I'm glad to be back. I hope others will be, too.
Many years ago, when I had little opportunity to fly frequently - growing family and military reassignments - I tried to estimate how and why stunt models arrived at their level of performance.
I'd had some "Intro to..." level courses involving basic aerodynamics the mid-1950's, at Brooklyn Tech, a great high school, which added to some "understanding" of the (usually wacko) theoretical 'explanations' of success in the modeling magazines. As other technical courses added awareness of structures, shapes and forms as well as loadings and design to meet them, I went a bit further.
I was humbled and proud that Igor mentioned my initial inadequate efforts, the main one of which was a BASIC program published in the 1980's on the now defunct CompuServe's Modelnet forum: STUNTIII, eventually. Some dynamics, some dimensional calculations, some loading estimates. Not rigorous, by any means. I found, nevertheless, that things I worked out helped me a lot on the infrequent occasions I could fly.
I'm not trying to claim any level of great insight. But a superficial awareness of the many factors involved intrigued me. Other things included?
Effects of our circular flight: the model is flown in a tethered circle. It meets what we usually mis-call Centrifugal Force. Fuel, a liquid, 'feels' a total force that results from the circling and from gravity. Three g out and 1 g down is a fair description for our level flight. Like the surface of water in a pail swung around, the result of those forces is a tilt of the free surface to be perpendicular to the resultant.
And on and on over several factors.
Lift across the wing's span? Inboard tip finishes one lap in the same time as does the outboard tip. Outboard flies a larger radius, so further in the same time. It goes faster, well, duh. Lift varies as velocity squared. The velocity of each increment from inboard tip to outboard tip increases with radius, so we could estimate what the difference at those two points would be.
But that ignores the incremental increases from one to the other. If we could find the point across the span where lift is equal for the inboard area and the outboard area, that would be where we should hang the weight of the fuselage with its engine, tail, etc. parts. If not, when we pull g's, those weights will be offset from the equal lift point, and will try to roll the fuselage. This is the basic argument for longer inboard panels!
So much else! Drag that comes with lift - Induced Drag - is small in level flight, and larger in rounds, much larger in corners. Like lift, that drag grows from inboard to outboard. If not centered, it is offset, and will try to yaw the model. So, 'centering' the lift effects is there again.
Power. Newton: F= MA. It takes more Force to Accelerate the same Mass from unmoving to a given speed. In level cruising fight, clean stunters have little drag. The Force to maintain speed is less that it was accelerating from standstill. When we pull g, drag increases: the model slows. Thrust load rises to try to maintain speed. (Modern engines and modes of operation make this less obvious, but the loads are still there.)
Torque? At cruise, not a whole lot. With sudden increase against effort to turn the prop? We get a greater torque reaction into the motor mounts, which could tend to roll the model.
On and on... So, I tried, with limited math and science, to estimate these and see which were significant and which were not. Guys like Igor, Brett and Howard can do the detail work, have done it and it shows in their results.