Posted: Mar 06, 2011 5:46 pm
So what starts the wheels turning?spork wrote:Four things to keep in mind:
1) The prop never turns the wheels. The wheels turn the prop
Would you mind backing that assertion up?
2) Inertia doesn't factor into it. Even exactly at wind speed we can tow a trailer all day long.
Actually they are traveling in a helical path, but nevertheless they are still traveling at exactly the speed of the wind. If it can't 'feel' wind then it can extract no energy from it.
3) When the vehicle is going directly downwind at wind speed, it feels no wind over it. The "prop" is also going downwind at wind speed. The blades of the prop however are not going directly downwind. The blades are following a spiraling path so they will always feel relative wind even when the cart is going downwind at wind speed - remember their tangential velocity.
4) When the cart is going the speed of the wind - it feels no wind. But that doesn't mean there is no wind. It simply means there is no relative wind. There's still wind moving over the ground, and that's precisely the energy this vehicle exploits. It leaves a path of slower moving air in its wake - having taken some of its energy.
How does it extract energy from air that is not moving relative to itself? You claim that the wheels turn the prop, so therefore the prop is pushing air, that is the prop is performing work on the air. How do you extract energy from the process of doing work on something?