# What means when center of pressure is out of physical dimension of wing?

Center of pressure(CoP) is point where total force vector acting at. If you hold wing at this point, wing will not rotate(moment=0). Example hanging point at hanglider.

I see at some diagrams for very low and negative AoA-s that center of pressure is out of wing physical dimensions. At diagram below for AoA 0.5°, -3°, 4° What does it mean in reality, no place where can I hold wing without rotation? Or if I extend wing with some stick and hold at this position, wing will not rotate?

At first I will tell that for every AoA, must be place on wing where moment is zero.But obviusly I am wrong. Hard to imagine to me how pressure distribution around wing must be to shift CoP so much out.

That also mean if you dont know what you are doing, you can design so bed hanglider wing that will shift CoP out wing dimension for some AoAs. This is dangerous situation, theoretically speaking.

• That's why the modern way to analyze the situation is treat the lift force as acting at the wing's aerodynamic center, and also include a pitching moment term. Still, the question appears to be answerable. Commented Dec 15, 2021 at 14:28
• "My logic tell me that for every AoA, must be place on wing where moment is zero, it can not be out of wing dimensions" is wrong. Surely, it's not out of the realm of imagination that, at some incidence angle, no matter where you place your finger on the airfoil, the airfoil would always rotate? In that scenario, the CoP is out of the dimension.
– JZYL
Commented Dec 15, 2021 at 14:34
• @JZYL So math again showing absolute truth. That mean you can design bed hanglider wing that will not have correct hangpoint position for some AoAs? Hmm this is scary. Commented Dec 15, 2021 at 15:04
• @JurgenM No, that's why you have tail or you use reflex airfoil with elevon, which guarantee feasible trim point at least until buffet/stall.
– JZYL
Commented Dec 15, 2021 at 15:07
• @JZYL Yes but in theory you can make so bed wing that will shift CoP out of wing.I talk theoretically Commented Dec 15, 2021 at 15:09