Engineered Surfaces for Mitigation of Insect Residue Adhesion

Abstract

Maintenance of laminar flow under operational flight conditions is being investigated under NASA's Environmentally Responsible Aviation (ERA) Program. Among the challenges with natural laminar flow is the accretion of residues from insect impacts incurred during takeoff or landing. Depending on air speed, temperature, and wing structure, the critical residue height for laminar flow disruption can be as low as 4 µm near the leading edge. In this study, engineered surfaces designed to minimize insect residue adhesion were examined. The coatings studied included chemical compositions containing functional groups typically associated with abhesive (non-stick) surfaces. To reduce surface contact by liquids and enhance abhesion, the engineered surfaces consisted of these coatings doped with particulate additives to generate random surface topography, as well as coatings applied to laser ablated surfaces having precision patterned topographies. Performance evaluation of these surfaces included contact angle goniometry of pristine coatings and profilometry of surfaces after insect impacts were incurred in laboratory scale tests, wind tunnel tests and flight tests. The results illustrate the complexity of designing antifouling surfaces for effective insect contamination mitigation under dynamic conditions and suggest that superhydrophobic surfaces may not be the most effective solution for preventing insect contamination on aircraft wing leading edges.

Critical considerations in the mitigation of insect residue contamination on aircraft surfaces – A review

“…Similarly, more recent work conducted by Kok et al [57] and Wohl et al [51,53], suggested that surfaces exhibiting hierarchical or multi-scale roughness structures, permit insect residue on low energy surfaces to adopt a Cassie-Baxter wetting state, as air is trapped in the cavities of the surface [130][131][132]. Surfaces possessing low surface energy hierarchical roughness designs have also been shown to be effective in bioadhesion control [133]; such surfaces are found in nature (e.g.…”

“…Other tests conducted in an ice-crystal environment showed that even for short duration, this effect is sufficient to remove or reduce insect debris below the critical height [23]. Erosion of insects has also been reported by Henke [124] within the A320 HLFC fin tests and suggested by Wohl et al for disappearance of insect residue in digital photographs obtained during flight tests performed with experimental coatings [53]. The work conducted by Lachmann [83] indicated that insect deposits collected only during take-off also showed higher adhesion compared to those collected on takeoff that subsequently flew a complete flight cycle.…”

“…This discrepancy in complete alleviation was attributed to a difference in surface microstructure. Further work conducted by Kok et al [57] and Wohl et al [51,53] indicated that the topographical properties of the surface play a significant role in insect residue-substrate interactions, as described in the next section.…”

“…The entomological factors to be discussed in Section 4 are insect species, life cycle stage, size, and properties of the haemolymph (i.e. blood) such as the viscosity and surface tension [48][49][50][51][52][53]. Aeronautical factors include airfoil type, impact angle and location, normal velocity and the airfoil boundary layer [41].…”

“…The insect residues obtained during flight [43,83] were determined to be well represented by laboratory insect contamination studies using D. melanogaster. As a result, many experimentalists have used this insect for their research [15,[49][50][51][52][53][84][85][86][87].…”