Veritasium wrong about faster than wind direct down wind. - Page 1
Forum section: electronics / general

author: electrodacus
author_rank: Super Contributor
timestamp: December 08, 2021, 01:39:24 am
content: I made a youtube video showing how Derek's explanation of the blackbird vehicle is completely wrong.His explanation will violate the law of conservation of energy so it is in the end an electrical engineering problem more than a mechanical one.It bothers me that I was not successful explaining how the vehicle works to anyone so I hope this video I made allows at least some people understand and then they maybe with much better skills at explaining stuff can do better.The video is unlisted for now but will be on youtube in a few days. I gave Derek a chance to watch the video first and if he understands the problem and makes a I video I will be happy to keep mine unlisted.It will be helpful if you can provide feedback maybe even notice some mistakes in my video that I can correct before release (sort of a peer review).I'm sure no wind powered vehicle can exceed wind speed directly down wind unless it uses energy storage and that is what I try to prove in this video plus point that his explanation was done with wrong formula (I guess he needed that wrong formula to justify his explanation).

author: Labrat101
author_rank: Unknown
timestamp: December 10, 2021, 10:58:50 am
content: Hi Nice video you have put a lot of work into this.Yes I watched it but not being in my field of expertise .Even though I still think its possible to travel faster than wind . As in sailing boats can do it even though they move in a zig-zag motion.Some how the Laws of Nature are not always predictable . (Maybe they are not meant to be solved )Such as a Bumble Bee can't Fly . and there are a few others that scientist will try to find a reason Why . without a conclusion .Why is the universe expanding ?? .

author: wraper
author_rank: Unknown
timestamp: December 10, 2021, 11:12:00 am
content: Quote from: electrodacus on December 08, 2021, 01:39:24 am

author: heutnoch
author_rank: Newbie
timestamp: December 10, 2021, 12:27:54 pm
content: If you go directly in wind direction there is now relative velocity between the vehicle and the wind, when you reach wind speed. So, there is no energy to accelerate. If you go faster than the wind, there is relative velocity but no possibility to transform the energy in a forward acceleration.It's different, if you go with an angle to the wind direction. There is a sidewards component of the wind and using Bernoulli's principle you can generate a forward pull. The air flowing along the curved side of the sail takes a longer way, must flow faster and as the dynamic pressure increases the static pressure decreases (like the wing of an airplane). You can use this principle to zigzag against the wind. And as far as I know you can zigzag against a relative contrary wind, you see by going faster as the wind, with a modern high-performance sailer.

author: electrodacus
author_rank: Super Contributor
timestamp: December 10, 2021, 04:43:30 pm
content: Quote from: heutnoch on December 10, 2021, 12:27:54 pmWhy is this obvious to you but not the majority of the other people ?Quote from: heutnoch on December 10, 2021, 12:27:54 pmI have not looked in to zigzag idea as this vehicle is not doing that. It seems that may work especially in the ideal case where you have no friction since one you got the vehicle to any speed there is no friction to slow it down.But this blackbird vehicle is not zigzagging so it can not take advantage of that.The blackbird exceeds wind speed but is based on stored energy in the pressure differential created by the propeller.So when it is below wind speed it can use as much energy as it wants and part of that energy it can use for propeller to increase the pressure differential and even well before getting to wind speed this pressure differential will start to be used so pressure differential will be reduced and when there is no longer enough to cover the friction losses the vehicle will slow down below wind speed.

author: electrodacus
author_rank: Super Contributor
timestamp: December 10, 2021, 04:44:53 pm
content: Quote from: wraper on December 10, 2021, 11:12:00 amCare to explain with words ? Your symbols can me anything.

author: electrodacus
author_rank: Super Contributor
timestamp: December 10, 2021, 04:46:27 pm
content: Quote from: Labrat101 on December 10, 2021, 10:58:50 amYes there was some work put in to this but it will helpfully be seen by someone that understand what I'm talking about and he can do a way better job at explaining to others.

