Come on guys, the relative angles of wing and stab (with or w/o elevator deflection) do not drive longitudinal stability.  That angle simply determines the trim airspeed for the configuration.  Note that stick forces should not be confused with stability.  Stick forces can be made light or heavy independent of stability.  Testing of stability is actually done stick free - i.e. no hands on the controls.

Driving parameters for static stability are primarily:  Lengths of the mean aerodynamic chords for the wing and stab, their relative distance to each other, the location of the CG relative to the MAC.  To actually determine the proper stab angle.  You also need pitching moment data for the airfoil sections, lift slope curves, your desired trim airspeed, and the wing down wash angle.

Dynamic stability gets a lot more complicated in a hurry.  Items such as aircraft mass moments of inertia are needed.

The overall recipe for best speed is to set the angle of the stab such that no elevator deflection is needed at the target speed.  Set the CG aft until either stability becomes and issue or the tail is flying at zero angle of attack.  Since we have all glued our stabs in place at one angle or another, the drag of counter weights sticking out in the airstream is pitted against trying to decrease the down force on the tail.  Flap position has a big influence on pitching moment of the section (especially our NLF section) and therefore determines how much work needs to be done by the tail. 

 

Chris Zavatson

N91CZ   

L360std