Can a wind powered vehicle travel down wind, faster than the wind?

[shropshire 0]

Seems so.......

(.)Y(.)
Chivalry is not dead; it only sleeps for want of work to do. - Jerome K Jerome

[vanair 0]

Yes, Ice boats, would have to look up, but I think they can go up to 4 times the actual wind speed due to the lift generated by the sail.

[shropshire 0]

Directly Down Wind?

(.)Y(.)
Chivalry is not dead; it only sleeps for want of work to do. - Jerome K Jerome

[Belgian_Draft 0]

Yep!

(Just can't sustain the speed for very long.)

HAMMER:
Originally employed as a weapon of war, the hammer nowadays is used as a
kind of divining rod to locate the most expensive parts adjacent the
object we are trying to hit.

[skyrider 0]

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Yes, Ice boats, would have to look up, but I think they can go up to 4 times the actual wind speed due to the lift generated by the sail.

Which is what a Blade is.....

[airtwardo 6]

Glider??

~ If you choke a Smurf, what color does it turn? ~

[ryoder 1,400]

Just search YouTube for "DWFTTW":

Here is one: http://www.youtube.com/watch?v=xHsXcHoJu-A

"There are only three things of value: younger women, faster airplanes, and bigger crocodiles" - Arthur Jones.

[LongWayToFall 0]

Ice boats can't go faster than the wind, directly down wind, unless they are jibing.

[Calvin19 0]

Yes, it can be done, but it requires a comparably complex and precisely controlled purpose-built machine to do it. There have been several land models that have done it.

-SPACE-

[Belgian_Draft 0]

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Yes, it can be done, but it requires a comparably complex and precisely controlled purpose-built machine to do it. There have been several land models that have done it.

Yes, it can be done. Yes, it has been done. And it doesn't take a complex vehicle to do it. It only takes a bit of jibing to build your speed up until it is over the wind speed, turn the vehicle so it is going in the same direction as the wind, and there you have it. Problem is, you now have a relative wind coming directly at you that slows you back down. Surpassing the wind speed is not a problem. Sustaining that speed without additional maneuvering or other energy input is impossible.
You can't push an object going "X" mph with another going "X" mph and get an acceleration. The pusher needs to be >"X" mph at some point.

HAMMER:
Originally employed as a weapon of war, the hammer nowadays is used as a
kind of divining rod to locate the most expensive parts adjacent the
object we are trying to hit.

[cocheese 0]

check out "dynamic soaring". R/C glider world record is over 400 mph now. Freaky
http://www.youtube.com/watch?v=Oix6sHKzOLU

[Remster 24]

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You can't push an object going "X" mph with another going "X" mph and get an acceleration.

That is not what is happening in those model that were built.

The wind on the propellers is not directly inline with the trajectory of the vehicle. It's always at an angle, due to the fact the the prop is turning, so it can continue to generate lift even if the wind is coming straight at the vehicle.

Remster

[Bertt 0]

Just a general comment; gliders are really more gravity-powered than wind-powered, so they don't count for the purposes of this discussion.

You don't have to outrun the bear.

[JohnMitchell 14]

When they are gliding downwards, they are using gravity for the motor. When they are soaring (staying up indefinitely) they are getting energy from the atmosphere, either updrafts (vertical winds) or using speed differentials in a horizontal wind shears, to increase their energy.

[vanair 0]

ok I looked it up. up to 10xs the wind speed
http://en.wikipedia.org/wiki/Ice_boat

[Remster 24]

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ok I looked it up. up to 10xs the wind speed
http://en.wikipedia.org/wiki/Ice_boat

But that is not straight downwind.

Remster

[Bertt 0]

Right, so the wind is mainly used to add potential energy, like putting gas in a gas tank, while gravity mainly provides the thrust, like the engine in a powered airplane.
Thought experiment: if you took a glider to, say, 10,000 feet, then turned off gravity, could the glider fly at all, much less go faster than the wind?

You don't have to outrun the bear.

[bfilarsky 0]

If you turned off gravity on a car, it wouldn't be able to do much either. Does that mean cars are powered by gravity?

Sure, gliders use potential energy as an energy sink, but it isn't the source of their power. Their power comes from the wind (specifically, in the vertical direction ie updrafts, thermals, mountain waves, etc) If gravity is what "powers gliders" how can they climb?

However, gliders aren't really what we're talking about, because they get their power from rising air. Sure, they can fly downwind (faster than the wind), but they are being powered by air moving up (or just turning some of that stored up potential energy into kinetic energy), not air moving horizontally like the objects of discussion.

[bfilarsky 0]

The point of the whole question is whether you can build a machine that will sustain a downwind speed faster than the wind. IOW, if your riding a vehicle downwind, and the speed of the wind (so you feel no relative air movement), can you generate thrust from that wind, and accelerate forward.

As mentioned, Ice boats, sail boats, and most things you've ever seen can not. Intuition would suggest it cannot be done period, and I would have said the same thing before seeing what they are doing to do it.

Take a look at the links provided above, and you'll see how it works. Pretty weird stuff, but it works!

[vanair 0]

Hey, READ the link I posted before you sound like an idiot. I'll post it again. http://en.wikipedia.org/wiki/Ice_boat
An ice boat can reach speeds of up to 10 times the wind speed.
i.e in a 10mph wind some ice boats can reach 100mph. READ.

[strop45 0]

Most sailing boats/wind surfers/ice boats etc can sustain speed greater than wind speed across the wind. None that I'm aware of can sustain speed greater than wind speed directly downwind.

The difference between stupidity and genius is that genius has its limits." -- Albert Einstein

[vanair 0]

ok I thought we were talking about going faster than the wind. I didn't
realize we were only talking about going directly downwind.

[Belgian_Draft 0]

Yeah, I read it and it will NOT go directly downwind and sustain a speed faster than the wind. It is impossible. What they are proposing to do is akin to powering a car with electric motors that run off current produced by generators driven by the wheels.
If their vehicle is going straight downwind, that is, no crosswind component, as sson as they reach the speed of the wind they will have 0 relative wind, and it is relative wind that drives ANY wind powered land vehicle.

HAMMER:
Originally employed as a weapon of war, the hammer nowadays is used as a
kind of divining rod to locate the most expensive parts adjacent the
object we are trying to hit.

[bfilarsky 0]

What you are talking about is perpetual motion. Obviously not possible to anyone with any grasp of physics. The machine they are building is NOT perpetual motion, because it does require wind.

Remember that even though the air is still around the machine AT the speed of the wind, there is still a velocity over the ground. This machine can not run without wind, ie it's not perpetual motion.

Look around the Internet about this. It's not a hoax.

[riddler 0]

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I didn't realize we were only talking about going directly downwind.

That's probably part of the problem - the topic should be called "Cross-Wind faster than Down-Wind".

Trapped on the surface of a sphere. XKCD