To be clear, air is a viscous fluid [sticky like molasses but much thinner
], and it affects both the top and bottom surfaces of wings & tails moving through it. That noted, the net effect on the tail in powered
, flapping ornithopter flt. is to push the tail down ["negative lift" vector pointing down] which raises the fronts of the wings so that they can provide [positive
] lift. In such powered flt., if the left side of the tail is higher than the right, for ex., the down-pointing
"neg-lift" vector is tilted slightly to the left .... pushing the tail left and the nose right (rotating around the CL & CG).
A right turn under power then.
But when gliding
with the same tilted tail, the airflow comes more from underneath, and the tail either has a positive
-lift vector, or ar least a less negative one. That means that the tail vector is in this case either tilted to the right or at least less tilted to the left .... The result is either a left turn or at least less of a right turn in the glide. But as noted in my previous post, there are of course also other factors involved in the flt. trim.
Further, with the same tail-tilt, if the orni is yawing too
much to the right in a powered
tight right circle or turn, the left-swinging tail acts a bit like a clockwise-rotating helicopter blade, and it will rise and help create a right spiral-dive [and the reverse in a left circle].