ORIGINAL: da Rock
because as the CP moves forward, it reduces lifting area from the tip towards the root, by exiting the wing's lift area (going ahead of leading edge).
Sorry, but where did you get that idea?
The CP doesn't move the lifting area with it at all.
True.
But, let's consider the delta wing with:
1 meter of root length
1 meter of trailing edge length
1.41 meter of leading edge length.
The CP is a lift resultant, so it's actually situated on longitudinal (chord) axis and moves forward and afterward, depending on AOA. Now, if we take a look at this delta wing from top projection, we'll see that the best spanwise lift distribution is when the CP is way backward (small AOA). As we increase AOA and move CP forward, the effective span is reducing (CP for each wing is moving forward, but towards the wing root, since CP can't be outside the lifting area) and so is spanwise lift distribution. However, the AOA increase produces higher overall lift increase (and drag), than the spanwise lift distribution reduces that same lift.
In the end, we get a gentler Cl/AoA curve, than that of the straight wing and that corresponds with empirical data.
Hm...does it makes more sense now?
