Mad Genius - Wind powered vehicle travels 2.8x speed of the wind

[Punx Clever]

It's all relative... seriously. There is only ONE transition, from not moving to moving.  Everything else is based on wind deflection.  I'll also add at this time that I'm a believer in Newton-based lift as opposed to Bernoulli-based lift, talk about a controversy! So, before I explain it, lets set some definitions

Beta = Blade angle = for this example, 10 degrees relative to tangential
N = Normal Wind: Relative wind vector in direction of travel (downwind)
T = Tangential Wind: Relative wind vector opposite of blade rotation (sideways)
R = Relative wind: Wind vector relative to the blade.  Combination of T and R
M = Magnitude of R
Theta = Angle of relative, with respect to tangential
Delta = Wind deflection in degrees



Uploaded with ImageShack.us

Stage 1: Cart standing still.
N = (1,0)
T = (0,0)
R = (1,0)
M = 1
Theta = -90

The cart is literally PUSHED by the true winds, causing it to roll forward and advance to the next stage

Stage 2: Cart moving forward, normal wind still positive (air still faster than cart).  For simplicity, normal magnitude is equal to tangential magnitude
N = (.5,0)
T = (0,.5)
R = (.5,.5)
M = 0.707
Theta = -45
Delta = -55

The wind is deflected (Beta - Theta) 55 degrees.  Regardless of whether the wind changes speed, it's direction has changed, and thus has accelerated.  This is where the force comes from (important!)

Stage 3: Normal wind is zero (cart moving same speed as air)
N = 0,0
T = 0,1
R = 0,1
M = 1
Theta = 0
Delta = 10

The wind is still being deflected, so a force is still being applied, but a substantially smaller force.

Stage 4: Cart is no longer accelerating
N = -0.2 , 0
T = 0 , 1.2
R = -0.2 , 1.2
M = 1.21
Theta = 10
Delta = 0

The wind is no longer deflected, so no force is being applied.  Cart stops accelerating.

QED

Now, granted I didn't account for drag on the vehicle, a more efficient curved blade (this analysis is basicaly assuming the blade is a flat sheet), or the fact that different points on a real blade would have different angles and tangential velocities.  All in all, experience in fluids tells me that this is a workable model, and if all other factors were introduced, similar results would be possible.

Like I said before, true wind speed doesn't matter... As Einstein would say, it's all relative.

[DucatiBastard]

Anybody else sometimes get an oily film on the water when they take a crap?

[Buckethead]

Anybody else sometimes get an oily film on the water when they take a crap?

Yup. It's usually a bad day when that happens. I like hot wings. They don't necessarily like me.

I much prefer the solid "volcanic island" craps, where you deposit enough to break the surface of the water. At that point, I feel as tho I've really accomplished something.

Also, I think it works. You're "storing" energy in the form of momentum in the fan blades until you get past the wind speed, at which point you start using your own speed to drive the fan blades/wheels.

[Punx Clever]

Also, I think it works. You're "storing" energy in the form of momentum in the fan blades until you get past the wind speed, at which point you start using your own speed to drive the fan blades/wheels.

If that were the case... then this (@ about 4:00 in) wouldn't work: Downwind Faster than the Wind (DWFTTW) Myth Challenge

[ducatiz]

Just imagine..

years ago..

no internet..

people had to actually get off their fat asses and go BUY a magazine or pick up a flyer to start believing stuff like this.

[Buckethead]

If that were the case... then this (@ about 4:00 in) wouldn't work:

Watch for about 30 seconds longer. Their model uses a "pusher" fan blade, which the original vehicle does not. Their "model" works, as I would expect it to. It pushes itself up the treadmill via air pressure from the fan blades, where as the original vehicle uses a wind "driven" propeller to drive an axle, clawing its way across the ground.

My assertion of storing energy in the form of momentum is directed at Sac Duc's "how does it go from slower than the wind to faster than the wind" argument. At a standstill, the "driven" propeller acts as a sail to a tailwind. While the vehicle is going slower than the tail wind, the propeller is actually fighting the wheels and robbing power.  When the wheels are driving it at the same speed as the wind, because of the gear ratio and the pitch of the blades, the propeller is already being driven by a headwind, imparting more driving force to the wheels and increasing acceleration, powering it through that "dead spot."

[Punx Clever]

Watch for about 30 seconds longer. Their model uses a "pusher" fan blade, which the original vehicle does not. Their "model" works, as I would expect it to. It pushes itself up the treadmill via air pressure from the fan blades, where as the original vehicle uses a wind "driven" propeller to drive an axle, clawing its way across the ground.

