ORIGINAL: BMatthews
Like you say the terms can mix us up a lot. I'd have to go and read up on it again but I'm sort of assuming here (and we all know what happens when you assume right?
) that the pitching torque is dependent on airspeed. The faster it flies the more pitching force or torque. In all the airfoil info I've seen about pitching the value was always given as a single number like a "coefficient" and that leads me to believe that you then match that pitching moment value with the airspeed to find the rotational force of the airfoil for any given speed. I'll have to look into this aspect when I'm not so tired. I've been playing hard today and my mind is mostly mush right now.
I can't remember where I saw the chart on the pitching coefficient, but from what I remember it actually goes the other way. Not remembering for sure has kept me silent about that, but I really think that the pitching moment of a wing is basically a function of the movement of the center of pressure (CP) fore and aft.
I believe one of the pitching forces in this Bee Tuck deal is the location of the CP relative to the NP of the airplane. Quite a few original NACA plots show the location of the CP and show it's movement with AOA changes. Since the guys who've seen tucking have all described it as happening as the airplane has been increasing speed, it would appear that it's something that happens when the CL is small and the AOA is moving from a shallow angle to a shallower angle. And what shows in the CP plot is that the CP hardly moves at all until the AOA is close to those smaller CLs, but when it approaches the zero lift AOA it begins to rapidly move forward.
I've not read much about CP but have seen it tied into pitching moment. And it seems logical that it would have measurable affect on the pitch attitude, especially when pitch trim is fixed while airspeed is moving in the range that would affect the CP movement most.
So I was hoping (I always hoped it was safer to hope than to assume
someone who knew about CPs would wade into this discussion. because.........
It looks to me like what might be doing the sudden pitching was the CP suddenly starting to shift, which it does at the lesser AOAs.
On the Clark-Y series, the CP basically is around the .3C to .4C until the very smallest AOAs but when those airfoils start into the zero and negative AOAs, the CP starts aft fast.
I'm guessing the tuck comes from the CP realtively fast move aft feeding in a moment or torque the tail can't handle anymore.
But it's just a guess. NOT AN ASSUMPTION