Downwind Faster Than the Wind by Veritasium: How Does it Work?
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- Опубліковано 12 чер 2024
- This is a response to @Veritasium 's recent video: Risking My Life To Settle A Physics Debate
• Risking My Life To Set...
I show all the extra steps that I used to understand what on Earth is going on here! Mostly I relate it to aerodynamics and especially the blade element method that is commonly used to analyse wind turbines. And I also show why it doesn't violate the laws of thermodynamics.
It is the subject of a $10,000 bet as tweeted here: / 1403130178197278720
I need to give the HUGEST thank you to Rick Cavallaro the designer of the Blackbird vehicle, for giving me extra design information and helping clear up all the physics and engineering involved until I understood it.
If you would like to help develop the Engineering with Rosie channel, you could consider joining the Patreon community, where there is a chat community about topics covered in the videos and suggestions for future videos and production quality improvements. / engineeringwithrosie
Bookmarks:
00:00 Intro
00:29 Bet between Derek Muller and Alexander Kusenko
02:14 Description of how the Blackbird cart works
02:58 Analogy: like a cyclist pushing off a car to go faster than the car
03:56 A perpetual motion machine? The wheels turn the propeller, but they don't power it
04:51 This clearly violates the laws of thermodynamics!
05:38 Energy balance with some simple numbers
07:22 How it gets moving from stationary
07:56 It's not a wind turbine
08:45 Why the propeller's thrust is larger than a push from the tailwind can be
09:32 Aerodynamic concepts: lift, drag, angle of attack, relative wind speed
10:29 Aerodynamics of a propeller
11:00 Blade element model of the Blackbird propeller
12:27 Aerodynamics (vectors analysis) of the Blackbird propeller at record conditions (2.8 times wind speed)
13:26 Propeller aerodynamics at faster than record conditions
14:01 Propeller aerodynamics at wind speed (zero relative wind speed)
14:43 Slower than wind speed
14:56 Link to more analogies from Rick Cavallaro the Great
16:29 Bonus analogy: a propeller is a kind of screw
Extra resources to understand the concepts in more depth:
Designer Rick Cavallaro's long speech with many analogies: • DDWFTTW Talk 2017-01-18
Putting numbers on iceboat performance (analysis and GPS data that shows boats moving many multiples of wind speed) www.nalsa.org/Articles/Cetus/...
Sailing yacht design for maximum speed: static1.1.sqspcdn.com/static/f...
Eyytee's animation showing how sail vehicles are able to outrun the wind, that pushes them (achieve a downwind velocity-made-good greater than true wind speed). As an analogy a wedge squeezed between two oblique edges is shown.
• DOWNWIND VMG GREATER T...
Performance of propellers lecture notes from MIT course "Thermodynamics and Propulsion"
by Prof. Z. S. Spakovszky (includes blade element method): web.mit.edu/16.unified/www/FA...
NASA propeller thrust page: www.grc.nasa.gov/www/Wright/a...
Aerodynamics for students Blade Element Theory for Propellers (nice simple version that I used):
www.aerodynamics4students.com/...
A written version of the same material is here:
rosemary-barnes.medium.com/do...
Image and footage credits:
Risking My Life
Defender By Donan.raven - Own work, CC BY-SA 3.0, commons.wikimedia.org/w/index...
Ice boat By HopsonRoad - Own work, CC BY-SA 4.0, commons.wikimedia.org/w/index...
Ice boat pdf www.nalsa.org/Articles/Cetus/...
Ice boat By Raul Kern - Own work, CC BY-SA 3.0, commons.wikimedia.org/w/index...
Ice boat By Pataki Attila István - Own work, CC BY-SA 4.0, commons.wikimedia.org/w/index...
Downwind faster than the wind wedge animation • DOWNWIND VMG GREATER T...
Screw animation By ja:User:＋－- Own work, CC BY-SA 3.0, commons.wikimedia.org/w/index...
The aeroplane on a treadmill image from xkcd
blog.xkcd.com/2008/09/09/the-...
#engineering #science #stem
Thanks for watching the video Downwind Faster Than the Wind by Veritasium: How Does it Work? - Наука та технологія
Great job, Rosie! Love the explanation and numerical simulation. I’m taking a second crack at this one this week to explain what went down with the bet.
Thanks 😁😁 it makes me very happy to have you as a visitor on my little channel!
I have really enjoyed thinking about this design, thanks so much for introducing me (and 6+ million others) to it.
I hope that you picked up 10k for this Derek. It's nearly worth that for riding in that vehicle as it looked scary as hell with that out of balance prop.
@@EngineeringwithRosie , Hi Rosie! A good video - you really did explain how the craft can travel faster than the wind!
Although I believe you made a slight mistake.
I also made a video about this machine on my teeny tiny channel where I explain that there is in fact no mode difference in propulsion above and below windspeed. ua-cam.com/video/CbNCz0_iO7c/v-deo.html
Please check it out, I'd love to know what you think!
@@chalichaligha3234 you have made some great illustrations there, well done. I really liked your explanations. I don't think I made the mistake you mention, but perhaps I wasn't very clear. The prop starts generating thrust as soon as the wheels start turning, so that is a constant as soon as it has any movement at all. But at very low cart speeds, the greater part of its forward-acting force will come from bluff body drag. Do you not agree there is any bluff body drag pushing the cart forward below wind speed that changes direction to start pushing it backwards as it crosses wind speed?
@@EngineeringwithRosie I think that at low speed the greater part of the force on it is coming from the drag _on the propeller._ This is evident with the small model cart, which doesn't have any body to speak of.
That video of Veritasium has exposed me to a lot of good channels that are existing on UA-cam and I never knew them!
Same here
Agreed!
I'm really happy to be one of them!
Yep this has been fun seeing people respond to this.
The windspeed measurements in the tests are nonsense. Behind a sail on a sailboat the windspeed is greatly reduced. You've built your whole model on the propeller reducing the speed of the wind to get power and then measure it downstream of the propeller. How about driving a car along at the same speed as the cart with wind indicators on a mast? If the system really works the wind direction will be reversed at that speed.
Congrats (from one of the Blackbird design/build team). Nicely done.
Wow, thanks! Right back at you: nicely done!
LMAO. April fools.
No one can see putting a wind turbine on backward doesn't make the vehicle go in reverse.
Hey John, will the next version allow you to make negatie pitch for faster starts?
@@EngineeringwithRosie why are you congratulating this abusive troll?
you coulda hidden the electric motors better, like the do in pro cycle racing.
I posted this comment also at Dereks video:
If you have a spool of wire (sewing thread, rope, electrical cord) and you pull the wire, you can make the spool roll towards you. If you make the wire come toward you from the underside of the spool, the spool will come toward you much faster than the wire end you pull. The calculations are strikingly similar.
If the spool is almost full, the speed ratio is very big. If it is completely full, you get the (v-w)=0 situation: 'infinite' ratio, but it won't start.
Beautiful! I had a hard time getting this to work in my head, this both cleared it up and jumbled my brain
Thank you! It's a great step forward to understanding it!
Bonus points for the pony-tail as a tell-tale at 0:18!
@@widgewunner I don't know if we deserve any respect, but I'd be a lot happier if we weren't being called idiots and charlatans.
Haha, What a comment from the man himself.
