What is "angle of incidence"

Angle of incidence \Angle of incidence\ (A["e]ronautics) The angle between the chord of an a["e]rocurve and the relative direction of the undisturbed air current.

Incidence \In"ci*dence\, n. [Cf. F. incidence.]

1. A falling on or upon; an incident; an event; an occurrence. [Obs.]
   --Bp. Hall.

2. (Physics) The direction in which a body, or a ray of light or heat, falls on any surface.

   In equal incidences there is a considerable inequality of refractions.
   --Sir I. Newton.

3. The rate or ratio at which something occurs; as, the incidence of murder in Los Angeles; the incidence of cancer in men over 50.

   Angle of incidence, the angle which a ray of light, or the line of incidence of a body, falling on any surface, makes with a perpendicular to that surface; also formerly, the complement of this angle.

   Line of incidence, the line in the direction of which a surface is struck by a body, ray of light, and the like.

n. 1 (context optics physics English) The angle that a straight line, ray of light, etc., meeting a surface, makes with a normal to the surface at the point of meeting. 2 (context aeronautics English) The angle, usually fixed, between the chord line of a wing or horizontal stabilizer and the axis of the fuselage, measured at the root. In UK called the angle of attack.

n. the angle that a line makes with a line perpendicular to the surface at the point of incidence [syn: incidence angle]

Angle of incidence is a measure of deviation of something from "straight on" and may refer to:

• Angle of incidence (aerodynamics), the angle between the chord of the wing and the longitudinal axis of the fuselage
• Angle of incidence (optics), describing the approach of a ray to surface
• A synonym for angle of attack, the angle between the chord of the wing and the undisturbed airflow

On fixed-wing aircraft, the angle of incidence (sometimes referred to as the mounting angle) is the angle between the chord line of the wing where the wing is mounted to the fuselage, and a reference axis along the fuselage (often the direction of minimum drag, or where applicable, the longitudinal axis). The angle of incidence is fixed in the design of the aircraft, and with rare exceptions, cannot be varied in flight.

The term can also be applied to horizontal surfaces in general (such as canards or horizontal stabilizers) for the angle they make relative the longitudinal axis of the fuselage.

The figure to the right shows a side view of an airplane. The extended chord line of the wing root (red line) makes an angle with the longitudinal axis (roll axis) of the aircraft (blue line). Wings are typically mounted at a small positive angle of incidence, to allow the fuselage to have a low angle with the airflow in cruising flight. Angles of incidence of about 6° are common on most general aviation designs. Other terms for angle of incidence in this context are rigging angle and rigger's angle of incidence. It should not be confused with the angle of attack, which is the angle the wing chord presents to the airflow in flight. Note that some ambiguity in this terminology exists, as some engineering texts that focus solely on the study of airfoils and their medium may use either term when referring to angle of attack. The use of the term "angle of incidence" to refer to the angle of attack occurs chiefly in British usage.

In geometric optics, the angle of incidence is the angle between a ray incident on a surface and the line perpendicular to the surface at the point of incidence, called the normal. The ray can be formed by any wave: optical, acoustic, microwave, X-ray and so on. In the figure below, the line representing a ray makes an angle θ with the normal (dotted line). The angle of incidence at which light is first totally internally reflected is known as the critical angle. The angle of reflection and angle of refraction are other angles related to beams.

Determining the angle of reflection with respect to a planar surface is trivial, but the computation for almost any other surface is significantly more difficult. The exact solution for a sphere (which has important applications in astronomy and computer graphics) was an open problem for nearly 50 years until a closed-form result was derived by mathematicians Allen R Miller and Emanuel Vegh in 1991.