Natural-laminar-flow airfoil for general-aviation applications

A natural-Iaminar-flow airfoil, the NLF(1)-0115, has been recently designed for general-aviation aircraft at the NASA Langley Research Center. During the design of this airfoil, special emphasis was placed on experiences and observations gleaned from other successful general-aviation airfoils. For example, the flight lift-coefficient range is the same as that of the turbulent-flow NACA 23015 airfoil. Also, although beneficial for reducing drag and producing high lift, the NLF(1)-0115 airfoil avoids the use of aft loading, which can lead to large stick forces if utilized on portions of the wing having ailerons. Furthermore, not using aft loading eliminates the concern that the high pitching-moment coefficient generated by such airfoils can result in large trim drag if cruise flaps are not employed. The NASA NLF(1)-0115 airfoil has a thickness of 15% chord. It is designed primarily for general-aviation aircraft with wing loadings of 720–960 N/m² (15–20 lb/ft²). Low-profile drag as a result of laminar flow is obtained over the range from c₁ = 0.1 and R = 9 × 10⁶ (the cruise condition) to c₁ = 0.6 and R = 4 × 10⁶ (the climb condition). While this airfoil can be used with flaps, it is designed to achieve a c_{1, max} of 1.5 at R = 2.6 × 10⁶ without flaps. The zero-lift pitching moment is held to c_m,⁰ = −0.055. The hinge moment for a 20% chord aileron is fixed at a value equal to that of the NACA 63₂-215 airfoil, C_H = −0.0022. The loss in c_{1, max} due to leading-edge roughness at R = 2.6 × 10⁶ is 11% as compared with 14% for the NACA 23015.