A cambered aerofoil generates no lift when it is moving parallel to an axis called the zero lift axis (or the zero lift line.) When the angle of attack on an aerofoil is measured relative to the zero lift axis it is true to say the lift coefficient is zero when the angle of attack is zero. For this reason, on a cambered aerofoil the zero lift line is better than the chord line when describing the angle of attack.
When symmetric aerofoils are moving parallel to the chord line of the aerofoil, zero lift is generated. However, when cambered aerofoils are moving parallel to the chord line, lift is generated. (See diagram at right.) For symmetric aerofoils, the chord line and the zero lift line are the same.
Famous quotes containing the words lift and/or axis:
“The axioms of physics translate the laws of ethics. Thus, “the whole is greater than its part;” “reaction is equal to action;” “the smallest weight may be made to lift the greatest, the difference of weight being compensated by time;” and many the like propositions, which have an ethical as well as physical sense. These propositions have a much more extensive and universal sense when applied to human life, than when confined to technical use.”
—Ralph Waldo Emerson (1803–1882)
“I make this direct statement to the American people that there is far less chance of the United States getting into war, if we do all we can now to support the nations defending themselves against attack by the Axis than if we acquiesce in their defeat, submit tamely to an Axis victory, and wait our turn to be the object of attack in another war later on.”
—Franklin D. Roosevelt (1882–1945)