How can an vehicle move faster than the wind that is powering it?

**Topher925** · Oct20-08, 09:25 AM

As I'm sure we all know, that when you go sailing your fastest speed isn't directly downwind but when you are traveling at an angle to it. This allows sailboats and iceboats to go several times faster than the wind speed that is powering them.

But how is it that a vehicle such as THIS, that is powered by the wind, can go DIRECTLY downwind faster than the wind that is powering it? Apparently, this is true of iceboats as well. Could someone please explain this so me.

**LURCH** · Oct20-08, 10:27 AM

It's probably a hoax. I suppose the principle on which it is meant to operate is that the blades are at an angle to the wind, and this allows them to go many times faster than the wind (like a sailboat or iceboat going cross-wind). But of course, once the entire contraption gets going at the same speed as the wind, it will experience no wind at all. What powers it then? I couldn't guess, but whatever it is, it proves that this vehicle can travel when there is no wind at all.

**pixel01** · Oct20-08, 11:47 AM

It's a hoax all right. But the idea can be: there's a flywheel which can store energy when the wind is strong, then when there's weak or no wind, the flywheel makes the cart move.

**FredGarvin** · Oct20-08, 12:08 PM

I stopped reading when they put the car on a treadmill. I wonder if it took off?

**Topher925** · Oct20-08, 12:11 PM

Originally Posted by pixel01

It's a hoax all right. But the idea can be: there's a flywheel which can store energy when the wind is strong, then when there's weak or no wind, the flywheel makes the cart move.

Pixel, consider this as an ideal situation not an realistic one. This "contraption" should still be able to constantly move faster than the wind assuming the wind has a constant velocity. Also consider the ground to be perfectly level and the cart's motion is only being influenced by the wind.

Also, does this also hold true for an ice boat? Consider the same phenomenon if the iceboat has a zig-zag type path and its magnitude velocity is greater than that of the powering wind. Could the ice boat's velocity component in the direction of the wind ever exceed the speed of this wind?

This isn't a trick question or a riddle, but a simple application of physics. There are a lot of people that believe this is not a hoax, but I consider most people on this forum to be experts in the area of physics so I would like your expert opinions.

**K.J.Healey** · Oct20-08, 12:18 PM

Looks like a hoax with an RC car pulling it with some fishing line.

**mgb_phys** · Oct20-08, 12:28 PM

Ironically it could go faster than the wind if the wind was from the side.
Then the power only depends on the wind speed and the size of the turbine - which you can make arbitrarily large.

**Topher925** · Oct20-08, 12:34 PM

Originally Posted by mgb_phys

Ironically it could go faster than the wind if the wind was from the side.
Then the power only depends on the wind speed and the size of the turbine - which you can make arbitrarily large.

Yes, I agree. And is why sailboats typically do not move directly down wind in order to achieve fast speeds.

I found this topic on anther forum, and this is one of the forum members explanation/logic about how this thing might work.

Imagine you were standing on the stationary trolley with your back to the wind. When the trolley is travelling at the same speed with the wind, what to you feel? still air? Yes!!.... BUT what are the blades doing in this 'still air'.....they are creating lift!!?

You are travelling the same speed as the wind so you should feel nothing, but the blade disc is creating lift.......in still apparent wind!!!. So the blades are creating lift over and above the wind speed.

So there are two components pushing the trolley along.
1. The thrust from the wind direct.
PLUS
2. The Thrust from the disc.

I've understood this just a bit more even whilst typing this post!!

Is their something wrong with this persons logic? Does it disobey any physical laws?

**Trond** · Oct20-08, 03:27 PM

You have to let go of the idea that it's the wind that is powering it by making the propeller turn. If that is the case it can never work.

Check out this:
http://www.ayrs.org/DWFTTW_from_Cata...3_Jan_2006.pdf

http://www.flixxy.com/sailing-yacht-research.htm

Can a wind powered vehicle sail faster than the wind? Yes - it can!
"The key point is that the propeller is a propeller, not a wind vane, and when the cart is rolling, the wheels are powering the propeller, not the other way around. With the right gearing, the propeller will always push backwards against the air, whether or not the air is moving forwards or backwards relative to the cart. The tailwind and the propeller action combine to make the wheels spin fast enough to keep the whole system rolling faster than the wind". Definitely counter-intuitive."(Jack Goodman)

**spork** · Oct20-08, 03:59 PM

Topher refuses to believe that ice-boats can maintain a downwind tack (at an angle to the wind) with speed sufficient to give them a downwind velocity component faster than the wind. I know it seems non-intuitive to some; but it's just a normal day out for the ice-boating community.