author: wraper
author_rank: Unknown
timestamp: December 10, 2021, 04:56:58 pm
content: Quote from: electrodacus on December 10, 2021, 04:44:53 pmMy reaction to your entitlement of giving him a chance to respond.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 10, 2021, 05:50:18 pm
content: The fan blades going aroung in circles are a bit like the zig zaging or a sail boat. Doing it this way may be possible, but would require really good aerodynamics. It may work in theory, but not sure it actually works with all technical limitations included. The way it is done in the video is way easier and does not need a really high performance porp / air / foil:Even if the vehicle is morving at the speed of the wind, it can still slow down the wind and this way extract energie from the wind. The trick is using the fan. With no external wind a fan can produce air movement and this way a force on the fan. This is how a propeller an a plane works. On the vehicle moving with the wind the fan is used to push the vehicle forward. As the fan sees only a relatively low relative velocity to the wind, this needs relatively low power.The wheels are used to power the fan. As the speed is relatively high (about the speed of the wind), only a faction of the force available from the fan can produce enough power to drive the fan. The rest is available to overcome friction and speed up the vehicle.An alterntive way to look at it is from the point of view of the vehicle or in the treadmill experiments: the ground is moving in one direction and provides the power to drive the fan to push forward against the moving ground with the fan.This is similar to the case of wind turbine to drive a vehincle against the wind, just with the role of wheels and turbine switched.

author: electrodacus
author_rank: Super Contributor
timestamp: December 10, 2021, 05:56:54 pm
content: Quote from: wraper on December 10, 2021, 04:56:58 pmI see... maybe that came out wrong.I had a long email conversion with Derek some months ago but I failed to convince him. All I wanted for him to get how this vehicle works and do a third video explaining that.Thus I put the effort in making this video but I have not posted youtube videos in years and I'm just not good at explaining things. But I just posted the video now so hopefully there will be at least a few views and at least a few people understand what I try to say so they can make better quality videos explaining how the blackbird vehicle actually works.

author: electrodacus
author_rank: Super Contributor
timestamp: December 10, 2021, 06:11:57 pm
content: Quote from: Kleinstein on December 10, 2021, 05:50:18 pmWhen blackbird is at say at same speed as the wind all air molecules around the propeller (ignoring the pressure differential) will have same speed as the propeller thus they can not interact with the vehicle in any way.When above wind speed things are even worse as now air moves relative to propeller but from the opposite direction of travel so not only that can not help but it will be counter productive.Quote from: Kleinstein on December 10, 2021, 05:50:18 pmTaking energy from the wheels means taking energy from vehicle kinetic energy that is directly proportional with vehicle speed.Before exceeding wind speed wind pushes the vehicle same as it pushes a sail vehicle so some of the power provided by the wind that way can be used for accelerating the vehicle and some can be used to rotate the propeller.If air was not compressible then powering the propeller will just be a waste of energy but since air is compressible energy can be stored this way by increasing the difference in pressure between the upwind and downwind side of the propeller. This increase in pressure differential can power the vehicle and allow it to exceed wind speed.The proof is simple just leave the vehicle drive until it gets to peak speed and the see how it starts to decelerate.Another proof can be made by going out in a day with no wind or large indoor space and push a vehicle to 6m/s or whatever the design speed is and the releasing it showing how vehicle will accelerate and so exceed the speed it was pushed at but then slow down as energy is used up.I will say this was sort of already demonstrated with the treadmill model.Ground or treadmill can not provide power to that model after the vehicle starts moving in the opposite direction.The pressure differential that was created by the propeller powered by treadmill when vehicle was held in place with the hand is what pushes the vehicle in the opposite direction that treadmill is moving.

author: Labrat101
author_rank: Unknown
timestamp: December 10, 2021, 07:06:51 pm
content: Take one extremely Hot Curry .4 Large Guinness I guarantee you . Your underwear will travel faster than the Wind .

