Positioning a Stack section is fundamentally different than with Fuselage sections. Primarily, each placement is based on a shift or delta in translation and rotation which means that each section’s placement in the component depends on the placement of all preceding sections. Each section’s placement is relative to the placement and orientation of the preceding section. So if the preceding cross-section has rotation, a delta-X, delta-Y, or delta-Z shift will be in the corresponding directions of the preceding cross-section.
Adding a section to a Stack is quite simple. All you need to do is choose the cross-section where you want to insert a new following section and click Insert in the XSec tab. A new section identical to the selected section will be concatenated to your model and all following sections will shift accordingly. To remove a section, simply click “Cut”. You also have the option of copying, cutting, and pasting sections in your component.
The Stack is one of the fundamental components in OpenVSP and is useful for modeling various geometries requiring a buildup approach rather than setting a known total length. The Stack places cross-sections relative to the preceding section by prescribing translation and rotation for each. By default, Stacks set a free design policy which means that each section may be placed anywhere in your model to create exceptionally complex geometries including engines, flow-through components, fuselages, wings, landing gear, rockets, projectiles, screws, paths, … the applications are almost endless.
One of the most common uses of a Stack is to parametrically vary a body based on the assembly of individual sections. For example, you may begin with a baseline fuselage configuration and wish to vary individual section length or size to examine a design space. A Stack enables the designer to quickly set individual section lengths for the cockpit, cabin, and tail without computing the percent length stations for each as would be required with a Fuselage component.
Cross-sections in a Body of Revolution define the profile that is rotated about the centerline axis. These settings will also determine the length of your component as well as other features such as thickness, camber, or height depending on the section type. For example, an airfoil cross-section will use chord to define the length (front to back) of the revolved body and the Camber or T/C will define the shape of the section. However, an ellipse will use Width to determine the length of the body and Height will determine the thickness.
The Body of Revolution Design Mode enables you to choose which section of the cross-section profile you wish to rotate. You may use the Flowthrough option which will use the entire cross-section and revolve it based on Diameter and Angle. You may also use Upper which only uses the upper (0.5 <= W <= 1.0) part of the cross-section curve or Lower which uses the lower part of the curve (0.0 <= W <= 0.5).
