Terminology

Aerofoil is the term used to describe the characteristic shape of the cross-section of an aircraft wing, and whose purpose is to generate lift. Discussion of aerofoil performance is the main purpose of this module, and so some descriptions and definitions of this shape will be essential. (Note that the aerofoil section is considered with its plane parallel to the relative airflow).

• Relative AirFlow (RAF) is the movement of the air relative to the aircraft (or aerofoil). (In practice, it is the aircraft which moves relative to the air, but in aerodynamic theory and wind - tunnel experiment, it is the air which is considered to be in motion).

• Leading Edge is the foremost point on the aerofoil.

• Trailing Edge is the rear-most point on the aerofoil.

• Chord Line is the straight line joining leading and trailing edges.

• Chord Length (C) is the length of the chord line.

• Camber Line is the line drawn through points equidistant from the upper and lower surfaces. (The camber line is usually a curved line; the greater the curvature, the greater will be the aerodynamic forces generated).

• Thickness of an aerofoil is the greatest distance between the upper and lower surfaces. Thickness / chord ratio = thickness divided by chord, normally expressed as a percentage.

• Angle of Attack - the angle formed between the chord-line and the relative airflow.

• Span (b) is the distance from wing tip to tip, measured perpendicular to the chord line.

• Aspect Ratio (AR) is Span / chord. If the wing is tapered, i.e. it has a varying chord, then the AR may be expressed as Span² / wing area

• Wing Area (S) is the area projected onto a plane perpendicular to the normal axis.

• Stagnation Point is a point on the surface of the aerofoil where the RAF has