Biomimetics in fixed-wing nano aerial vehicles: a comprehensive review on aerodynamic efficiency and design challenges

Fixed-wing nano aerial vehicles (NAVs), having wingspans under 15 cm and weights below 50 g, have drawn growing interest due to their satisfactory endurance and lift-to-drag ratios compared to flapping-wings and rotary-wings, making them suitable for missions related to surveillance and environmental monitoring. Despite their several advantages, fixed-wing NAVs remain underexplored, a research gap that this review addresses. As the operating regime of fixed-wing NAVs is under 15 000 Reynolds number (Re), they face several aerodynamic challenges associated with early flow separation and unpredictable stall behavior, eventually reducing the aerodynamic efficiency. This review systemically examines the major performance parameters governing the fixed-wing NAV performance, i.e. planform selection, wing geometry, aspect ratio, effects of Re and Strouhal numbers, alongside flight control mechanisms and power sources that limit the operational capabilities. The main focus of this review is on the feasibility of biomimetic design solutions inspired from owls, sharks, skimmer birds, humpback whales, and various plants and insects, where exciting features like leading-edge (LE) serrations, riblets, LE tubercles, and sharkskin topography have shown remarkable aerodynamic benefits in unmanned aerial vehicles, although their direct implementation on fixed-wing NAVs remains largely unreported in the literature. Bridging this gap, this paper outlines practical implementation pathways and highlights how high-fidelity numerical methods, advanced nanoscale fabrication techniques, and AI-assisted aerodynamic modeling could combinedly accelerate progress toward efficient NAV platforms.