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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: bdunham7 on December 17, 2021, 10:59:11 pm ---
How would that be violated by a sail dissipating all or most of the wind energy and only transferring a small portion of that energy to the vehicle?

--- End quote ---

I was talking about the wrong explanation of how blackbird works and that will be indefinitely above wind speed (not possible).
Under wind speed you can drive as much as you want as you have access to wind power.
If a sail vehicle is less efficient due to friction losses then it will just accelerate a bit slower but you will need to have horrible wheel friction to take 1.66 seconds to get to 1m/s in 10m/s winds with 1m^2 sail and 100kg mass.



--- Quote from: bdunham7 on December 17, 2021, 10:59:11 pm ---The formula used earlier that seems to be widely accepted as correct (the drag equation) is also exponential and doesn't diverge to infinity as the vehicle speed approaches zero.  In fact, it doesn't matter whether the vehicle is stationary or moving beyond how that changes the relative speed of the wind and vehicle. 

So now you are positing some new drag or sail formula that would give you an extremely high pressure and thus an extremely high initial acceleration for a 10m/s wind and a stationary vehicle.  So what would the pressure and acceleration be if you had an 11m/s wind and a vehicle moving at 1m/s?  Would that be different?

What experimental tests are you referring to?

--- End quote ---

I'm very confident that online calculator that I liked is accurate in describing pressure on either a wall or a sail directly downwind.
It is also similar to how pressure differential looks on a axial fan the graph from wikipedia.
As mentioned no matter the method used if implemented correctly will provide the same result and using the results from that calculator for pressure behind the sail (pressure is variable decreasing as you get away from the sail/wall and it makes perfect sense for a compressible fluid).
If you use that variable pressure then how fast the vehicle accelerate will look exactly the same as the one predicted by my formula where wind power and kinetic energy where used.
Both formula for wind power and kinetic energy where the correct ones so the result not only look correct they match reality if you were to add the friction.
The thing is even in that ideal setup a direct downwind vehicle can not exceed wind speed without energy storage.
Also as an extra result no vehicle can also travel at any speed direct upwind unless it also uses energy storage and a trigger mechanism like stick slip hysteresis.  Not only that is the conclusion for correct use of equations but also I demonstrated that in practice.
fourfathom:

--- Quote from: electrodacus on December 18, 2021, 12:45:43 am ---
--- Quote from: dunkemhigh on December 17, 2021, 10:41:06 pm ---
--- Quote ---That energy storage device will be charged during the initial acceleration phase
--- End quote ---

Where is the acceleration phase on the treadmill?

--- End quote ---

I think I explained that before here but it is when you put the vehicle on the treadmill.

--- End quote ---

When you put the vehicle on the treadmill and hold it in place, this is equivalent to the vehicle traveling downwind exactly at windspeed [  (wind speed - vehicle speed) = 0 in your equation ]  So according to you, there's no energy to be stored -- and you're right, at least about that.    But when you let go, the vehicle instantly rolls forward, faster than the wind.
electrodacus:

--- Quote from: fourfathom on December 18, 2021, 01:08:09 am ---
When you put the vehicle on the treadmill and hold it in place, this is equivalent to the vehicle traveling downwind exactly at windspeed [  (wind speed - vehicle speed) = 0 in your equation ]  So according to you, there's no energy to be stored -- and you're right, at least about that.    But when you let go, the vehicle instantly rolls forward, faster than the wind.

--- End quote ---

There is maybe a second or two when you touch the vehicle to treadmill until all energy storage devices are fully charged up that means all wheels get to same speed as the treadmill the propeller gets to nominal speed and the pressure differential is created.
For that small treadmill model we are talking about 0.25 to maybe 1Ws (1J) of total stored energy.
The kinetic energy needed for that vehicle to accelerate from zero (when you release) up to 1m/s (never got that fast in the video) is 0.5 * 0.5kg * 1m/s^2 = 0.25Ws (0.25J) basically nothing is needed to be stored in pressure differential to be able to accelerate that small vehicle to 1m/s even to 2m/s will not take much and vehicle was only demonstrated for way lower speed.  The treadmill is just to short to show the vehicle accelerating to whatever max speed it is designed for and then show also how it will slow down (that will take again as much as to get there).
fourfathom:

--- Quote from: electrodacus on December 18, 2021, 01:28:14 am ---
--- Quote from: fourfathom on December 18, 2021, 01:08:09 am ---
When you put the vehicle on the treadmill and hold it in place, this is equivalent to the vehicle traveling downwind exactly at windspeed [  (wind speed - vehicle speed) = 0 in your equation ]  So according to you, there's no energy to be stored -- and you're right, at least about that.    But when you let go, the vehicle instantly rolls forward, faster than the wind.

--- End quote ---

There is maybe a second or two when you touch the vehicle to treadmill until all energy storage devices are fully charged up that means all wheels get to same speed as the treadmill the propeller gets to nominal speed and the pressure differential is created.
For that small treadmill model we are talking about 0.25 to maybe 1Ws (1J) of total stored energy.
The kinetic energy needed for that vehicle to accelerate from zero (when you release) up to 1m/s (never got that fast in the video) is 0.5 * 0.5kg * 1m/s^2 = 0.25Ws (0.25J) basically nothing is needed to be stored in pressure differential to be able to accelerate that small vehicle to 1m/s even to 2m/s will not take much and vehicle was only demonstrated for way lower speed.  The treadmill is just to short to show the vehicle accelerating to whatever max speed it is designed for and then show also how it will slow down (that will take again as much as to get there).

--- End quote ---

What stored energy is there when the vehicle is stationary?  You claim that there is zero available energy when the relative windspeed is zero, so there's nothing to store.  By your thinking, all the storage occurs when the vehicle is traveling slower than windspeed.

So, how long would we need to hold that vehicle stationary for all that "stored energy" to dissipate?  And why do we care about max speed?  Isn't any speed beyond wind speed proof that it works?

Your model, and your understanding, is flawed.
electrodacus:

--- Quote from: fourfathom on December 18, 2021, 01:43:57 am ---
What stored energy is there when the vehicle is stationary?  You claim that there is zero available energy when the relative windspeed is zero, so there's nothing to store.  By your thinking, all the storage occurs when the vehicle is traveling slower than windspeed.

So, how long would we need to hold that vehicle stationary for all that "stored energy" to dissipate?  And why do we care about max speed?  Isn't any speed beyond wind speed proof that it works?

Your model, and your understanding, is flawed.

--- End quote ---

What do you mean by stationary vehicle ? Vehicle before it touches the treadmill ? if yes then of course there is no stored energy.
There is zero wind power when vehicle speed equals wind speed but blackbird and by extension the treadmill model have store energy that they can use to accelerate past wind speed.
The stored energy will not be used unless you release the vehicle so same amount of store energy will be present no matter how long you keep the vehicle in place. Once you let go it will start to use that stored energy and you do not want to interact with vehicle in any way after that just let it run on that stored energy and you will be able to see how acceleration rate drops to the point that it will start to decelerate down below wind speed.

Vehicle works as shown. I never claimed that blackbird either the large one or the treadmill model is not working as shown in tests. What I insist on is that current explanation of why is works is completely wrong.
Vehicle can not be powered as claimed by wind when above wind speed directly down wind but it is powered by store energy and since this stored energy is limited and there is friction the vehicle will be able to get to some peak speed and then start to slow down as there is no longer any stored energy and it will slow down way below wind speed.

It is just clear to me that energy storage is not something people think to much about but it is as prevalent and important as friction in real world.
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