|Feb 09, 2007, 11:15 PM|
Joined Sep 2004
Ok, here is what I noticed. The streamer is being blown forward and sometimes toward the cammera so the wind is blowing at the back of the vehicle, so yes the are traveling down wind. The problem is that if the wind was moving the prop, the prop would be turning in the opposite direction. Look at the pitch. It's set to spin the other way with the wind comming from behind. The other video has a vehicle traveling into the wind. I think this one is as well, but I cannot explain the streamer. I also don't heare any noise other than the wind and the wind vehicle. It appears that they are in a car or something and I don't hear an engine. considering how noisy the wind powered vehicle is, you would think you would hear something from the chase vehicle. Tire noise at least. I think I do here some engine noise toward the end from the chase vehicle but it's faint.
|Feb 09, 2007, 11:54 PM|
The wheels are geared to turn faster than the pitch speed.
When matching the speed of the wind-
If there is no air moving through the prop then there is no pitch speed.
So why would it speed up any more?
A gust was the best answer lol
If there is no airspeed over the prop then the wheels will be driving the prop.
since they are geared to spin faster they have little leverage working the other way around so it would slow down.
They do not claim perpetual motion but are claiming the sail/airfoil effect of the blades is giving more speed.
Their explanations ask you to picture boats etc... but not explanation that directly explains this effect with the prop.
Since a prop is in front of the ribbon it is silly- the ribbon should be up high away from the prop.
The subject seems difficult to talk about or figure out. very confusing.
I'm very interested in the mental fallacies behind this or my own mental fallacy for not understanding it!
|Feb 10, 2007, 12:26 AM|
Joined Sep 2004
Ok, let me see if I got this right. The wind is pushing the trike (let's call it). This causes the wheels to turn which makes the prop turn pushing the the vehicle faster. now the prop rotation makes since to me. I get it, but it doesn't seem possible does it. I'm willing to believe it, but now I want to build one just to see it work. Very interesting. does it give a web site for the creator? I can't seem to find a link.
|Feb 10, 2007, 01:53 AM|
I think they are saying the wind turns the prop.
The prop is geared to the wheels like a ten speed bicycle in hard gear.
So pedals would be on the prop shaft and the tire on the road for a bike analogy.
The wind turns the pedals which pushes it along faster than the wind.
Instead of pedals they use the prop to power the rotation.
A chain or shaft to translate it in a geared fashion to the wheels.
When it accelerates to the speed of the wind you need to remember there is no longer force on the prop. So it doesn't matter if it is geared to go faster than the pitch speed.
They are playing off a generic understanding of sailing diagonal to the wind and trying to mix us up with the prop pitch angles and gearing.
See this sailing page:
Downwind (diagram at left) is easy. If the wind is 10 kt, and the boat makes 6 kt in the same direction, then the crew feels a wind of 4 kt coming over the stern of the boat. The true wind vw equals the speed of the boat vb plus the relative wind vr.
The equation vw = vb + vr tells us the problem: as the boat speed approaches the wind speed, the relative wind drops towards zero and so there is no force on the sail. So you can't go faster than the wind. When the wind is at an angle, we have to add the arrows representing these velocities (vector addition). Upwind (right), exactly the same equation holds: vw = vb + vr.
(scroll down to how boats sail faster than the wind)
This person asks the question here and if you click the link below it there is an explanation:
Finally this explains why you can't sail faster than the wind and why sailing at an angle lets you go faster:
They have completely included the idea of airfoils in sails yet even with multiple sails state that you can not go faster downwind than the wind.
It is amazing that these silly sailors have not put windmill props on their boats which gear the underwater prop and make them go so fast! What are they thinking?
Kbear- you are the man! Thanks for trying it!
Holding it in the air with a fan blowing on it will make the wheels go faster than the airspeed of the fan!
Next turn off the fan to simulate when the trike matches the airspeed. How much do the wheels speed up?
Are we to think sailors are so against flight that they would not stick propellers on their boats instead of sails since it allows downwind travel faster than the wind?
|Feb 10, 2007, 02:01 AM|
Besides being wrong I've a 3rd explanation-
the air is not perfectly behind it
It is coming a bit diagonal.
The prop may do the sail tilt to get some lift from the side wind.
Since the wheels prevent it from sliding sideways with the wind that force is induced to forward speed.
The builders and testers may be honest but are not accounting for cross vector gusts.
|Feb 10, 2007, 02:17 AM|
It's a brain teaser invented by an aeronautical engineer named Andy Bauer at Douglas Aircraft (before it became McDonnell-Douglas now a branch of Boeing). I think it has something to do with the lift to drag ratio of the blades. There's a picture of the full size windmill cart here:
|Feb 10, 2007, 04:24 PM|
Joined May 2006
Years ago I build a much smaller trike powered by about a 10" balsa propeller, using a rubberband belt drive. It was very crude.
When placed in front of a fan, this little contraption would move steadily straight INTO the wind, which kind of amazed me. Nonetheless, it did it and there was no doubt about it.
A sailboat cannot sail directly into a wind but this thing could!
Therefore, I would have to be open to the idea that the thing in the video is legitimate. There is no question that a vehicle, in a broad reach, can easily travel faster than the wind - in the case of an iceboat, by a great deal.
|Feb 10, 2007, 05:00 PM|
but you have it reversed allan- this one is not going into the wind.
the wind is hitting it from the rear and as it speeds up the wind passes more slowly over it.
The iceboat can not travel directly into the wind nor can it travel directly downwind faster than the wind. See links above.
I believe your contraption worked and think that is very cool!
Here is a guess:
Because the wheels are connected to the ground and there is leverage from the prop over the wheels you can use the wind to drive it forward. The loss in forward speed makes up for the othwerwise loses on a 1:1 gear ratio due to wind resistance.
Because a sail boat does not have traction it can not do this.
We'd be able to talk about this reasonably if there was a scientific test for this being performed vs. a rural road with unknown everything.
|Feb 10, 2007, 05:02 PM|
Anyone have time to make a little boat?
A hybrid boat with a prop for a sail.
The prop is like a weather vane so it always faces into the wind.
The vane is connected to the keel to always steer the boat into the wind.
The air prop drives the water prop. The water prop has lots of torque but moves the boat very slowly forward- but with force.
|Feb 11, 2007, 05:37 PM|
Joined Oct 2004
the wind is actually pushing a "sail" that moves "backward" on the contraption... it's a bit complex to explain it in full, but in this way it makes sense.
By the way, look up the terms "turbosail", there's a few interesting pages about this sort of things. and anyone remembers the movie "Waterworld"?
|Feb 11, 2007, 09:52 PM|
There was a thread on this subject a couple years back where the task was to have a propellor driven car advance into a head wind.
ISTR the task was accomplished with a prop geared to the wheels.
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