Here's just one document that talks a bit about it:

http://www.nalsa.org/Articles/Cetus/...ance-Cetus.pdf

And a couple of diagrams from the article:

I'm well aware this doesn't relate *directly* to going STRAIGHT downwind faster than the wind, but once you realize your downwind component can be much faster than the wind, the steps to get to that nifty cart in the video are somewhat easier.

**Jeff Reid** · Oct20-08, 06:22 PM

Originally Posted by spork

Topher refuses to believe that ice-boats can maintain a downwind tack (at an angle to the wind) with speed sufficient to give them a downwind velocity component faster than the wind.

and he would be correct. The diagrams appear to be wrong. In the second diagram, the boat is probably going 8 degrees from perpendicular to the wind, not 8 degrees from parallel to the wind.

Assuming Vb of 70 mph, and an angle of 8 degrees downwind of perpendicular, the boat would be going 9.74mph downwind (a bit over 1/2 the downwind speed), and 69.32mph cross wind. Relative to the air, the cross wind component remains the same at 69.32mph, the "up wind" component (boat is moving downwind slower than the air) is 18 mph - 9.74 mph = 8.26 mph. The boats speed relative to the air or it's "apparent wind" is sqrt(69.32^2 + 8.26^) = 69.81mph.

**spork** · Oct20-08, 06:53 PM

Originally Posted by Jeff Reid

The diagrams appear to be wrong. In the second diagram, the boat is probably going 8 degrees from perpendicular to the wind, not 8 degrees from parallel to the wind.

And you base this on what exactly? This will be news to the iceboat community where they do it all the time. And how would you explain the GPS data?

**DaveC426913** · Oct20-08, 07:20 PM

Originally Posted by Jeff Reid

In the second diagram, the boat is probably going 8 degrees from perpendicular to the wind, not 8 degrees from parallel to the wind.

Did you allow for "apparent wind" in determining this? The angle of the wind from the PoV of the vehicle will be quite different from the angle of the wind from an exterior PoV. (This is why sailboats seem to have a headwind when in fact, they're more like 45 degrees from head-to-wind).

**russ_watters** · Oct20-08, 08:00 PM

Originally Posted by spork

And you base this on what exactly? This will be news to the iceboat community where they do it all the time. And how would you explain the GPS data?

I'm not sure about the underlying issue (I believe sailors actually do go downwind at an angle for the purpose of increasing their speed to their destination), but the GPS data does not support the contention. I don't know what the calculation is based on (there is no explanation of where the data came from), but it does not match the GPS output.

**Jeff Reid** · Oct20-08, 08:13 PM

From that article: "Beta (β) is the angle between the apparent wind and the yacht vector." If Beta is small, then the apparent wind is mostly a headwind, with a small crosswind component:

If Va is 55mph, and Beta is 8 degrees as stated in the second diagram, then the apparent wind components, relative to the boat, break down into a head wind of cos(8) x 55 mph = 54.465 mph, and a cross wind of sin(8) x 55 mph = 7.655 mph. Still this doesn't give an overall picture of what's going on.

Wings divert the air, they don't accelerate air backwards in the opposite direction of travel. If the wind speed is 18mph, then the downwind component of the ice boat must be less than 18mph. If the speed of the boat is 70mph, the angle between wind direction and boat direction must be greater than 75.1 degrees (arccos(18/70)).

I'll research this and reply later.

**ThinAirDesign** · Oct20-08, 08:25 PM

Topher, so much of debate is about definitions. I'd like to ask you a question that will help me (and perhaps others) determine exactly what your question and position is.

Many folks wonder ... “Can a ice boat (or other sailing craft) travel downwind faster than the wind itself?”. Most of us will concede that the ‘land speed’ of these craft greatly exceeds that of the wind, but there is much debate as to the downwind component of the path or the velocity made good (VMG) of the craft.

My scenario setup and question to you Topher, is this:

On a frozen lake, with a steady 15mph wind from north to south a start point is defined. Directly south, one mile away a finish point is defined. The ice boat takes a ~45degree track (say SW) and comes across the start point at full speed. At the moment the ice boat passes the start point, a neutral buoyancy balloon is released, floating to the south in the wind. At the ~halfway point, the ice boat tacks to the SW and takes aim at the finish point.

Can the ice boat win the race to the finish point, or will the balloon always win?

Thanks Topher (and anyone else who cares to answer).

JB