Arthur Smith

The important point to be aware of is Blackbird in its downwind mode is using a propellor, not a turbine. The propellor is being powered by a chain driven from the wheels, it is not driving the wheels. Until the vehicle nears windspeed it is not contributing to the vehicle's motion. The propellor pitch is variable. Imagine pitch set to zero thrust (blades at right angles to wind direction). The vehicle approaches wind speed more quickly, then stabilized at just under windspeed (due to rolling resistance). Then pitch is set to achieve maximum thrust. The question is can that thrust exceed the wheel drag and that larger force cause the vehicle to accelerate beyond windspeed. The pro-argument is that gearing allows a smaller force times larger distance to produce a larger force times smaller distance.

Perhaps the difference is there is less support for the position "Jesus is real and the Bible proves it" than there was even just eight years ago.

I recently became aware of the claim that the Old Testament is a recent compilation written in Greek by a group of Jewish Scholars living in Alexandria around 300 BCE and drawing extensively on the resources of the library, without any first-hand knowledge of Biblical Israel. The Hebrew OT was a product of translation from that source. ETA typo plus not my theory but interesting nonetheless

What old Hebrew texts? ETA correct typo

Well, maybe. But why was he writing in Greek, rather than Aramaic (the lingua franca of the time and region) or Latin, the official language? Thanks for finding that. I'll have a look through, though 2014 is a while ago. Can't argue with that! On glancing through the previous thread on reality of Jesus, there's a lot of chaff in the wheat.

I'm a life-long atheist so there may be some bias (or ignorance) in my following remarks. The surviving texts that finally ended up being referred to as the New Testament are all written in demotic Greek. Not Aramaic, which gets a brief mention. Not Hebrew. The authors are anonymous, attribution murky, especially considering where the apostles, some who were simple Galilean fishermen, would have learned to write, let alone in competent Greek. By some accounts' the historical and geographical references are doubtful. Paul, according to his own writing, never met Jesus and his earliest writings post-date Jesus's death by at least twenty years. There's nothing to support the New Testament events in other contemporary text sources or in archaeology. Whoever developed the stories in the New Testament may have based stories and ideas on a human figure or figures but there's almost nothing other than the Bible itself to suggest there was a real figure of the stature and influence described there. Also, who decided what went in to the NT and, perhaps more importantly, what was left out? Nicea, Constantine, all happening in the 300s. On the other hand, I have heard it argued that there are many parallels in parts of the New Testament with Homer's poems: the Iliad and the Odyssey. Was there something from mythers?

DDWFTTW discussions have happened and often became heated since Rick Cavallaro became obsessed by the brain teaser. The issue was never whether there was a practical application. Different folks have proposed different analogies to model the effect. Imagine an airship floating in wind trailing an cable pulling an electrical generator on wheels which drive the generator, the generated electricity used to power a propellor mounted at the pointy end of the airship. Can the additional power supplied by the movement of the generator be enough to accelerate the airship above windspeed? Me, I take the empirical view. The various demos convince me. Seeing a bumblebee fly is a stronger argument for me than sheets of calculation proving a bumblebee can't fly. PS, I see your name has cropped up in another very-similarly-named forum in connection with the moderator, Oceanbreeze. PPS Some impressive footage of racing yachts exceeding windspeed:

Here's a short video of a model shown at the physics department of the Free University of Berlin, during the "Long Night of the Sciences" (open house). Thanks to everyone who participated in the thread. I can't help being a little disappointed that nobody took the skeptical view that travel downwind faster than the wind is impossible because some fundamental law of the universe is being flouted.

They could definitely do with some.

Indeed. That was my initial reaction until I realised, watching a video of Blackbird perform, that the prop is turning against the wind on starting. No fixed sail arrangement will enable you to sail directly downwind at greater than windspeed. Granted, the latest racing yachts (that lift hulls clear of the water on aerofoils) can achieve 3 times true windspeed going cross wind and ice yachts 8 times or more. But not directly downwind. Blackbird has got to nearly 3 times windspeed. Of course there is no practical application. Rick Cavallaro just wanted to prove a point.

You may be misreading something I wrote earlier. I've known about Blackbird for a few years. I've no doubt it works and how it works. When I first came across that discussion, I was initially skeptical as at first glance I found it counterintuitive. I'm referring to people in the link you didn't follow.

No he's a bona fide physics prof. https://en.m.wikipedia.org/wiki/Alexander_Kusenko Still some find it hard to believe: https://www.scienceforums.com/topic/38721-the-1969-blackbird-wind-turbine-sailing-craft-concept/

Many people, including me to start with, think it flouts the law of conservation of energy. How, they ask, can the thrust generated by the propellor exceed the drag produced by the wheel on the road?

Shucks. I was hoping for more controversy before the spoiler. Rick Cavallaro built a wind-powered vehicle "Blackbird" capable of exceeding windspeed while moving downwind in 2012. Last year he won a bet with a physics professor who claimed it was impossible. https://www.businessinsider.com/youtuber-won-10000-bet-with-physicist-over-wind-powered-vehicle-2021-7?r=US&IR=T

Just to be clear, directly downwind, in the same direction as the wind and in excess of windspeed.

No. One thing sailboats can't do is sail directly upwind. They can travel upwind by tacking and high-performance yachts can exceed wind speed when doing it. The best they can do sailing directly downwind is to approach windspeed.

Is it possible to conceive of, design and construct a vehicle that, powered only by the wind, can sustain speed in excess of that wind while travelling in the direction of that wind? I'm a new member so, if this teaser has been asked before, my apologies.

I'm more interested in where the edges of a human lie. Topologically we're distorted doughnuts so gut contents don't count? Bladder contents? Dead skin cells? Ah, I see your point.

And nobody has mentioned Avogadro's number yet. (6.02214076×1023 mol−1)