how to create geodesic web on a double-curvature surface

[Anonymous]

I'm trying to put a web of geodesic 'ribs' on the inside of a double-curvature surface. fancy way of saying I want to mimic the geodesic structure of this WW II wellington bomber:

Wikipedia has it 'The principle is that two geodesic arcs can be drawn to intersect on a curving surface (the fuselage) in a manner that the torsional loads on each cancels out that on the other.' 

wonderful if this can be created in a mathematically accurate fashion, but right now I can't even create anything that looks similar to this on a generic fuselage section with double-curvature surface.

what i've done so far is to draw a simple grid pattern in a sketch, extrude, and trim off the excess using the shell. see below. i've spent lots of time to use the web and rib feature in Fusion, but the limit to use a planar sketch to generate these features and that the web/rib is generated normal to the sketch makes it unusable, unless i'm missing something. I think the geodesic structure should be made such that the 'ribs' should be perpendicular to the local surface everywhere along the ribs.

i've checked out every post on geodesic sphere and a lot on web/ribs

grid sketchextrude the grid patternfinal trimmed product

Help is much appreciated.

[Anonymous]

surprised to find no takers? I think this is a very common need when you design for 3d printed light weight structures.

[lichtzeichenanlage]

IMHO: the infill is normally calculated by the slicer software, not within the design tool.

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@Anonymous wrote:

surprised to find no takers? I think this is a very common need when you design for 3d printed light weight structures.

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[Anonymous]

infill as available from Cura/S3D (i only use these two) are just haphazard filler to afford strength and support top surfaces. They are constrained to the build direction and offers poor strength/weight ratio for structures that need to handle multiple load cases. normal infills just ain't gonna cut it. Need custom webs!

When I printed and tested my crude models I use 0% infill and 1 layer shell. A 18g shell with a diameter of 16cm can easily take expected airload imposed on it flying at 100+ kmh. Inertial load will require more but still the strength/weight ratio drives the decision to go custom.

[TheCADWhisperer]

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@Anonymous wrote:

surprised to find no takers?

Same basic technique as demonstrated here (see Attached).

[Anonymous]

since you emphasized it's basic technique, can you tell me how to apply that sweep to a 3D spiral path and a non-circular profile so that the profile is perpendicular locally to the double curvature shell? in essence, variable twist at all lengthwise stations?

Sweep was the very first thing I tried. I used circular profiles, triangles, and rectangle profiles. single twist angle means they deviate from vertical very rapidly from the initial station. I could theoretically approximate the desired shape using a loft with multiple profiles, but that would be a labor-intensive process with many different profiles if the rib/stringer 'pitch' is small. I just thought that somebody might have met this problem and figured out something elegant.

[TheCADWhisperer]

If I were to do a design like this - I would be using Autodesk Inventor Professional rather than Fusion.

Just too much work in Fusion for the available time that I have.  

[phill_scott]

And how would Inventor Pro help with this problem?

OP, I am trying to do something similar - isogrid structural reinforcing of double curvature panels parallel to the local surface normal. 

[TheCADWhisperer]

@phill_scott 

>>Inventor Forum<<  is over here - be sure to fully describe your Design Intent.

If you are looking for an "Easy Button" solution, I am not aware of one.