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Electroboom: How Right IS Veritasium?! Don't Electrons Push Each Other??

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electrodacus:

--- Quote from: dunkemhigh on July 07, 2022, 01:37:32 am ---
Completely irrelevant diversion. Settle on the equation and then you can think about values. You don't change things to suit the result you've already decided upon.

--- End quote ---

So you think that just providing a random (made up) equation was what I was looking for ?
I only asked for the equation that provides available wind power to vehicle in ideal case.

By adding the Pp you subtracted the power needed to supply the propeller and that is fine but is now less than available wind power.
To correct for this you decided that "wash speed" will reflect the output from the propeller but for conservation of energy to hold there will be a relation between Pp and wash speed so that Pw can never be higher than zero at wind speed.

It is you thinking that 100W put in to propeller can provide you with 101W in propulsion which is not possible.

Pp can not be higher than 0.5 * air density * area * (wind speed - vehicle speed)3
And similarly "wash speed" can not be larger than wind speed.
And the relation between the Pp and "wash speed" is so that wind power can never be higher at any vehicle speed than the original equation provides that means zero wind power when vehicle speed equals wind speed.

Keep in mind the above is true for the case where energy can not be stored (vehicle with no energy storage). Because I can already read you writing that Blackbird exceeds wind speed and that is true only because there is an energy storage device there called pressure differential and it is thanks to combination of propeller and compressible fluid.

PlainName:

--- Quote from: electrodacus on July 07, 2022, 02:05:11 am ---
--- Quote from: dunkemhigh on July 07, 2022, 01:37:32 am ---
Completely irrelevant diversion. Settle on the equation and then you can think about values. You don't change things to suit the result you've already decided upon.

--- End quote ---

So you think that just providing a random (made up) equation was what I was looking for ?

--- End quote ---

Not at all. I gave you what you asked for. What, exactly, is wrong with it?


--- Quote ---By adding the Pp you subtracted the power needed to supply the propeller and that is fine but is now less than available wind power.
--- End quote ---

What? The available wind power is the same - it hasn't disappeared.


--- Quote ---To correct for this you decided that "wash speed" will reflect the output from the propeller but for conservation of energy to hold there will be a relation between Pp and wash speed so that Pw can never be higher than zero at wind speed.
--- End quote ---

Mate, wind speed of what? The thrust is acting as a sail to the wind, so when the thrust is static against the wind (zero relative wind speed) the vehicle will be traveling faster. I know that's probably blown your mind, but that's how it could be. You need to work out the values to discover if it actually occurs, and without doing that you can't say.


--- Quote ---It is you thinking that 100W put in to propeller can provide you with 101W in propulsion which is not possible.
--- End quote ---

You're making things up: I have never suggested that. In fact I am saying right now you wouldn't get even that 100W out.

Further, you're mistakingly assuming that the thrust is providing ALL the motive force. It is not - the thrust could be really very teeny tiny.  A mere breath.

I've highlighted that so that when you skim this you might at least pause to read that bit and digest it.


--- Quote ---Pp can not be higher than 0.5 * air density * area * (wind speed - vehicle speed)3
And similarly "wash speed" can not be larger than wind speed.

--- End quote ---

Mate, you're the one that's saying that. Nowhere has there been a suggestion that the wash speed is large than the wind speed. In fact, as above, it is very VERY much less than the wind speed


--- Quote ---And the relation between the Pp and "wash speed" is so that wind power can never be higher at any vehicle speed than the original equation provides that means zero wind power when vehicle speed equals wind speed.

--- End quote ---

Oh, for crying out loud! Tell you what, why don't YOU come up with an euqation that covers the propeller turning and sucking power out of the wheels? It is there - you can SEE the damn thing turning in the video. You  KNOW the wheels turn it. Even if you think it works the other way (prop drive the wheels) it is happening, and yet your equation ignores it completely. So, write one that accounts for the prop.

I bet you can't, because what you're good at is cut'n'pasting stuff off t'web. That equation you posted was the best you could find to give power, but it is meaningless except for the exact situation where it ends up as zero. It tells you nothing else and doesn't apply to this situation.

