To add points to an Edit Curve, either set the desired U location along the curve and click “Split U” or click the “Split Pick” button and click on the desired cut point on the curve in the display. In either case, a new point will be added to the curve and any necessary interpolation will automatically take place to maintain the existing curve shape. Note that adding a control point to a Cubic Bezier type will result in new control point tangencies for the new point and adjacent points. Adding a control point to a PCHIP Spline will result in a slightly different curve due to the new enforced point.
To remove points from an Edit Curve, either select the point using the arrows to cycle the active point then click “Delete Selected” or click “Delete Pick” and click on the desired point to be removed. Similar to adding a point to a Spline, removing points will result in a relofted curve. Also, removing a point from a Cubic Bezier curve will not alter the adjacent points’ tangencies or locations. With Cubic Bezier curves, only the primary control points (not the adjacent tangency points) may be deleted.
The Scale XSec group under the Curve tab in the Curve Editor is where users will find the scaling parameters for the cross-section such as height, width, and area. Recall that the parameterized curve defined by the control points is in one coordinate space which is then scaled along the horizontal and vertical axes by width and height, respectively to achieve the final shape. Because the Edit Curve is an integrable function in all three curve types, the area bound by the curve may be computed. Alternatively, if the area is fixed then OpenVSP may iteratively solve for the remaining parameters. This is particularly useful for supersonic or flow-through sections.
Under normal circumstances, the range of the X and Y coordinates of the Edit Curve are from -0.5 to 0.5 or having unit distance. This ensures that the scaled height and width correspond to a representative physical dimension in the model. However, the curve is under no such constraint to prevent the range from being larger or smaller than the +/- 0.5 values. For example, a cross-section with height = 2.0, having Y coordinates from -1.0 to 1.0 (distance of 2.0), would have a measured physical height of 4.0. Again, users must take great care when setting control points in the display or in the Control Points fields to ensure that their design intent is being maintained.
OpenVSP includes a manual curve editor that enables users to modify existing cross-sections or create entirely unique shapes with simple, click-and-drag operations. The curve editor is intended to make cross-section modification as user-friendly as reasonable while maintaining remarkable customization including multiple curve types (linear, spline, Bezier), three-dimensional control, symmetry, numerous display options, corner radii, and U-spacing distribution.
Users are encouraged to test this cross-section type to become familiar with the Edit Curve features but are warned that this is an advanced capability. If your model cross-sections can be implemented with other curve types such as ellipses, rounded rectangles, etc., then we recommend using those. Edit Curve sections should be used when the parameterization of existing cross-sections (including the number of control points or corners) is insufficient to accomplish your goals.
The subjects in this Chapter focus on advanced OpenVSP techniques and modeling practices that require a firm grasp of the fundamentals from prior Chapters to implement well. Users are encouraged to experiment with these features and techniques to build their knowledge and skill (or just for fun).