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.Be able to 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.Historically, the design of airfoil shapes for specific applications has proceeded evolutionarily, with wind tunnel experiments, theoretical analysis, and flight testing all being used synergistically to develop the best airfoil shapes for application to specific flight vehicles. Airfoils for high-speed aircraft, especially for supersonic flight, are much thinner with more pointed leading edges and much less camber. To this end, not all airfoils are created equally, and different airfoil shapes will be better suited for one application versus another.įor 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. This entry was posted in Radio Controlled Airplanes on by Mark VandeWettering.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, UAVs, etc. (You could probably make it look prettier with a bit more work.) The important bit is to set the size ratio: without it gnuplot will change vertical and horizontal scales to fit the data in the window. There is a trick to getting gnuplot to work. I then dusted off my dim knowledge of gnuplot to draw this (properly scaled) version of the airfoil. It has data definitions for literally hundreds of airfoil profiles, including coordinates for the Clark Y. A few minutes of googling revealed a fascinating resource, the UIUC Airfoil Data Site. ![]() I had seen references to the “Clark Y” airfoil, but didn’t know how it was defined, so I set out to figure it out. ![]() I snapped awake at 5:30AM this morning, and couldn’t get back to sleep, so I started a loaf of bread to bake later tonight, and then settled in to thinking about airfoils some more.
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