@@Rick_Cavallaro you work for military intelligence. so yeah, idiot & charlatan is about right.
This is an example of one of those things in life that I suspect is true. Likely I’ll never be able to fully understand or convincingly explain to someone else.
just keep trying. that is how you eventually get it.
No matter how fast the vehicle is going, as long as there is any wind at all, there will always be a differential between ground speed an wind speed to exploit. Thank you! That's the bit that really hurt my head, and it sounds so obvious now.
When that ribbon flipped around, I cried for some reason.
The air speed at the ribbon is not the same as the distant wind speed, because:
- The ribbon is before the prop. The prop is accelerate the air backwards, so it deccelerate the wind. The ribbon is in wind shadow.
- The wind speed near the ground is lower than higher.
- May the wind and the cart direction not egsactly the same.
- Usw.
Id like to say how much I've enjoyed all the videos leading to your success!
Wow this makes the problem so much easier to grasp, thanks a lot!
Thanks! This video broke me free of thinking the design should work with zero tailwind if already moving. The drag would be larger than the thrust and the vehicle would slow down.
Hi,
I've have same thoughts. We have initially still car and no wind at all. We push the car to certain speed. Can the thrust be bigger or equal to the drug. /Biker can use still cars to accelerate himself/?
@@malingeorgiev2962 "We have initially still car and no wind at all. We push the car to certain speed. Can the thrust be bigger or equal to the drug."
No, it is essential that the air is moving *relative* *to* *the* *ground* or else the cart cannot extract energy from the air to accelerate.
Thanks Rosie! I had come to the same conclusion that the reason the professor thought it was impossible was probably because he overestimated drag and underestimated lift when thinking about the balance of forces (as most people not familiar with aerodynamics do---as a sailor I have to face that a lot, even with other sailors), and I got into a debate where I was having trouble giving a convincing explanation using only words. But then I found your video and spreadsheet, and it did it! Made me discover your channel and love it, subscribed now.
where is the spreadsheet?
@@nadavsofer2686 It's the one she shows in the video
@@SmirkyWaters How did you get the spreadsheet?
@@anterokaarakka62 It's the one she's showing in the video. You could probably get it from her or reproduce it.
This is probably my new favorite channel. She's really good at teaching wind energay.
this was the best explaination i've heard for myself so far!
Your excellent analysis reminded me of the magic moment my 6th grade teacher, Ms Rochfort, described how a sailboat can go fast and almost directly up wind. That moment of wonder inspired me over the decades of my work. It’s a joy to see your enthusiastic videos doing the same for younger players.
How about putting a pair of electronically controlled motor/generators between the wheels and the propeller like a Tesla EV? For fun, add a Lithium Battery too.
You were lucky to have a 6th grade teacher who understood how sails work!
You’d have conversion losses to deal with twice, but there may still be an envelope where it can work?
I was a lot more surprised that people refused to believe this was possible than that it was but thank you for going into the detail as to exactly how this works.
Yes yes yes! I had the same thermodynamics question! Thanks for the explanation!
In the moving vehicle frame of reference, energy is extracted from the earth (earth is slowed down a tiny bit) and added to the apparent headwind (headwind is sped up). The earth surface is moving backwards, and the forwards force exerted by the wheels onto the earth surface slow the earth down (from the vehicle frame of reference) by a very very tiny amount, extracting energy from the earth ~= ground force x ground speed (from the vehicle frame of reference). Reduction gearing is used to produce a greater thrust at a lower speed at the propeller. The 1877 Brennan torpedo is an example of the same principle: two powered spools pull wires backwards off of two spools on the torpedo, which in turn drive the propellers forwards at a greater force but lesser speed than the wires, so that pulling the wires backwards results in the torpedo moving forwards. if the wires were attached to two posts in a river, the torpedo would go downstream faster than the stream. A similar example is dynamic soaring which exploits air moving at different speeds across a relatively thin shear layer. In the case of radio control gliders, this is done on a ridge, where the ridge blocks the crosswind somewhere below and behind the ridge. The upwind side of the ridge is used to launch the glider and gain some altitude, after which the glider is circled at an angle on the downwind side of the ridge, repeatedly out of and back into the crosswind. The current dynamic soaring record is 564 mph by Spencer Lisenby.
Someone made a machine which does a similar thing moving between a table and a plank of wood, and it moves "downwind faster than the wind" in that if you move the plank, it moves in the direction of the plank, but faster than the plank. I can't find the schematic for it anymore though :-( It was convenient 'cause it was something you could build at home using simple parts and watch it work.
Oh that sounds cool 😊 I did see a few other examples of downwind faster than the wind, maybe I'll pull them all together on a post later on.
@@EngineeringwithRosie You'll find that on my channel: "under the ruler faster than the ruler" :)
The engineer and sailor, Theo Schmidt was the first to do it with a model. He published an article over 20 years ago in Catalyst, the journal of the Amateur Yacht Research Society. It may be available online.
@@petersharp6833 - The Brennan torpedo operates on the same principle, and was made in 1877. The physics people at the time had already determined it would work, before committing the money it took to build the setup. Wikipedia has an article on Brennan torpedo.
It's strange for something so counter intuitive to be physically sound. So far I've never had so much trouble understanding something about physics.
I think your explanation has made me understand. But I certainly wouldn't be able to explain it to anyone else :D
I think if the problem was explained properly in the Veritasium video, it wouldn’t have come across as counter-intuitive.
The Veritasium video misleads you to think that the propeller is a turbine driving the wheels, but this is not the case, the wheels drive the propeller which is what produces the thrust, like the propeller on a plane.
My view is the initial video is very misleading
Edited to correct propeller
@@philippetts1701 The veritasium video never claimed that. Also, if you cannot explain it to someone else, you do not understand it...
thanks so much Rosie! after watching the original video from Veritasium a while back (two or three times), i was still left with an unclear understanding of how it worked. but now after watching your video once, i understand it at least twice as good! thanks so much for your brilliant video and you just being your brilliant self!
Glad I could help!
I like your screw analogy at the end. Early boat propellers looked very much like screws, and then they realized that a few blades were more efficient.
I wish there were a polite way of saying this is fucking awesome
Well I am Australian so that counts as polite here. Thanks!
That's maybe the most polite thing I've seen on the topic. :)
Actually just call her a Bloody Legend, Cheers from Las Vegas!
There is...you simply say "wow! That's awesome!" Or if you are English you can say "My word!" or "Good Lord!" or even "Oh, I say!"
@@funquay2219 "my word" ? Are you like 1000 years old?
[Rosie shows a bunch of maths] my brain: "Uhm, I see, so the propeller goes BRRRRRR".
Ah, fascinating.
So propellers work in the same way as money printers... BRRR
@@ak205 Air conditioning makes me go BRRRR!
I love it! And I'm right with you.
It’s funny because basically that’s what’s happening. As long as you get enough thrust from the wind on the blades when it’s relatively stationary to develop a little bit of vehicle momentum you can get the prop to just do prop things. It won’t really do you a hell of a lot good on a draggy keelboat, but the transition from prop-as-static-sail to prop providing thrust driven by craft’s mass acting on the wheels (or underwater prop if you wanted to try this with a boat) when you’ve got your drive ratios and pitches right on an efficient-enough platform, is essentially there from a very low speed above rest
Such great explanations, it finally makes sense now! Instant subscription!
