Incorporation of Aircraft Performance Considerations in Inverse Airfoil Design

Abstract

Although significant advances have been made in inverse airfoil design methodology, the tailoring of an airfoil to maximize one or more aircraft performance parameters still involves cycling between airfoil design and aircraft performance computations. A design formulation is presented that incorporates aircraft performance considerations in the inverse design of low-speed laminar-flow airfoils for piston engine driven propeller-powered airplanes. Two aircraft performance parameters are considered: level-flight maximum speed and maximum range. It is shown that the lift coefficient for the lower and upper corners of the airfoil low-drag range can be appropriately adjusted to tailor the airfoil for these two aircraft performance parameters. The design problem is posed as a part of a multidimensional Newton iteration in an existing conformal-mapping based inverse design code, PROFOIL. This formulation automatically adjusts the lift coefficients for the corners of the low-drag range as required for the airfoil‐aircraft matching. The design formulation also has the capability to handle a constraint on the stall speed by automatically adjusting the wing area to account for changes to the airfoil maximum lift coefficient. Two examples are presented to illustrate the process for a general aviation aircraft, and the results are validated by comparison with results from postdesign aircraft performance computations. Nomenclature A R= wing aspect ratio b = wing span C D = aircraft or wing drag coefficient based on Sw Cd = airfoil drag coefficient based on chord CL = aircraft or wing lift coefficient based on Sw Cl = airfoil lift coefficient based on chord