At low CL the vortices are skinny and weak but grow as CL increases. At high CL the tip vortices affect the flow about 1 to 1.5 times the tip chord inboard of the tip and delay separation but at low CL the vortices are very skinny and probably don't have much effect farther inboard than a few inches.

Thank you for the clarification, it make sense now.

I read the post you linked:

It doesn't help that we aren't all speaking the same language either. The notation from different labs can look a bit different and notations from different countries have changed over time. CP is probably the worst example of this drift over time. Before about 1935 everybody plotted the position of the center of pressure (c.p.) which

leads to infinities because the pitching moment does not drop to zero when the AoA is such that the wing isn't producing lift. So by the mid 1940s all the labs had switched over to using the theoretical AC at

c/4 and a moment coefficient (Cm) so the engineer has real numbers that he can do math with. Now we also have a new notation, Cp, that stands for "coefficient of pressure".

Cp is the pressure distribution on the airfoil surfaces

**not **the old c.p. but it's a similar looking notation so gets confused with the older notation.

Sorry this is kind of short and disjointed. I may wright something better after the holiday

What you wrote left me confused, what is the difference between center of pressure and coefficient of pressure? There's two different Cp? Many sources I read define cp as center of pressure, for instance in Airplane performance, stability and control by Perkins and Hage: ''center of pressure, cp, is the distance from the leading edge to a point on the chord through which the resultant of all the pressure forces on the airfoil section is assumed to act.''

About the aerodynamic center, from the same book:

''Hydrodynamic theory shows that for a particular position on an airfoil section the corresponding moment coefficient is a constant, independent from lift coefficient. This point is defined as the aerodynamic center ac. The aerodynamic center usually lies very close to the chord and from 22 to 26 per cent of the chord from the leading edge.''

Now, from what I learned:

CG is where the weight is applied, and neutral point being the most aft location at which the CG can be placed in order for the airplane to remain stable

CP is where the resulting lift and drag forces are applied, this point moves forward as alpha increase

AC is the 'fulcrum' around which mg and L acts

Then, I put together what I found on the relationship between CG, AC, CP and Cm (correct me if I'm wrong):

at CG-> Cm = f(alpha)

at CP-> Cm = 0

at AC-> Cm = constant

Now, is Cm around the AC caused by torque caused by mg and lift force around the AC or is it a separate moment created by the action of air on the wing and 'inherent' to the airfoil shape? I tried to represent both scenarios with a statics diagram but it doesn't seem to work.

If the position of AC determines where we put our CG to stay inside a given SM and that the usual 'put the CG ahead of the quarter MAC' can lead to dangerous situations, it seems to me that knowing the exact position of the AC is vital.

Thank you for bringing up that subject.

If I'm too off-topic I see no objection to the above been moved elsewhere.