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Old Nov 27, 2005, 12:10 PM
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Pacific Northwest
Joined Feb 2004
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Originally Posted by RobinBennett
At low speed, and especially when the wing is stalled in a 3D manover, the LE shape is going to make virtually no difference.
In a perfect world and for those of you who only fly indoors this may be close to correct. When airflow is slowed the affects are minimized but the affect is still present. We don't live in a perfect world. When you step outside and encounter any type of breeze this is absolutely not correct.

Anytime airflow encounters a 90 degree step on a surface or when it is being split between two sides of a surface as with a wing, it must move the same dirrection and distance as the step plus half the distance of that step farther in the same dirrection before it can BEGIN to follow its original path. This is true regardless of the airflow being generated by airspeed of the craft or wind speed and dirrection. Changes in angle of the step change how far and at what angle opposed the air must travel before airflow can follow its original path and what distance of the chord it must be detached from the wing surface before becoming laminar again. These vorticies between the airflow and the wing surface at the LE that are created by the airflow being sheared in an opposite direction from its normal flow are what cause the darty behavior.
Now add in a slight gusting breeze and start thinking dynamically. The 90 degree step will have greater changes with gusts of "airspeed" in the size and shape of this created vortex causing larger changes in lift and drag than that of a rounded LE. Now think about this in a fully stalled 3D hover. When the wing tips encounter this wind speed generated airflow from the side, airflow is split in a similar manor even if it is 90 degrees to that of a flying wing and all of the same rules apply. So now you have these vorticies causing unpredictable lift and drag on the tips of the wing causing more unpredictable changes in the crafts rotational position around the prop center than the rounded wing tips. Every edge in every instance that encounters airflow will be affected the same way every time. It is simple physics that can't be escaped.

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