https://www.youtube.com/watch?v=y7Hyc3MRKno
https://www.youtube.com/watch?v=5zI9sG3pjVU
Nobody want’s to be smarter every day? To learn something new that have direct connection to Real World Physics and Aerodynamics?
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Some wings are so efficient that the air flow over the top of the aerofoil remains laminar across the greater part of the chord of the wing. This is typical of a high performance sailplane. The wings are often so efficient in this respect that a zig-zag turbulator strip has to be placed close to the trailing edge of the aerofoil to trip the airflow and make it become turbulent, here is a photo example. The use of this technique/method is not limited to sailplanes. At first look, it appears contradictory to place a rough surface on a wing when you want it to be as smooth as possible. Ah, but you need to do some more reading if you are interested. Follow the link below. 
Charles
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