By your logic (which I accept), you have have a choice of...
- A single value of Va, combined with means of determining whether normal acceleration limits have been exceeded, and a defined value of
Vb, or...
- Multiple values of Va at different weights.
Clearly combat aircraft prefer the former, whilst part 23 aircraft (at-least the non-aerobatic ones) prefer the latter (although they do normally define
Vb - although see my note below). I can see that either makes since in the operating environments for which the respective aircraft are designed.
Incidentally, I've just been looking at part 23 and a couple of POH.
Vb is not required by part 23 to exceed Vc - which effectively means that they become co-incident. Then the Piper and Cessna POH that I've got on the shelf don't declare either, but give Vno, defined as "Maximum structural cruising speed - do not exceed this speed except in smooth air and then with caution". This seems permitted by part 23 which requires
Vb to be defined, but not to be declared in operating data. A subtly different definition of Vno to that used in Def-Stan 00-970 which uses it as a speed with a safety margin below Vne.
Speaking for myself I'd rather have more instruments and single non-variable limits than less instruments and variable limits that you can get wrong.
G