author: PlainName
author_rank: Super Contributor
timestamp: December 10, 2021, 11:46:12 pm
content: QuoteThis is what you are missing. The propeller is turning, so there is lateral movement relative to the air. Since there is movement relative to air, there is potential energy to be tapped. Thus, even when the vehicle is going at wind speed, the prop is STILL moving relative to the air and can transfer power.If an airplane is standing on a runway, how can it take off if there is no wind? That's exactly the same situation where the vehicle is moving at windspeed but the prop is turning.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: December 10, 2021, 11:50:27 pm
content: Quote from: dunkemhigh on December 10, 2021, 11:46:12 pmI was about to ask how a desk fan can make wind since the propeller is not moving relative to the desk?Or for that matter, why does it take less time flying to Germany from Canada than the other way?Or if you build a Veritasium vehicle but reverse the gearing so the prop blows forward.Will it run slower than the wind or not?

author: electrodacus
author_rank: Super Contributor
timestamp: December 10, 2021, 11:53:35 pm
content: Quote from: Alex Eisenhut on December 10, 2021, 11:50:27 pmBig difference is that desk fan is not powered by that wind it creates. It has an external energy source.

author: electrodacus
author_rank: Super Contributor
timestamp: December 10, 2021, 11:58:48 pm
content: Quote from: sleemanj on December 10, 2021, 11:57:30 pmYes I saw that video.Steve is smart enough not so say anything about direct down wind.

author: PlainName
author_rank: Super Contributor
timestamp: December 11, 2021, 12:10:15 am
content: QuoteYou're skipping ahead. Clearly, the prop turns. Is it powered by the wind or wheels? Leave that for the moment and just consider that it's turning.That is simple refutation that the air molecules are moving at the same speed as the prop. They are not. Once you realise that (actually, accept that because even after having pointed this out a few times it seems you still haven't), we can consider what causes the prop to turn.Regarding the desk fan and taxiing airplane, we are talking vastly different leverage. In both of those the propeller is turning at massive speed, producing (or using) a lot of wind. With the FTTW vehicle it is orders of magnitude less. But that's not important, is it? The effect is either there or it is not - the scale of the effect is only meaningful when we consider what it can do, but before that we just want to agree that it exists.

author: electrodacus
author_rank: Super Contributor
timestamp: December 11, 2021, 04:35:01 am
content: Quote from: dunkemhigh on December 11, 2021, 12:10:15 amThere is a stored pressure differential that powers the blackbird even before exceeding wind speed. That pressure differential is created by the propeller using wind energy while vehicle speed is well below wind speed.The vehicle will continue to accelerate past wind speed as long as there is enough stored energy and will start to slow down when that is all used up.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: December 11, 2021, 07:23:35 pm
content: Quote from: electrodacus on December 10, 2021, 11:53:35 pmThen what does the relative movement have to do with anything? The power source, as you state yourself, is the stored energy of the moving vehicle using some energy to spin the prop.How fast would the vehicle move if the prop blew forward?

author: electrodacus
author_rank: Super Contributor
timestamp: December 11, 2021, 08:44:36 pm
content: Quote from: Alex Eisenhut on December 11, 2021, 07:23:35 pmYou mean the vehicle kinetic energy ?If you take out energy from there to generate some at the wheel and then put back in propeller the net result will be same end kinetic energy in ideal case and lower kinetic energy in real case.Say kinetic energy is 100Ws and you take 1W for 1s at the wheel then result will be 99Ws vehicle kinetic energy then put that 1W for 1 second in the ideal propeller and get back to 100Ws so ideal case no acceleration real world deceleration.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 11, 2021, 09:18:44 pm
content: Quote from: electrodacus on December 11, 2021, 08:44:36 pmNo, this simple calculation is wrong. It would work this way with zero wind speed.However with wind speed you have to take the energy of the wind into account too. With the wind in the same direction as the movement an ideal propeller can add more to the kinetic energy of the vehicle than the power it needs, as it also takes some energy from the wind. The important point is that there are different relative volocities that the wheels (to the ground) and the propeller (to the air) see. The propeller only has to work against the relative wind speed (low), but the energy added to the vehicle is from force times speed to ground (assumes the ground as the reference to calculate kinetic energy). So more energy can be added to the vehicle than the work the propeller does. That extra energy comes from the wind, that is slowed down by the prop.