Great job! Love the spreadsheet calculations.
I watched this with my son, who is an engineer. Both of us were unconvinced at the start but your explanation persuaded both of us. Thanks.
That's a HUGE testament to Rosie's talents!
@@satunnainenkatselija4478 the cart initially accelerates from a stand-still in a tail wind (simply being pushed by the wind as a bluff body). Once it's moving, the propeller begins to generate thrust which is able to take it to, and beyond, wind speed.
Most engineers do not sail, I guess ^_^
@@Rick_Cavallaro But Mr.Cavallaro, you didn't answer my question under your video:
If the propeller is generating thrust, then the cart could also move in a still atmosphere provided we give it an initial velocity. The cart doesn't need any wind.
What is the role of the wind BEFORE (I repeat BEFORE) the cart reaches the wind speed? It has no role at all. The cart can move forever.
@@MitkoGorgiev
>> If the propeller is generating thrust, then the cart could also move in a still atmosphere provided we give it an initial velocity.
The prop won't generate thrust on a still day.
>> What is the role of the wind BEFORE
It pushes the cart.
>> (I repeat BEFORE) t
I repeat IT PUSHES THE CART!
>> It has no role at all.
I'm sorry, I thought you had a question. You find this is a better way to learn things?
>> The cart can move forever.
NO.
I don't get why it was confusing for so many physicists.
Have no one of them ever heard about Oberth effect? Or just in general how momentum and kinetic energy are related to each other?
It took me less than 5min to figure it out when I first saw this, and I am not a physicist. It's really confusing that this is confusing..
I saw one talking the math on it, and saying that it couldn't. Lol does he still have a job? I know he lost $10k on the bet.
>> Have no one of them ever heard about Oberth effect?
The Oberth effect is in fact a super nifty thing, but it's unrelated to how this works.
Shit - now I think I've made a fool of myself. I have never stopped to realize this lever effect ends up manifesting as the Oberth effect. My apologies!
I'm leaving the above comment in place as a testament to me being wrong. :(
@@Rick_Cavallaro, shows good caricature!
I love the ponytail in the illustrations! You make engineering fun.
Thanks! I enjoyed drawing myself into that cart 😀
Absolutely fascinating! Thanks.
After I’m done picking my brain cells off the floor, I’ll come up with a witty comment.
Spot on analysis! made my job understanding it easier!
Thanks, I'm really glad it helped 😀
Thanks Rosie for the clear explanation
Excellent work and explanation! Thanks!
Thanks Rosie. You are just the right person to explain this. I understood what was happening with the original test, as I design sailboats. When I tell people that an ice-boat can sail at 8-times the speed of the wind, people think I'm crazy. But people don't understand that the Apparent Wind is very different from the True Wind. In the case of this machine, it is the Apparent Wind that the prop blades 'see' that supplies the force to drive the machine forward. As you say, once you understand the physics, it's not impossible.
>> As you say, once you understand the physics, it's not impossible.
Even if you don't understand the physics, it's still possible. :)
If you sail directly downwind, you do not exceed the velocity of the wind.
8 timed the speed of the wind?
The record for landsailors is arround 4 times , 135mph and an iceboat has never been recorded that fast.
You've made me look at spreadsheets off work. And I wanted more.
I'd like to see a first order differential graph on so many things here.
Ha ha! Well there is more to the spreadsheet than I showed, but in the end I felt I would be setting a bad example to show too many details of my spreadsheet model with about 10 design variables that I calibrated with a single design point...
@@EngineeringwithRosie Can we see the spreadsheet?
@@EngineeringwithRosie Yes, it is a bit of a laugh, really.
Hey Rosie... nice to see the spreadsheet... I been playing with the maths of it for about 10 days. Trying to figure out ideal wheel diameter, gearing, propeller length, pitch, and chord. With a variable leading edge to the propeller, you can use the propeller to drive the wheels from rest to get it moving. Then rotating the leading edge, use the wheel to drive the propeller when in motion. and change the pitch to get peak performance. The current crop of America's Cup yachts use D shaped leading edges, and twin skinned sails, so can effectively alter pitch and chord.
I have to admit that it blew me away!! Subscribed
A smile is on my face!!!!!
The theme became super-popular:)
it’s strange that you didn’t figure it out, look at the explanation,
странно что вы не разобрались, вот посмотрите объяснение
ua-cam.com/video/MEpdIaW60Ew/v-deo.html
@@Olexsy952 Это объясняет движение пропеллера, но не системы тележка-пропеллер. Как только тележка достигнет скорости ветра никаких сил, со стороны ветра, на пропеллер действовать не будет и тележка будет продолжать двигаться только за счет иннерции всей системы, постепенно приходя в состояние равновесия сил.
На мой взгляд, фокус кроется в стойках поддерживающих пропеллер. Уж очень напоминают парус-крыло. Учитывая что ветер не ламинарный поток, а вихревой это создаст ту самую таинственную силу, позволяющую превысить скорость ветра.
Но, теперь движитель не пропеллер, а парус.
yes it's the new flat earth. google promoted that too.
Such a more thorough explanation than given in the original. Thank you!
I mean the first video explained it better than was done in the follow-up wager video. You combine the two expertly, and with the simplicity which I understand.
Thanks for the explanation I really love how you made us understand
Honestly the best explanation I found on the topic. You really nailed the aspect that may generate confusion such the actual role that the tailwind plays and how it delivers energy to the system.
For me the operational theory only gelled when I visualised that the air behind the cart was left moving slower than the surrounding air, and that's where the energy was extracted from. In the same fashion that sailboat leaves a wake of slower air. Otherwise it has a whiff of perpetual motion machine.
I still don't get it. As I understand it, the wind pushes the cart and is where all the ultimate energy comes from. The wheels now rotate, and being chained to the propeller, it also rotates. So, the wind is pushing the cart AND rotating the wheels against the ground + propeller chain resistance AND rotating the propeller via the wheels. And I understand that whatever wind energy the propeller takes up in being turned continues to be replenished by MORE wind until the cart is at wind speed. Thus the cart is absorbing more energy from the wind than one without a propeller would. I get that. Now the propeller converts this extra wind energy absorption very efficiently into forward motion, so it more than makes up for its drag and maybe the cart gets up to wind speed sooner than a plain cart.
BUT
the instant the cart goes faster than the wind, the wind is no longer pushing it. No energy is being input into the system. All the saved up energy in the propeller turning will allow the cart to exceed wind speed for a while but ultimately without any push to overcome the drag and frictions the propeller should slow down by degrees until the cart is back at wind speed again.
UNLESS
the answer lies in the fact that the propeller converts energy into forward motion (and turn the wheels) more efficiently than the turning wheels and chain create drag???
But that's perpetual motion, except for the fact that you do need a wind input.
I DON'T UNDERSTAND
@@greatbriton8425 "the instant the cart goes faster than the wind, the wind is no longer pushing it. No energy is being input into the system."
There's still energy being input into the system. Even though the cart is going faster than the wind the propeller is spinning fast enough that overall the cart is *slowing* wind down behind it rather than accelerating it. This is where the energy is extracted from.
@@greatbriton8425 in the test, the measurements for the wind speed was a streemer in front of the propeller.
That will give you a FALSE reading slower than the actual wind speed.
