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Old Mar 02, 2004, 12:27 AM
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Punta Gorda, FL
Joined Apr 2002
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Here is a thought experiment.

Take a wing and put it in a wind tunnel and orient the wing so the 25% chord line is aligned to the free stream direction of the air flow. The wind tunnel velocity is set at 7.07 meters per second. How much lift is produced?

Now reorient the wing so that its 25% chord line is perpendicular to the free stream direction and the angle of attack is 10 degrees above the zero lift angle of attack. The wind tunnel velocity is still 7.07 meters per second. The wing spans the width of the tunnel. How much lift is produced?

Lastly, increase the air velocity to 10 meters per second and orient the 25% chord line to 45 degrees relative to the free stream velocity and the angle of attack of the wing at ten degrees relative to the component of the free stream velocity perpendicular to the 25% chord line. The wing spans a narrowed tunnel such that the area of the wing is the same as in the second case above. How much lift is produced?

If a vector, V, is analyzed into two components, v1 and v2, and the effect of v1 is zero, then the effect of V and v2 are equal.

BTW, in a windtunnel where a wing spans from one side wall to the other, the vortices are cut at the walls and the flow over the wing is very close to two dimensional and, in the direction of the free stream when viewed in plan. It is just that one component of the flow is effective and another component has virtually zero effect.

In this description I am ignoring the very, very small decrease in velocity in the 25% chord line direction due to friction.
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Last edited by Ollie; Mar 02, 2004 at 12:33 AM.
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