Biomimetics has become an increasingly important approach in aerospace engineering, offering innovative design solutions inspired by the flight mechanisms of living organisms. Birds, insects, and bats demonstrate exceptional aerodynamic efficiency, maneuverability, and adaptability, which have motivated the development of bio-inspired aircraft and unmanned aerial vehicles (UAVs). This systematic review aims to synthesize and critically evaluate existing research on biomimetic principles derived from biological flight and their application to aircraft and UAV design. A systematic literature review was conducted following PRISMA guidelines, using major scientific databases to identify relevant peer-reviewed studies linking biological flight mechanisms with aerospace engineering applications. The selected studies were categorized according to biological sources of inspiration, including avian wing morphology and feather-based flow control, insect flapping-wing aerodynamics for micro-air vehicles, and bat-inspired flexible membrane wings. The results show that biomimetic approaches can significantly enhance aerodynamic performance, improve maneuverability, increase flight stability, and reduce energy consumption, particularly in UAV and small-scale aircraft applications. Despite these advantages, several challenges persist, such as material constraints, structural complexity, and difficulties in scaling biological mechanisms to full-size aircraft. This review highlights current trends and research gaps in biomimetic aerospace design and emphasizes the potential of biologically inspired flight principles to support the development of next-generation, efficient, and sustainable aircraft and UAV technologies.