@@lelandtsnyder9684 No, the streamer was to indicate speed of wind RELATIVE to cart.
@@greatbriton8425 that what I said. You won't get that the n front of the propeller.
I particularly like thw timestamps in your video. This is something that all content creators should try to do. Thanks
Finally a good explanation! Thank you :)
If I may add a consideration, the chain linking the wheels to the rotor has the same function as the keel on the boat: it forces the sail to a given angle of attack. In other words, for every meter downwind, the blades are forced to move laterally for a given amount, same way as a boat when tacking at a given angle.
^^^^ THIS
Changing the gear ratio between the wheels and the prop is the equivalent of using the rudder on the sailboat to change the angled path through the water (point of sail). Changing the pitch of the blades is the same as rotating a wing-sail on an AC racing yacht.
Not quite the same. From the boat's frame of reference, the source of energy is the apparent wind, and a component of lift (which by definition, is perpendicular to the apparent wind), is in the same direction as the boat, propelling the boat forwards. From the DDWFTTW cart's frame of reference, the source of energy is from the ground (the forward force of the wheels accelerates the surface of the earth by a very tiny amount, reducing the angular kinetic energy of the earth from the cart's frame of reference). Through reduction gearing, the drivetrain converts the higher speed, lower force from the ground into a lower speed, higher force at the propeller, despite losses. There is no analogy to reduction gearing for the boat.
@@rcgldr yes, the analogy is the angle between course and real wind. Have a high gearing (rotor spins fast) is like sailing at a wide angle. Low gearing, you are more parallel to the wind. No gearing and is like when you are sailing straight downwind. You have to find the optimal angle/gearing to optimize VMG.
@@markotrieste - A propeller is used because it's an efficient way to produce thrust. If turbine compressor with axis perpendicular to direction of wind was efficient enough, then it would work, with no equivalent to tacking. It is easier to see this in the case of a cart that interacts with two solid surfaces, where energy loss is not an issue. There is reduction gearing from table to ruler, so the cart moves under the ruler, faster than the ruler. There nothing that resembles tacking for this cart.
ua-cam.com/video/k-trDF8Yldc/v-deo.html
@@rcgldr just watch at 9:39. Sailboat at an angle.
It's just like rowing in a river to push more in the river stream way so you will move faster than the river stream
Yes! That is a very clear analogy... wish I thought of it 😁
Great idea. And if you can imagine an axle across the boat, spanning the river with wheels on the two river banks, giving the rotational power to mechanically drive the oars you'd have an exact analogy.
But with rowing, we'd have an external source of energy to push the water away, right?
@@punya1621 Not if it's mechanically driven by the relative speed difference of the stream to the bank, via the wheels and axle, rather than a person. Rather than oars, you could drive a screw instead.
@@hankdewit7548I hate to admit it but even after watching two explainer videos on this (Steve Mould being the other one), I still don't understand it. 😔
Excellent explanation. Thank you very much!
Brilliant explanation, Rosie, a seriously deep dive.
that video was hard on my brain, but I think i got it the second time, just to see your video now, and trying to remember how and losing the sense of it again xD
😂 oh man this exact thing happened to me about fifty times during the making of this video. Even now I sometimes wake up in a cold sweat thinking I've found another "paradox"!
I think a rear-facing propeller would be better, since the supporting structure wouldn't disturb the vortex nearly as much.
Actually, two of them would be better for stability, one over each rear wheel, along with them being triple-blade, to avoid some resonance.
I see everything simplificated : I see an open system that extracts energy from outside ( from the wind ) and powers a light weight vehicle in a smart way ! I don't understand why that profesor threated this like if it was a closed system or a perpetum mobile wich is not ! :))) PS : Energetical Engineer here lol .
This basically boils down to pulleys/gear ratios. I find it kind of funny that what we call "simple machines" are still stumping scientists.
research zero point energy and overunity effects. Wings have "negative" drag here in this vehicle. Some large industrial vacuum pumps speed up shortly when they are shut down. If one would apply a brake to keep the system in that state, one could extract energy. They did it on the atomic level, slowing down a hydrogen atom with a laser until the proton should collapse into the core at 0 Kelvin. But this doesn´t happen and one can continue to cool it down forever. Tesla an Viktor Schauberger understood these sweet spots in vortex systems.
"an open system extracting energy from the wind" that puts it in a nutshell and makes everything clear. The more formal explanation of this video is very nice too though.
@@martinjandt9573 no, it’s nothing to do with “overunity”. It’s extracting energy from the relative motion between the air and the ground.
No need for zero point energy here.
@@dreamok732 if you think that puts it in a nutshell then I don’t think you understand the issue.
That statement is true, the energy comes from the relative motion between the air and ground but the mechanism it uses is totally counterintuitive. How’s this for weird. If the prop and transmission efficiencies are 100%, the force accelerating the kart is infinite when the kart reaches wind speed.
Tell me that makes sense!?!?!
And now the number of subscribers of this channel will go sky high. And that's great.
I'm also one of them now.
All the best!
Loved it! Well done.
Hey Rosie. Great video! Just a quick UA-cam tip in case no one else has brought it up. When creating your bookmarks in the description, make sure to start the list with a 00:00 entry. You can title it "Intro" or something more appropriate. Only this way will UA-cam be able to segment the timeline with all bookmarks. Without it, you still get links to the timestamps but your timeline remains unbroken.
Oh wow are you serious?! I have been doing it wrong this whole time! Thanks so much for taking the time to tell me that 😀😀😀
Would a spinnaker (or one way flapping loungers) on the front of the car get the car up to wind speed faster, and then just collapse out of the way?
If this actually worked, you wouldnt even need a wind at all. You would only need to push it up to sufficient speed and it would run forever.
@@ronalddump4061 That's not true. Wind relative to ground is crucial for it to work.
Great description of the wind propeller cart's theory of operation.
Thank you, this explanation is very good. At first glance it looks impossible, but as long as there was no violation of laws of thermodynamics I accepted it, but your explanation was very good.
Summarizing seems to me we can say whenever there is energy intensity difference between substances or mechanical objects we can tap into it to gain energy to our advantage. Seems to me that Sterling engine falls in this category as well.
Stirling engine works on a temperature difference which is a bit different.
Really cool! So do the blades in the Blackbird cart pitch?
Yep they pitch, but manually. If I were to build one, I think I would try to make the pitching at least semi-automatic. And put a derailleur on it so I could change gears to optimise for both low and high speeds. A propeller is like a wind turbine in that its optimised for a single tip speed ratio (except that they are weirdos and use the inverse) and you mess that up as you go faster if you can't change gear.
@@EngineeringwithRosie One reason for the fixed gear ratio is to prevent using stored rotational energy of the propeller to accelerate. If the propeller rotation slows down, then so must the rotation of the wheels. They had to meet very strict NALSA requirements preventing any stored energy use for propulsion for their sailing record.
@@EngineeringwithRosie so in for example a plane, they don't change the RPM of the propeller to keep at the designed TSR? I think we're going to try to make a Blackbird in Ashes, it's just too cool not to do it!
@@AshesWindTurbineSimulation I volunteer in advance to help you however I can to beat our record. I have no doubt it's doable.
