This thesis presents the algorithms and methods to represent the skin of an engineering model with non-uniform, hierarchical B-spline surfaces. Non-uniform, hierarchical B-splines offer the mechanical designer many advantages: parametrically defined components may be added to a surface while maintaining C² surface continuity; detailed features may be added to a surface without globally affecting the B-spline control net; and an appropriate geometric basis for finite element meshing and analysis in the conceptual design phase can be established. These algorithms are applied to ASCYNT, a conceptual aircraft design code, to verify and validate the algorithms. A single-surface definition of an aircraft skin, appropriate for computational fluid dynamic and radar and infrared cross-section analysis, is designed using non-uniform hierarchical B-spline surfaces. / Master of Science