Symmetrical airfoil?

Question

I thought that airfoils were used to distort the airflow above causing the airflow to have less contact with the wing surface reducing friction, but I saw a picture of this airfoil and it said "symmetrical airfoil" WHAT? How does that work? Would there be high pressure below and low pressure above like the Clark Y, or does this airfoil work differently? And what aircraft are these used on?

Answer 1

People all ready answered your other two questions so ill answer this one.

Airfoil sections are of two basic types, symmetrical and nonsymmetrical.

Symmetrical airfoils have identical upper and lower surfaces. They are suited to rotary-wing applications because they have almost no center of pressure travel. Travel remains relatively constant under varying angles of attack, affording the best lift-drag ratios for the full range of velocities from rotor blade root to tip. However, the symmetrical airfoil produces less lift than a nonsymmetrical airfoil and also has relatively undesirable stall characteristics. The helicopter blade (airfoil) must adapt to a wide range of airspeeds and angles of attack during each revolution of the rotor. The symmetrical airfoil delivers acceptable performance under those alternating conditions. Other benefits are lower cost and ease of construction as comparedto the nonsymmetrical airfoil.

Nonsymmetrical (cambered) airfoils may have a wide variety of upper and lower surface designs. The advantages of the nonsymmetrical airfoil are increased lift-drag ratios and more desirable stall characteristics. Nonsymmetrical airfoils were not used in earlier helicopters because the center of pressure location moved too much when angle of attack was changed. When center of pressure moves, a twisting force is exerted on the rotor blades. Rotor system components had to be designed that would withstand the twisting force. Recent design processes and new materials used to manufacture rotor systems have partially overcome the problems associated with use of nonsymmetrical airfoils.

Answer 2

They're best for aerobatics because they work just as good upside down. All performanc aerobatic planes like the Pitts Specials have them. Helicopter rotor blades are symetrical too. Because you don't want them producing any lift at flat pitch on the ground. Other than that they work like any other wing. You increase angle of attack for lift.

Answer 3

Symmetrical airfoils are used usually on supersonic military aircraft. There will need to be a positive angle of incidence as this is the only way we have our pressure differential to create lift with out this the wind will act like a sword. If you move a sword or any similar shaped object through the air quickly it will make a small noise where the air moves  over it. A sword is in effect a symmetrical airfoil. When the angle of attack is changed to a positive one the sword or similar object will create a small amount of lift.

       Now there is more surface area from leading edge to trailing edge on a real symmetrical wing. This will mean more lift can be created. With a symmetrical wing the chord line and the mean camber are equal.