author: electrodacus
author_rank: Super Contributor
timestamp: December 11, 2021, 10:14:10 pm
content: Quote from: Kleinstein on December 11, 2021, 09:18:44 pmYes there is no available wind power when vehicle speed is the same as wind speed or above (above is actually worse as it is negative).formula for wind power for a vehicle traveling directly down wind is this0.5 * air density * area * (w-v)^3This can not be changed just so that it fits some experimental data that is not fully understood.There is energy storage and that can be calculated separately and added to the balance of power but wind power formula is the one I mentioned not as Derek showed where he subtracted wind speed from vehicle speed.And you can not use one formula for below wind speed and above it needs to be the same one as it is the same vehicle (no changes are done to vehicle when wind speed is exceeded).

author: fourfathom
author_rank: Super Contributor
timestamp: December 11, 2021, 10:54:11 pm
content: Do we agree that when the wind is blowing that there is energy available to a stationary device?Does this change if the device is moving? There is still a speed difference between the wind and the ground, regardless of the speed and direction of the device.In the case where the device is moving directly downwind at windspeed, there is zero apparent wind (a sailing term, wind relative to the boat), but there is groundspeed, and the available energy still exists.Accept this, and there is no need for energy storage, "slip-stick hysteresis", or any of that stuff. All that remains is to devise a method of extracting energy from the air/ground speed difference. This has been demonstrated.

author: electrodacus
author_rank: Super Contributor
timestamp: December 11, 2021, 11:37:58 pm
content: Quote from: fourfathom on December 11, 2021, 10:54:11 pmThere is a potential energy available yes that will be 0.5 * vehicle mass * (wind speed)^2That potential energy can be converted in to kinetic energyThis is true for a vehicle with no energy storage device like a sail type vehicle.This type of vehicle can drive directly down wind up to wind speed (depends on friction losses) and can not drive directly upwind at any speed.Quote from: fourfathom on December 11, 2021, 10:54:11 pmIf vehicle is not moving there is no power available just a static force.Power available to a vehicle moving directly down wind is this: 0.5 * air density * area * (w-v)^3 where w - wind speed and v- vehicle speedFrom this you see that vehicle speed can be any as long as it is between zero and wind speed since when vehicle is at wind speed no wind power is available.Quote from: fourfathom on December 11, 2021, 10:54:11 pmIf you want to exceed wind speed directly down wind then you need an energy storage device so that you can store energy while below wind speed and then use the stored energy to exceed wind speed.Yes what was demonstrated was a vehicle with an energy storage device (pressure differential) and that can exceed wind speed. The test was incomplete else it will have showed how vehicle will start to slow down below wind speed as stored energy was used up.It is fairly frustrating to see this disregard for energy conservation on an electronics forum.If you have electrical knowledge think about this:You have a 10V 3A CC-CV lab power supply and you can not output higher voltage or current using a device that has no energy storage device same for a negative voltage relative to ground/GNDYou will need to use either inductors or capacitors or both in order to build a DC-DC boost converter. Using just resistor dividers you can get any voltage as long as it is between 0V and 10V to get more or less (negative) you need an energy storage device.

