# CP, AOA , AC, CG – WHAT is…. and HOW is the relationship between

[Ref. Pilot’s Handbook of Aeronautical Knowledge, FAA-H-8083-25B Page 4-8]
CP
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.
`Tag: #CP #center of pressure #centre of pressure #What's`

[Ref. Pilot’s Handbook of Aeronautical Knowledge, FAA-H-8083-25B Page 4-8]
AoA , CP    – relationship
high angles  of attack, the CP  moves forward,
while at low angles of attack the CP moves aft.
AOA ↑ , CP moves forward
`Tag: #CP #center of pressure #centre of pressure #AOA #relationship`

[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?)

CG v.s Stalling Speed?

Summary:

1. AOA ↑  ⇒  Lift force (magnitude); CP moves FWD  Nose-down pitching moment NO CHANGE! (provided that AOA within “normal” range)
2. CG forward of the CPnose-down pitching tendency

My Hand Notes:

Read more: # Aerodynamic Centre (AC)