Control Surface Refinement


The chordwise length and end angles may be further refined for Control Surfaces (CS). The chordwise length may be set as constant for the span of the surface or may have different lengths depending on your application. The end angles may also be set manually and either set to be equal or different than each other. By default, the angles are defined to align with the component X-axis. The leading or trailing edge is the reference for these angles. For example, an angle setting of 90° will result in the CS end to be normal to the trailing or leading edge of the wing. This is very easily visualized with highly swept wings. By leveraging unique lengths and angles at the start and end of a CS, users are capable of defining a variety of interesting deflection surfaces for analysis, export, or visualization.

Users should also be aware that the Num Points in the Surface End Angle box sets the number of points used to spline the UW curve for the CS. Very low numbers of points will result in a curved or “wiggled” CS boundary in some cases but you’ll find that the default value of 15 will result in a generally straight side. Highly variable or stretched surfaces such as a heavily swept vertical tail root fairing or tip will potentially lead to odd deflections in the CS boundary. In these cases, try adjusting the length or Num Points to clean up the edges.

Subsurface Finite Lines


Subsurface Finite Lines are similar to subsurface Lines except that the start and end U and W locations may be controlled independently at any points on a component surface. Finite Lines are an excellent way to mark regions where you want to include additional feature lines or intersections, particularly when working with exported file formats. Note that Finite Lines do not have the ability to section off regions of the surface in the same way as other types because they typically will not completely enclose or split the surface. Similar to Lines, Finite Line subsurfaces are an interesting way of visualizing the surface Bezier curves defined by the component parameters.

Rotor Collision Example


In this tutorial, the Snap-To feature is used to demonstrate how a model may be queried for component collision in a “real-world” application such as rotor strike. The demonstration shows how a seemingly small change to a model parameter, from a certain orientation, can have a significant impact on the aircraft. Snap-To can be a very powerful tool for checking a model for impact and clearance.

Manual Collision Detection


Working from the Snap-To window, you will have access to all of the settings that drive the collision detection process including the geometry Set, the target distance, and the manipulated parameter. You may also check the clearance of all components in the Set with a single click!

To perform a manual collision detection or Snap operation, select the desired parameter to be altered from the dropdown menus or simply drag the parameter button to the window to select automatically. Choose your desired target minimum distance and Set and then click “Increase” or “Decrease” as needed to change the model.

Note that the manual collision detection method tends to be more reliable than the interactive “click-and-drag” mode because the manual mode is not dependent on the slider range for updates.

Interactive Collision Detection


Snap-To may be controlled interactively by dragging individual component parameters using “Alt/Opt + Drag”. This is a quick way of manipulating component placement and design to reach your target minimum distance. However, you may notice that the reliability of Snap-To using this method is dependent on certain settings.

First, even though you are using Snap-To outside of the feature window, the settings chosen in Snap-To still apply. For example, if you are trying to snap a component to the surface of another with all other geometries hidden but the Snap-To Set is “All”, then the component will snap to the nearest geometry in the entire model. The target minimum distance is also enforced.

Secondly, the update speed of the GUI will affect how easily Snap-To can find a solution. Recall that the parameter sliders in OpenVSP have variable ranges where much larger or smaller steps are taken with each “update” as the component changes depending on the range. With very large steps, Snap-To may skip over a solution to the next available. This can be corrected by re-dragging the slider in the proper direction until you find the placement you needed. Alternatively, you can decrease the slider range using the left and right collapse range buttons (>|<) and Snap-To will have an easier time of catching the solution.