A new nonlinear guidance logic, that has demonstrated superior performance in guiding unmanned air vehicles (UAVs) on curved trajectories, is presented. The logic approximates a proportional-derivative controller when following a straight line path, but the logic also contains an element of anticipatory control enabling tight tracking when following curved paths. The method uses inertial speed in the computation of commanded lateral acceleration and adds adaptive capability to the change of vehicle speed due to external disturbances, such as wind. Flight tests using two small UAVs showed that each aircraft was controlled to within 1.6 meters RMS when following circular paths. The logic was ultimately used for air rendezvous of the two aircraft, bringing them in close proximity to within 12 meters of separation, with 1.4 meters RMS relative position errors.

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stability of the discrete, homogeneous, linear, minimum variance estimation formulas is investigated. ditions for uniform asymptotic stability in the large are derived. The conditions, if satisfied, also imply stochastic controllability and observability of the plant. Sufficient con-

Abstract-Many firms expend a great amount of effort to increase the customer value of their product development (PD) processes. Yet, in PD, determining how and when value is added is problematic. The goal of a PD process is to produce a product "recipe" that satisfies requirements. Design work is done both to specify the recipe in increasing detail and to verify that it does in fact conform to requirements. As design work proceeds, certainty increases surrounding the ability of the evolving product design (including its production process) to be the final product recipe (i.e., technical performance risk decreases). The goal of this paper is to advance the theory and practice of evaluating progress and added customer value in PD. The paper proposes that making progress and adding customer value in PD equate with producing useful information that reduces performance risk. The paper also contributes a methodology-the risk value method-that integrates current approaches such as technical performance measure tracking charts and risk reduction profiles. The methods are demonstrated with an industrial example of an uninhabited combat aerial vehicle.Index Terms-Lean, performance measurement, product development, project management, risk management, systems engineering, value stream.