Profile tendon
The chord (engl. Chord ) is a technical term used in fluid mechanics and the Wing design . This is understood to be the imaginary connecting line between the profile nose and the profile rear edge.
In the graphic above you can see the profile chord drawn as a red line.
use
The chord is the reference line for defining angles ( angle , setting angle , Einstellwinkeldifferenz ) to the profile. In addition, profile contours are usually described in a right-angled coordinate system in which the profile chord forms the X-axis and the profile nose is at the coordinate origin . The numbering of the profile points begins and sometimes ends at the rear edge of the profile (Eppler profile).
Demarcation
In the early days of empirical profile development (e.g. Göttingen profile catalog - Aerodynamische Versuchsanstalt ), the profile tangent (red line in the lower wing section in the figure) was often used as the corresponding reference line , as this was easy to determine with the concave profiles customary at the time.
The term profile tendon is also used today for the length of the profile. In this case one speaks more of the tread depth (also chord ).
Geometric definition
The definition of the two points that determine the profile chord is not trivial . At the rear edge, the contour of the theoretically specified profile usually converges to a point ; then the case is clear. In the case of profile definitions that specify a practical end flag of finite thickness, the point is in the middle of this end flag.
The case is more complicated because of the profile nose. Since the skeleton line on the profile nose is normally inclined, there is a slight "overhang" of the profile contour over this nose point.
FW Schmitz put the "theoretical profile tendon" for thick profiles below the center of the nose circle according to the definition "The tendon goes through the intersection of the nose circle with the skeleton line ".
Today the approach is "the tendon goes through the greatest length of the profile" (i.e. through the center of the nose circle). This chord is also the X coordinate when defining the profile contour. The intersection of the tendon with the nose circle is the profile nose .
String on the variable profile
If nose flaps or landing flaps are operated on the aircraft , the points that were used to define the chord and the curvature shift. Viewed in this way, the profile chord is changed. For practical reasons, information on the angle of attack and the aerodynamic parameters that depend on it are usually still based on the original chord. Instead, valve deflections are described as an additional influencing factor . The flap deflections change the parameters of the profile such as lift , drag , torque , and zero lift angle .
swell
- ↑ Schmitz, FW; Aerodynamics of the flight model; Aero, 1983, ISBN 3-934596-08-8
- ↑ Abbott, I.; v. Doenhoff, AE: Theory of Wing Sections; New York, 1949; ISBN 0-486-60586-8
- ^ Althaus, D., Wortmann, FX: Stuttgart profile catalog; Braunschweig, 1981; ISBN 3-528-08464-2