why centre of pressure moves forward when lift increase?

[dolpinsky]

the notes say will be explained later, but got no info

[QJB]

I am quite likely wrong but I recall it being to do with the adverse pressure gradient causing flow separation beginning at the trailing edge and moving forward as the angle of attack is increased toward the stall, the area of separated flow produces relatively less lift and consequently the centre of pressure for the wing as a whole moves forward.

[PappyJ]

Let me try a simpler explanation.

The greater the angle of attack, the greater the lift. Lift increases because the distance the air must flow along the upper camber increases. As this angle changes, the point where the airflow is fastest (lowest pressure/separation point) moves forward relative to the total distance the air must flow, therefore, so moves the centre of pressure (lift).

If you want the really long version, I'm happy to help.

[Teldorserious]

Increasing lift with airspeed, for a given alt, moves COP back.

80kts at 4000 ft is the same lift as 100 kts at 4000 ft. AOA of 80kts is higher, lift is the same, COP more forward. Did a forward COP create more lift in this scenario? Nope. Lift = Weight in both cases.

So the conditions of flight seem relevent when you consider a broad brush statement such as this.

[PappyJ]

Nobody suggested that total lift changed, only that point where the lift occurred moved forward with a increase in AOA for a given velocity.

[Natstrackalpha]

QJB

You`re right and at the point of stall (or very soon after) the CoP moves back.

[PappyJ]

Sorta like it moves rearward with a of decrease AOA and an increase in velocity, all the way up to 'mach tuck'.

I'm going to bed now....at zero angle of attack!

[dolpinsky]

thx everyone!
i think i understand you!