual.

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Yes, the wind is still a major factor as it also pushes on every moving surface.

Yes, if you can find another way to calculate that power, can post it.
If we use a wind turbine calculator its about 20W, but, no idea if that is relevant here.


OK :) I needed to have fun so apparently a human has no problem pedaling upwind at 1km/h with headwind of 230km/h
(Attachment Link)

Keep in mind 300W is not "no problem" for most people, its a lot of effort.
« Last Edit: December 16, 2021, 12:53:22 am by thm_w »
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Offline electrodacus

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OK :) I needed to have fun so apparently a human has no problem pedaling upwind at 1km/h with headwind of 230km/h
(Attachment Link)

Keep in mind 300W is not "no problem" for most people, its a lot of effort.

300W is within most humans capabilities now some in better shape can sustain that for much longer than others.
Now just consider that is a fit person and can sustain those 300W. Do you know what 230km/h sustain speed means ?
That person even if tied to the ground will have the meat removed from the bones.


230km/h is about 143mph not gust sustained.
Anyone that builds such an online calculator should test the extremes to see if it makes sense and if not he will be able to realize something is wrong.
Just notice you are Canadian so you know what km/h are.

Offline electrodacus

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Let me improve the explanation (maybe I make it worse but I want to try).

You have one of those 40% propeller based wind turbines and you put one of those on a vehicle and say swept area is 1m^2 just for simplicity.

In 10m/s wind while the turbine is stationary it will produce  0.5 * 1.2 * 1 * 10^3 * 0.4 = 240W
Now say there is no wind but you drive with the turbine on top of your vehicle at 10m/s (vehicle speed no wind speed).
Will the turbine not produce the same 240W ?
If not why not ? 

Online bdunham7

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Do you know what 230km/h sustain speed means ?
That person even if tied to the ground will have the meat removed from the bones.

So how do people go that fast on motorcycles without being defleshed?  It's a lot of wind and the turbulence might be tough on a bicycle, but if you were on a heavy, stable pedal-driven machine with approximately the frontal area of an upright rider you could indeed pedal into a 230km/h wind.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline electrodacus

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Do you know what 230km/h sustain speed means ?
That person even if tied to the ground will have the meat removed from the bones.

So how do people go that fast on motorcycles without being defleshed?  It's a lot of wind and the turbulence might be tough on a bicycle, but if you were on a heavy, stable pedal-driven machine with approximately the frontal area of an upright rider you could indeed pedal into a 230km/h wind.

People on a motorcycle are shielded by the motorcycle body there is no 0.5m^2 of human exposed to those speeds.

Offline IanB

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

You guys do realize we are dealing with a troll here, right?

Have you observed that our friend disagrees with, or contradicts, every statement made in this thread, however basic, and finds a reason to reject every experimental result and every external authority?

Nobody could disagree with 100% of all points made, without doing it deliberately. Every normal person would have at least some points of agreement.
 

Offline Brumby

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

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

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

You guys do realize we are dealing with a troll here, right?
It's just about impossible to consider any other alternative.  Even the Dunning-Kruger explanation is at a reach.

Quote
Have you observed that our friend disagrees with, or contradicts, every statement made in this thread, however basic, and finds a reason to reject every experimental result and every external authority?
Reason?  Most of the time it seems to be a simple statement of "that is wrong" - with little, if any, valid argument.

Quote
Nobody could disagree with 100% of all points made, without doing it deliberately. Every normal person would have at least some points of agreement.
Looking at it from the reverse angle - that's the magic of lying/misdirecting properly.  Have just a taste of accurate bits mixed up in a soup of ignorance.  Then you will be greeted with indignation about the "accurate bits" when you were actually challenging the crap.


I have little interest in correcting our recalcitrant as they aren't interested in proper understanding - but I'm having more fun watch how they dodge the discussion points.