author: fourfathom
author_rank: Super Contributor
timestamp: December 12, 2021, 12:27:35 am
content: Quote from: electrodacus on December 11, 2021, 11:37:58 pmSo why doesn't this sail-type vehicle not have the compressed-air energy storage you claim powers the propeller-type vehicle?And what is the time-constant of this energy storage? You've been talking about air compression behind the propeller. How much energy is stored and how quickly does it bleed off into the surrounding medium? I think this storage, if any appreciable, lasts for milliseconds -- and the vehicle accelerates beyond windspeed much longer than that.Quote from: electrodacus on December 11, 2021, 11:37:58 pmThere is potential energy, and it can be tapped.Quote from: electrodacus on December 11, 2021, 11:37:58 pmPerhaps this holds with a flat sail. But a spinning propeller is not a flat sail.Quote from: electrodacus on December 11, 2021, 11:37:58 pmThis is a flawed comparison.Sure there is some sort of energy storage in a switching regulator, or even in a transformer. But these are not "energy storage" devices, and can run continuously: 10V/1A input, 5V/2A output (assuming no losses). The energy storage you are claiming is more like a battery being depleted, and it doesn't apply in the DDWFTTW case. Your analogy is flawed, your models are flawed, and your equations are flawed.

author: electrodacus
author_rank: Super Contributor
timestamp: December 12, 2021, 01:18:22 am
content: Quote from: fourfathom on December 12, 2021, 12:27:35 amIt has that but it is not useful as you can not add more to it. You can imagine you push a vehicle but instead of pushing directly you add a spring between you and the vehicle. Still vehicle you are pushing can not exceed your speed.For blackbird is like it can compress the spring from the other side so that when it is at wind speed the spring is still compressed so it has energy to continue to accelerate the vehicle is like there is still a wind speed from the back relative to vehicle.Spring analogy may not be perfect but for a sail type vehicle when sail speed equal wind speed the spring is fully decompressed no more energy.Quote from: fourfathom on December 12, 2021, 12:27:35 amYes there is potential energy exactly 0.5 * vehicle mass * (wind speed)^2And this can be converted to kinetic energy as soon as you remove the breaks or rise the sail or remove whatever it keeps you from moving.When all potential energy was transformed in kinetic energy (ideal case) your sail vehicle will now have same speed as the wind and the remaining air potential energy is zero while vehicle kinetic energy is 0.5 * vehicle mass * (vehicle speed)^2In the mean time you can stay at say a quarter of the wind speed and capture as much energy as you want to fry eggs or heat the air or anything you want but your speed will remain constant if you use all that available power at that speed and so one thing you can do is store that energy as much as you want in a battery and then you can use that stored energy to accelerate way above the wind speed for a limited amount of time.Quote from: fourfathom on December 12, 2021, 12:27:35 amIt is not and is more complicated to calculate area that will vary from just blade area when is not spinning up to swept area of the propeller when power output of the propeller matches the wind power.As you put power (over time energy) in to propeller that results in increased pressure differential so as far as the vehicle is concerned it will look like higher apparent wind speed.Quote from: fourfathom on December 12, 2021, 12:27:35 amAs any analogy it may have some limitations but for the direct upwind version the DC-DC converter analogy works perfectly well other than frequency of charge discharge is at least kHz for a DC-DC and it is just a few Hz for the direct upwind.For the direct down wind an inductor is the best analogy but it will be a massive inductor .The same way an inductor stores energy in the magnetic field around it and as long as current is constant that field will remain constant and is similar to a propeller fan runing at constant speed.if you reduce the current energy from the magnetic field will flow in to your circuit similar how pressure differential will drop but in that time it will push the vehicle.The propeller has another type of energy storage similar to a capacitor but that alone can not help with exceeding the wind speed (unless gear change is allowed or propeller pitch change) that other type of energy storage will be called a flywheel and definition is just two words (spinning mass).While you may not think at a normal capacitor as a large capacity energy storage device there are massive flywheel that can store many kWh of energy.To get some sense of the numbers.During blackbird record test a total of 6Wh of energy was used probably about that amount was stored in the pressure differential (it was fairly close to start slowing down when it got to 30mph even if wind peak at 15mph and it helped multiple times).I do not have exact weight from Rick but my rough estimations get around 2Wh or so stored in the propeller flywheel type energy storage so all this numbers are not that large considering the size of that propeller 5.3m diameter (huge 20m^ swept area).Your regular inductor or capacitors are nowhere near that massive