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Mess with your minds: A wind powered craft going faster than a tail wind speed.
PlainName:
--- Quote from: electrodacus on December 28, 2021, 07:21:15 pm ---
--- Quote from: dunkemhigh on December 28, 2021, 07:09:08 pm ---The real issue is your habit of diverting when it looks like something is going places. As I pointed out earlier, you're afraid that you might be shown to be wrong, so you do or say whatever is necessary to ensure we never get there.
I might remind you of the outstanding questions I asked which were designed to be small steps along such a route, but you appear to have figured there might be something in it and dropped it pretty quickly.
--- End quote ---
If there was some question you asked and I did not answered was likely because it was useless for me to do so and probably answered before.
Most important equation for any wind powered vehicle is the one showing the available wind power to the vehicle and of course if that is wrong you will get to wrong conclusions.
--- End quote ---
Wrong again. The aim was to end up with full agreement on both sides at the position where a single small thing, easily resolved, diverges. But due to your propensity to continually disappear off-piste it was necessary to get you to agree to each tiny step along the way. Which, of course, you now won't because you know you will stumble at the final hurdle.
electrodacus:
--- Quote from: Kleinstein on December 28, 2021, 07:31:43 pm ---
The wheel based versions can be interpreted both ways. It is just a question on which plane is identified as the ground or "wind". It is somewimes a bit trikcky to look at the same thing with different referene frames, but this a major point of doing though experiments.
Quite some wheeled models may show some slip stick like action, but this does not say that this is essentially for them to work, there are some with little visible slip stick.
The equation for the power from a sail vehicle is not used in the calculatoins for the backbird at all, as there is no sail involved, only an active driven prop. So there is no need and no sense in using the equation for a sail dirven vehicle.
Trying to use the equation to show that the blackbird vehickle would not work also makes little sense, as at best this would only show that with passive sails it would not work downwind. This is accepted and one would even get the some conclusion with the wrong (w-v)³ type form and the correct (w-v)²*v type form. However this does not proof that a different type of vehicle could no work - it just does not apply.
To proof that the backbrid vehicle would not work the way would be to calculate the power available from the wheels and the power needed to drive the prop. If the prop needs more power than the wheels can provide, it does not work (at least not without energy storage or other methods not inlcuded in the model). So this already quite close to the calculation in the video. Just need to calculate (e.g. get an upper / lower limit) the power needed to drive to prop, so kind of the other way around from a wind turbine, maybe include the Betz limit or a similar factor for the prop.
There may have been other before, but the first to bring up the mistake here was electrodacus.
The form with (wind speed - vehicle speed)2 only applies to vehicle speed < wind speed or would need to include the sign of (wind speed - vehicle speed), but at least it gets the low velocity range right.
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No you can not interpret something in both ways as only one can be correct and since the other one is impossible is clear witch one is correct even trough elimination.
And yes both energy storage and stick slip hysteresis is essential for them to work else they are just a locked gearbox as I showed by eliminating the slip of the generator wheel.
Wind can interact with a vehicle any vehicle only by pushing against an area thus all vehicle work the same as the sail vehicle.
That wind power equation is universal and applies to any wind powered vehicle including blackbird.
The correct form of that equation contains (w-v)3 or if you prefer (w-v)2 * (w-v)
I can prove this equation is true you will not be able to prove that wrong equation is true unless wind speed is zero.
gnuarm:
The equation 0.5 * air density * area * (wind speed - vehicle speed)3 may be the right equation, but for the wrong purpose.
In determining the power required to move the vehicle into (or away from) the wind, the above equation is wrong. It uses (wind speed - vehicle speed) as the speed of the applied force which would be talking about the power of the wind. No one is asking about the power from the wind. The question is the power applied to the VEHICLE to maintain a speed relative to the ground, "vehicle speed".
So the full equation for the power applied to the vehicle through the wheels is
0.5 * air density * area * (wind speed - vehicle speed)² * vehicle speed
It's very simple. You need to apply the right equation to the right purpose. This equation tells you how much power is needed to move the vehicle. I don't know for sure what the other equation is telling you. It probably includes the power lost in turbulence and all the hard to calculate effects when trying to calculate turbulent air flow. Many PhDs have been earned in that field.
Listen and learn son... listen and learn.
PlainName:
--- Quote ---... may be the right equation, but for the wrong purpose
--- End quote ---
Reminds me of (jump to 1:21):
electrodacus:
--- Quote from: gnuarm on December 28, 2021, 08:19:33 pm ---The equation 0.5 * air density * area * (wind speed - vehicle speed)3 may be the right equation, but for the wrong purpose.
In determining the power required to move the vehicle into (or away from) the wind, the above equation is wrong. It uses (wind speed - vehicle speed) as the speed of the applied force which would be talking about the power of the wind. No one is asking about the power from the wind. The question is the power applied to the VEHICLE to maintain a speed relative to the ground, "vehicle speed".
So the full equation for the power applied to the vehicle through the wheels is
0.5 * air density * area * (wind speed - vehicle speed)² * vehicle speed
It's very simple. You need to apply the right equation to the right purpose. This equation tells you how much power is needed to move the vehicle. I don't know for sure what the other equation is telling you. It probably includes the power lost in turbulence and all the hard to calculate effects when trying to calculate turbulent air flow. Many PhDs have been earned in that field.
Listen and learn son... listen and learn.
--- End quote ---
For a wind only powered vehicle the most important equation is the one that provides you with the answer to how much wind power is available to the vehicle.
The correct one is (if you prefer to be written like this)
0.5 * air density * area * (wind speed - vehicle speed)² * (wind speed - vehicle speed)
This is provable both in theory and in practice.
I think swimming in a river was a good example but you can think on a boat on a river or a submarine in a river.
Think about the power you need to just stay still relative to ground.
Air is not different it is a fluid same as water.
Or you can imagine balls hitting the vehicle.
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