Aerofoil
An aerofoil is a shape designed to produce lift when air flows over it. It is commonly used in the design of aircraft wings and propeller blades. The shape of the aerofoil causes the air pressure above it to be lower than the pressure below, resulting in upward lift.
4 Key excerpts on "Aerofoil"
eBook - ePub- Rose G Davies(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
...The airflow over a finite wing is three-dimensional. A finite wing is a real wing. Wings on existing aircraft are generally finite wings. Theory of Lift The main function of an Aerofoil is to produce lift. The airflow around an Aerofoil with a positive angle of attack can be observed with a pattern as shown in Figure 4.6 (a). The streamlines in Figure 4.6 (a) show that airflow speed is higher over the upper surface than the airflow under the lower surface, and there is prominent downwash at the trailing edge, and upwash at the leading edge. The air pressure around the Aerofoil is not uniform as it would be in the free-stream. There is a pressure distribution around the Aerofoil, and Figure 4.6 (b) shows the distribution of Δp = p – p fs around the Aerofoil. The negative sign “−” means that the local pressure is less than the free-stream pressure, and the positive sign “+” means that the local pressure is greater than the free-stream pressure. Overall, the pressure on the lower surface of the Aerofoil is higher than that on the upper surface, so we know, in principle, the Aerofoil produces lift. There are various theories of lift which have been developed to quantify the lift. They all depend on the descriptions or the assumptions about the airflow field around the Aerofoil. Some of these are simple and relatively easy to understand, but operate under very strict assumptions, for example, the Bernoulli theorem. Some of them are very comprehensive with detailed mathematical description of the fluid field around Aerofoil, for example, 3-D computational simulations of Navier–Stokes equations...
eBook - ePubFly the Wing
A flight training handbook for transport category airplanes
- Billy Walker(Author)
- 2018(Publication Date)
- Aviation Supplies & Academics, Inc.(Publisher)
...When an airfoil is moved through the air, a stream of air flows under, over, and around it. If the airfoil has been well designed (by the engineers who need all the theoretical knowledge), the flow will be smooth and will conform to the shape of the moving airfoil. If, in addition, the airfoil is set at the proper angle and is made to move fast enough, the airflow will support the weight of it. And since the airfoil or wing is attached to the airplane, it will support the entire weight of the aircraft. This then is the whole story—the nature of the action that enables wings to sustain, to furnish enough lift, and to support heavier-than-air craft in flight. Airfoils are usually curved surfaces to take advantage of Bernoulli’s theory. But if you hold a piece of paper in front of you, you will find that you can cause the paper to rise simply by blowing over the top of it. All you have done is to create a low-pressure area over the paper. The pressure beneath, which is now relatively greater, does the rest. If, in addition, you hold the paper at a slight angle, causing an airstream to strike the bottom of the paper while it is being held at an angle to the wind, the resultant dynamic force will contribute to the force lifting the paper. Consequently—and this must be apparent—the force exerted on a surface held at an angle to the relative airstream around it is a result of the pressure difference created above and below the surface. The importance of the speed and angle of the lifting surface to flight performance is easily seen by sticking your hand out the window of a speeding automobile. If you hold your hand flat and level, no sensation is felt other than that of the air flowing over, under, and around your hand. If you raise the forward part of your hand, causing it to move through the airstream at an angle, you will immediately encounter a force that tends to lift your hand. You have just induced lift...
eBook - ePubFlight Theory and Aerodynamics
A Practical Guide for Operational Safety
- Joseph R. Badick, Brian A. Johnson(Authors)
- 2021(Publication Date)
- Wiley-Interscience(Publisher)
...The upper trailing edge has a downward curve to restore lift lost by the flattening of the upper surface. The benefit of this design in the high‐speed realm of flight, as well as other supersonic airfoils, is discussed in Chapter 14. Application 3.1 Symmetrical airfoils are found on many different types of aircraft, from light to heavy aircraft, and within general aviation to those designed solely for military operations. Identify various aircraft that incorporate symmetrical airfoils into their design. Where are these airfoils located on the aircraft, and why was the symmetrical airfoil design utilized instead of a cambered airfoil design? DEVELOPMENT OF FORCES ON AIRFOILS Leonardo da Vinci stated the cardinal principle of wind tunnel testing nearly 400 years before the Wright brothers achieved powered flight. Near the beginning of the sixteenth century, da Vinci said: the action of the medium upon a body is the same whether the body moves in a quiescent medium, or whether the particles of the medium impinge with the same velocity upon the quiescent body. This principle allows us to consider only relative motion of the airfoil and the air surrounding it. We may use such terms as “airfoil passing through the air” and “air passing over the airfoil” interchangeably. Pressure Disturbances on Airfoils If an airfoil is subjected to a moving airflow, velocity and pressure changes take place that create pressure disturbances in the airflow surrounding it. These disturbances originate at the airfoil surface and propagate in all directions at the speed of sound. If the flight path velocity is subsonic, the pressure disturbances that are moving ahead of the airfoil affect the airflow approaching the airfoil (Figure 3.18)...
eBook - ePub- Mohammad H. Sadraey, Peter Belobaba, Jonathan Cooper, Allan Seabridge(Authors)
- 2020(Publication Date)
- Wiley(Publisher)
...In 1950s, airfoils have been classified by the NACA, the forerunner of present NASA, and have been cataloged using a four/five digits code. Figure 4.3 shows the 6‐series NACA 63 3 –218 airfoil section with a thickness‐to‐chord ratio of 18%. Selecting an airfoil is a part of the overall wing design. Selection of an airfoil for a wing begins with the clear statement of the flight requirements. For instance, a subsonic flight design requirements are very much different from a supersonic flight design objectives. On the other hand, flight in the transonic region requires a special airfoil that meets Mach divergence requirements. The designer must also consider other requirements such as airworthiness, structural, manufacturability, and cost requirements. Several graphs indicate the behavior of an airfoil in a flow field; they are employed in the selection of the best airfoil. Aerodynamic theories are applied or wind tunnel tests are conducted to plot such figures for each airfoil. Figure 4.4 shows the typical variations of drag coefficient as a function of lift coefficient for a laminar airfoil; such as in 6‐series NACA airfoils. This is one of the significant graphs which are utilized to decide about the wing airfoil section...
