Applied Aeronautical Fluid Mechanics: Theory, Practice, and Design Tools for the 21st Century Aircraft bridges the gap between classical fluid mechanics and the practical realities of modern aerospace engineering. Written by Dr. Adrian M. Caldwell, a chartered aerospace engineer and former jet-engine designer, this book combines engineering theory with real-world aircraft applications, showing how fluid mechanics governs everything from wing aerodynamics and high-lift systems to gas turbine engines, computational fluid dynamics, and emerging eVTOL technologies. Beginning with the fundamental principles of fluid flow, the book develops the concepts needed to understand lift, drag, compressible aerodynamics, turbulence, propulsion, aircraft stability, and aerodynamic performance. It then explores modern engineering tools including CFD, reduced-order modelling, machine learning, digital twins, and aerodynamic optimisation before examining practical case studies covering high-bypass turbofan engines, regional jet high-lift systems, and urban air mobility. Designed for aerospace engineering students, professional engineers, pilots, technicians, and aviation enthusiasts, the book explains complex subjects using clear language, practical examples, engineering insight, and real aircraft applications. With SI units and Imperial equivalents throughout, it serves equally well as a university textbook, professional reference, and practical guide to understanding the fluid mechanics behind modern flight. Whether you are studying aerospace engineering, designing aircraft, maintaining propulsion systems, or simply fascinated by aviation, this book provides a comprehensive introduction to the science that makes flight possible.