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Mess with your minds: A wind powered craft going faster than a tail wind speed.
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bdunham7:

--- Quote from: electrodacus on September 03, 2021, 02:01:17 am ---I will make this problem as a reply to all of you and even do the calculation for you just let me know if I'm wrong.

Start conditions:
Wind speed 0m/s
Vehicle speed 0m/s
Vehicle mass 1kg
Available energy 10Ws
Wheel efficiency 90%
Propeller efficiency 70%

So vehicle will end up with 9Ws of Kinetic energy if energy is used to power the wheel and 7Ws if propeller is used.
Thus you probably agree that using wheel for propulsion is best option thus 9Ws is kinetic energy and vehicle is at 4.24m/s

Now at this point with vehicle at 4.24m/s will there be any logic in taking energy from the wheel and putting in to propeller ?
I hope you agree it will make no sense.
Now let say same conditions with vehicle at 4.24m/s but now there is a wind speed of 2m/s in same direction as the vehicle.
Will this change anything ? Will it make sense to take energy from the wheel and power the propeller ?
If your answer is yes please provide the calculation showing that vehicle can increase the current 9Ws kinetic energy using that 2m/s wind.

--- End quote ---

OK, that is easy enough.  Assuming your wheel generator has the same 90% efficiency and the propeller 70%, load the generator so that there is a 1N force (backwards) on the car.  I can't be more detailed because I don't know the radius of the wheel, but that won't matter. ( 1N * 4.24m/s * 0.9 efficiency ) = 3.816W.  Now if you take the 3.816W and use the propeller to generate a force, you will get a larger force because...power is force * speed and you don't have to generate that force at 4.24m/s, but rather 2.422.24m/s, the airspeed that the propeller sees.  So the force generated will be (3.816W * 0.7 efficiency / 2.422.24m/s) = 1.1041.1925N.  The net force (propeller force minus wheel force) will then be 0.1925N and the vehicle will accelerate at 0.1925m/s2.  Thus the vehicle will continue to accelerate even though it is already travelling at over twice the wind speed.  In this example, the propeller is providing 2.6712W of power, which is obviously less than is taken out at the wheels, but the wind provides (1.1925 * 2m/s) = 2.028 2.385W of additional power for a total of 4.6992 5.0562W, which is more than is being taken out at the wheels, so a net gain of (4.69925.0562- 4.24) = 0.8162W.  And then you can check the math to make sure that the net power I just gave you results in the acceleration stated--which is why I had to go back and fix my numerical transpositions.

But I think I've made an additional error, so wait a bit.

Edit:  Should be all good now.  If not, someone point out the errors.
electrodacus:

--- Quote from: bdunham7 on September 03, 2021, 03:14:19 am ---
--- Quote from: electrodacus on September 03, 2021, 02:01:17 am ---I will make this problem as a reply to all of you and even do the calculation for you just let me know if I'm wrong.

Start conditions:
Wind speed 0m/s
Vehicle speed 0m/s
Vehicle mass 1kg
Available energy 10Ws
Wheel efficiency 90%
Propeller efficiency 70%

So vehicle will end up with 9Ws of Kinetic energy if energy is used to power the wheel and 7Ws if propeller is used.
Thus you probably agree that using wheel for propulsion is best option thus 9Ws is kinetic energy and vehicle is at 4.24m/s

Now at this point with vehicle at 4.24m/s will there be any logic in taking energy from the wheel and putting in to propeller ?
I hope you agree it will make no sense.
Now let say same conditions with vehicle at 4.24m/s but now there is a wind speed of 2m/s in same direction as the vehicle.
Will this change anything ? Will it make sense to take energy from the wheel and power the propeller ?
If your answer is yes please provide the calculation showing that vehicle can increase the current 9Ws kinetic energy using that 2m/s wind.

--- End quote ---

OK, that is easy enough.  Assuming your wheel generator has the same 90% efficiency and the propeller 70%, load the generator so that there is a 1N force (backwards) on the car.  I can't be more detailed because I don't know the radius of the wheel, but that won't matter. ( 1N * 4.24m/s * 0.9 efficiency ) = 3.816W.  Now if you take the 3.816W and use the propeller to generate a force, you will get a larger force because...power is force * speed and you don't have to generate that force at 4.24m/s, but rather 2.422.24m/s, the airspeed that the propeller sees.  So the force generated will be (3.816W * 0.7 efficiency / 2.422.24m/s) = 1.1041.1925N.  The net force (propeller force minus wheel force) will then be 0.11925N and the vehicle will accelerate at 0.11925m/s2.  Thus the vehicle will continue to accelerate even though it is already travelling at over twice the wind speed.  In this example, the propeller is providing 2.6712W of power, which is obviously less than is taken out at the wheels, but the wind provides (1.1925 * 2m/s) = 2.028 2.385W of additional power for a total of 4.6992 5.0562W, which is more than is being taken out at the wheels, so a net gain of (4.69925.0562- 4.24) = 0.8162W.  And then you can check the math to make sure that the net power I just gave you results in the acceleration stated--which is why I had to go back and fix my numerical transpositions.

