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Overall the sum of the forces of drag on an object must of course be negative. But is it possible to have areas of an object that contribute to negative drag?

I have the pressure distribution over a NACA 0015 (symmetrical aerofoil about x-axis) at many angles of attack and I need to calculate lift, drag,etc..

Some of the pressure readings are indicating negative drag at multiple points at multiple angles of attack...unless I am thinking of it entirely wrong..

The picture below (not actual aerofoil!) shows a point on the aerofoil at 0 degrees AOA where the static pressure is lower than the freestream pressure. Does this mean that the resultant force on this point is the red arrow?

And as you can see from the equations this means positive lift and negative drag at this point?

Thank you in advance,

Jez

I have the pressure distribution over a NACA 0015 (symmetrical aerofoil about x-axis) at many angles of attack and I need to calculate lift, drag,etc..

Some of the pressure readings are indicating negative drag at multiple points at multiple angles of attack...unless I am thinking of it entirely wrong..

The picture below (not actual aerofoil!) shows a point on the aerofoil at 0 degrees AOA where the static pressure is lower than the freestream pressure. Does this mean that the resultant force on this point is the red arrow?

And as you can see from the equations this means positive lift and negative drag at this point?

Thank you in advance,

Jez

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