Mitigation of Insect Residue Contamination on Hybrid Laminar Flow Control Leading Edge Surfaces: Part 1. An Investigation of Commercially Available Materials

Flight tests have demonstrated that in many operational environments, insect residue buildup on the leading edge of an aircraft wing can cause the loss of laminar flow. The airborne insect threat occurs between ground level and 152.4 m with the highest population concentration occurring during light winds (2.6 – 5.1 m/s), high humidity, and temperatures between 21-29°C. Under these conditions, mitigation is needed during takeoff, initial climb, approach, and landing. When insect fouling reaches a critical height, laminar flow is disrupted leading to increased drag and hence additional fuel consumption for the duration of the flight. This critical height is highly dependent upon the airfoil and Reynold’s number. Several techniques (e.g. paper, scrapers, surfactants, flexible surfaces, etc.) investigated to date have the potential to mitigate this problem; however, implementation has proven to be impractical thus limiting their utility. For example, the Kreuger flap (illustrated above) has been shown to negate insect excrescence from the wing leading edge while also improving lift during takeoff. However its complexity and physical discontinuities may induce early boundary layer transition on the lower surface.