Back in 2010, a wind-powered car was clocked by U.S. researchers as traveling down a runway nearly three times faster than the wind pushing it, seemingly breaking the laws of physics.
Since then, the ‘downwind faster than the wind’ or ‘DWFTTW’ debate has raged on, both on the internet and within the academic community, with some concluding the tests to be illusive and others proposing theories to validate the result. Youtuber and host of Veritasium Derek Muller, has even gone so far as to place a $10,000 bet with UCLA Professor Alex Kusenko, that he can conclusively prove DWFTTW possible.
Muller’s recent video publicising the high-profile wager has already racked up more than 5.5 million views, but now fellow Youtuber ‘Integza’ has also waded into the debate, proving his theory using 3D printing. When placed on a treadmill, Integza’s wind-powered replica is able to recreate the DWFTTW effect and prove the critical role of relative speed in how it all works, bringing clarity to a long-running debate.
‘Breaking the laws of physics’
Built by Rick Cavallaro, as Chief Scientist of the now-defunct Sportvision Inc, the ‘Thin Air Designs’ wind-powered concept car was originally designed to prove his calculations correct that DWFTTW is possible. Cavallaro’s claims were initially met with skepticism, thus he got backing from wind turbine firm Joby Energy as well as Google to produce a prototype.
An initial version playfully known as the Big Ugly F***ing Cart or ‘BUFC,’ managed to achieve speeds greater than the down wind speed, at a lakebed in Nevada during March 2010, thus Cavallaro and his team set about building a definitive testing model called the ‘Blackbird,’ which reached a top speed in later tests of more than 2.85 times faster than the wind blowing at the time (13.5 mph).
Back then, Cavallaro explained that Blackbird was able to achieve DWFTTW thanks to its propeller, which wasn’t actually turned by wind but by its wheels, which spun the blade in the opposite direction to the wind, allowing it to pick up pace. Unhappy with this theory, the internet has continued to debate these ten-year-old tests, thus Muller and Kusenko have now sought to settle things over a $10,000 bet.
Muller’s $10,000 gambit
Broadly speaking, Kusenko’s objections to DWFTTW revolve around the car’s wind speed, gradient, human steering and data analysis. For Kusenko, variations in wind speed could have led a large gust to push Blackbird forwards before dying down suddenly, temporarily creating the illusion that it was travelling faster than the wind.
Compared to its wheels, the concept car’s propeller is also considerably higher, and given that wind usually travels faster at lower altitudes, this could create an inconsistency that causes a similar effect. Add to this, the fact that post-analyses are often carried out on treadmills using hand-deployed replicas, and data analysis has left open the possibility of ‘infinite speed,’ and Kusenko may have a point.
In an attempt to prove Kusenko wrong, Muller boldly bet him $10,000 last month (in front of Bill Nye and Neil deGrasse Tyson no less) that he could prove DWFTTW possible. According to Muller, the Blackbird’s ‘telltales’ show that every part of the vehicle was moving at the same speed, debunking Kusenko’s ‘sudden gust’ idea.
During his viral response, Muller also used a pulley system to demonstrate how an object can move faster than the one pushing it, before working with fellow Youtuber Xyla Foxlin to 3D print a treadmill test model. The Blackbird-like replica was able to ‘accelerate’ faster than the wind pushing it, and ultimately Kusenko conceded the bet, forking out $10,000.
Despite this, Integza now thinks that he can do better, and has recently released a new video, explaining DWFTTW in a less convoluted way, without the equations explained by Muller during his rebuttal, using a 3D printed model of his own.
Proving a point with 3D printing
In his video, Integza largely comes to the same conclusion as Muller, albeit with the aid of a simulation model, produced using an Elegoo Mars Pro2 3D printer. Featuring a gear-driven propeller system similar to that found on the Blackbird, the Youtuber’s simple-yet-efficient design has allowed him to replicate the ‘rotating-sail’ concept which drove the original.
After his first design failed initial testing, Integza found that pitch was critical to the car’s performance, and 3D printed a new foam-like propeller in which this could be adjusted manually. The revised concept proved capable of DWFTTW at 6.7 km/h, and thanks to its basic design, the vehicle clearly shows how the relative speed at which the wind hits its blades enable it to travel ‘faster than the wind.’
In his video, Integza also goes on to use his model to demonstrate that drag and wind resistance eventually prevent the car from accelerating, thus it cannot accelerate forever or travel at ‘infinite speed.’ As a result, the Youtuber’s video provides a simplified explanation of how it’s possible to outrun the wind, illustrated via an easy-to-build and accessible 3D printed model.
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Featured image shows Youtuber Integza’s 3D printed model of the Blackbird. Image via Integza, Thingiverse.