The original carts blades are set up to pull the vehicle.  The leading edge is clearly forward, as seen in the picture below, and the blades are curved to be driven by the wheels, not by the wind as easily seen at the beginning of the video below the picture

DDW.mov

The difference between the model and the cart is the same as the difference between these two airplanes:

My assertion of storing energy in the form of momentum is directed at Sac Duc's "how does it go from slower than the wind to faster than the wind" argument. At a standstill, the "driven" propeller acts as a sail to a tailwind. While the vehicle is going slower than the tail wind, the propeller is actually fighting the wheels and robbing power.  When the wheels are driving it at the same speed as the wind, because of the gear ratio and the pitch of the blades, the propeller is already being driven by a headwind, imparting more driving force to the wheels and increasing acceleration, powering it through that "dead spot."

Yes, from the cart's perspective, the cart goes from slower than the wind to faster than the wind.  But, from the fan blade's perspective the wind is always moving from the leading edge to the trailing edge except from stand-still, so there never is a transition from slower than the wind to faster than the wind with respect to the fan.

I suppose the best way to convince you that the wheels are driving the prop as opposed to a turbine driving the wheels is their website itself... we engineers are pretty picky about what turbomachine devices are called.  A fan or propeller pushes air, whereas a turbine is pushed by the air.  They (the engineers behind this) call it a prop:
http://www.fasterthanthewind.org/2009/12/for-next-phase-assembly-and-layup-of.html

[reksio]

Also, I think it works. You're "storing" energy in the form of momentum in the fan blades until you get past the wind speed,

No, you cannot use the energy stored in prop rotation to accelerate past wind speed. To extract that stored energy you would have to slow down the prop rotation, but that would slow down the wheels and thus the entire cart.

at which point you start using your own speed to drive the fan blades/wheels.

No, using your own speed to accelerate yourself doesn't work. But slowing down the true wind to accelerate yourself does work.

When the wheels are driving it at the same speed as the wind, because of the gear ratio and the pitch of the blades, the propeller is already being driven by a headwind, imparting more driving force to the wheels and increasing acceleration,"

No, the rotor is never driven by the apparent headwind above windspeed. I explained why on the last page: It would create more wind, instead of extracting wind energy. They also have ratchets that prevent the prop from driving the wheels. Only the wheels can drive the propeller.

powering it through that "dead spot."

There is no dead spot. The apparent wind at the rotating propeller blades never drops to zero. It always creates lift that pushes the cart forward.

[reksio]

Punx Clever explained all very well but I have a minor nitpick:

A fan or propeller pushes air, whereas a turbine is pushed by the air. 

According to Newtons 3rd Law both rotors push the air with the same but opposite force as the air pushes them, so "who is pushing whom" is not a good criteria, as it is physically irrelevant. The most general difference between turbine and propeller is rather:

- Turbine rotates in accordance with the torque exerted by the air.
- Propeller rotates opposite to the torque exerted by the air.

There are other less general definitions, based on the direction of energy transfer, but they are frame dependent and fail in special cases, like a propeller working in reversed flow (as is the case here below windspeed).

They (the engineers behind this) call it a prop:

That is correct. The rotor always turns opposite to the torque exerted by the air, and in accordance with the torque transmitted from the wheels.

[Punx Clever]

Minor details. Potato - potato

[ducatiz]

Wind turns fan.

fan turns wheel

wheel twists big rubber band

big rubber band eventually twists enough

goes faster than wind.

easy

my kid has pull back toys, same principle

[reksio]

Wind turns fan.

Look at the videos. It turns opposite to the torque from the air.

rubber band

The vehicle was inspected by officials from the North American Land Sailing Association (NALSA) before the record runs:
http://www.nalsa.org/DownWind.html

Quote from their report:
http://www.nalsa.org/BlackBirdDDWSR/Observers%20ReportNALSA%20C4BlackbirdJuly2and%2032010.pdf

S2: We found no evidence of any energy storage devices. There has been some discussion on www discussion groups that the rotating propeller constitutes a form of stored energy that might be converted to propulsion by slowing it down or changing its pitch. Since the propeller is connected to the wheels with a constant ratio connection slowing the propeller to harvest some of its rotational energy also slows the craft.

[ducatiz]

Look at the videos. It turns opposite to the torque from the air.
The vehicle was inspected by officials from the North American Land Sailing Association (NALSA) before the record runs:
http://www.nalsa.org/DownWind.html

Quote from their report:
http://www.nalsa.org/BlackBirdDDWSR/Observers%20ReportNALSA%20C4BlackbirdJuly2and%2032010.pdf

it was an invisible rubber band

and how do you know it was turning opposite to the torque from the air?  which way was the air torquing?

NALSA?  really?  a bunch of old farts who invent a sport in 1972 can't be bought? 

people worry about the FDA and the FBI, but nooooo.. when NALSA says something it much be holy writ!

[sno_duc]

Everybody missed it.
Soapbox derby.
Apply this to a soapbox derby car, you'd win everytime until either it was outlawed or a competetor built a better one. 

[reksio]

it was an invisible rubber band

Or invisible dwarfs pushing it, or a giant invisible magnet pulling it... or simply a wind powered vehicle.