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Old 08-02-2010, 06:20 AM   #55 (permalink)
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GasDwarf - '13 Volkswagen up! EcoFuel CNG
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Originally Posted by 3-Wheeler View Post
I think that there may be a rendering problem with the airfoil shape from 70% to 100% length. I made several larger circles (shown in forth picture with blue line) that hugged the airfoil from 70% t0 90%, then veered away from the airfoil from 90% to 100%.
If anyone has any ideas, please let me know.
That's normal for a trailing edge on a classic airfoil.

The upper and the lower airflow must meet up with as little turbulence as possible, so the angle between both flows is reduced when the flow reaches the trailing edge - both airflows are lined up.

On laminar flow and supercritical wings, you'll see "the circle" continuing on top, while the airflow line-up happens through an S-curve on the underside.
See :

(wing section from a Pipistrel light aircraft)

In this design the air flows downward when leaving the wing.
That's probaby also what keeps the higher pressure "bubble" on the aft part of the wing.

Some low-drag vehicle designs have already utilised this sort of airfoil section - but then the trailing edge is relatively high up from the ground.

When the tail is close to the ground a net downward flow will likely increase drag through its turbulent interaction with the ground.
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