01 august 2010

Ride Like the Wind (only faster)

Kan et kjøretøy konstrueres slik at det kan drives med vindkraft, men gå raskere enn vinden? firmaet Thin Air Design har , i samarbeid med San Jose State University, funnet en løsning på det problemet.

Konseptet forklares her:
The downwind car is designed with a propeller that pushes it along like an aircraft's propeller does, it is not a windmill or a turbine. Instead of an engine to turn the propeller, the propeller is geared to the wheels of the car, so that as the car moves forward, the propeller spins in such a way that the car will speed up if there is energy available from a tailwind. The following explanation will show how this works by analyzing the forces acting on the vehicle and the energy flow through the system.

In order for the car to travel downwind faster than the wind using only the wind for power, the total resistive force on the vehicle must be less than or equal to the thrust provided by the propeller (force balance) and the power provided at the wheels must be greater than or equal to the power consumed by the propeller (power balance). (Note: In this explanation we are describing the power balance as seen by an observer riding with the car, so the power for the propeller appears to come from the wheels. A similar analysis can be done from the ground-based reference frame, but it is more complicated.) The force equation tells us that the sum of the wheel resistance equals the propeller thrust when traveling at maximum speed (we are ignoring vehicle drag for simplicity in this explanation). The power balance tells us that the wheel force times the car speed (power input) must be equal to or greater than the propeller thrust times the relative velocity of the air (Vcar-Vwind) divided by the propeller efficiency (power output). Note: we are also neglecting drive train losses in this simplified analysis.

Kilde: Fasterthanthewind.org

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