Direct Downwind Faster Than The Wind #3 (DDWFTTW)

Some tests and demos with our latest DDWFTTW cart

Category:

Science & Technology

Tags:

• DWFTTW
• DDWFTTW

[Jangle2007]

See...now this is where the physics and mechanics behind this concept just LOSES me!

In the downwind vehicle, I understand that the swept area of the propellor rotor generates more "power" than is necessary to move the vehicle at the observed speed. What I don't get is how the propellor generates pwoer when the vehicle has outrun the wind speed?

Can somebody help me? I'm fascinated!

[spork33]

@Jangle2007

That question can be tricky, but I think the best way to think of it is to imagine the prop blades as a couple of sailboats spiraling their way along a long skinny cylindrical earth. Given that a sailboat can tack its way downwind faster than the wind, our prop blades should be able to do so on a long continuous helical downwind tack. Make sense?

[mebedavis]

I'm trying to duplicate this result with a cart of my own, but I'm finding the gearbox to be a REAL PAIN to build. Can anyone tell me where to buy a _cheap_ right-angle transmission, or offer advice on how to build one. I've shopped out all the local hobby stores, and I can't even find a decent set of 1:1 bevel gears, so I'm trying to cobble the thing together out of a combination of spur and crown gears of thickness ~.5 mm. I just can't seem to keep them stable enough to keep them enmeshed.

[spork33]

@mebedavis

I've posted a series of three build videos to make a cart like this. Look for it under spork33. It gives the part numbers and sources for the gearbox. It's the tail-drive for a radio controlled helicopter.

[t0rc]

this is not some sort of perpetual motion machine. I don't know if this is supposed to be a demonstration of such: The 3 factors here are: gear ratio of the large front wheel, vs the prop rotation and the pitch of the prop itself

In this case the thrust produced by the prop is slightly greater than rolling speed of the drive wheels. energy is added to this system by the treadmill, and the drive wheels act as a flywheel.

[spork33]

@t0rc

It is not intended to be a demonstration of a perpetual motion machine. It is a demonstration of a wind powered vehicle going directly downwind faster than the wind.

And there is no need for a flywheel as we make no use of stored energy or momentum.

[spork33]

Consider that a sailboat can maintain a 45 degree downwind tack such that it's downwind velocity component is much faster than the wind. From there it's easy to see that the tips of our props are simply two such sails following continuous spiraling downwind tacks. The wheels and transmission simply replace the boats keel in providing the kinematic constraint that keeps the prop blades on the right track.

[Jangle2007]

@spork33 You refer to "apparent wind", correct? So far so good. But at true wind speed x, how does the prop continue generating energy when the vehicle speed reaches x? I understand that a portion (or all?) of the prop travels faster than the true wind speed, but I'm not seeing how the system continues to capture energy above vehicle speed x directly down wind.

[Jangle2007]

@t0rc I'm not aware that there is an electric motor. Only a tranmission to exchange power between the wheels and the propellor.

[Mr41432]

@t0rc dude did you not see the beginning of the video? the wind was pushing the car not a treadmill the treadmill was simply there for a test

[t0rc]

There may not be a need for a flywheel but you would think it would be wise to add one so you can store enegry which pushes the vehicle forward during gusts of wind

[t0rc]

when you put the device on the treadmill, enegry from the electic motor is trasnferred via the drive belt to the wheels which in turn produce thust, which if geared correctly will drive the device faster than the rolling speed of the treadmill.

its not magic, you might as well just attach the electirc motor into the propeller because in effect its the same thing driving the propellor