Given both a straight and swept wing (identical otherwise), exposed to the same airflow, would the direction of lift be the same? Please see below a crudely drawn example of my thinking.

enter image description here

Additionally, as angle of attack is defined as the angle between the airfoil's chord line and the direction of oncoming flow, is there a name given for the angle between the span line and direction of oncoming flow?


2 Answers 2


The Lift on an aircraft is the vector sum of one component of the aerodynamic forces pressing on the surface of the aircraft as they are distributed over the surface of the aircraft. At each and every point of the aircraft surface (top, bottom, sides, everywhere) the air is pressing on the surface normal, (perpendicular) to the 2-D surface. The vector sum of all these forces is the total aerodynamic force (**one component of which is lift). If the aircraft is laterally symmetrical, then of course the total vector sum will be straight up (as any lateral component from one side of the aircraft should more or less be counteracted by an equal but opposite lateral force from the other side.

The individual forces (acting on each point of the surface, including the wing), if pictured as a distribution of force over the surface, are always normal to or perpendicular to the surface. So if the wing has dihedral, then they are indeed angled in towards the fuselage. But in your "perhaps?" illustration, with a wing with zero dihedral, they would all be pointing straight up.

** The Lift component is the component of this aerodynamic force which is perpendicular to the flight path of the aircraft, the Drag component is the component parallel to the flight path.


Considering that the lift, together with drag and side forces are the resultant of the distributed air pressure on the surface, their definition highly depends on the axis system used. For example, the lift is defined as projection of the resultant force of the distributed pressure into the plane of symmetry, perpendicular to the flow direction. So, the lift direction is defined by the symmetry plane and flow direction, and change of lift direction with sweep, dihedral, or other wing parameters are meaningless. But, it should be said how the pressure distribution changes with the variation of wing parameters.

Regarding your second question, I have never heard something about span line, but if locking in the front view, the angle between the span and the horizon is called the bank angle. If you look from up-view, the angle between the fuselage and air flow is called side-slip angle (considering AOA=0).


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .