BullSh*t Science...

[Christie]

A flat plate, wing or disc wheel will generate lift when in flow at a 15 degrees angle of attack. This is a basic aerodynamics. Lift vector will be perpendicular to the flow, in this case at 75 degrees. There will be a drag vector at 165 degrees. So the lift vector will have a component in the direction of the foreward movement, and a component perpendicular to it. The drag vector will have a component perpendicular and to the rear. The question is : What is the lift to drag ratio in this case? If the lift is big in proportion to the drag, the resultant could theoreticaly have a foreward component, in other words if the component of the lift vector in the fwd direction is bigger than the component of the drag vector in the fwd direction. This will depend completely on the profile of the aifroil /wheel.

I dont like the term "negative drag" and I also wonder when the cross wind is strong enough to make a disc unstable.

Christie2007-09-04 00:29:47

[AfreekduSoet]

Engineers are so freakin funny 

[bruce]

A flat plate' date=' wing or disc wheel will generate lift when in flow at a 15 degrees angle of attack. This is a basic aerodynamics. Lift vector will be perpendicular to the flow, in this case at 75 degrees. There will be a drag vector at 165 degrees. So the lift vector will have a component in the direction of the foreward movement, and a component perpendicular to it. The drag vector will have a component perpendicular and to the rear. The question is : What is the lift to drag ratio in this case? If the lift is big in proportion to the drag, the resultant could theoreticaly have a foreward component, in other words if the component of the lift vector in the fwd direction is bigger than the component of the drag vector in the fwd direction. This will depend completely on the profile of the aifroil /wheel.

I dont like the term "negative drag" and I also wonder when the cross wind is strong enough to make a disc unstable.

[/quote']

 

And since they fail to specify the forward velocity of the wheel, or the wind speed, it is actually impossible to quantify any of the vectors and prove them wrong (or right for that matter).

 

Probably written by some marketing guy that overheard two of the engineers discussing the behaviour of the wheel when riding into a gale force side wind at a speed of 300km/h.

[GoLefty!!]

A flat plate' date=' wing or disc wheel will generate lift when in flow at a 15 degrees angle of attack. This is a basic aerodynamics. Lift vector will be perpendicular to the flow, in this case at 75 degrees. There will be a drag vector at 165 degrees. So the lift vector will have a component in the direction of the foreward movement, and a component perpendicular to it. The drag vector will have a component perpendicular and to the rear. The question is : What is the lift to drag ratio in this case? If the lift is big in proportion to the drag, the resultant could theoreticaly have a foreward component, in other words if the component of the lift vector in the fwd direction is bigger than the component of the drag vector in the fwd direction. This will depend completely on the profile of the aifroil /wheel.

I dont like the term "negative drag" and I also wonder when the cross wind is strong enough to make a disc unstable.

[/quote']

 

And since they fail to specify the forward velocity of the wheel, or the wind speed, it is actually impossible to quantify any of the vectors and prove them wrong (or right for that matter).

 

Probably written by some marketing guy that overheard two of the engineers discussing the behaviour of the wheel when riding into a gale force side wind at a speed of 300km/h.

 

Yip I agree. Without windspeed data their claim of Thrust production is more than a little fishy.

Sails generate thrust but only through the interaction with the kee; and rudder.

An airfoil shaped wheel could generate thrust at the right angle of attack but that corridor is typically very narrow for  high aspect ratio (width to thickness) foils.

 

The zipp claim would only be correct for a very definate scenario but the same would be true for any other aerodynamically shaped wheel.