## Symmetrical Airfoil

The airfoil is considered to be symmetrical or uncambered when the upper section of the airfoil from the centerline mirrors that of the lower section, i.e., the upper and lower surfaces are identical. Symmetrical airfoil produces less lift than asymmetrical airfoil.

A typical airfoil:

Chamber line: The line equidistant from the upper and lower surface of the airfoil.

Chord line: The imaginary strength line that joins the leading line to the trailing line of the airfoil.

Angle of attack: The angle between the flow direction and the chord line. The larger the angle of attack, the greater the lift.

In the case of the symmetrical airfoil, the chamber line and cord line are the same. At zero angle of attack, the symmetrical airfoil produces no lift. Thus, a positive angle of attack is required if the lift is to be generated. The center of pressure remains relatively constant for a small change in angle of attack. Thus, for a wide range of velocities, symmetric airfoil provides a good lift-drag ratio.

Typically, symmetrical airfoil is incorporated in helicopter rotors or lightweight aerobatic airplanes. The pressure balance provided by symmetric airfoil allows precision performance for such lightweight aircraft.

Airfoil selection is an important aspect of design in aerospace engineering. Understanding the characteristics of different airfoil sections is important to identify the lift and drag produced during flight. Between the basic airfoil designs: symmetric and cambered or asymmetric airfoil, designers must make a careful selection of design that enhances the flight characteristics for optimal aircraft performance.

This repository contains basic data on the symmetrical airfoils: profile coordinates and performance data, including lift coefficients, drag coefficients, and pitching moment coefficients for various Reynolds numbers. For each coefficient distribution by the attack angle, corresponding relations are constructed and can be used in design calculations via SplineCloud API.

The Reynolds number is a dimensionless value that measures the ratio of inertial forces to viscous forces and descibes the degree of laminar or turbulent flow. Systems that operate at the same Reynolds number will have the same flow characteristics even if the fluid, speed and characteristic lengths vary.

Reynolds number range from 50,000 to 1,000,000 in approximatly logarithmic steps.

Ncrit value is used to model of the turbulence of the fluid or roughness of the airfoil.

Current repository contains data for average wind tunnel with Ncrit=9

Mach number has been left at the default value of zero.

## References

http://airfoiltools.com/