Originally Posted by
Andy_P
Yup, I am still in the elementary stage, hence the reason I put my hand up and asked the question. FWIW, I just looked up my text book and can confirm that is says most conventional aircraft have the CoG foward of the CoP. ...
And the primary reason for that is longitudinal stability.
Pitch excursion (due turbulence, say) down, speed increases. Downward "lift" on tailplane/elevator increases. Mainplane lift increases. Plane pitches up.
Some types, like the PA28, are very stable longitudinally. You can see it easily by moving the tailplane through its full range on a preflight. So in stable trimmed flight there's quite a lot of downward force produced by the tail.
Friend and I flew a 181, 2 up, on a quick 30 mile trip. When I climbed into the back seat, and he re-trimmed to compensate, it was good for another 10kts IAS.