Sailing into the Wind (with propellor)

[pjh]

Here's a video purporting to show a prop wind-driven vehicle going faster than the wind blowing it.

aJpdWHFqHm0

Here's the original post on BoingBoing, which contains links to other discussions and a PDF explaining it.

http://www.boingboing.net/2007/02/06/video_can_a_vehicle_.html

So is it possible or is it a hoax?

[NeilC]

The title is "can a vehicle move downwind faster than the wind?"

Doesn't seem to mention going against the wind

[pjh]

The title is "can a vehicle move downwind faster than the wind?"

Doesn't seem to mention going against the wind
My bad, title fixed

[Just thinking]

pjh,

From reading your initial comment ... "Here's a video purporting to show a prop wind-driven vehicle driving against the wind." ... I'm not sure you understand what is going on, or being attempted. The vehicle is purported to be going with the wind -- not against it. What's more, to the point of accelerating to speeds faster than the wind. Watch the little white flag and you'll see it indicate relative wind direction from back to front and then from front to back, once going faster than the wind.

My question is, if this is legit and the wind is in fact coming from directly behind the cart, why is it that the prop appears to continue spinning in the same rotational direction? Shouldn't it at some point stop and begin spinning the other way around?

[pjh]

pjh,

From reading your initial comment ... "Here's a video purporting to show a prop wind-driven vehicle driving against the wind." ... I'm not sure you understand what is going on, or being attempted. The vehicle is purported to be going with the wind -- not against it.
Look I changed it, my original point that I didn't make very well is that once the vehicle is moving faster that the wind, the net effect is the same as a wind blowing in the other direction, it is in all practicality 'moving against' the wind.

My original post was badly worded and didn't properly reflect the BoingBoing post, however I'd like to move the discussion onto whether the video we see is faked (downhill or towed/powered somehow) or genuine, rather than my understanding and poorly worded initial post.

[Just thinking]

Look I changed it, my original point that I didn't make very well is that once the vehicle is moving faster that the wind, the net effect is the same as a wind blowing in the other direction, it is in all practicality 'moving against' the wind.

My original post was badly worded and didn't properly reflect the BoingBoing post, however I'd like to move the discussion onto whether the video we see is faked (downhill or towed/powered somehow) or genuine, rather than my understanding and poorly worded initial post.

I noticed that after I posted ... and if you read what I typed below my initial comment, you'll see I addressed your concern.

[ponderingturtle]

Where are they showing the level that we can determine that the road is really level? It just doesn't seem right the way it trys to say it is going as it would be essentialy free energy as it would work and keep going if the air was stationary as well.

Going faster than the wind is possible, but it is going across the wind not with it.

[Ocelot]

haven't viewed the video but did see somethign simlar on the BBC TV Programme "Tommorrows World"

The design means that you can sail into the wind.

The presenter jokingly suggested that as you go faster into the wind the relative wind speed increases and you might end up going faster still.

As turtle suggests goign faster then the wind spped is possible but of course if you're running before the wind it's not possible as at some point you'd be stationary relative to the air.

[Just thinking]

... if you're running before the wind it's not possible as at some point you'd be stationary relative to the air.

And that was my point. It is then (or shortly thereafter) when the prop should have to stop and spin in the other direction -- if truly wind driven, of course.

[ponderingturtle]

And that was my point. It is then (or shortly thereafter) when the prop should have to stop and spin in the other direction -- if truly wind driven, of course.

Which would mean that you would have to reverse the gearing as you exceed wind speed. if it was rotating in a verticle axis it would be different, but as it was a normal propeller in a horizontal axis it is not what it claims to be.

[casebro]

Big deal. Sail boats have been going faster then the wind for centuries, and into the wind too. But not directly, they have to go cross wind. Catamarans can actually go down wind faster than the wind, but have to zig-zag a bit to do it. Lemme think of the name for the graph that shows boat speed to wind speed as a circular chart... Vertical down is wind direction. Catamarans have a butterfly shaped pattern. Other boats are an up-side down heart shape, they can't sail as fast quartering into the wind.

ETA, it's called a "Polar Diagram". Thay are available for some boats, or the capain can make his own.

[MortFurd]

Which would mean that you would have to reverse the gearing as you exceed wind speed. if it was rotating in a verticle axis it would be different, but as it was a normal propeller in a horizontal axis it is not what it claims to be.

