down wind faster than the wind

[gregm]

this is real, and i assure you i am not an overly stupid person.

http://www.boingboing.net/2007/02/06...-vehicle-.html

be sure to check out the above youtube vid


http://www.btinternet.com/~sail/dwfttw01.htm

http://www.gummy-stuff.org/boat-and-wind.htm




i personally think it could work, the propellor cart anyway, because the wind would be pushng against the cushion of compressed air behind the propellor.

[squirrelmurphy]

but what if it's on a treadmill?

[gregm]

but what if it's on a treadmill?

Well here you go Mr Smartypants:

[Ted Striker]

i personally think it could work, the propellor cart anyway, because the wind would be pushng against the cushion of compressed air behind the propellor.

...and what year did you drop physics?

"I can calculate the motion of heavenly bodies, but not the madness of people."
The guy who said that came up with a few 'laws' that would suggest that the wheeled land version of that machine cannot go DWFTTW without an additional source of power (like gravity).

[NorthernSpotted...]

I'm going to preface this by saying I quit my mechanical engineering degree after two years and I haven't taken a physics class in about 8 years so I may be talking out of my ass buuuut....

I don't think the treadmill thing proves anything. The motor is providing the power via the belt. If the gearing, propeller, and treadmill speed are set correctly, the force of gravity/treadmill and the force of the propeller will exactly counteract each other. It's like the orbit of the moon around the Earth in way. It's always "falling". No big revelation there.

The wind thing? A little trickier. With the propeller geared to the wheels, the cart has more kinetic energy stored in reserve than it would if it was just a cart with a sail. Therefore, it can maintain speed a little longer if it looses its power source, wind in this case, temporarily (think flywheel). Therefore, a little gust will accelerate the cart and it will be moving faster than the steady wind speed. When the wind dies a bit the flywheel effect will allow the higher speed to continue a little while longer than otherwise possible until the next little gust charges up the propeller again. So, the cart may be able to maintain an avg velocity than is faster than the steady wind speed if the conditions are absolutely perfect. I can see how this could be deceptive to an observer outside laboratory conditions but I still don't think the whole DIMWIT thing works.

Anyone else care weigh in? I spent a great deal more time thinking about this than I care to admit and I don't want to feel like a total nerd. Wait, it's too late for that. Someone at least give me some company please.

[milton]

.
.

Anyone else care weigh in? I spent a great deal more time thinking about this than I care to admit and I don't want to feel like a total nerd. Wait, it's too late for that. Someone at least give me some company please.

Here you go, 24 pages of company-
http://www.tetongravity.com/forums/s...ad.php?t=41643


better now?

[toast2266]

Here you go, 24 pages of company-
http://www.tetongravity.com/forums/s...ad.php?t=41643


better now?

but the jet thing is completely different; with the jet, the wheels are completely irrelevant. Here, however, the wheels are powered by the propeller.

I have no idea whether the down wind thing would work or not. It seems like it shouldn't, but I watched the two videos, and I'm gullible, so therefore I am convinced.

[NorthernSpotted...]

Here you go, 24 pages of company-
http://www.tetongravity.com/forums/s...ad.php?t=41643

better now?

Meh, I'm over it. I had a minor buzz going last night and became temporarily ensconced in the problem. I realized later that a lot of what I wrote wasn't all that well thought-out and was full of holes. I was almost glad this morning when I found it disappeared by the crazy server nonsense.

[Skipig25]

well ain't that nifty

[hafilax]

If the wind or the treadmill stop the device stops so it doesn't seem like perpetual motion to me. I would also guess that for a given setup it only works for a limited wind speed range. I didn't really like the test in the video for starting it only with wind. In the first gust the propeller spun the wrong when then it skipped and skidded a couple of times before settling into the normal mode. That test would work better in a wind tunnel where the air speed could be ramped up in a controlled fashion.

If you could build a similar device that would go upwind then I think that would be perpetual motion. A slight push and you'd be able to sail along in still air for ever.

I looks like a complex optimization problem mostly between the angular speed of the wheels, losses in the gears and bearings, the angular momentum of the propeller, thrust and drag losses from the propeller and finally the drag of the wind on the whole thing.

[Yeti]

From the planes on treadmills department: a nerdy bump for a new Wired article covers going downwind faster than the wind.

http://www.wired.com/autopia/2010/08/ddwfttw/all/1

[Beaver]

I believe. I did it this morning, just mashed the right foot down.