@@AshesWindTurbineSimulationif you make the simulation, I'll make a video about it... and maybe Rick can help us try to improve on the Blackbird design and make a new record attempt!
brilliant explanation thank you! - now I understand what is going on, all the other explanations I'd seen didn't make sense
I am an older father with kids just starting college. Notwithstanding my kids belief that I am the least intelligent person on the earth, I want you to know that your videos are a wealth of knowledge and a joy to watch - I can even understand them (actually I studied biochemistry as an undergrad, before getting a master’s in pubic policy and then a law degree that have been the foundation of a 30-year career in environmental law in the US). Your pleasant disposition, clarity of thought, and infectious smile - not to mention the interesting content - just make me happy. Thank you for showing people everywhere that science matters and human actions have an effect on this earth (of course, all in line with the first two laws of thermodynamics). Ha! I have some crazy ideas that do not. Please keep the videos coming. Thank you.
This video's great! You cover the one element that I think was ignored in the other videos - the lift from the propellers.
I felt the "sailboats on a cylinder" thing was neglected a bit but to me was the key for sails travelling faster than wind.
Sailboats can travel faster then wind - IF the wind hasn't the same direktion then the boat. With only complete tailwind it is impossible! Faster then wind are only the blades of the Propeller but not the vehicle. In my opinion it is a very good fake.
@@guri311
//"Faster then wind are only the blades of the Propeller but not the vehicle. "//
This is incorrect. The entire vehicle is traveling directly downwind, faster than the wind.
@@johnborton4522 No, this is not possible, because then the force to the blades gets a direction AGAINST the driving direction. Why should there be a forward force, when the propeller wants to turn in the opposite direction? There ist no reason.
@@guri311
It's a brainteaser. Keep trying ... you'll figure it out.
I have sailed catamarans. If you go directly down wind, you just go at the speed of the wind... *BUT* ... if you go *DIAGONALLY* downwind, the relative velocities (boat air) are actually faster, and your net downwind speed is FASTER. Note that we're using the phenomenon of lift (like an aircraft's wing) so you get lift in a different direction (i.e. not so useful) but the lift is GREATER, so there's a net benefit, i.e. a net gain in down-wind speed.
This just proves that there is a way to extract more energy from the difference of two velocities (air v. water) and you are effectively using a gear ratio.
So here is my question: after this video i literally feel the tumbleweeds blowing from one ear to the other in the vacuum in my head.
But how is it possible that something can be blown around in a vacuum?
Radiation pressure?
Maybe I missed something. Did the video say something can be blown around in a vacuum? Why would you ask this? The video talked about high pressure air and low pressure. You can't blow air if the air is removed. You can blow photons...which is electro magnetic radiation... to push a solar sail.
Woah. The bonus analogy was awesome!
Brilliant explanation.
Excellent, very clear explanation. I find the screw analogy very helpful: often, people get stuck on the idea of wind "pushing" an object instead of seeing that the propeller moves the cart _through_ the air. In the end it comes down to this: yes, a device can move faster than its input _in the direction of that input._
Good, but surely her assertation that below the windspeed the cart is pushed by it's body's drag force is incorrect. I demonstrated in my video that even if the body had no interaction with the air, the cart would accelerate from rest up to it's maximum speed.
@@chalichaligha3234
Chali, I am one of the primary designer/builders of the Blackbird so I have a complete understanding of the craft. I watched your excellent video and it's clear that you too have grasped the concepts in their entirety (nice work).
As far as the initial motion from rest (where the propeller has not yet begun to develop thrust), it takes very little drag against the tailwind to get it started. You are likely correct that if the body magically had no drag at all, merely the drag against the propeller would get the vehicle moving. Conversely, if you took the propeller entirely off the Blackbird, the drag on the chassis alone would be enough to get it started rolling at accelerated to some percentage of windspeed. In the end, since by necessity they both exist on the craft, it is the drag from both that start the initial motion.
@@chalichaligha3234
One more comment on your excellent video.
You use the word "turbine" to describe the rotor of the Blackbird. You are correct that the function of the *entire vehicle* is to act as a turbine and slow the wind relative to the ground. You can even argue (as you did) that that is the function of the rotor itself.
You're not wrong in that, but we find that to get people to understand how the device works, we first have to get their minds out of the track that it is the wind hitting the blades directly that is turning them (like a normal wind turbine).
Most people understand how a wind turbine works (input thrust, output torque). Most people understand how a propeller works (input torque, output thrust). Since the rotor of the Blackbird functions as the latter, we find it confuses people less to describe it individually for what it is ... a propeller.
In the end, use whatever words or concepts you need to get your understanding of the craft across to people -- you're one of the few who truly get it right as to how it works. Well done.
@@johnborton4522 , I am humbled by your praise. I'm just happy that my explanation did justice to the machine in your eyes.
I understand what you mean about confusing people if considering it a turbine. One of the several commenters on Steve Mould's video after taking in the consensus we had reached on the thread produced a diagram that is perhaps the simplest explanation of the machine. I couldn't find it, but have recreated it: ibb.co/1b8jh0d
It shows that a faster than the wind downwind machine can be powered by a Savonius turbine, which of course would not work if the wheels were driving it, as this type of turbine cannot double as a propeller.
@@chalichaligha3234
Again, you are spot on -- there are numerous ways to design a device which can travel directly downwind faster than the wind apart from one using a propeller.
A few good examples from Rick here; ua-cam.com/video/X6oJpnSJyV8/v-deo.html
However, IF you simply put a turbine rotor on a tower and put a cart under it (which is what people see when they look at the Blackbird), it will never work.
Hi Rosie. Please rewatch original video at 12:14, can you explain whats going on? Propeller is accelerating against the wind without a movement. From where the energy come from? motor?
The energy is coming from the wind.
@@seneca983 but it spins against the wind, its wrong direction
@@sebastjansslavitis3898 If the propeller were to spin in the opposite direction it would slow down the cart. It is the right direction. Consider the inertial frame tied to the ground. In that frame the wind gets decelerated by the propelled behind the cart so the air is losing kinetic energy and the cart is gaining some.
@@seneca983 it is right direction to produce thrust, but its not the direction wind would spin it. And thats the problem. It accelerates where it should decelerate
@@sebastjansslavitis3898 "its not the direction wind would spin it"
The wind is not directly spinning it. It's being spun by the wheels to such direction that it generates thrust.
Rosie it has been a month since your last video and I have missed them. You are so down to earth and make this stuff fun. (Your AWESOME Ozzy accent doesn't hurt either.) LOL Keep these coiming.
3:33 - FINALLY I understand - the propeller pushes against MOVING air. Thank you!
Of course that doesn't mean I understand the rest of it. But this broke my brain last night.
And the propeller “pushes” against the air using what energy? The energy of the air molecules. When a flat sail is used instead of a propeller, the second Newton law applies: the air pushes the sail in one direction and the sail pushes the air in the opposite direction ( backwards). Is a rotating propeller that dissipates energy by pushing some molecules sideways more efficient that a sail? Why are we not using propellers instead sails in sailboats?
Me: Followed you every step of the way. You: Explain it back to me. Me: Not a chance.
Me as someone who plan to major in accounting : "hmmm, interesting"
Awesome! Thank you.
Really enjoyed this, thanks.
