Symmetrical airfoil
![symmetrical airfoil symmetrical airfoil](https://d3i71xaburhd42.cloudfront.net/7fc90c78431d4a547747f7b2a339886448bfde5f/10-Figure9-1.png)
For helicopter rotor blades, flightpath velocity is equal to rotational velocity, plus or minus a component of directional airspeed. For airfoils on an airplane, the flightpath velocity is equal to true airspeed (TAS). Flightpath velocity-the speed and direction of the airfoil passing through the air.
![symmetrical airfoil symmetrical airfoil](https://i.stack.imgur.com/5bDvd.jpg)
![symmetrical airfoil symmetrical airfoil](https://dragonplate.com/images/thumbs/0010322_streamlined-symmetrical-airfoil-carbon-fiber-tube-237-id-x-095-id-x-24.jpeg)
Leading edge-the front edge of an airfoil.The profile thickness and thickness distribution are important properties of an airfoil section. By varying the point of maximum camber, the manufacturer can tailor an airfoil for a specific purpose. The location of maximum camber and its displacement from the chord line are expressed as fractions or percentages of the basic chord length. Maximum camber (displacement of the mean camber line from the chord line) and its location help to define the shape of the mean camber line. The shape of the mean camber is important for determining aerodynamic characteristics of an airfoil section. Camber refers to curvature of the airfoil and may be considered as curvature of the mean camber line. The chord line connects the ends of the mean camber line. Mean camber line-a line drawn halfway between the upper and lower surfaces of the airfoil.Chord-the length of the chord line from leading edge to trailing edge it is the characteristic longitudinal dimension of the airfoil section.Chord line-a straight line intersecting leading and trailing edges of the airfoil.Blade span-the length of the rotor blade from center of rotation to tip of the blade.Airfoils are carefully structured to accommodate a specific set of flight characteristics. In some conditions, parts of the fuselage, such as the vertical and horizontal stabilizers, can become airfoils. The main and tail rotor blades of the helicopter are airfoils, and air is forced to pass around the blades by mechanically powered rotation. Certain airfoils, such as rotor blades, combine some of these functions. Airfoils are also used for stability (fin), control (elevator), and thrust or propulsion (propeller or rotor). Airfoils are most often associated with production of lift. An airfoil is any surface producing more lift than drag when passing through the air at a suitable angle. Helicopters are able to fly due to aerodynamic forces produced when air passes around the airfoil.