Airfoil design via cubic splines - Ferguson's curves revisited

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Description/Abstract

Few aerospace design topics have had so many pages devoted to them as airfoil parameterization. Claims of novelty must therefore be made with caution in this area, so we declare our starting point simply as a fresh perspective on legacy techniques, prompted by related developments in design technology. We revisit the Ferguson spline formulation, known since the 1960s, and we propose it as a means of airfoil parameterization, it being ideally suited to implementation in commercial Computer Aided Design (CAD) engines. The development providing the impetus: off-the-shelf CAD tools are taking a widening role in the design process even at its lowest, conceptual levels. We argue that, since similarly constructed splines lie at the heart of modern CAD modeling, the most natural way to describe, say, a wing geometry is via Ferguson-style cubic splines. Further, we show that in the interest of parameterization parsimony, adequate airfoil shape control can be achieved without knots (other than those on the leading and the trailing edge), at least at the conceptual level of any design process.