Formation of a Starting Vortex for Symmetric Aerofoils (NACA 0015)

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Question regarding lift force on a symmetric aerofoil
Greetings!

An aerofoil experiences life because the velocity of flow at the top surface of the airfoil is higher, causing a pressure difference. This higher velocity is attained as a consequence of the conservation of angular momentum due to the formation of a starting vortex at the trailing edge of an aerofoil. However, I have read that symmetric aerofoils (like the NACA 0015) do not generate lift at a 0 angle of attack. Why is this so? Is it because there is no starting vortex at zero angle of attack for symmetric foils? And if so, why? What determines the formation of the strating vortex and subsequent lift genaration?
Starting vortex - MIT.gif
 
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Symmetric airfoils facing airflow at zero AOA induce an exactly equal pressure distribution profile (amount of disturbance to the molecules of air) on each side.

That pressure profile is a reflection of the ways in which the velocity of the molecules in contact with each surface varies from the stagnation point (at the leading edge) all the way to the trailing edge of the wing.

The vertical stabilizer of any airplane is a good example of this.
Please, see:
https://en.wikipedia.org/wiki/Vertical_stabilizer

Pressure-distribution-for-a-symmetric-airfoil-at-0-and-10-angle-of-attack.png


ztMCG.png


 
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  • #3
Uh, fit flaps / ailerons and/or analogous devices ?
Given you need such to control the wannabe lawn-dart in absence of thrust vectoring etc...
Or have I misunderstood the question ??
 
  • #4
Nik_2213 said:
Uh, fit flaps / ailerons and/or analogous devices ?
Given you need such to control the wannabe lawn-dart in absence of thrust vectoring etc...
Or have I misunderstood the question ??
I was just curious about the formation of the starting vortex in symmetric airfoils, and how it may explain why symmetric foils show 0 lift at 0 AoA. Thanks!
 
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