Challenge: MythBusters and Cruisers Forum

[ThinAirDesigns]

Nalsa has now ratified a new World Record for the Blackbird of 2.8x the speed of the wind while traveling dead downwind using only wind power and no stored energy.

Record ratification reports at: http://www.nalsa.org.

And a great article by Kimball Livingston, an editor at Sail Magazine:

http://kimballlivingston.com/?p=3971

JB

[Therapy]

Originally Posted by ThinAirDesigns

Nalsa has now ratified a new World Record for the Blackbird of 2.8x the speed of the wind while traveling dead downwind using only wind power and no stored energy.

Record ratification reports at: http://www.nalsa.org.

And a great article by Kimball Livingston, an editor at Sail Magazine:

http://kimballlivingston.com/?p=3971

JB

Well I'll be................................

And I don't understand it at all. Looking at the video when it starts the propeller starts turning the opposite way I would think it would with wind from the rear.

<object width="640" height="385"><param name="movie" value="http://www.youtube.com/v/5CcgmpBGSCI...</param><param name="allowFullScreen" value="true"></param><param name="allowScriptAccess" value="always"></param><embed src="http://www.youtube.com/v/5CcgmpBGSCI..._embedded&fs=1" type="application/x-shockwave-flash" allowfullscreen="true" allowScriptAccess="always" width="640" height="385"></embed></object>

[Maine Sail]

Nice job guys and thank you for always keeping your cool on the SA thread. You guys are a breath of fresh air over there.. I've watched this from the beginning and it was entirely entertaining for the whole duration! A big IN YOUR FACE to the doubters!!

[FxdGrMind]

Thanks ThinAirDesign!

Fantastic link. Just amazing!

Now I wonder how many decades it will be before the America's Cup uses this type design......

[teejayevans]

Originally Posted by Therapy

And I don't understand it at all. Looking at the video when it starts the propeller starts turning the opposite way I would think it would with wind from the rear.

Think of the propeller blade as a wing, but symmetrical, the forces (lift) would occur if the wind was either direction. The wind is not pushing the blades, its using the aerodynamic lift of the prop blades.
I disagree with the fact they aren't storing energy, the rotating blades have stored kinetic energy that keeps the blades moving while the car goes through the transition of wind direction.
Tom

[David M]

I have an idea. Lets put a fixed blade on a boat that has no complex moving parts to break that is extremely light and efficient. We could call it......a sail!

[kmason]

Originally Posted by teejayevans

Think of the propeller blade as a wing, but symmetrical, the forces (lift) would occur if the wind was either direction. The wind is not pushing the blades, its using the aerodynamic lift of the prop blades.

An airfoil has a critical angle of attack that when exceeded will stall the airfoil defeating lift. Wind coming from 180 degrees or directly under (in this case aft of) the airfoil is an attempt to produce lift from a stalled angle of attack.

The answer is that they have a variable pitch airfoil that starts the machine by spilling the air out to gain momentum and then as the apparent wind changes to 0 degrees the pitch of the airfoil is changed so the air is still producing lift. This is evident as the driver stalled the airfoil about 0:45 into the run then re-adjusted the pitch at about 1:10 to regain kinetic energy in the drive. You will notice a dramatic increase in speed after the 1:10 minute spot on the video.

At first I thought this was BS but as I watched the pitch of the airfoils vs the speed of the machine it made more sense. Looks like the same guy (Richard Jenkins) broke the wind powered land speed record with another design... a sail!

[senormechanico]

Originally Posted by Therapy

Well I'll be................................

And I don't understand it at all. Looking at the video when it starts the propeller starts turning the opposite way I would think it would with wind from the rear.

I believe it starts movng just from windage on the entire rig.
The prop is indeed turning the opposite way the wind would turn it.
As it hits zero apparent, the wheels which have always turned the prop, begin to turn it to accelerate the chassis.
IMHO, there is a certain amount of "stored power" in the mass of the rig, driver etc.

Pretty cool link.

[Dave_S]

Drag up an old thread day.

I hadn't heard of this untill the Blackbird Land Yacht came up in discussion on another thread on Friday.

I was stressing over how this works but I'm happy with it now, very interesting stuff.

I tried to find a reference to it from MythBusters but can't find anything does anyone know if they did a feature on it ?

[double u]

"...on a boat that has no complex moving parts to break..."