[The AD]

From the planes on treadmills department: a nerdy bump for a new Wired article covers going downwind faster than the wind.

http://www.wired.com/autopia/2010/08/ddwfttw/all/1

Let’s not worry about how the cart gets up to speed for now

Yes, let's worry. This seems like a pretty lame scenario when their example is to tow the vehicle up to a speed higher than the wind speed.

[QuikR12]

Well its an easily explainable phenom. The cart isn't actually propelled 'by the wind,' as say, a stiff sail actually being pushed by wind, but it's propelled by the propeller/drive shaft/gear mechanism. The wind speed drives the light propeller on a perpindicular axis, which generates a wheel speed greater than the speed of wind, simply because the propeller is spinning much faster than the wind. Just like wind turbines, Simple mechanics, really.

If you could build a similar device that would go upwind then I think that would be perpetual motion. A slight push and you'd be able to sail along in still air for ever.

This is plausible, i believe. By affixing the wind propeller to a spin-able mast, one could harvest the mechanical force of the oncoming wind, diverting it through the drive and into a wheel (or boat propeller) below. The biggest obstacle would be the aero dynamics and balance of the craft and after perfecting that, getting a net gain of velocity over wind would be pretty incredible.

[toast2266]

Yes, let's worry. This seems like a pretty lame scenario when their example is to tow the vehicle up to a speed higher than the wind speed.

did you watch the video?

There wasn't any towing involved.

[Poop~Ghost]

I think my favorite part of the faster than wind hub-bub was the complete FAIL of so many people including the smarty-pants physics/math heads.

Talk about laying the ultimate internet smack down on them.

[The AD]

did you watch the video?

There wasn't any towing involved.

Yes, but I'm talking about the explanation. A proper explanation would have to include how the vehicle got up to speed. It's a lot easier to explain how something can travel faster than the wind when the initial condition is that the vehicle is traveling faster than the wind!

[f2f]

Yes, but I'm talking about the explanation. A proper explanation would have to include how the vehicle got up to speed. It's a lot easier to explain how something can travel faster than the wind when the initial condition is that the vehicle is traveling faster than the wind!

[Poop~Ghost]

Yes, but I'm talking about the explanation. A proper explanation would have to include how the vehicle got up to speed. It's a lot easier to explain how something can travel faster than the wind when the initial condition is that the vehicle is traveling faster than the wind!

Math speak from aerodynamicist and M.I.T. professor Mark Drela: http://www.boatdesign.net/forums/att...s-boat-fvp.pdf

Original explanation: https://docs.google.com/View?docID=0...=_latest&hgd=1

It's all there - and not that difficult to understand.

[f2f]

another good video:

[Dantheman]

Talk about laying the ultimate internet smack down on them.

Yep, 3x windspeed = complete and total ownage.

[ArmadaBC]

Well its an easily explainable phenom. The cart isn't actually propelled 'by the wind,' as say, a stiff sail actually being pushed by wind, but it's propelled by the propeller/drive shaft/gear mechanism. The wind speed drives the light propeller on a perpindicular axis, which generates a wheel speed greater than the speed of wind, simply because the propeller is spinning much faster than the wind. Just like wind turbines, Simple mechanics, really.

Its the fucking lever just 2000 years in the future, now things are making much more sense.

Part of the problem conceptualizing the whole thing is that so much of physics tells you energy is a closed system or that you can't get more than you put in so for physics JONGS like myself your initial reaction is no fucking way.

[The AD]

It's all there - and not that difficult to understand.

I think you guys are missing my point. I'm only saying the Wired article had a pretty weak explanation when their example of how it works starts with the assumption that the vehicle is moving faster than the wind:

There are several ways to explain how the vehicle works. We’ve already described how it is equivalent to a high-performance sailboat circling a cylindrical planet. But we can look at it from an energy point of view as well. In this view we can think of the craft as a simple lever. As with any lever, we can trade a small force moved through a large distance (the long end of the lever) for a much larger force moved over a shorter distance (the short end of the lever). But how does this relate to our DDWFTTW cart? Let’s not worry about how the cart gets up to speed for now, but instead see what happens if we tow it up to speed. For this purpose we’ll tow it to 55 feet/second (about 37.5 mph), and we’ll do that in wind moving 44 feet/second wind (about 30 mph). Of course with a tailwind of 44 feet/sec the cart only feels an 11 feet/sec (7.5 mph) headwind when it goes downwind at 55 feet/second.

At least to me, the difficult part is understanding how the cart can accelerate past the wind speed. It isn't difficult to imagine how it can accelerate if it's already traveling faster than the wind speed.

[The Duke of Hurl]

Down hill faster than the wind. Oooh, Ahhhh.

[bio-smear]

Ha.

Burp.

Ha.