Analytical development of an equivalent system mismatch function

A mismatch function is used to check the validity of a low-order equivalent system model that has been derived from a high-order system representation. If the difference between the low- and high-order models is greater than allowed by the mismatch function, the flying qualities predictions obtained from parameters of the low-order equivalent system may not be representative of the ratings a pilot would give the actual aircraft. A methodology is developed in this paper to derive equivalent system mismatch functions analytically. The methodology is used to analytically determine a mismatch function for the longitudinal axis of a class IV fighter aircraft in the category A, nonterminal flight phase.