Okay all you wizards of wind... this is a world renowned physics claiming a wind driven vehicle can be made to go down wind faster than the wind —- mind blown!!!!
Last edited:
Some will hate this!!!
- Thread starter rgranger
- Start date
Their thought experiment with the cylindrical world really helps show how it works.
Haven’t watched the whole video yet, but there’s no reason that it wouldn’t be possible. The America’s Cup boats now routinely sail downwind at faster VMG than windspeed. The propeller experiment is pretty much the same idea, except the spinning propeller takes the place of the tacking/gybing boat.
I believe this has to do with the "apparent wind" seen by the blades, which is a vector sum of the rotational speed and horizontal speed.
Actually once he explained that the prop is propelled, then it makes a lot of sense. All you are doing is converting the differential energy between the ground and the wind into motion. An even simpler way to think of it would be to attach a post that can pivot at ground level. If the wind pushes just above the base of the post, the top of the post will move faster than the wind. Effectively this is what you are doing, only it is continuous motion rather than just a single arc.
All in all, this reminds me of the time I took several friends on their first time sailing. We sailed down wind for some time, putting along quite slowly. We then did almost a 180 into the wind and of course the boat took off. They were quite amazed and had a hard time excepting what they were experiencing.
All in all, this reminds me of the time I took several friends on their first time sailing. We sailed down wind for some time, putting along quite slowly. We then did almost a 180 into the wind and of course the boat took off. They were quite amazed and had a hard time excepting what they were experiencing.
No, an ice boat does essentially the same thing as a sailboat, just with less drag. This is quite different because it's the mechanical connection to the ground that makes it possible. Because the wheels are on the ground, the prop is driven at a speed that puts the airfoil section of the prop at a "broad reach" angle relative to the wind. Without that, this wouldn't be possible.
So the first "mind blown" item is sailboats can sail faster than the wind. Mine won't but cats and foiling boats will. So there are flat out undeniable existence proofs of sailboats going 2x the wind speed. They do this on a reach however where the sails still act as foils. Dead Downwind is the real mind blown part of this. In a sailboat dead downwind the sails are stalled there they are pure drag devices and as such you can only go at best the speed of the wind. So going faster than the wind dead downwind is thought to be impossible. But seems if you are clever it isn't.
Exactly. The clever part was in realizing that, although the vehicle is going dead downwind, the airfoil section of the prop isn't.
I love this perspective.
What's interesting to note is how much power is actually in the wind. The idea that wind, at a given speed can actually have enough power to push a vessel of any tonnage is amazing enough, but that wind has enough power to push a vehicle faster that the wind itself is mind boggling.
The idea seems to defy physics until it actually does, then it becomes "apparent" that there is a lot of unrecognized and untapped power in the wind.
-Will
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 22,819
Folk around the world say we should tap that power. Build boats to sail across the oceans. No need for oil. But wait we have done that.
Build wind mills to cover the land with blades that cover the skyline. But wait we are doing that.
Fill the bays and coastal waters with windmills to capture the winds that blow.
Cut the trees down in Maine to run the electrical wires to power the cities. We are doing that.
But wait. Should we?
Interesting idea. Mechanical energy converted to kinetic energy. I would think they'd want some sort of sail to more efficiently move the cart down wind. The only windage on it are the two foil supports for the propellor assembly. On the other hand once they exceed the wind speed that device would become a brake. So, it would need to be retractable. It could have flaps that come out from the side in the low speed mode and retract while exceeding the wind. That would be kewl.
wind is not linear. the wind near the deck is not the same as the wind aloft. wind swirls. he says that he likes to imagine it as all the wind is going 10 kms. very false statement. wind getting sucked by the prop changed the yarn? it could have been blowing 14 at the top of the blades. no one knows. ZERO SCIENCE! direct false statements.
stupid is as stupid does
stupid is as stupid does
Last edited:
What exactly are you suggesting, Jon? You aren't suggesting they didn't actually succeed in getting the wind to move their vessel faster than the wind while heading dead down wind, are you?
My understanding is that once the vessel was moving faster than a certain point with the wind, the windmill became a fan driven by the wheels rolling over the ground. It's push to send the vessel forward had the added benefit of pushing against a following wind, so the air movement that caused forward movement was additive between the rearward moving air of the fan and the forward moving air that initially drove the windmill.
Obviously, the speed and angle of attack of the air on the blades is going to be very different near the hub than out by the tips. That means only a small portion of the blade can be expriencing an optimal condition for best lift force. As Jon points out, air movement at the tips when the blade is at the top of its turn is going to be different than air movement at the tip of the blade at the bottom of its swing. Yet, the average across the whole device is still enough to drive a vessel faster than the wind speed.
Absolutely amazing.
-Will
My understanding is that once the vessel was moving faster than a certain point with the wind, the windmill became a fan driven by the wheels rolling over the ground. It's push to send the vessel forward had the added benefit of pushing against a following wind, so the air movement that caused forward movement was additive between the rearward moving air of the fan and the forward moving air that initially drove the windmill.
Obviously, the speed and angle of attack of the air on the blades is going to be very different near the hub than out by the tips. That means only a small portion of the blade can be expriencing an optimal condition for best lift force. As Jon points out, air movement at the tips when the blade is at the top of its turn is going to be different than air movement at the tip of the blade at the bottom of its swing. Yet, the average across the whole device is still enough to drive a vessel faster than the wind speed.
Absolutely amazing.
-Will
I'm not prepared to say you are wrong, but this guy has a tremendous reputation as a science educator and a PhD in physics from Syndney.stupid is as stupid does
Derek Muller - Wikipedia
en.wikipedia.org
I have watched a lot of his youtube posts and always find my mind blown... just a bit. He has been featured on several other famous scientists feeds.
If you want to go down a deep rabit hole... check out his site.
Well for a sailboat to make better than the wind -- down wind-- it has to gybe downwind. So, it is not sailing directly down wind and the answer is no... a sailboat cannot sail faster than the wind if it is sailing directly down wind.
And to the best of my knowledge, a sailboat cannot sail directly upwind. As it speeds up, the aparent wind shifts forward but that is another conversation.
By using a spinning propeller they’re leveraging the same effect as a sailboat gybing. In both cases the foil is going with the wind and across it, generating lift to pull the vehicle downwind. A sailboat gybes because it can’t keep going to one side indefinitely. The propeller spins around the hub to change directions.