So, write one that does apply, that does show the props effect. Even if it you think it works the wrong way (or not works) you can write the equation to show that, so do it. Shit or get off the loo.

electrodacus:

--- Quote from: dunkemhigh on July 07, 2022, 02:49:33 am ---So, write one that does apply, that does show the props effect. Even if it you think it works the wrong way (or not works) you can write the equation to show that, so do it. Shit or get off the loo.

--- End quote ---

I see that you get frustrated but important question is what is the available wind power to vehicle.
For ideal case (so best case scenario) that equation provides the wind power available to any wind powered vehicle driving directly downwind not just a simple sail based one.

What you do with that available wind power is your choice but if the vehicle does not have an energy storage device then it can not exceed wind speed
And if it has an energy storage device as it is the case with Blackbird then it can exceed wind speed even significantly but only for a limited amount of time proportional with the amount of stored energy.


To get back to a real world example the direct down wind powered vehicle with 1m2 equivalent area facing the wind the wind speed of 6m/s and vehicle speed of 3m/s total wind power ideal case is 16.2W

If you take that 16.2W from the wheels and say use it to supply an incandescent lamp the vehicle will no longer accelerate as all wind power will be used to supply the lamp.
So vehicle will no longer accelerate.
You can disconnect the lamp and vehicle will continue to accelerate using this 16.2W at that point dropping as vehicle speed increases. Now say vehicle speed is maybe 4m/s and you again connect that 16.2W lamp.
What will happen is that at 4m/s wind power available to vehicle is just 4.8W so the delta at that moment of 16.2 - 4.8W will be provided by the vehicle stored kinetic energy so vehicle will decelerate until will get again at the equilibrium point that 3m/s where wind power available to vehicle is equal exactly the 16.2W the lamp requires.

Now you can do whatever you want with the wind power available to vehicle but you will never be able to accelerate faster than a sail vehicle or exceed the wind speed unless you add an energy storage device.

So if all you have are those 16.2W you can apply that to a wheel (most efficient) or to a propeller in a non compressible gas all that you will get ideal case is 16.2W.
Applying that to a propeller in air will result in less thrust as good part of the energy will be stored in pressure differential resulting in lower acceleration rate but the advantage of using the stored energy latter.

PlainName:

--- Quote from: electrodacus on July 07, 2022, 03:12:18 am ---
--- Quote from: dunkemhigh on July 07, 2022, 02:49:33 am ---So, write one that does apply, that does show the props effect. Even if it you think it works the wrong way (or not works) you can write the equation to show that, so do it. Shit or get off the loo.

--- End quote ---

I see that you get frustrated

--- End quote ---

Yes, sorry for the intemperate language. This is very trying, you know.


--- Quote --- but important question is what is the available wind power to vehicle.
--- End quote ---

That's partly where you're going wrong. Your euqation shows the wind speed at which power is zero. It also shows the power available at any particular speed. But... so what?

All it's showing is the possible power, but how much does the vehicle need to move? When you look up on t'web how much power something needs to do, say, 15mph it's not relevant to this because most of that power will be overcoming drag. There isn't any drag here. Actually, it is negative drag, which is what's pushing the thing along. So you have all this power available but where is it going? It's accelerating the vehicle.

Now, if there were a little less power available, perhaps because something is sucking it off, would that make the vehicle go backwards? Of course not! It will just accelerate a little less. It is literally a brake on the wheels, but there is still enough to power available from the wind to drive the vehicle forwards.

The vehicle, without the prop, would never get to wind speed. It would be very very close but there is friction, so it's not quite there. Your formula will tell you how much power you have at that 'very close to wind speed' speed, and I'll bet you it's a surprisingly small amount because there is no drag to overcome. So just think how much extra power would be available if the vehicle was a little bit slower than that.

So, that formula tells us how much power we have and when it would theoretically run out. It doesn't tell us how fast we go, how much we can divert for other usage, how quickly we can accelerate, nothing.


