When doing preliminary layouts and configuration evaluations we apply a set of 'filters' that determine first orders of feasibility and one that occurs often is assessing the directional stability and controllability of some novel design.
The formula for horizontal tail volume co efficient is about as simple and intuitive as it gets (it is the 'eyeball' test put into measureable terms) --in fact it looks more like a rule of thumb that might not have a rigorous derivation --does anyone have a source for it's origin ? The damping factor for dynamic stability and the other extraneous factors that impact on pitch plane stability should in theory make for a much more complex equation but don't seem to .
The picture with VERTICAL tail design is much less clear as is the derivation -- for example we can have a stable and controllable aircraft with NO vertical tail or rudder (eg flying wings,birds ) --and sometimes very short coupled aircraft with seemingly inadequate vertical tail seem to work OK ( eg Genesis sailplane, Marske tailess (that's horizontal tail -less ) the SG1, FS 26 and others --or just tip fins of the winglet type (SB 13, Mitchell wing etc ) or "Weltensegler" type --- some (most) of these are long span aircraft which should require massive vertical tails 'by the book' (and rearswept wings should supply some directional stability by some of "fin less" or small fin types named are in fact forward swept or unswept (Fauvel etc )
Do any of you aero gurus have any comments on how to assess the amount of vertical tail or other yaw control on some more exact or even empirical basis ? Or an explanation for how these aircraft 'get away' with so little Vtv ?