Chord (aeronautics)
The chord ( chord engl. ) is a technical term from the fluid mechanics and the Tragflächenbau. It refers to the imaginary line connecting the leading edge and the trailing edge.
In the graph you can see in the picture above the chord drawn as a red line in the picture below you can see an older definition for concave profiles.
Use
The chord line is the reference line for the definition of angles ( angle of attack, approach, Einstellwinkeldifferenz ) to the profile. Also profile contours are generally described in a rectangular coordinate system in which the chord of the X-axis and forms the leading edge is located at the origin of coordinates. The numbering of the profile points begins and ends but sometimes also at the trailing edge ( Eppler profiles).
Demarcation
In the early days of the empirical profile development (eg Göttingen profile catalog - Aerodynamic Research Institute ) was used as corresponding reference line often the profile tangent ( red line in the lower wing section in the figure ), because it was easy to identify with the then usual concave profiles.
The term chord is now also used for the length of the profile. One speaks in this case, but rather on the profile depth ( engl. also chord ).
Geometric definition
The definition of the two points which define the chord is not trivial. At the trailing edge the contour of the theoretically specified profile usually runs together to a point; then the case is clear. In the case of profile definitions that set out a practical Endfahne of finite thickness, the point lies in the middle of this Endfahne. More complicated is the case of the leading profile. Since the skeleton line of the leading profile is normally inclined, there is a slight "overhang" of the profile contour nose on this point.
FW Schmitz put the " theoretical chord " of profile thickness or below the nose circle center point according to the definition " The tendon passes through the intersection of the nose circle having the skeleton line ."
Today, the approach " The tendon passes through the greatest length of the profile " (ie through the center of the nose circle ) holds. This tendon is at the same X-coordinate in the definition of the profile contour. The intersection of the chord with the nose circle is the profile nose.
Tendon at the variable profile
Be operated on the aircraft nose flaps or flaps, then move the points that were used to define the chord and the camber. Seen in this way results in an altered chord. For practical reasons, but usually refers to the angle information and the dependent by him aerodynamic characteristics still on the original chord. Flap deflections are instead described as an additional influencing factor. The flap deflections change the characteristics of the profile variables such as lift, drag, torque, zero-lift angle.