DDFTTW

Sailing directly downwind faster than the wind - No it is NOT impossible!

Description of the vehicle at http://www.ayrs.org/DWFTTW_from_Catalyst_N23_Jan_2006.pdf

Category:

Howto & Style

Tags:

• sailing
• DDFTTW

[nytugmaster]

I see no proof that the wind was consistent for the duration of the run. We have only the commentator's word for the windspeed and  s.o.g. (speed over ground) It's hardly a controlled environment, though the concept is interesting. This is a neat idea, but not convincing in it's portrayal of DDFTTW

[ayrshquk]

True, you have only the commertatot's word in this example; but I have no reason to believe he lied.

For those who need more convincing, NALSA (North American Land Sailing Assoc) have just confirmed another cart (manned this time) as travelling directly downwind at 2.8 times the speed of the wind. NALSA were not involved in the attempt other than as independent scrutineers.

We will leave this clip on YouTube for its historical significance, but we will not respond to any further comments.

[subductionzone]

I have to admit I was wrong on a previous comment. This is possible, check out the smaller scale models posted by spork33. It runs off the difference in speed between the wind and the ground. Do not think of the wind blowing directly on the cart and it might help. Since it works off of a difference in wind speed it would no work if there was no wind. There is no perpetual motion or over unity involved.

[planetofthescums]

@ayrshquk People are consistently wrong.

[cwcordes]

Just look at the cotton telltale.. if it's points back, the vehicle is going faster then the wind. Compare that to the cotton telltale at rest.

[subductionzone]

@flinchey I know that, but the ultimate source of power is the difference between the speed of the wind and the speed of the road. If you saw the various treadmill videos you would see why I worded it that way. In that case the wind (the air in the room) is stationary and the road (the treadmill belt) is moving.

And yes, the wheels turn the propeller which forces the cart DDWFTTW.

[flinchey]

@subductionzone no, it runs off the wheels spinning the prop (or impeller, can never remember which it is)

[subductionzone]

@MrTweetyhack That's right. I worded it the way I did because many people think that the wind "goes away" when the cart is moving at the speed of the wind. Even when the cart is moving at wind speed there is still a difference between the speed of the wind and the speed of the ground that the cart can harvest.

[piratewoodleg]

@MrTweetyhack

No, it cannot accelerate from wind-speed, using stored momentum. To extract the stored energy it would have to slow down the propellers rotation. But that would slow down the wheel rotation and thus brake, instead of accelerating.

It uses wind power directly, not stored power, so it stays above wind-speed, as long as there is wind. The rotor is always a propeller. The individual rotor blades are always sails tacking downwind on a broad reach.

[MrTweetyhack]

my thoughts. it's an additive force. the propeller first acts like a sail, until the cart matches the speed of the wind. During that time, the propeller has been storing energy in the form of momentum(in the spinning propeller). But wind is still pushing. So wind + stored momentum = faster than wind. Ya?

[MrTweetyhack]

@subductionzone the difference between the speed of wind and ground is the speed of the wind. ie speed of wind - 0 = speed of wind.

[eyytee]

@utlo

It is radio controlled.

Google "The cart that launched a thousand flame wars" for an interview with the builder, and "What I've Learned About Wind Carts" for an article with background info on it.

[utlo]

Okay this is clearly fake. Ignoring the physics of how the contraption works, how is the contraption steering? The front wheel appears to be a caster and I see no mechanism that would allow it stay on the road. The obvious answer it it is being pull by something just off screen.