The History of the Slotted Natural-Laminar-Flow Airfoil for Improved Fuel Efficiency

It is well established that increasing vehicle efficiency enables the achievement of N + 3 sustainable air travel goals. To this end, the integration of a slotted natural-laminar-flow airfoil with a transonic, truss-based commercial wing configuration is projected to significantly decrease fuel consumption demand. The slotted natural-laminar-flow airfoil is designed with two elements to extend favorable pressure gradients further aft than single-element airfoils. This two-element design increases the extent of laminar flow to approximately 90% of the airfoil surface, thus decreasing streamwise instabilities, which in turn reduces the wing profile drag. The slotted natural-laminar-flow airfoil also exhibits the dumping-velocity effect and achieves an off-surface pressure recovery, both critical to achieving laminar flow and overcoming single-element airfoil limitations. Given the potential of this novel concept, the objective of this literature review is to discuss the history of slotted natural-laminar-flow airfoils, recent research to mature the design, and future work needed for the implementation of this airfoil on a commercial aircraft.