Downwind Faster Than the Wind by Veritasium: How Does it Work?
This is a response to @Veritasium 's recent video: Risking My Life To Settle A Physics Debatehttps://www.youtube.com/watch?v=jyQwgBAaBag&t=376sI 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: https://twitter.com/veritasium/status/1403130178197278720I 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. https://www.patreon.com/engineeringwithrosieBookmarks:00:00 Intro00:29 Bet between Derek Muller and Alexander Kusenko02:14 Description of how the Blackbird cart works02:58 Analogy: like a cyclist pushing off a car to go faster than the car03:56 A perpetual motion machine? The wheels turn the propeller, but they don't power it04:51 This clearly violates the laws of thermodynamics!05:38 Energy balance with some simple numbers07:22 How it gets moving from stationary07:56 It's not a wind turbine08:45 Why the propeller's thrust is larger than a push from the tailwind can be09:32 Aerodynamic concepts: lift, drag, angle of attack, relative wind speed10:29 Aerodynamics of a propeller11:00 Blade element model of the Blackbird propeller12:27 Aerodynamics (vectors analysis) of the Blackbird propeller at record conditions (2.8 times wind speed)13:26 Propeller aerodynamics at faster than record conditions14:01 Propeller aerodynamics at wind speed (zero relative wind speed)14:43 Slower than wind speed14:56 Link to more analogies from Rick Cavallaro the Great16:29 Bonus analogy: a propeller is a kind of screwExtra resources to understand the concepts in more depth:Designer Rick Cavallaro's long speech with *many* analogies: https://www.youtube.com/watch?v=X6oJpnSJyV8Putting numbers on iceboat performance (analysis and GPS data that shows boats moving many multiples of wind speed) https://www.nalsa.org/Articles/Cetus/Iceboat%20Sailing%20Performance-Cetus.pdfSailing yacht design for maximum speed: http://static1.1.sqspcdn.com/static/f/572109/24503675/1394724903587/Sailing+Yacht+Design+for+Maximum+Speed.pdf?token=5pzNaaWIFu%2F7e3pN5RiQ2e6MmmM%3DEyytee'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.https://www.youtube.com/watch?v=H_OKNr120t4Performance of propellers lecture notes from MIT course "Thermodynamics and Propulsion"by Prof. Z. S. Spakovszky (includes blade element method): https://web.mit.edu/16.unified/www/FALL/thermodynamics/notes/node86.html#SECTION06374200000000000000NASA propeller thrust page: https://www.grc.nasa.gov/www/Wright/airplane/propth.htmlAerodynamics for students Blade Element Theory for Propellers (nice simple version that I used):http://www.aerodynamics4students.com/propulsion/blade-element-propeller-theory.phpA written version of the same material is here:https://rosemary-barnes.medium.com/downwind-faster-than-the-wind-by-veritasium-how-does-it-work-536a3e43939e?sk=60990c3cb04af804ba466298131f66b4Image and footage credits:Risking My Life Defender By Donan.raven - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=28858489Ice boat By HopsonRoad - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=38929718Ice boat pdf https://www.nalsa.org/Articles/Cetus/Iceboat%20Sailing%20Performance-Cetus.pdfIce boat By Raul Kern - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=17614013Ice boat By Pataki Attila István - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=89038435Downwind faster than the wind wedge animation https://www.youtube.com/watch?v=H_OKNr120t4Screw animation By ja:User:＋－- Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=28858489The aeroplane on a treadmill image from xkcdhttps://blog.xkcd.com/2008/09/09/the-goddamn-airplane-on-the-goddamn-treadmill/#engineering #science #stemThanks for watching the video Downwind Faster Than the Wind by Veritasium: How Does it Work?