Problems generating trimmed surface .STEP file

[Charlie Raskopf]

Hi! I'm new to this software, been working on a model in VSP, and exporting .STLs just to create little models just back-and-forth, and doing janky heat-molding to fit components to make a small flying model. Now, I have to actually go into Inventor or Fusion and make the structure and sections of the airframe, so I can make it full-scale (Been using a 12inch wingspan model, need to make the final one 71inch wingspan) and I've had nothing but trouble when it comes to creating the intersections between pods that will host brushless motor mounts and between each wing surface and the main stack (main wings and the butterfly tail). If you have any advice and/or fixes, that would be great. 

Thanks, 

Charlie R. 

[Brandon Litherland]

The biggest problem is that your fuselage has XZ symmetry turned on so you effectively have two of them on top of each other.  Turn that off and see how CAD exports go.  I recommend using Trimmed Surfaces.

[Charlie Raskopf]

Fixed that, it resolved the issue with trimmed surfaces. How do you recommend going about designing internal structures? Brute-forcing using Planes in Fusion/Inventor? Anything better? 

Thanks! 

[Brandon Litherland]

If you're at the point of building up internal structure, then you've moved past OpenVSP.  You can perform structural layout setup and export to different solvers (see 2025 OpenVSP Workshop presentations by Sandoz) but VSP won't design the actual ribs and spars for you.  It all depends on what kind of structural analysis you're planning.  If you're just using handbook methods (which for an aircraft this size would be fine), then set the spacing and build the ribs, spars, bulkheads, and stringers. If you're planning an optimization, then use VSP structures to lay out the internals and run your analysis until it closes how you like.

[Charlie Raskopf]

I've been using Inventor, trying to add internal complication is a PITA. I don't know what you mean by " You can perform structural layout setup and export to different solvers (see 2025 OpenVSP Workshop presentations by Sandoz)", or what. My goal is to make this FDM 3d printed using rolled carbon rods as stringers to give it as much strength as possible at joints. 

[Brandon Litherland]

https://openvsp.org/wiki/doku.php?id=workshop2025 

Look for the Structures content.

Have you done any analysis to determine how many frames, bulkheads, longerons, and stringers make sense for this aircraft? How thick is the skin/shell? What is it made of?

In lieu of all that analysis, you can simply build one with however many structural elements seem about right and test it.  Plastic is cheap so go and break it. Add or remove elements depending on your needs.  In this case, it sounds to me like some old school build iteration would get you a good answer quickly.