A digital model reference scheme is presented for the control of the longitudinal modes of an EBF-STOL aircraft. The method used is based on Liapunov's direct method and is used to update feedback and feedthrough matrices. An equilibrium point of the EBF-STOL is chosen about which to constrain performance to follow that of a linearized decoupled DC-9 model. The change of control matrix elements is controlled by

(1) an error vector equal to the difference between state variables of the model and those of the STOL,

(2) the present values of the pilot inputs and STOL state variables,

(3) a P matrix obtained from the equation

A_mᵀPA_m - P = - I

where

z(k + 1) = A_m z(k) + B_m u_p

is the equation of motion for the model,

(4) selected gains, and

(5) a matrix B₋ᵤʳ⁻¹ whose elements are determined by the inverse of an n x n partition of the linearized input matrix B₋ᵤ of the STOL.

A method for smoothing control action is discussed.