ImbracableCrunk… on a weathervane, the rear part has the majority of the mass and the most arm from it's vertical axis so the wind acts on it, rotating it around it's axis until it lines up with the wind. If the wind sways a little sideways, it'll hit the rear part, bringing it back into line.
I think I've got a better understanding of this weathercock theory and I still contest it's use; I believe it's the wrong term for what's really happening. I've never heard of a "variable weathervane"… the whole point of a weathervane is to have it "non-variable" so that the wind will act on it, producing the change.
Looking at nature… a fish must "weathervane" through the water, which I don't think would be correct to say. An object in motion tends to stay in motion, therefore requiring another force to change it's path. the control surfaces at the tail impart that force. About 99% of the time, the aircraft will be "streamlined" with the relative airflow, only when another force, such as control surfaces, applies itself will there be a change. Fluids take the path of least resistance, so instead of piling up at the rudder like bullets, they smoothly get deflected and then impart an opposite force on the vertical stab. So what I'm saying are that these are forces "initially" imparted "by" the aircraft, not the wind. These forces are what makes the aircraft turn! A weathervane doesn't have a wing or horizontal stab or rudder… remove those from the airplane and I will fully agree that it is weathercocking as it's accelerating towards the earth!
rudderrudderrat… sorry I wasn't clear there, I meant that the elevator would be causing the nose to "come around" while in the turn, to "point" the aircraft in a circle. I fully agree the horizontal lift component is what's pulling the aircraft "into" the turn. I also think that there is a tiny component of thrust that would help turn the aircraft… like stated, there is usually a bit of downforce on the horizontal stabilizer in level flight, take that and add even more downforce required in the turn to stay level and you're adjusting your thrust angle so you have slightly more of a thrust component acting with the lift vector, perpendicular to the wings. Very small for sure, but I believe it's still there.