Low-speed natural-laminar-flow airfoils: Case study in inverse airfoil design

A systematic study of the trends in low-speed natural-laminar-flow airfoils for general aviation applications is presented. The airfoils have been designed using a multipoint inverse airfoil design method, which allows for specification of velocity and boundary-layer properties over different portions of the airfoil. A panel method with a coupled boundary-layer scheme is used to analyze the characteristics of the resulting airfoils. By systematically adjusting the specifications, families of airfoils have been designed with different lift, drag, and pitching-moment characteristics. Parametric studies are presented to study the tradeoffs involved in designing laminar-flow airfoils for general aviation. Although the results of the study are specific to the class of airplanes considered, the design philosophies and the design approach used in the study are applicable to a wide range of airplanes. In addition, the examples presented in the paper form an excellent case study to demonstrate the power of modern inverse design techniques in controlling the performance of an airfoil to a fine degree and in generating a custom database of airfoils suitable for airplane multidisciplinary optimization and trade studies.