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Modified supercritical airfoil database4/25/2024 ![]() Some of the earliest known “concavo-convex” airfoil shapes were patented in the late 1880s. Phillips also tested these airfoils in one of the very first wind tunnels. Notice the thin, highly cambered profile shapes, which are now known to have poor aerodynamic efficiency compared to modern airfoils, at least under the operating conditions of most flight vehicles. Taking inspiration from nature is nothing new in engineering, but history shows that it should not necessarily be a basis for our engineering. Some of the earliest known airfoil sections considered for aircraft concepts were patented in the 1880s by Horatio Phillips, as shown in the figure below, which were inspired by the wings of birds. Taken from “ Aeronautical & Miscellaneous Note-Book of Sir George Cayley,” Cambridge University Press, 1933. Cayley’s sketch of the cross-section of a trout looks remarkably like a modern airfoil section. Cayley obtained the profile shown in the drawing below by measuring the cross-sectional shape of a trout, which, interestingly enough, conforms closely to modern low-drag “laminar” airfoil sections. Cayley made essential observations about drag, including “It has been found by experiment that the shape of the hinder part of the spindle is of as much importance as that of the front in diminishing resistance ” Cayley referred to the shape of a wing as spindle-shaped. Sir George Cayley, often revered as the “Father of Aeronautics,” delineated the problem of sustentation, i.e., aerodynamic lift, from that of drag, i.e., the component of aerodynamic resistance. In this regard, theory and experimentation (e.g., wind tunnel testing) have been used to design airfoils to meet specific operating requirements for different aircraft types, including low-speed airplanes, high-speed airplanes, helicopters, propellers, wind turbines, etc. Historically, the most suitable airfoils for most practical engineering applications were obtained through an evolutionary process. Understand the differences in the shapes between subsonic, transonic, and supersonic airfoil sections.Know how to construct a NACA airfoil profile geometrically using a camberline shape and a thickness envelope.Identify and explain the significance of the critical geometric parameters that define the shape of an airfoil.Appreciate the historical evolution of airfoil sections for aircraft applications.Throughout this process, considerations specific to the intended application must be integrated to ensure that the optimized airfoil shapes meet the unique requirements of particular flight vehicles. Subsequent flight testing may give further assessments as to the validity of the selected airfoil(s), allowing engineers to iteratively refine airfoil designs based on actual aircraft performance. Wind tunnel experiments can validate these predictions, providing empirical data for any design changes and aerodynamic refinement of the airfoil section. Engineers often begin by selecting candidate airfoil shapes with the desired characteristics and then employing mathematical models and CFD simulations to predict aerodynamic performance. Historically, the design of airfoil shapes for specific applications has advanced through an evolutionary process, synergistically combining theoretical analysis, wind tunnel experiments, and flight testing. Airfoils for high-speed aircraft, especially for supersonic flight, are much thinner with more pointed leading edges and much less camber. For example, airfoils for use on the wings of low-speed airplanes are generally thicker (in terms of their thickness-to-chord ratio) and have more surface curvature or camber. To this end, not all airfoils are created equally, and different airfoil shapes will be better suited for one application versus another. Aerospace engineers must know how to select or design suitable cross-sectional wing shapes (often called airfoil profiles or airfoils) for use on a diverse range of flight vehicles such as subsonic, transonic, and supersonic airplanes, various types of space launch vehicles, as well as helicopter rotors, propeller blades, wind turbines, unoccupied aerial vehicles (UAVs), etc.
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