I think we can think of this in terms of three phases:
1. Start from a dead stop
2. Acceleration to a speed superior to that of the wind
3. Post acceleration performance
1. I am guessing that the contraption just starts moving forward because of the
push of the wind on its vertical surface, e.g. prop, structure, passenger
cockpit, etc.
No wind = no movement
Note how slowly the thing starts to move.
2. As the wind increases the speed of the prop, it transmits more power via a
belt/chain to the wheels, probably via a fixed gearing, but it could be variable
The wind keeps pushing the thing until its speed equals that of the
wind. When the speed exceeds that of the wind, the thing faces a drag. I am
going to guess that the thing moves faster than the speed of the wind for a
(short) while due to the mass/kinetics/momentum of the prop, which continue
after reaching wind speed/vehicle speed equilibrium and so impart some energy
to the wheels to exceed wind speed.
3. But how long can this excess speed be maintained? The clip shows the vehicle
slowing pretty quickly after it exceeds the wind speed. This is attributed to
the brakes in the clip, but perhaps it is no more than drop in the
mass/kinetics/momentum of the prop that occurs when the wind is no longer
maintaining its speed-increasing motion.
Assuming the thing works as advertised, I suppose the vehicle could move
downwind with an oscillating speed, dropping to the point where the prop begins
to supply positive drive, and then re-accelerating to the point where wind
speed is no longer sufficient to do so.
Of course, we are making one critical assumption: that the vehicle is actually
moving straight down-wind, rather than at an angle to it. (Think of a
gyrocopter, mounted vertically, with the wind providing the forward thrust.)
Interesting....and impressive to a sailor like me who has often cursed
down-wind speeds.
Lawry
On Sep 21, 2010, at 2:41 PM, Lawrence de Bivort wrote:
> I am guessing that the propeller propels a belt/chain which is geared into
> the wheels.
>
> Lawry
>
>
> On Sep 21, 2010, at 1:26 PM, Jed Rothwell wrote:
>
>> I do not see how this can work! They are going with the wind, so if they
>> start to travel at the same speed as the wind, the propeller should stop
>> turning.
>>
>> Maybe I am missing something.
>>
>> - Jed
>>
>
