Importing from OpenVSP

One of the most common tools for designing aircraft is OpenVSP, a design tool created by NASA and made available to aircraft designers around the world. After completing aerodynamic design in OpenVSP, the next step in exporting into unconstrained CAD. Unfortunately NASA was not thinking about Rhino7 when they created OpenVSP, so exporting into Rhino7 is not exactly straight forward.

Eagle_Ray_4.2(20211203).3dm (18.0 MB)

Attached are three attempts at using STL, STEP, and IGES export options from OpenVSP. Our objective is to create a solid with defined elevons and rudders. Any help would be much appreciated.

If you want to look at the OpenVSP File or try a different set of export parameters: 20210920_KWF-EagleRay_V4.2.vsp3 - Google Drive

Hi Ronald - those are some messy objects - it might be possible to fix these things but in truth it would probably pay to re-create most if not all in Rhino weith some clean surfaces, using what you have as reference. It looks like the step and iges versions are simply converted from meshes.

-Pascal

HI Pascal - I agree and am working with the OpenVSP developers on an alternative way to export that will be more compatible with Rhino7.

Did you try with these settings?

HI Seghier - I took your advise and exported from OpenVSP using the Untrimmed STEP Option. It imported into Rhino7 as left and right open surfaces that look good. Now if we can just join the left and right open surfaces, close the left and right open surfaces, convert to solid the left and right surfaces, and/or Boolean union the left and right sections. Unfortunately none of these operations seem to work on this file and Rhino7 is not providing much in the way of explanation.

Eagle_Ray_4.2(20211203Compressed).3dm (9.9 MB)

Hi Ronald - as is, this appears in Rhino as two very complex and nearly unsuable surfaces. They are still faceted and far too complex to use in my opinion… But -you can break each up into a polysurface with DivideAlongCreases remove all the faces at the centerline and at the planar tips of the wings. Join the two halves and then Cap to close up the ends again.

-Pascal

You can fix it with Grasshopper , there is a straight line in XAxis you must delete it in the original file

The problem really isn’t with OpenVSP, but with how you’ve used it.

Years ago, OpenVSP (v2 and VSP before that) used the OpenNURBS library to write out native 3dm files. When we got IGES and STEP files working, we dropped 3dm support because Rhino was just as good at reading our IGES and STEP files as the 3dm files – and everything else would prefer to work with IGES or STEP directly. So, dropping OpenNURBS was one less software dependency to wrestle and we didn’t loose anything. The point here is that the file format didn’t really matter, (when using the untrimmed surfaces export under the File… menu) OpenVSP is sending Rhino a piecewise quilt of Bezier patches. File conversion and interoperability is not the problem – the problem is with non-ideal surfaces.

This wing is severely over-defined, with twenty ‘hard’ cross sections – each defined as file airfoils.
Blending is not used effectively to create a smooth LE and TE – so most of those cross sections are actually G1 discontinuous. Some of the airfoils are clearly not correct – in particular, the 5th from the root (#4) is clearly not what is intended.

I would suggest you choose the option ‘Rotate foils to match dihedral’ when lofting a wing with a strong winglet like this one.

From what I can see, many of the sequential foils are identical, so perhaps you are trying to specify a complex twist distribution. If not, deleting most of the sections and using blending to recover the planform shape will give you much better surfaces.

Some of the airfoils are varying, but you would get a better surface definition if you specified less and let OpenVSP’s lofting handle the interpolation where it can.

How did you go about coming up with the airfoil stack, planform details, and twist distribution? I’m assuming you used some other program – does that program have more planform information? This model is not doing a great job of reflecting the intent of a well designed wing.

I know it sounds crazy, but If you really believe you need complex and smooth control of twist and other wing design parameters, you might actually try modeling the wing with a propeller blade. However that takes an experienced hand and I would like to see you understand and master the mistakes made here before taking a significant jump in complexity like that.

Certainly following the advice to turn off the ‘Split Surfaces’ option is a good one if that is not what you want.

You might try using the ‘Trimmed Surfaces’ option under ‘Analysis’ to write out a BREP solid STEP file if you would prefer that. There might be file compatibility issues there, but it should result in a solid from the start with nothing needing to be done in Rhino. That said, your geometry is a single part, so it should be easy either way.

If the root and tip caps are giving Rhino problems for some reason, they can be easily turned off in OpenVSP. The root caps aren’t doing anything for you - and the tip caps will get better if you ‘Rotate foil to match dihedral’.

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Hi user1917 - Even if I had not recognized you from your photo, I would have from your lecture style! Indeed Mark provided the initial airfoil stack from another program, then student interns morphed it through several stages, and finally a team in Nepal optimized it further using another set of tools. I can use what we have to 3d print a desktop display, but to proceed with a flight model we need to do some serious work. Justin has been providing guidance while working on his autonomous greenhouse, but no one could replace your lecture style. If you can spare an hour, I would much appreciate if you would participate in another virtual meeting – this time to guide our Team in converting the mess into a clean design.