The average of the pressure variation ( for any given AOA ) is referred to as the center of pressure (CP). Aerodynamic force acts through this CP, which is along the chord.
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high angles of attack, the CP moves forward,while at low angles of attack the CP moves aft.
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[Ref 080 Principles of flight]
AoA , Nose-down pitching moment – relationship
Relationship between AoA, Lift and nose-down pitching moment:
AoA increase at “normal” AoA range, lift force will increase but lift at CP will also move FWD which shorten the distance from CP to AC. However, the moment about the AC remains the same at any AoA within “normal” range.
[Ref. Pilot’s Handbook of Aeronautical Knowledge, FAA-H-8083-25B Page 5-8]
CG , CP – relationship
CG is generally forward of the CP, and so the aircraft has a natural nose down pitching tendency;
In contrast, if the CG is rearward of the CP (i.e CP is forward of the CG) , a nose up pitching moment is created – however, in modern jetliner, rearward CG (in event of in-trim condition), cursing would be more fuel efficiency. (#Why?)
- AOA ↑ ⇒ Lift force (magnitude) ↑ ; CP moves FWD ⇒ Nose-down pitching moment NO CHANGE! (provided that AOA within “normal” range)
- CG forward of the CP – nose-down pitching tendency
Read more: # Aerodynamic Centre (AC)