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

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Kleinstein:
The motor power is given by force times velocity seen by the motor. The velocity seen by the motor is w-v, as the indicated speed in the graphics.
So this gives: P_motor = F_M * (W-V). For the steady state with no extra friction F_M = F_G.
A positive value would be power generated by the motor and one may want to set this to 0 instead. A negative power is actual power send to the motor.

The net power or excess power available to overcome friction is then P_net = P_in + P_motor.
So for the 3 example cases this would be 30 W (or 10 W if the motor is not allowed to generate power), 10 W and 6 W of net power.

IanB:

--- Quote from: electrodacus on December 11, 2021, 08:39:38 pm ---
--- Quote from: Kleinstein on December 11, 2021, 09:10:25 am ---The 3 examples really show a lack of understanding.

--- End quote ---

Are you saying that wrong formula was applied ?
If so please provide yours for all 3 cases.

--- End quote ---

You are wasting your time arguing with formulas, when actual, real-world experiments prove the case. All of us know we can build a craft that will run faster than the wind indefinitely, and all of us know we can build a craft that will run directly into the wind.

Since this is a fact that is provable by experiment, it doesn't really matter that you keep trying to say that it is "impossible". It is like trying to argue that it is impossible for airplanes to fly, when airplanes are flying over your head.

We don't need to prove anything to you, because we know already what the facts are. You are the one who needs to figure out for yourself how these things work. It is not our problem to convince you.

electrodacus:

--- Quote from: Kleinstein on December 11, 2021, 09:02:38 pm ---The motor power is given by force times velocity seen by the motor. The velocity seen by the motor is w-v, as the indicated speed in the graphics.
So this gives: P_motor = F_M * (W-V). For the steady state with no extra friction F_M = F_G.
A positive value would be power generated by the motor and one may want to set this to 0 instead. A negative power is actual power send to the motor.

The net power or excess power available to overcome friction is then P_net = P_in + P_motor.
So for the 3 example cases this would be 30 W (or 10 W if the motor is not allowed to generate power), 10 W and 6 W of net power.

--- End quote ---

Motor is what is says a motor not a generator. The back wheel is always powered by the front wheel that is the generator.
Same vehicle is used in all 3 case the vehicle construction can not be changed and will be the same for all 3 cases.

If I understand right your answer is net power acting against vehicle is always positive and this are the values.
A) 10W
B) 10W
C) 6W

Is that correct ?

It seems that you agree in steady state (referenced to vehicle) FG = FM due to Newton third law.
Without any connection between generator and motor both generator and motor will free spin with no friction (all ideal case).
You can decide what power you want to take out of generator and send to motor in my example I used 10W
Then if 100% of that generated power is sent to the motor Pout will always equal Pin plus or minus some extra depending on speed and direction of the wind treadmill.

To make it easier to replay I will post again the photo with the 3 cases

electrodacus:

--- Quote from: IanB on December 11, 2021, 09:06:32 pm ---You are wasting your time arguing with formulas, when actual, real-world experiments prove the case. All of us know we can build a craft that will run faster than the wind indefinitely, and all of us know we can build a craft that will run directly into the wind.

Since this is a fact that is provable by experiment, it doesn't really matter that you keep trying to say that it is "impossible". It is like trying to argue that it is impossible for airplanes to fly, when airplanes are flying over your head.

We don't need to prove anything to you, because we know already what the facts are. You are the one who needs to figure out for yourself how these things work. It is not our problem to convince you.

--- End quote ---

Yes real case for B will be different but there is a good reason for that.  The reason is energy storage plus stick slip hysteresis and I have the videos to demonstrate that is the case.
So you see the real experiment but do not understand why you have that result.
No vehicle can exceed wind speed directly down wind or travel directly upwind without energy storage.
They are different case with direct upwind using small capacity energy storage and stick slip hysteresis with charge discharge cycles of many times per second.
The direct down wind uses large capacity pressure differential energy storage and can last for a few minutes depending on design.
For direct upwind you can travel forever using those mini charge discharge cycles and stick slip hysteresis as you always have access to wind energy
For direct downwind you can only travel for a limited amount of time as while above wind speed you have no access to wind energy only stored energy in pressure differential.

Kleinstein:

--- Quote from: electrodacus on December 11, 2021, 10:00:43 pm ---
--- Quote from: Kleinstein on December 11, 2021, 09:02:38 pm ---The motor power is given by force times velocity seen by the motor. The velocity seen by the motor is w-v, as the indicated speed in the graphics.
So this gives: P_motor = F_M * (W-V). For the steady state with no extra friction F_M = F_G.
A positive value would be power generated by the motor and one may want to set this to 0 instead. A negative power is actual power send to the motor.

The net power or excess power available to overcome friction is then P_net = P_in + P_motor.
So for the 3 example cases this would be 30 W (or 10 W if the motor is not allowed to generate power), 10 W and 6 W of net power.

--- End quote ---

Motor is what is says a motor not a generator. The back wheel is always powered by the front wheel that is the generator.
Same vehicle is used in all 3 case the vehicle construction can not be changed and will be the same for all 3 cases.

If I understand right your answer is net power acting against vehicle is always positive and this are the values.
A) 10W
B) 10W
C) 6W

Is that correct ?

It seems that you agree in steady state (referenced to vehicle) FG = FM due to Newton third law.
Without any connection between generator and motor both generator and motor will free spin with no friction (all ideal case).
You can decide what power you want to take out of generator and send to motor in my example I used 10W
Then if 100% of that generated power is sent to the motor Pout will always equal Pin plus or minus some extra depending on speed and direction of the wind treadmill.

--- End quote ---

I don't agree with the red part: the net power is not acting against the vehicle - power has no geometric direction. A positive net power means there is power to spare, e.g. to turn on some lights or overcome friction. So not all power needs to be send to the motor in the steady state for the 3 cases shown. If all the power is send to the motor it would accelerate the vehicle and thus no longer the steady state.

The orange part is some-how self-contradicting, or I don't understand what it should mean: if all the power is send to the motor, Pout=P_motor= Pin and thus no net power.

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