Or reverse the pitch on the blades.

[Just thinking]

Which would mean that you would have to reverse the gearing as you exceed wind speed. if it was rotating in a verticle axis it would be different, but as it was a normal propeller in a horizontal axis it is not what it claims to be.

Correct -- and such a mechanical reverse is doable by taking some of the initial rotational energy (once the prop starts to reverse rotation) to activate a simple one-time transmission that switches the gearing. That way, once in the reverse rears, the reversed spinning prop would still propel the cart forward (or in the same direction). However, all this is moot since we don't see the prop reversing.

[Just thinking]

Or reverse the pitch on the blades.

That doesn't seem likely on this model, as the prop appears solid. Pause the video just as he walks up to it after realizing the brakes were still on -- it's not one with variable pitch.

[Wavicle]

Here's a video purporting to show a prop wind-driven vehicle going faster than the wind blowing it.

aJpdWHFqHm0

Here's the original post on BoingBoing, which contains links to other discussions and a PDF explaining it.

http://www.boingboing.net/2007/02/06/video_can_a_vehicle_.html

So is it possible or is it a hoax?

Having viewed the video I think it works something like this:

The propeller is driven by the wind, and the wheels of the cart are driven by the propeller.

The cart only goes "Down Wind Faster Than The Wind" for short periods of time. I think it is entirely possible that what we're seeing during those times is a lull in the wind and the residual kinetic energy of the prop driving wheels of the vehicle faster than the wind.

Also it is not clear that the road is perfectly level or that the wind is coming very close to 180 degrees from the front of the cart. If these two conditions are satisfied (the road is level and the wind is to the rear) then I have great difficulty believing one could keep this up for very long. If you are moving at 10 MPH with a tail wind of 10MPH, the relative air motion around you should be 0. With no relative air movement around you, there will be nothing to drive the propeller, thus nothing to drive the wheels, except the energy already present in the system.

[Schneibster]

Many people don't know it, but a sailing ship can sail faster than the wind. It is, however, more common on those ice boats, since the friction there is so much lower. Remember that a sailing ship, and the ice boat as well, can tack- that means that they sail across the wind. So they don't lose their driving force by out-sailing it. They aren't sailing in the direction it's blowing. What they can't do is have the windward (that is, along the direction the wind is blowing) component of their velocity be greater than the wind's.

If that, or some variant, is what the vehicle is doing, yes, that will work. If it's something else, then no, it's a hoax.

[pjh]

Freeze the video at 1:16 remaining and have a look at the angle of the pole, seems to indicate that the run is on a slope.

the speed at which the prop spins (in what must be almost still air) seems to indicate that the thing is gravity driven. Also the close-up of the model, and the fact we never see a pan looking forwards seems to leave ample room that it is being towed.

[Wavicle]

Catamarans can actually go down wind faster than the wind, but have to zig-zag a bit to do it.

I'm a little confused by what you're saying here. If there is a port 50 miles due west of a catamaran, and the wind is blowing steady at 10 MPH from the east, are you saying that the catamaran could arrive at the port in less than 5 hours?

I know you can play clever vector tricks to travel faster than 10MPH by moving a direction other than due west, but can you exceed a strictly westward velocity of 10MPH?

[Schneibster]

Mmmfff, looks like casebro beat me to it and I didn't catch it. Yes, that's the idea. The zig-zagging is called "tacking." In other words, the ship sails first across the wind one way, then across the wind the other; they're called the "starboard tack" and the "larboard tack."

One correction, however: neither that cart, nor the catamaran, nor any wind-driven vehicle, can actually make progress in the direction the wind is blowing faster than the wind is blowing; their speed in the direction they're traveling can be faster than the wind is blowing, but since they're moving across the wind, they're not moving completely in the direction the wind's blowing.

If you look carefully at the little flag on the cart, you'll see it's showing that the wind is partly blowing across the road.

ETA: it's also worth noting that by tacking, a well-designed ship can beat upwind, actually moving toward the direction the wind is blowing. Sailors can often be found discussing the qualities of a ship and mentioning "how close she lies to the wind." What this means is, how close can the ship's course be set to the eye of the wind and still make forward progress along that course? When you really get into it, they also talk about "making leeway," which means that the ship doesn't actually move in the direction it's pointed, it also moves some in the direction the wind is blowing, into the "lee," or side of the ship that's facing away from the wind.