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  #31  
Old 11-06-2010
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Quote:
Originally Posted by rmeador View Post
It just occurred to me that if you can build this (and I believe it is real), you should be able to build a vehicle that can sail directly upwind using similar principles.
Yes, on water it is even simpler to go slowly directly UP wind than directly DOWN wind faster than wind, because the water drag is the main problem.

Quote:
Originally Posted by rmeador View Post
Has anyone done that yet?
Sure.

On water:
YouTube - Windmill Driven Boat
In controlled conditions:
YouTube - indoortanktest_0001.wmv

On land:
YouTube - Windturbinerace 2009
In controlled conditions:
YouTube - wind powered vehicle-!

However, as far as I know nobody has yet gone directly UP wind faster than the wind, which is theoretically possible as well. The BlackBird team will attempt this next year.
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  #32  
Old 11-06-2010
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Quote:
Originally Posted by LarryandSusanMacDonald View Post
It sounds to me that with one of these devices strapped to your back, you could, theoretically, jump out of an airplane (oh, all right, a blimp, or hot air balloon) and fly back to it.
This car is not flying. It has surface contact and uses it.


Last edited by eyytee; 11-06-2010 at 02:50 PM.
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  #33  
Old 11-06-2010
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Any sailor have tried to go from A to B faster than the wind by tacking effectively, right? (unless sailing an old shoe) So there's more energy to it than the velocity component of the wind, E.g. a more efficient keel-shape on a boat will make it go faster and/or higher.
Wind Turbines wouldn't produce much if there weren't - and it's not perpetual motion, if the wind stops, the vehicle (or boat) stops.
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  #34  
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Capt. Larry,
I was browsing Sailnet for a different reason and came across this post today. Indeed, you're gonna be tasting some shoe leather here - whether you ever admit to it or not.

I'm a cruising sailor in FL who happens to be really good friends with the guys who've set this DDWFTTW record. Believe me, they have no interest in creating any hoax, however they are both extremely interested in proving things like this.

I noticed that your current location is 'permanent vacation'. If you are cruising in FL, let me know. We'll get together and I'll explain it to you - using my hands for reference. I'm a very average guy in intelligence and was finally able to fully understand what's going on with the directly downwind cart.

If you just don't WANT to believe that it could happen, or maybe it doesn't fit into YOUR definition of a sailing vehicle, I can understand your take on it, but if you're just gonna stick to you guns on it being a hoax, well you're just wrong.

Let me know if you're in FL.

Capt G.
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  #35  
Old 11-08-2010
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Quote:
Originally Posted by eyytee View Post
Okay this is a pretty awesome illustration. 100 points for "worth a million words".

Where'd you get it?
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  #36  
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Also if it can work on a cart with wheels, why not on a boat with an underwater propeller or paddlewheel?
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  #37  
Old 11-08-2010
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The catamaran with the windmill is actually quite crude. About 25 years ago there was mention of a monohull with a windmill, and a magazine writer from Sail or Cruising World actually found the guy who built it. He got pictures and went out for a sail on it. The windmill drove a standard inboard prop shaft, and it easily went directly upwind. It was estimated that the power was about equal to a sail of area equal to the swept circle of the windmill blades.

Gary H. Lucas
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  #38  
Old 11-09-2010
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Still munching on my shoe leather. I remain unconvinced, but not unconvincible.

These are the points I'm having trouble wrapping my old balding head around:

The only wind a moving object is affected by is apparent wind. The True wind will affect apparent wind - but a moving object is only affected by apparent wind. If true wind and apparent wind are equal, the object in question is at rest. Am I correct so far?

I was confused when I initially looked at the video as I thought the propeller was acting as a turbine and turning the wheels. But now I understand that the wind is moving the entire vehicle causing the wheels to turn which in turn cause the blades to turn and thus it is a propeller. Correct so far?

The vehicle continues to accelerate with the wind propelling it and the blade also propelling it. This continues until the vehicle reaches the speed of the wind at which time the apparent wind is zero and the only thing propelling the vehicle is the propeller, powered by the wheels. Now this is where I start to get confused - the vehicle continues to accelerate. What causes this acceleration?

Okay, I'll bypass that point by assuming that the wind, which has been in the past known to fluctuate, slows down slightly. Now the vehicle is moving faster than the true wind and the apparent wind is from the front of the vehicle. At this point the propeller becomes a turbine, i.e., it is driving the wheels, rather than the wheels driving it. Is my understanding correct so far? And the vehicle continues to accelerate. I do not completely understand why it should continue to accelerate - maybe someone can explain this in terms the more simple minded (that is, those of us who eat shoes) can comprehend.

It seems to me that if the vehicle will accelerate with an apparent headwind, that you could turn the vehicle around initially and face it into the wind. Turbine from dead start turns the wheels and it would accelerate dead into the wind. Am I missing something or would this work?

Two more unrelated questions:
Can anyone suggest a good wine which would go well with shoe leather.

Can anyone tell me the correct spelling of 'unconvincible"?
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  #39  
Old 11-09-2010
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Quote:
Originally Posted by AdamLein View Post
Okay this is a pretty awesome illustration. 100 points for "worth a million words".

Where'd you get it?
I did that one myself. Here the second part that works continuously :



You will find more visualizations of here:

YouTube - eyytee's Channel
YouTube - coolaun's Channel
YouTube - axelerat3d's Channel
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  #40  
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Quote:
Originally Posted by LarryandSusanMacDonald View Post
This continues until the vehicle reaches the speed of the wind at which time the apparent wind is zero and the only thing propelling the vehicle is the propeller, powered by the wheels. Now this is where I start to get confused - the vehicle continues to accelerate. What causes this acceleration?
Acceleration is caused by a non-zero net force. In this case:
F_thrust_prop > F_braking_wheels

Quote:
Originally Posted by LarryandSusanMacDonald View Post
Now the vehicle is moving faster than the true wind and the apparent wind is from the front of the vehicle. At this point the propeller becomes a turbine,
No, it never becomes a turbine. A turbine.going DDWFTTW would push the air forward and accelerate the true wind. To extract wind energy you have to slow down the true wind : push the air backwards in the downwind case. This is similar to tacking downwind with VMG > windspeed:
YouTube - DOWNWIND VMG GRATER THAN WINDSPEED (STREAM LINE)
From there it is just a small step to the DDWFTTW propeller:
YouTube - Sail_to_Prop.mov

Quote:
Originally Posted by LarryandSusanMacDonald View Post
It seems to me that if the vehicle will accelerate with an apparent headwind, that you could turn the vehicle around initially and face it into the wind. Turbine from dead start turns the wheels and it would accelerate dead into the wind. Am I missing something or would this work?
Not if you just turn it around (it would go downwind backwards in that case). But if you change the gear ratio or the blade angle, the propeller becomes a turbine, and you can go directly up wind. This case is shown here:
YouTube - Directly Down & Up Wind Faster than the Wind

Last edited by eyytee; 11-09-2010 at 11:11 AM.
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