Wind-Powered Cart Goes Faster Than the Wind

Maybe they have done this, but the explanation was exceedingly poor.

One can only say WHY?

it is clear that the 2.8 figure is for one wind speed only, and is not a constant number. It is also clear to me that they are just wasting energy turning the prop/wheels, based on the fact that wind racers like this can accomplish world record speeds. (for wind racing)

From what I've seen about this, they are trying to prove a point about a wind-powered vehicle moving directly downwind, unlike the wind-powered racer you linked which attains a high ground speed tacking across the direction of the wind. (Right?) What Rick Cavallaro and his crew are doing has long been considered 'impossible' bordering on 'perpetual motion'.

The explanations and video provided don't help much: A turns B which pushes A which turns B...; the video is not a continuous, uninterrupted shot of the vehicle that shows wind direction, wind speed, vehicle direction or vehicle speed. A video on their website of a toy/model of the vehicle running on a treadmill was laughable.

Well as I see it, on of the advantages of wind-propeller powered craft is that you can move in one direction regardless of wind direction, as shown in an old sailcraft design of mine.. (living off shore) Normal sailboats have to 'tack' left & right in order to move into the wind.. but this sort of idea uses the vane to orient the prop into the wind, which subsequently can turn water-propellers to drive the craft in the desired direction.

I don't know if the wind powered racer in question does this.. but it would seem to be moving with the wind. (and faster than it.)

Chris

See also Jacques Cousteau's Alcyone. (Basically a vertical-axis windmill driving a conventional prop.)

This seems to be over unity. I need a better explanation. Rear wheels drive propeller- got that.

if this indeed works then why the upper limit for speed? wind resistance, ground effects?

If this works we would seem to have a perpetual motion machine. When do we get to examine it in detail?

>This seems to be over unity.

Things are not always as they seem. No laws were broken (or even harmed) in the making and operation of this vehicle.

>>if this indeed works then why the upper limit for speed? wind resistance, ground effects?

One you are accelerating DDW faster than the wind, you begin to of course encounter a relative headwind. This increasing headwind on the components is the primary limiter.

>When do we get to examine it in detail?

Any time you wish -- the vehicle resides in Mountain View, CA. Our project blog is http://www.fasterthanthewind.org.

JB

I do not believe this, at least as "explained" so far.

If the vehicle's speed exceeds the wind speed, the ambient air is then blowing relatively backwards on the propeller, which would slow the vehicle down.

There might be gusting winds that momentarily speed up the vehicle, which might continue to coast after the wind slows down. By cleverly selecting the time of measurements, one could get examples of the vehicle momentarily exceeding the wind speed, but such measurements would not be sustained over time.

Finally !! someone who saw thru the deceitfull explanations !!

Of course, this vehicle will not keep on moving at a constant speed of 2.8 times that of the wind, its velocty profile would be more like the positive half of a sine wave.

After one thrust, it will coast to almost a stop, waiting for the wind to reach the propeller again.

2.8 times the speed of the wind would quickly put you out of the reach of such wind, thus not having anymore impulse from it.. unless you sit in there and wait for it.

This is what brakes their transmissions (I'm glad, I hope they spent a lot of money).

Yahlasit

The approach is new to me but there's nothing wrong with the physics. Here is the recognized land and ice speed records location. You will also notice that at the Wikipedia sight on the Physics of Sailing that:

Iceboats can typically sail at 5 times the speed of the wind.^[11]

Now ice does have much lower friction than the rolling friction of tires. So I'm not surprised that this superb achievement is at a lower ratio than an iceboat. But unlike an iceboat this craft does not have a fixed sail that responds only to the air speed that is travelling past the craft. An iceboat thus must achieve these speeds by tacking away from the wind direction to eventually achieve this higher than wind speed velocity. A University in Sydney Australia has a nice sight that shows how a fixed sail craft can move faster than the wind, while tacking. Like the tacking boat that gets an effective wind speed greater than the actual wind speed to use, this craft uses a spinning sail (windmill) that gets its aerodynamic thrust (lift) from the spinning airspeed effect. I'm fairly certain that this spinning sail has also been designed to allow the pitch of these sails to be modified. So essentially the sails themselves are always tacking into the wind but the craft is moving directly into the wind. Now the net rotational force runs through a transmission that converts this rotational force into a forward force. Oh, in the last link there is a video of one of these crafts that has some some small red streamers attached to poles. If you pay attention to these streamers you can see when the craft exceeds the incoming wind speed.

Agreed. That finally does make sense.

redfred:

>>So essentially the sails themselves are always tacking into the wind but the craft is moving directly into the wind. >>

That is exactly correct. The twin sails are running at an angle to the wind just as an ice-boat sails would be while between them they drag the vehicle chassis DDWFTTW.

Here is an animation that gives a good visual:

http://www.youtube.com/watch?v=UGRFb8yNtBo

JB

The just released NALSA world record observers report:

http://www.nalsa.org./BlackBirdDDWSR/Observers%20ReportNALSA%20C4BlackbirdJuly2and%2032010.pdf

JB

Congratulations on doing something I did not think was possible. good engineering!

Thanks silvcrow -- it was a fun project.

JB

I think because the propeller is mounted backwards, the relative wind actually helps the wheels turn it.

The wind from the rear pushes the car to stara it because the prop, before it starts turning, is acting like a sail and not a propeller.

Once the prop starts turning it pulls itself into the relative wind while pushing itself against the true wind.