But I think I've made an additional error, so wait a bit.

Edit:  Should be all good now.  If not, someone point out the errors.

--- End quote ---

Good effort but you forgot something super important. What is the kinetic energy of the vehicle before and after you did the break ?
Say you maintain that 3.816W break for one second now the vehicle kinetic energy is reduce by 3.816Ws
Now you apply 3.816W * 0.7 = 2.671W for one second and you can see you end up with lower kinetic energy than you started with.
And is irrelevant if you do that for 1 full second or a 1ms or even 1us the end result is that vehicle speed will be reduced.
The wind can not provide anything unless you refer to stored energy. As long as wind speed is lower than vehicle speed there is nothing to gain from that.

Forces have no role here since all you care is vehicle kinetic energy change. If you end up with lower kinetic energy then vehicle has slowed down.
Do you see a difference in kinetic energy gain between a vehicle traveling at 2.24m/s with no wind and one traveling at 4.24m/s and 2m/s wind when power is applied to the propeller ? 
bdunham7:

--- Quote from: electrodacus on September 03, 2021, 04:56:32 am ---Good effort but you forgot something super important.

--- End quote ---

You're right, I forgot that you're a stone headed cretin that clearly can't comprehend any of this.  I give up.  And I don't give up easily.


--- Quote ---Forces have no role here

--- End quote ---

OK, in a universe where forces have no role in basic mechanics, then I have nothing to offer.  My entire education was a complete waste.
electrodacus:

--- Quote from: bdunham7 on September 03, 2021, 05:09:37 am ---OK, in a universe where forces have no role in basic mechanics, then I have nothing to offer.  My entire education was a complete waste.

--- End quote ---

To be honest education of most people seems to have been a waste of time.  Only knowing the formula and not knowing how to apply or what result you should expect is sort of pointless.
If you think you are frustrated try to be in my place where almost nobody understand how basic physics works including people teaching others.

If you want to know if vehicle will increase or decrease in speed you do not need to be concerned with forces just with power. Breaking power and propulsion power. As long as breaking power is more than propulsion power vehicle will slow down unless there is something else that can offer propulsion.
That something else could be wind but only if wind speed is higher than vehicle speed when direction is exactly the same or as it is in this particular case earlier stored energy.

What if wind speed was 6.24m/s so higher wind speed than vehicle speed ? Based on how you applied the formula this will be a fairly bad thing.
Kleinstein:

--- Quote from: electrodacus on September 03, 2021, 12:08:21 am ---
--- Quote from: Kleinstein on September 02, 2021, 10:26:09 pm ---
--- Quote from: electrodacus on September 02, 2021, 09:18:58 pm ---
Blackbird or the Zeppelin can not use any energy from the tail wind when vehicle speed is above that tail wind speed.


--- End quote ---
The red part is repeated over and over again as an argument, but it is plain wrong. Not so obvious, but still wrong.

--- End quote ---

The red part is not wrong and there is no trick to make that right as if it was to be right it will violate the conservation of energy.
You always mention force when force has nothing to do with conservation of energy.
You only care about power and since propeller is powered by the wheel generator the power you take from the wheel is the most in ideal case you put in the propeller. In real world propeller output may be just 70% of what is available at the wheel so without stored energy the vehicle could never exceed wind speed.
Because of this misconception you also think that the wheel only vehicle in my diagram can move from left to right when that is not possible and you will never be able to prove something impossible.

--- End quote ---
You missed / cut out the more important point: for the dicussion the red sentence in question is not an agument, but part in question.
This has nothing to do with physics but plain logic. Using the claim you want to prove is not working.

Forces are importand to calculate power and thus to get the balance of power right.
The wind / treadmill are power sources and you have to include there power in the energy balance.
The power available to the (generator-) wheel is not just coming from the powered wheel / prop, but also from the treadmill / wind.

The proof that it can work is allready there in the tread several times:


--- Quote from: Kleinstein on September 02, 2021, 10:26:09 pm ---The result may be confusing, but the math is simple:
The power needed by the prop to generate a fixed amount of thrust is independent of the wind speed.
The power the generator can produce is force times speed. The speed is wind-speed plus a little from the movement in the air.

Plot the two in a graph (X= speed relative to ground, Y = power)  and the result is clear:
Given enough wind speed the generator can produce more power than the prop needs to pull it.

--- End quote ---
:horse:

The power from the wind is there as the wind speed contribution to the speed of the vehicle. For a start you can even neglect the power of the prop going back to the wheels.
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