Wonderfull explanation! I was obsessed too, still am a bit, even made a cart going uphill on treadmill. Instead of propeller I used one axle with wheels to rest on the stationary relative to tredmill belt rims. So instead of using energy intensity difference between moving tredmill belt and room's air, my cart "catches on" the frame of treadmill(edges) to get propulsion and accelerate into apparent headwind. This way the energy source is not hidden by apparent wind, because is physically different substace: treadmill frame versus air. Both share the same feature, same relative velocity relative to treadmill belt, so both can do the same job. My clip is on youtube, called "Going faster than wind or relative nature of mechanical energy".
It's like storing the winds power in the forward momentum of the car like a flywheel.
YES! And when the flywheel kicks in to power the propeller to accelerate the vehicle to go faster than the wind there is no longer any wind pushing it, no more transfer of wind energy to the vehicle so that stored flywheel-stored energy gets used up and the vehicle slows down. The best you could do is fluctuate between a little bit faster than the wind and a little slower, with the AVREAGE SPEED of the vehicle being simply the wind speed.
@@RogerGarrett No, a cart like this can consistently exceed wind speed. It can accelerate even when going faster than the wind.
@@seneca983 The claim is that it's the wind that provides the motive force. The wind pushes the vehicle from behind, accelerating it forward. If there's no friction (e.g. wheels against the ground, other mechanisms) then the vehicle MY accelerate up to the point where the vehicle is moving at the exact same speed as the wind. At that point there is NO FORCE pushing the vehicle. If the vehicle slows down (friction) then there will again be wind force against the back of the vehicle that can possibly once again accelerate it up to moving at wind speed. But once the vehicle is at wind speed there is no force, so what is it that powers the propeller? The vehicle certain is moving, it has MOMENTUM, and that momentum can indeed power the propeller (for some period of time). But that propeller DEPLETES the momentum of the vehicle, meaning that the vehicle will slow down, MUST slow down, and the propeller will turn more slowly. The wheels rotating against the ground only serve as the mechanism for TRANSFERRING the vehicle momentum into propeller motion, they are not a "source" of energy. Rather, the source of energy, once the vehicle is at wind speed, is the momentum of the vehicle. When that momentum is tapped into it explicitly means that the vehicle slows down. Slower vehicle means less momentum available for rotating the propeller.
And IF, by some magic, the vehicle is ever actually going faster than the wind then there is no pushing force on the back of the vehicle but rather a relative pushing force against the FRONT of the vehicle, counteracting the momentum of the vehicle and further SLOWING IT DOWN. In other words, when the vehicle is going faster than the wind the wind is NOT powering the vehicle, yet the claim is that this vehicle is fully powered, at all times, directly by the wind, and in particular they discount the assertions concerning stored energy via momentum.
So, HOW DOES IT WORK?
@@RogerGarrett "At that point there is NO FORCE pushing the vehicle."
No, that's not true. Even at that point the propeller (powered by the wheels) is spinning and pushing the cart forward.
Why aren't the wheels, which power the propeller then slowing the cart by at least as much? It's because the air is moving *relative* to the ground.
@@seneca983 It IS TRUE that the WIND is not providing a force to push the vehicle, which is what I was saying in that statement. The claim is made over and over, even by the original builder of the vehicle, that momentum is NOT what powers the propeller but that it is only the wind. The vehicle certainly is moving and its momentum can continue to cause the wheels to rotate, TRANSFERRING some of that momentum to the propeller. The wheels are NOT a "source of power", unless you figure in the momentum of the rotation of the wheels. Heck there's stored momentum even in the propeller and the shafts and drive train. But all of that momentum is NOT coming from the wind once the vehicle is going the same speed as the wind. And as any and all of that momentum drives the propeller that momentum gets used up and that explicitly SLOWS DOWN the vehicle.
And again, if the vehicle ever WERE to be going faster than the ground-relative wind, the vehicle would then encounter a vehicle-relative wind coming at it from the front, being a DRAG on the vehicle and slowing it down.
The claim is made that once the vehicle is going faster than the wind it gets its energy from the interaction of the wheels and the ground, which powers the propeller, and the propeller causes the vehicle to ACCELERATE, which causes the wheels to rotate even faster, which causes the propeller to rotate even faster, which causes the vehicle to move even faster, which goes on and on in an endless feedback loop. Now, seriously, where is all that extra energy coming from? Doesn't that look an awful lot like an Over-Unity claim, a mechanism that creates more energy than it uses?
Really good explanation
Thanks for the great detail! 🖖
Actually, in the first few seconds of the video, you revealed the secret. The wheels turn the propeller. If the propeller turned the wheels, then it would be impossible for it to go faster than the wind, because as soon as the speeds matched, there would be no input from the wind.
Yes, she is good at the con.
A friend just sent me this old Mythbusters episode where they did something similar on water, powering a sailboat with an on-board fan: ua-cam.com/video/uKXMTzMQWjo/v-deo.html
That is a different principle, and basically is a poor implementation of reverse thrust as used on commercial airliners.
Nice explanation. I made a comment on the Veritasium Vid a few weeks ago suggesting nearly exactly that solution. Thanks that you did it! :-)
Ha ha, just for you 😉
I'll have to take your word for it.
I think the hard part to grasp is that the ground itself is part of the mechanism. I find it hard, anyway :-)
It could be me but as explained, it seems to me that if there is no wind, pushing it to sufficient speed should keep it in motion too.
I'd love to see them put that to the test, even if it's just the driver pedaling until the prop starts accelerating the vehicle.
@@Neetje42ever no, because you need to be able to detract power from the wind.
She mentioned in the beginning that an outside observer will see the wind behind the turbine being slower than in front. This won't be the case when there is no wind. ;)
@@Robbedem True but I wasn't looking at the general wind speed differences. If you look at 12:27 and beyond you'll see that a lot of the forward force isn't generated directly by thrust, but by lift. An aerofoil can generate a lot more lift compared to the drag it induces. The wheels have a lot less effort needed than it appears to keep the propeller spinning and generating lift.
But I'm not an engineer and considering this sounds an awful lot like a perpetuum mobile, I'm just going to call bs on my own claims.
@@Neetje42ever actual energy is extracted from DIFFERWNCE in speed of GROUND AND WIND
@@Neetje42ever No, you are right, you don't need wind. You can move the ground instead, like the small modells they put on treadmills. ;D But it's the same thing as wind blowing, but i had to think about it for a few minutes.
Galilean relativity still blows my mind every time I try to think about it. It's the reason rockets produce a forward thrust in a vacuum despite having nothing to push against.
Awesome - I thought I had some idea how it worked before, but turns out I had no idea really :) Going to have to watch through again, with a pencil and paper to keep up with the details!
There are lots of ways to understand it. My background is aero and specifically wind turbines, so I analysed it like that. People who sail think of it like a tacking sailboat, and many people think the gears/ level/ screw way to understand is the most intuitive.
Realizing you had it wrong after you thought you understood it is 93.7% of the battle. Watch the video carefully (and repeatedly if necessary) and I'm confident it will become clear. But I warn you that lots of people do finally get it, and then find their mind questioning aspects of it. I think Rosie said she went through a bit of this if I recall correctly.
The first boat propeller was literally a screw. It was a scaled up screw that was several meters long. It extended out the back of the boat underwater. It was made out of cast iron, so was very brittle. On the 2nd or 3rd outing, the screw hit something underwater and broke in half. The boat then sped up.