With their clumsy attempts at misdirection and mathematical torture, I keep wondering if they had a failed career as a magician.
« Last Edit: December 16, 2021, 02:58:04 am by Brumby »
 

Offline electrodacus

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Nobody could disagree with 100% of all points made, without doing it deliberately. Every normal person would have at least some points of agreement.

If there is something I agree with why will I need to comment on that ?
The thing I disagree with merits the most attention.

I made those points clear

No vehicle without an external energy source or energy storage device can exceed wind speed direct down wind.
I showed the correct equation for wind power that relates to such a vehicle 0.5 * air density * area * (wind speed - vehicle speed)^3

I was thinking that giveing numerical examples will help but it seems nobody is shocked by driving against wind speed on a bicycle in 230km/h = 64m/s head winds.
0.5 * 1.2 * 0.5 * (64)^3 = 78.6kW of drag with just 0.3kW on input power.
How much more extreme you need the values to be in order to seems shocking.

Offline Psi

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No vehicle without an external energy source or energy storage device can exceed wind speed direct down wind.

Then your argument has nothing to do with blackbird, you're trying to argue against the accepted scientific facts about sailing boats.

The fact that the boat achieves sailing directly downwind faster than the wind from point A to B through a series of indirect zig-zags is irrelevant, since the length of each zig/zag has no effect on mechanism causing faster than wind travel. 
If the sail boat could change direction in an instant with no time needed to stop, rotate and move the sails, then it could move downwind faster than the wind through a series of zig-zags that were so tiny that they were imperceptible and it would, in effect, be a straight line downwind faster than the wind.

« Last Edit: December 16, 2021, 08:23:50 am by Psi »
Greek letter 'Psi' (not Pounds per Square Inch)
 

Online BrianHGTopic starter

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Most of that excess power difference is due to rubber tires on asphalt which is really affected by tire pressure.
I know that over-inflated 125psi high pressure narrow racing tires take half the effort compared having the same tires inflated to 80psi.  Even worse compared to fat underinflated mountain-bike tires.

Like a train, if your bike had metal wheels driving on a flat steel beam, then wind preasure would be more dominating.

Definitely not half the effort for slightly higher inflated tires.
The difference in rolling resistance for 100 vs 120psi on GP5000 tires at 29km/h is ~0.7W: https://www.bicyclerollingresistance.com/road-bike-reviews/continental-grand-prix-5000-2018
So 80 vs 125psi would be ~3W at most (10-13W total).

Sure fat mountainbike tires will be worse, but, calculator is not using them.
The resistance drop on under inflated tires tends towards an exponential curve, not linear and it also depends on the weight of the driver.  I used to be 250lb, an 80psi tire was mushed close to the rip and believe me, I was adding a good additional 50-75 watts just to maintain 25km/h compared to 120psi tires at that weight.
 

Offline Kleinstein

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I showed the correct equation for wind power that relates to such a vehicle 0.5 * air density * area * (wind speed - vehicle speed)^3
That is the power theoretical available to a wind turbine on the vehicle, but not the power needed to more the vehicle. So a "correct" formular. but for a different problem.

0.5 * 1.2 * 0.5 * (64)^3 = 78.6kW of drag with just 0.3kW on input power.
How much more extreme you need the values to be in order to seems shocking.
I am quite shocked by this result - not by the number, but by the units:  the drag is a force and not a power ! :horse:
 

Offline jonovid

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the earth is moving through space and spinning so how are we not ripped apart and flung into the sky by centrifugal forces.
as what we stand on is not static.  :-//
Hobbyist with a basic knowledge of electronics
 
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Online BrianHGTopic starter

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Ok, give me a vote to go ahead and flip 'electrodacus' head this weekend making him convince himself that a wind powered craft going faster than a tail wind speed with his own logic...

How many here would like to see that happen?
 

Offline Brumby

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Go for it.
 

Offline Labrat101

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I second it . Go for it ..
Please record it . We need a good  :-DD:horse:
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