If I start watching this sort of stuff I'll die on Monday :-).
So, without having seen the videos or read the comments apart from a quick
skim, here's my 1st take - see if it makes sense.

Short:  He's essentially cheating :-) . The car is going directly down wind
- the blade essentially isn't. Vector sum of velocities generates lift whos=
e
primary component is downwind.

Long:  An airfoil can travel at speeds greater than the air stream which
derives it by creating an apparent wind velocity vector which is the vector
sum of its own motion and the incident wind. Modern WTs (Wind Turbines)
typically run a5 say 5:1 - 7:1 TSR (tip speed to wind speed ratio). You can
run at 10:1 or even higher but noise becomes severe and blade erosion
becomes severe  due to the high blade velocities.

Ina typical HAWT (horizontal axis WT) the wind passes through the blade, th=
e
blade travels at approaching 90 degrees to the wind (the difference being
the AOT (angle of attack). The instantaneous change of speed of the blade i=
s
not directly related to wind speed but to the lift forces on the blade whic=
h
in turn are related to the vector sum of its own current velocity and air
velocity.

In the current situation the vector sum as far as the car is concerned =3D
Vforward - Vwind.
If the wing is angles (aerodynamically if not visually physically) to the
stream it generates lift.
If Vforward is at least double Vwind then net forward velocity over the
airfoil is >0.

Getting to this happy state seems hard, at first glance. I have not seen th=
e
videos, but I'd expect it easier if they started at an angle and pulled ont=
o
downwind as speed exceeded twice windspeed. Maybe not.

If their system had a potential TSR of say 10:1 then they may be able to ge=
t
say 8+:1 ws.

The above seems to be able to argue that you can run downwind at high speed
with NO wind at all  and that the less wind there is the better :-). I'd
have to draw myself pictures to see if the above makes sense and I'm not
going to start !!! There has to be energy input from somewhere and airfoil
needs to derive a velocity vector which is different to the available speed
somewhere else within its system (no flow, no lift). Explain it to me :-)


        Russell
--=20
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