A cambered aerofoil generates no lift when it is moving parallel to an axis called thezero-lift axis (or thezero-lift line.) When theangle of attack on an aerofoil is measured relative to the zero-lift axis it is true to say thelift coefficient is zero when the angle of attack is zero.[1] For this reason, on a cambered aerofoil the zero-lift line is better than the chord line when describing the angle of attack.[2]
When symmetricaerofoils are moving parallel to thechord line of the aerofoil, zerolift is generated. However, whencambered 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.[3]
See also
editReferences
edit- Anderson, John D. Jr (2005),Introduction to Flight, Section 7.4 (fifth edition), McGraw-HillISBN 0-07-282569-3
- 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. 76, eighth edition), Pitman PublishingISBN 0-273-31623-0
Notes
edit- ^Anderson, John D. Jr,Introduction to Flight, Section7.4 (fifth edition)
- ^Such a line is called theline of zero lift orneutral-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.
Kermode, A.C.,Mechanics of Flight, (p.76, eighth edition) - ^Clancy, L.J.,Aerodynamics, paragraph 5.7(a)