This is why to this day propellers are often called "screws".
I've also read that the geared prop has been connected to the screw of a boat, allowing it to travel faster upwind than wind speed. I want Rosie to take that on next, considering the effects of water and air slippage for both the water screw and the air screw. Let's not forget to give credit to Joby, the maker of the cart.
why does nobody visualize this problem showing the constant air pressure difference from above? The car obviously changes the surrounding air pressure difference. It will accelerate so long as the additional air pressure difference is greater than the drag it puts through to the ground via the wheels.
Sounds like you need to make that video visualising it in this way!
Best answer yet. You win the internet today!
In my mind, I picture an expanding 'teardrop' of red (indicating higher pressure) behind the propeller, which the prevailing wind is pushing against (and, of course, a corresponding 'blue' region of low pressure, in front). For me, the 'a-ah' was when I started to think of the wind blowing against the propeller, and pushing the whole vehicle forward. As the propeller turns, it begins generating an expanding volume of 'compressed' air, behind itself (thrust). At a certain point, the prevailing wind is no longer pushing directly on the physical propeller. Instead, it is pushing against this expanding volume of high pressure air, which resists being further 'compressed', and in turn, pushes the propeller forward, faster and faster, as the vehicle's wheels drive the propeller to expand that volume of compressed air, further and further behind.
@@CineSoar this high pressure wind buffer is a very common misconception with this vehicle. When we're moving faster than the wind, we don't have a tail wind pushing us anymore. At that point the propeller is pulling us through the air mass it finds itself in. But it has an advantage in that air mass since it's moving more slowly through that air than the wheels are moving over the ground.
The aerodynamics around and through our propeller are exactly the same as that of a propeller on the front of a Cessna. In the case of a Cessna we don't imagine that the propeller has to create a high pressure air buffer for the wind behind it to push on.
Another way I'm picturing it, after further thought... You have a car, there is a 100' long screw, threaded through the body, most of it's length is coming out the front. The wheels are geared, to rotate the screw, which moves it out the back of the car, as it advances. If you push against the screw, you begin moving the car forward, faster than you are pushing the end of the screw. The difference is the ever-growing length of screw, between you and the car. Now wind is 'mushier' than that screw, but that is a minor adjustment to the scenario.
Consider this variation to a Brennan torpedo. For the Brennan torpedo, two wires are pulled back from spools that each drive a propeller, geared so that the higher speed, lower force from the wires is geared down to a lower speed, higher force at the propellers. The wires move backwards, the torpedo moves forwards. If the wires were attached to posts, the torpedo would move downstream faster than the stream. The torpedo could be replaced by a model river boat, with the spools geared down to drive a paddle wheel. In this case, there is nothing that would resemble tacking.
Sorry, it takes energy to to pull back on those wires, energy that is lacking in Rosie's overly rosy explanation. See my separate comment above - It is for sure possible to cause a wind powered craft to go faster, even much faster than a buoyantly neutral balloon traveling with the wind, but the craft can not sustain that speed, it will slow down. The best you can do is pulse the speed of a wind powered craft.
@@roberthigbee3260 Energy is there, in plenty, supplied by the relative movement between the wind and the ground. The vehicle takes advantage of the difference in speed of the two mediums to harvest velocity. It wouldn't work if the vessel were in contact with just one of them (that would require another energy source to "pull the wire", as you said in the case of the Brennan torpedo). I was struggling myself with this too until I saw Derek's cart demonstration, see at 14:00 here: ua-cam.com/video/yCsgoLc_fzI/v-deo.html (to be honest I still find it counterintuitive)
@@roberthigbee3260 - you missed the part "If the wires were attached to posts, the torpedo would move downstream faster than the stream." So from earth|posts frame of reference, only the water and the boat are moving, and there's no energy being used to pull back on the wires. As for sailboats downwind component of speed, called "velocity made good", the high end catamarans used in the America's cup racing have achieved an average downwind component at about 1.8 x true wind speed over a sustained period of time.
@@rcgldr I will look into your America’s cup boat claim which I am interpreting from your statement to mean that those high end cats, while zig zagging with the wind can actually go faster than a buoyantly neutral balloon floating with the wind. I am assuming you are not confusing the velocity vector of the boat pointing straight out the bow with the wind velocity vector. Boats for sure can go faster than the wind, but at an angle with respect to the wind. However, on an intuitive basis, and because it is hard to fake the performance of America’s cup yachts, I am predisposed to believe you, without further proof, that a boat’s velocity vector in the direction of the wind can also exceed wind speed. But boats, with their sails and tacking and keel-water interactions, operate entirely differently than the prop-car we are discussing. Bringing up boats muddies the discussion… it is part of the magician’s purposeful misdirection. I am not sure why you are also continuing with the Brennan torpedo analogy, this is also a totally different thing and is another misdirection. Also, many others arguments in support of this prop-car, not necessarily you, say the words “it’s all about relative speed” are just repeating stuff they heard others say without understanding. They also start talking about “lever action” without really knowing anything. Rosie talks about “energy balance”, but does not rigorously and conclusively prove where the energy is coming from. A lot of fuzzy thinking. To be fair to you, I will watch that video link you gave me about the $10,000 bet tomorrow to see if it has any meat to it. Thanks for your reply…. BTW, I once saw, with my own eyes, a guy saw a lady in half… I saw it, so it must be true right?
@@gastonpossel I watched the Veritasium $10,000 bet video and I am now a believer, but a big part of the confusion lies with false and confusing statements by everyone including Veritasium in parts of his video (he is a classic “over seller”). Here is what I wrote in the $10,000 Veritasium video comments:
Life is a process. This Veritasium video is a process. This video has a lot of wrong and misleading statements, but at the end, gets the explanation correct, sort of. At the end, he still is promoting the treadmill experiment, which is for sure not doing what the Blackbird is doing (some aspects are similar, but it confuses things more than it helps).
My next comments dissect this video by explaining what is said incorrectly or in a misleading way, but also congratulating Veritasium on the one good explanation he comes up near the end. Also, spoiler, the Professor ended up giving Veritasium the $10,000!
Time mark 11:45 - false/misleading statement - “power is input into the system by the ground moving under the car”. The error in this statement is that there is zero energy created as the wheels interact with the ground. A transfer of energy within the “system” is all that can happen at the wheels. Saying “power is input into the system” at the wheels is the key not-true part of this statement. Presumably, he means the “system” is an imaginary dotted line (a “control volume”) that encompasses the entire vehicle (wheels, chassis, chain drive, mast & prop). The bottom line, clear as a bell, concept regarding energy, is that for Blackbird to accelerate, energy of some form has to enter this control volume. “Control volume” is a favorite concept with the Thermodynamic folks, but is it very useful in this discussion. The energy input could be that the ground was not really level and the energy input was really the exploitation of the potential energy due to Blackbird being higher at the start than at the finish, or due to momentary wind gusts as first proposed by the Professor.
Olive branch - If the wind was steady, if the ground was level, if there were no hidden power sources on the vehicle, if the data was recorded properly (no hanky panky) and the Blackbird really and truly can go faster than the wind, in the same direction as the wind and for sustained periods at constant or accelerating velocities, then the only logical available external power source that can enter the system control volume is the wind (let’s ignore solar energy input for now). So, there must be some sort of unaccounted for prop thrust amplification factor that is sustained by the interaction of the wind and the control volume.
