Wind driven cart goes downwind faster than the wind

[F-X]

You haff zeen droo my evil plan

[Dingfod]

Originally Posted by Ensign Steve

WTF is this shit? According to wikipedia, the Star Tracks is about outerspace, not San Francisco in the 80's.

Nice try, guys, but you have to get up pretty early in the morning to put one over on me!

Holy crap, I think the brunette was Sharon Stone.

[Sock Puppet]

You're right, ES. The movie they're talking about was the one with socially inept characters trying to save a whale via a dubious plot device. You know, Free Willy.

[F-X]

YouTube- Forever Electric car ( by wind force...

[F-X]

With out a spork, these threads never go anywhere.

[F-X]

For the record, they set the record.

[Corona688]

As I see it: Don't imagine the propeller as a fan or a sail. It's a wing. (Two wings, one upside-down.)



Wings don't push back against the air like a sail flat to the wind -- they work edge-on, and are pushed up by the Bernoulli effect. The air passes around them smoothly and their shape causes higher air pressure on one side than the other, pushing up, not back. There's some drag of course, but that's not related to the lift, it doesn't cancel out.

This is an amazing confirmation of the Bernoulli effect. I've seen a lot of people deny that wings work through pressure differential, just shoving air downwards for Newtonian up-force instead. This device would be impossible if that were true, since the force pushing back would be equal and opposite to any gain it gets. (So would gliders, when you think about it -- they'd need constant force to keep flying, but have no engines...)

This isn't a perpetual motion machine either. The faster it goes, the more lift it gets, sure -- but the faster it goes, the more drag it has as well.

[yguy]

Originally Posted by Corona688

As I see it: Don't imagine the propeller as a fan or a sail. It's a wing. (Two wings, one upside-down.)

Wings don't push back against the air like a sail flat to the wind --

I believe I can safely say the designers of the cart think of the propeller blades as the aerodynamic equivalent of sails on vessels tacking downwind.

[But]

Originally Posted by Corona688

As I see it: Don't imagine the propeller as a fan or a sail. It's a wing. (Two wings, one upside-down.)

A better idea would be, I think, to imagine the propeller as a fan and a sail.

Wings don't push back against the air like a sail flat to the wind

Because they are usually not flat to the wind.

-- they work edge-on, and are pushed up by the Bernoulli effect.

Among other things. Look at the insane angle of attack on those propeller blades.

There's some drag of course, but that's not related to the lift

Uh, yes it is.

it doesn't cancel out

Sure, partly because it has a different direction.

I've seen a lot of people deny that wings work through pressure differential, just shoving air downwards for Newtonian up-force instead.

So wings violate Newton's third law? Could this mean that night flying restrictions cause global warming, because all those planes pull the Earth towards the Sun?
If those people treat that question as an either-or, of course that's nonsense. But air has to be shoved downward, whatever you choose to call the multitude of effects or principles or whatever involved.

This device would be impossible if that were true, since the force pushing back would be equal and opposite to any gain it gets.

Please explain.

So would gliders, when you think about it -- they'd need constant force to keep flying

Actually they do, as long as they are denser than air (even if you ignore friction on the wings and fuselage). You may have noticed that they do come down after a while.

[But]

Thread necromancy

Risking My Life To Settle A Physics Debate -...

A Physics Prof Bet Me $10,000 I'm Wrong - YouTube

[slimshady2357]

I missed this thread I guess first time around.

So a second for you!

Great videos and well worth the watch.

[Ari]

The jankyness of the car is amusing.

Originally Posted by Image in every textbook

I think I’ve decided it’s this basic image that is the culprit of so much confusion.

As drawn, no this doesn’t produce lift. Parallel laminar flow that perfectly separates around an object and then returns to parallel probably didn’t impart anything more than drag on the object, but this isn’t what the airflow over a wing looks like at all, air that moves over the top of the wing ends up going downward, not returning to parallel.

Spoon on a string in the sink seems like a great demonstration of what’s really going on. I also spent way too much time the other night playing with different spoons and flow rates, the smaller Teaspoon worked remarkably well. (It too get’s claimed to be Bernoulli’s principle even though it’s blatantly clear it’s not (you can also do it with a fork)).

[Ari]

In general this has been on my mind as I’ve been thinking of ways to explain basic physics to kids, especially since I think there’s some reasonably complex things kids or high schoolers could be led to discover so long as they are given a good foundation at the the start.

I also think this common textbook representation causes extra confusion by flipping frames for the teachers benefit, not the students.
It’s always drawn with air rushing over a static wing, and then some quick mention of frame independence, blah blah blah. However I think people see the wind rushing over the static wing, and look up and see an airplane flying through the sky and connections get confused (even though I know the spoon does just that).


If you’re wondering well how the hell does the airplane wing shape work then?
Similar to how the water sticks to the surface of the spoon and flings off in a different direction, air sticks to the top of the wing and gets flung downward from the trailing edge. Downward flung air imparts an upward force on the wing.

From the frame of a wing zooming through the sky, it feels so easy to see what is really going on here, and how air at the wings surface is getting dragged by the wing along its downward shape.

The air is a whole bunch of tiny free flowing molecules, almost like a ton of little balls and we, jackass humans trying to fly, are going to ram this wing through them!

The wing’s leading edge moves left slaming into the once stationary air, that suddenly starts moving left and at a slight angle up, if this was a vacuum it would fly off forever but in atmosphere it travels just a tiny fraction until running into other balls that bounce it back towards the wing, which has advanced every so slightly so this time when it bounces it’s further along the wing, while another ball hits the spot it previously did. Over and over the molecules that contact the wings surface get bounced in tiny clockwise spirals at the very surface of the wing as it pushes from right to left through the air.

CAD:HO!
Confusingly Animated Demo: Hoard Only.

<——

It doesn’t feel much of a stretch to then see that as this set of spiraling balls expands a bit, it reaches into the more still and laminar air, before being bounced down into a few resting balls, that go through a few of these tiny spirals before becoming still again, causing these spirals to grab at the stiller air above them. This spirally grabbing action is what is attaching the top of the wing to the air above it like spinning velcro, this stickiness combined with a low friction ‘ball barring’ like layer over the top of the wing wing makes following the downward contour the easy and optimum path. (The switch from stable or slow growth in this turbulence layer to unstable or fast growth is what sets the wings stall angle, and yes that does indeed sound fractalish).

In the old ‘wing reference frame’ I would be trying to convince you that the closer the air gets to the wing the slower it goes, until right at the wing it is stopped. Certainly a bit shorter and still correct but it also sounds like sciencey-woo magic, that I’m just telling you to accept.

[-FX-]

Originally Posted by But

Thread necromancy

Oh sure, it's OK when you do it

[LarsMac]

I never saw this, before. By thanks for it.
I am puzzled by all the critics.

We actually did the same thing in an airboat on Lake Okeechobee some years ago.
OK, a lot of years (and Beers) ago.

Once explained, it seems quite intuitive.

[Edit]
I am not saying that the idea is terribly practical, mind you. There are way too many "moving parts" that create far too many opportunities for failure to make this a truly practical mode of transportation real-world.
But as a toy, it's pretty far out.

[-FX-]

Originally Posted by LarsMac

I never saw this, before. By thanks for it.
I am puzzled by all the critics.

After almost 14 years of following the subject, the men behind the quest, the various builds, the testing, the reaction from different forums, the fact it popped up again, and had an actual bet, and a resolution to the bet, it's a brain teaser that delivers.

There were a few skeptics who ended up a tree, and never backed down, no matter what, but they faded away with no fanfare. The nature of this means it will show up again in another decade.