--- Quote ---And if it has an energy storage device as it is the case with Blackbird
--- End quote ---

Give it up. There is no energy storage device there. If you're convinced there is, prove it with your new modified equation that shows how Blackbird can (temporarily if you wish) exceed wind speed.

electrodacus:

--- Quote from: dunkemhigh on July 07, 2022, 03:34:16 am ---
That's partly where you're going wrong. Your euqation shows the wind speed at which power is zero. It also shows the power available at any particular speed. But... so what?

All it's showing is the possible power, but how much does the vehicle need to move? When you look up on t'web how much power something needs to do, say, 15mph it's not relevant to this because most of that power will be overcoming drag. There isn't any drag here. Actually, it is negative drag, which is what's pushing the thing along. So you have all this power available but where is it going? It's accelerating the vehicle.

Now, if there were a little less power available, perhaps because something is sucking it off, would that make the vehicle go backwards? Of course not! It will just accelerate a little less. It is literally a brake on the wheels, but there is still enough to power available from the wind to drive the vehicle forwards.

The vehicle, without the prop, would never get to wind speed. It would be very very close but there is friction, so it's not quite there. Your formula will tell you how much power you have at that 'very close to wind speed' speed, and I'll bet you it's a surprisingly small amount because there is no drag to overcome. So just think how much extra power would be available if the vehicle was a little bit slower than that.

So, that formula tells us how much power we have and when it would theoretically run out. It doesn't tell us how fast we go, how much we can divert for other usage, how quickly we can accelerate, nothing.


--- End quote ---

Yes available wind power is accelerating the vehicle plus it covers frictional losses (but we can ignore those if you talk about ideal case where there is no friction just to get the best case scenario).

If the power you take at the wheels is less than available wind power the vehicle acceleration rate will just decrease.
If you take more power than available from wind then vehicle will decelerate as in the example I gave before when 4.8W of wind power was available with vehicle speed at 4m/s and and 16.2W of braking power was applied to wheels in order to power a 16.2W incandescent lamp. In that case the vehicle continued to decelerate until vehicle speed dropped to 3m/s and at that point wind power was 16.2W exactly covering the power taken at the wheels for the lamp.

And yes the slower the vehicle speed the more wind power is available but if you can not store energy then that power will just accelerate the vehicle witch is a form of energy storage (kinetic energy) but not the type that will allow you to exceed wind speed.
     
I think I mentioned before but I can (anyone can) build a vehicle that uses no propeller and exceeds the wind speed exactly the same way Blackbird is doing and actually be more efficient.
All that is needed is a sail (collapsible will be best to get rid of the drag when above wind speed) the propeller is doing this in a natural way).
Then 3 or 4 super capacitors 3000F 2.7V as each can store about 3Wh so in the same range as the large Blackbird.
The capacitors will be fully charged well before the vehicle gets to half the wind speed and from there the wind power and sail are no longer needed as the stored energy allows a 300kg (same weight as Blackbird) to be accelerated to about 3x the wind speed maybe even 4x will low enough friction losses.

To accelerate a 300kg vehicle from say 3m/s (half the wind speed of 6m/s) to 13m/s (a bit higher speed than Blackbird record of around 12.4m/s).
Vehicle kinetic energy at 13m/s is 0.5 * 300 * 132 = 25350Ws = 7Wh to this some frictional losses will need to be added but it will not be much.
So if I charge 4x 3Wh = 12Wh super capacitors (way smaller and less dangerous than a huge 20m2 swept area propeller) I can easily exceed blackbird speed record.
I don't want a 20m2 sail as that will be to crazy but with say a very manageable 2m2  sail 10x smaller than blackbird swept propeller area I will need to spend:
Say charging when vehicle is at 1m/s that is 6-1 = 5m/s wind speed relative to vehicle 0.5 * 1.2 * 2 * 53 = 150W so I will say generator is just 80% efficient still 120W available to charge the supercapacitors.
I need 12Wh to fully charge that is 43200Ws so I need 360 seconds (a bit slow if nobody pushes the vehicle like it was the case with Blackbird) and if there are no wind gusts above 6m/s to help still 6 minute charge time is reasonable then just a few minutes to accelerate to top speed of 13m/s maybe even more dempensing on friction losses.
Or I can increase the sail size to 20m2 and then I can charge the capacitors in just over half a minute.

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