BTW, the treadmill experiment is not a proof at all. There the energy input to the control volume is for sure at the wheels - the sloped treadmill transfers mechanical power to the wheels and then to the prop that generates thrust that moves the car forward and up the slope of the treadmill. This is not how the Blackbird interacts with the air. Consider a level surface, with zero wind - you could tow the Blackbird behind a pickup truck and watch the Blackbird catch up with and pass the truck, heck, it could then tow the truck… this ain’t gonna happen, but Veritasium’s mishmash of fuzzy explanations would make one think that could happen.
Another error at time mark 12:40 - lever action and bicycles going up hill are inappropriate comparisons. Yes, a lever exists, yes, mechanically, the torque at the wheels can be less than the torque at the prop drive shaft because the rotational speed is faster at the wheels (Torque, lb in = (63025 * HP)/RPM). So, yes, the force acting at the periphery of the wheel can be smaller than the force generated by prop, this is plain old everyday physics, no magic, no mystery, not new. The missing concept is the source of the energy entering the control volume. The kid is the energy source on the bike, a lever does not move unless you expend energy to push down on one side of it.
Time mark 14:20 - The “ah ha” moment - The little cart & 2x4 experiment - First off, and I don’t think he was trying to fool us, and he points this out too, watch carefully how the top big wheel is rotating counter clockwise. So, due to the ratio of the drive train, the small clockwise rotating wheels will drive the big wheel due to his energy input by shoving the board forwards, and the big wheel will “walk” along the board and go faster than the board’s velocity.
**** The key here is that board is both the energy source as well as a body for the big wheel to push against. ****
This was really the “ah ha” moment for me. Replace the board with the wind and imagine that the top big wheel has paddle wheel fins attached to each side such that they also rotate counterclockwise. The essential fact here is that the wind is the energy input and the paddle wheels have to have enough “bite” (call it friction sort of) to claw itself faster than the wind. Paddle wheels are too inefficient. The prop does the trick. I still stand by my earlier texts that the real problem here were the false and incorrect explanations from every one and that, from early on, I felt that for this thing to work, the interaction of the prop with the wind must be causing some sort of thrust amplification effect. Kudos to Veritasium for finally stumbling onto a good explanation, and that is what matters in the end.
Amazing! I never had a doubt this was feasible. Downwind jibing has been a thing for awhile, and sailing straight downwind feels so slow, it's all about the reference frame..
I am curious on the old-fashioned wind mills. You touched on it here, but It might be a subject for a full video. How did they evolve, how the sails were managed etc....Also the various types, flour mill lumber mill etc...
That's a good idea for a video, thanks for the suggestion!
And also, I only learnt that term "jibing" after I recorded this video... I always get the sailing terms wrong every time I mention it in a video!
I would like to thank you for your videos explaining Veritasium faster-than-wind vehicle, it helps clearing up some concepts.
I would like to ask you about a confusion I have on the calculations at 12:38 of that video on lift and drag force, and thrust and torque. The calculations seems to be done for 0.7 degrees instead of for 0.7 radians (arctan 11/13).
(Intuitively, the thrust force couldn't have been equal or even close to the lift force for a triangle with sides 11, 13, and ~17)
Can you clarify this? Thanks!
I love content like this, physics brainteaser explanations are the best!
Congratulations to that great Inventor with winning nice and cool $10G! ;)
And in case of a battle between scientist and engineer I'd always take engineer's side - because his point of view usually based on already proven reality, not just theory that can be faulty or incomplete!..
>> in case of a battle between scientist and engineer I'd always take engineer's side
I'm the one that conceived of it and built it with a friend, but I can't call myself the "inventor" because we learned that at least one other person had the same idea decades before me. That being said, I'm an engineer, but my title at my day job is "Chief Scientist" so I'm not sure which to root for. :)
@@Rick_Cavallaro Well, we - Russians, call people who mastered to perfection their engineering and craftsmanship skills "Levsha" ("Lefty" - character from one great fictional story) or Kulibin (Russian inventor).
-You're, Sir, 100% deserve any of them!
@@AaaAaa-ly3on I've worked with lots of Russian engineers and I take that as a great compliment.
The basic principle can be demonstrated with a bicycle.
If one pushes forward with a hand ( the wind) on the top of the rear wheel the bicycle moves forward at 1/2 the speed of the hand ( the wind). The wheel rolls without slipping on the ground. The wheel center is 1/2 way between the hand and the center of rotation, the wheel contact point with the ground.
If one puts the hand near the center of the wheel the wheel center and the bike move at the same speed.
So far so good...
Now if one puts the hand ( the wind) 1/2 down from the wheel center along a vertical spoke and pushes forward, the wheel center and the bike will move at twice the speed of the hand ( the wind) as the vertical spoke rotates instantaneously around the wheel contact point with ground.
As the hand is moved lower the speed ratio increases. That is what the Blackbird of the video is doing. The wind is the hand, the propeller( the bicycle spoke) makes contact with the air, The Blackbird rear wheel contact point with the ground is the bicycle wheel contact point. The ratio between the distances between the bicycle ground contact and the wheel center and the hand correspond to the combined Black bird wheel/propeller gear ratio and propeller pitch.
Note that as the Blackbird speed increases above the wind speed the more air it can slow down so the more energy it can extract from the wind. The max energy extracted is when the air speed with respect to the bird in the wake of the propeller is equal to the wind speed. ( note that propeller is the correct word when used with respect to the Blackbird), in the reference of the ground the propeller wash has zero speed!
Note also that the Blackbird can go straight up wind. In the bicycle analogy this corresponds to putting the hand on an imaginary spoke extending below the ground contact point. As one pushes, the wheel center and the bike move in reverse. For a more realistic analogy imagine a rail cart wheel on a rail. Pushing forward on a point of the flange below the wheel-rail contact point, makes the wheel wheel move backward with respect to the hand while the flange below the contact point will move forward. The hand does positive work.
Have fun!
I think you hit the nail on the head when you said it was powered by the ground [the difference between the air speed and the ground].
The latest Veritasium video had a good demonstration of this, where they used a wooden plank with a multi-wheel device. It clearly showed it was the difference between the wood and floor that provided energy to move the device forward much further than the plank move.
1:53 "my idea of a fun time"
me: laughs
also me: *cries in engineering student*
Me too
I think the simple way to understand this is just to remember that the wheels drive the prop.
I think the simple way to understand this is a HOAX is just to remember that above wind speed the only forces acting on the wheels are gravity & drag.
@@pl2727 and the force generated by the propeller. The propeller pushes against the wind no matter how fast its going. I mean, how do you explain the treadmill models that people make that work perfectly?
And what does drive the wheels???
@@jetison333 They don't work. They don't work without fan behind them. And they aren't going faster in the air than the fan's wind speed.
@@belamizsak161 Sounds like a conspiracy theory to me.
This is a very good example of why it is important to solve a problem objectively not just look for evidence to support your opinion.
Hi Rosie, I understood the condition we need to drive the cart to move faster than the downwind.
In my understanding, from the perspective of the cart, the linear velocity of the wheel must be faster than the velocity of the propeller relative to the wind no matter in a downwind or treadmill system. Am I correct?