A two-dimensional profile is given in the x-y plane of its own coordinate system. It is either a closed, airfoil-like profile with a leading and a trailing edge, e.g. the profile of a nacelle section (nacelleProfiles), or a curve through its points, e.g. the rotation curve of a nacelle (curveProfiles). The referencing element scales, rotates and positions the profile.
Representations
The geometry of a profile is given by exactly one of the following representations:
| Element | Geometry | Intended for |
pointList | smooth curve through the points in the order of the list (see pointListXYVectorType) | closed profiles and curves |
cst2D | airfoil defined analytically by the class-shape transformation, with the coordinate normal to the chord along y (see cst2DType) | closed profiles |
Closed profiles
Closed profiles are normalized with the leading edge at (0, 0) and the trailing edge at x = 1, so that the scaling of the referencing element is the chord length. The points are ordered from the trailing edge along the lower side to the leading edge and then along the upper side back to the trailing edge. Plotted with x to the right and y upwards, they therefore run clockwise. The trailing edge may be sharp, with identical first and last point, or blunt, with first and last point differing. The trailing edge point lies in the middle between first and last point; the leading edge is the point of the list with the largest distance from it, so the point list has to contain the leading edge. The chord line connects leading and trailing edge point. The line between first and last point is perpendicular to the chord line; crooked trailing edges are not allowed.
A position on a closed profile is given by the relative coordinate ζ, e.g. for guide curves and rotation curves of nacelles (fromZeta, startZeta). ζ is −1 at the first point, 0 at the leading edge and +1 at the last point. In between, it is proportional to the arc length along the lower side (ζ from −1 to 0) and along the upper side (ζ from 0 to 1), respectively.
Figure (a) shows the closed profile of the example below. The positions ζ = −0.5 and ζ = 0.5 lie in the middle of the lower and the upper side, measured along the profile, not along the chord.
In a nacelle section, +x of the profile points in the direction of the nacelle axis (+x) and +y radially away from the axis. The lower side is therefore the inner side of the nacelle, facing its axis. For a section at 0°, +y of the profile points in the direction of +z.
Curves
A curve runs through its points from the first to the last point. The rules for the point order, the leading and the trailing edge and the coordinate ζ of closed profiles do not apply. The referencing element defines whether the coordinates are normalized and how positions along the curve are given. Figure (b) shows the curve of the example below: it follows the lower side of the closed profile from the trailing edge to the leading edge.
Example
A closed profile (NACA 4412 with 13 points) for the sections of a nacelle and a curve along its lower side for the rotation curve of the same nacelle:
<profiles>
<curveProfiles>
<curveProfile uID="RotationCurve_points">
<name>Lower side of the nacelle profile</name>
<pointList>
<x>1;0.9319;0.7476;0.4988;0.2544;0.0736;0</x>
<y>0;-0.0008;-0.0047;-0.014;-0.0249;-0.0273;0</y>
</pointList>
</curveProfile>
</curveProfiles>
<nacelleProfiles>
<nacelleProfile uID="NacelleProfile_points">
<name>NACA 4412, 13 points</name>
<pointList>
<x>1;0.9319;0.7476;0.4988;0.2544;0.0736;0;0.0604;0.2456;0.5012;0.7524;0.9341;1</x>
<y>0;-0.0008;-0.0047;-0.014;-0.0249;-0.0273;0;0.0519;0.0936;0.0917;0.0575;0.0177;0</y>
</pointList>
</nacelleProfile>
</nacelleProfiles>
</profiles>