The objective of this investigation was to develop and evaluate a nonlinear technique for the stability assessment of high-performance aircraft in the time domain. The technique employed is compatible with popular digital flutter and/or vibration mathematical models and is adaptable to various aircraft control systems arid/or modal information. The aircraft may possess servocontrol systems of high complexity and may dictate the use of aerodynamic schemes of the user's choice. The method of approach involves the use of the Advanced Continuous Simulation Language (ACSL), chosen because of its hybrid computer-like features and its conversational language. All modules of the simulation are solved in the time domain as the vehicle is subjected to disturbances of the user's choice. The vehicle motion rates are then output in the time domain for the engineer's concluding assessment of stability. Instabilities experienced by an early version of the F-16 aircraft are used as check cases. The stability boundary obtained is unconservative in its agreement with that determined in flight test, whereas the frequencies obtained are in excellent agreement. Conclusions include the following: 1) the simultaneous solution of large systems of aerodynamic, inertial, elastic, and servocontrol equations can be obtained using advanced simulation languages with mnemonic features that aid in their implementation and use; and 2) some improvements, when compared to frequency domain results, can be obtained using this nonlinear time domain simulation approach, especially when studying the behavior of phenomena with nonlinear effects or response. NomenclatureA = tensor or matrix of inertia terms; see Eq. (20) a = acceleration B = direction cosines b = reference length for lateral equations C = stability derivatives, conventional subscripts c = mean chord D = collection of 7 terms; see Eq. (20) F =force / = function to be searched (G) = generalized force vector g = gravitational constant H = angular momentum h = altitude 7 = inertia terms J = integer used in search algorithm [K] = stiffness matrix L,M,N = body moments analogous to the three components of the vector M i _[M] = mass matrix M -Mach number m = mass [P] = load vector p,q,r = roll, pitch, and yaw rates; see Fig. 1 Q = intermediate vector; see Eq. (14) q = dynamic pressure, VipV 2 [q] = normal coordinates R = position vector S = reference area, wing planform s = Laplace transform variable T = thrust t = time u, v, w = velocities along x,y, z axes x,y,h = positional coordinates X,Y,Z = force components x ' = variable for aerodynamic functions V = velocity => = stands for, or implies a = angle of attack |8 = sideslip angle 5 f j = Kronecker delta d = control surface deflection = permutation symbol = roll angle = mode shape matrix = yaw angle = pitch angle = rotation rate vector = circular natural frequency Subscripts a = aileron B = body-fixed axes c.m. = center of mass E = Euler (inertia!) axes F = flaperon HT = horizontal tail ij t k = tensor notation indices L,R -left, right N = nor...