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Building Integrity
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Date:  12-10-2015
Number of Hours:  0.50
Manual Reference:  Section 2
Brief Description:  a twist to the VG story

These VG's are telling a twisted story here. I read from a published presentation by Terry Schubert that a 1/4" tall VG is able to recover 99% of the airflow where a 2"+ boundry layer exists. WRONG. I placed my VG's back where they worked the best and sanded down to 1/4" height and my temps are now worse than without them. This lead me to some better research tonight. I read a thorough study from the University of Catalonia on the subject after finding that the boundry layer at this point on a long ez is easily 1.5" thick. The study exposed a LOT for me. Here are the most important conclusions:
1. The VG must reach tall enough to charge the higher velocity air into a vortex.
2. My VG's at first worked good but are still too short and can work much better
3. Using 2 VG's as I have throws the Vortex away from the opening of the Naca Ramp rather than down into it.
4. It may work better to use only 1 VG with its trailing edge just in front of the Naca opening which will direct the developing vortex down the throat of the Naca.
5. My 1/4" VG's are acting like an air dam rather than doing good.

Either way, this calls for a new position for Saturday's flight and most likely making a couple new VG's even taller this time. More to come!
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sanding them down to 1/4

sanding them down to 1/4" tall

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Best temp position so far

Best temp position so far

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A better study

A better study

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