I know for static stability reasons, the derivative of the moment coefficient of an aircraft has to be negative.
What I do not understand, why the moment of coefficient (cm) at all is allowed to be positive? Because when it is positive the aircraft pitches up.
Is it because when cm>0 I use my tails for trimming ? But is this "static stability" when I actively use my tail ?
I struggle with:
alpha = 0 ° --> e.g. cm=0.3 : the tail is used for trimming so that it counteracts the positive moment of the wing
alpha = 2° -- > e.g. cm=0.4 : now the pilot could also use the tail for trimming the higher moment
Thank you for your hints