The physical properties of a lifting line are defined in this section. The properties of the lifting line are allowed to vary along the composite curve used to define its geometry. To describe this variation, one or more tables of lifting line properties are defined. The first table defines the distribution of chord length and quarter chord offset along the composite curve. Optionally, the second table defines airfoil properties along the same curve. Finally, if flaps are present, flap hinge point locations are defined in the last table. Plots of the lifting line properties will be generated, if requested by the plotting control parameters.
Since lifting line properties are given along the composite curve that defines its geometry, table entries are associated with a parameterization of this curve, by means of the curvilinear coordinate, s, or axial coordinate, x. The table entries can be defined in two mutually exclusive manners. If CoordType = AXIAL_COORDINATE, all coordinates must be axial coordinates and are introduced by the keyword @AXIAL_COORDINATE, whereas if CoordType = CURVILINEAR_COORDINATE, all coordinates must be curvilinear coordinates and are introduced by the keyword @CURVILINEAR_COORDINATE.
The airfoil chord length, c, and quarter-chord offset, q, are defined in a single entry table. Table entries consist of a sequence of curvilinear or axial coordinates. As depicted in fig. 1, axis a2 is along the airfoil zero lift line, pointing towards the leading edge. The quarter-chord offset is measured along the same axis, positive aft. If the airloads are computed internally, the airstation location will be modified so as to coincide with the airfoil quarter-chord point. Otherwise, the airstation location is left unchanged.
The airtables associated with the airfoils along the lifting line composite curve are defined next. Airtables tabulate the airfoil lift, drag, and moment coefficients as a function of angle of attack and Mach numbers. The airfoil characteristics are defined in a discrete table. Table entries consist of a sequence of curvilinear or axial coordinates. If no airtables are defined, the default coefficients defined in the section air property definition are used.
It is possible to define a flap associated with an airstation. If an external code is used to compute airloads, the airstation locations on the wing and flap are arbitrary. However, if the airloads are computed internally, AirloadsScheme = 2D_AIRFOIL, the locations of the airstations in the wing and flap must be matched, AstLocation = MATCHED and the location of the flap hinge must be defined here. The flap hinge location, denoted d, is shown in fig. 2. The non-dimensional flap location, defined as the distance the flap hinge is aft the mid-chord normalized by the semi-chord length, d = 2d/c, is given in a table. For instance, for a 15% trailing edge flap, d = 0.70. Table entries consist of a sequence of curvilinear or axial coordinates and non-dimensional flap locations, d.