One of the intriguing problems in nonlinear unmanned aerial vehicle (NUAV) control using one of its linearized model based controllers at the inner loop is generating admissible control inputs for which the aircraft trajectories are confined to its stability region. It is an initial condition selection problem that is not necessarily applied at initial time but can be applied at any part of the flight duration where a bifurcation is needed, say, to avoid a collision with an obstacle. So, valid initial condition options at a given time instant can generate a stable constant speed maneuver tree that can be augmented to an existing autopilot and enhance autonomous characteristics at the decision points where changes in flight path directions are needed. In this paper, a procedure to select these initial conditions is presented. The time response bounds of the NUAV in its stability regions are developed. Both zero input response without pilot inputs and total response with pilot inputs and initial conditions are analyzed. A three degree of freedom NUAV in pitch plane is considered to illustrate the hierarchical initial conditions for which the time responses are bounded.
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