# Zero-lift axis

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{{Short description|Aerodynamic concept}}
thumb|300px|right|A typical lift coefficient curve.
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](/source/angle_of_attack) on an aerofoil is measured relative to the zero-lift axis it is true to say the [lift coefficient](/source/lift_coefficient) is zero when the angle of attack is zero.<ref>Anderson, John D. Jr, ''Introduction to Flight'', Section7.4 (fifth edition)</ref>  For this reason, on a cambered aerofoil the zero-lift line is better than the chord line when describing the angle of attack.<ref>''Such a line is called the '''line of zero lift''' or '''neutral-lift line''', and would in some senses be a better definition of the chord line, but it can only be found by wind tunnel experiments for each aerofoil, and, even when it has been found, it is awkward from the point of view of practical measurements.''<br />  Kermode, A.C., ''Mechanics of Flight'', (p.76, eighth edition)</ref>

When symmetric [aerofoil](/source/aerofoil)s are moving parallel to the [chord line](/source/Chord_(aircraft)) of the aerofoil, zero [lift](/source/Lift_(force)) is generated.  However, when [cambered](/source/Camber_(aerodynamics)) 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.<ref>Clancy, L.J., ''Aerodynamics'', paragraph 5.7(a)</ref>

== See also ==
* [Angle of attack](/source/Angle_of_attack)
* [Aerobatics](/source/Aerobatics)
* [Aerobatic maneuver](/source/Aerobatic_maneuver)

==References==
*Anderson, John D. Jr (2005), ''Introduction to Flight'', Section 7.4 (fifth edition), McGraw-Hill {{ISBN|0-07-282569-3}}
*[L. J. Clancy](/source/L._J._Clancy) (1975), ''Aerodynamics'', Sections 5.6 and 5.7, Pitman Publishing, London.  {{ISBN|0-273-01120-0}}
*Kermode, A.C. (1972), ''Mechanics of Flight'', Chapter 3, (p.&nbsp;76, eighth edition), Pitman Publishing {{ISBN|0-273-31623-0}}

==Notes==
{{reflist}}

Category:Aerodynamics
Category:Aerospace engineering
Category:Aircraft manufacturing
Category:Aircraft wing design

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