Hi all, I am trying to model an old style aircraft wing with ribbing, i.e. canvas stretched on wing ribs. While it is a breeze to generate a split-second full wing with a curve network, and not much trouble to generate an upper wing with a 2-rail sweep, putting in the ribbing is more of a challenge. I got a reasonably fine output with a 2-rail sweep with a scaling rail that has all the required pinches and curves, it does not exactly gets me the result I need.



I tried several point control gimmicks with the scaling rail, that gave le the corresponding change in shape, but I feel I am missing some control, as the ribbing is constant across the wing and goes from zero to zero elevation from rail to rail, while I probably would want this to leave a bit of smooth wing on both the leading and the trailing edges.

Has anybody a suggestion on how best to tackle this to achieve an effect like in this fine model of a WWI French aircraft?


Thanks in advance,

Jean-Paul

Hi Jean-Paul, it can be tough to model small "lumps and bumps" with NURBS modeling, overall the mechanisms in things like sweep are more oriented towards creating broader curved surfaces instead ones with little wiggles and bumps.

Often times one of the best methods for adding in small details is to put them in at rendering time using a Displacement, Bump, or Texture map instead of trying to explicitly model them.

Also there are some brush-based detailing programs like 3Dcoat or ZBrush that are oriented towards sculpting those kinds of raised details on a base model, one of those tools may be a better fit for creating those details.


If you do want to try and model those details in MoI, usually the best way to gain additional control is to build the model in smaller pieces instead of trying to do too much all in one go of a surfacing command (like all in one sweep or all in one loft, etc...).

So for example you might start with a broad smooth wing and then model each rib as as some kind of small independent piece, and then merge them together, or possibly let them just push through each other if you are going for rendered output only.

But I would probably first try applying those details as a rendering process rather than as a modeling process and see if you can get good results with that.

- Michael

Hi Michael,

Thanks for your quick reply. I can see your point about using a sub-d or brush-based tool. The thing is that the ribs are a bit more than just nice to look at features. They are really part of the wing and I would need to have them modelled and included into the 3dm file as the target is to generate stereo lithography masters. The real issue is not so much about making the ribs, but rather (as always with my woes with NURBS, like for wing transition into fuselage) to ensure seamless continuity.

This being said, I am starting to suspect that I have been making my life unnecessarily difficult. Judging from the first test pieces I got back from the maker, actual 1/350 scale STL objects do not display less-than-perfectly continuous surfaces in such a disturbing way as Flamingo or Modo renderings do, especially at 500+ magnification on a big screen. The matter is really to decide how much is good enough.

I had another stab at it this evening, trying to model a subset of the wing (the inner top surface), then blending with the edges that I had generated before. This works better (although I got mixed up with the alignment – having a wing generated in one go is way less fiddly, but as you say, such are the limits of NURBS).

Hi Jean-Paul,

Just out of curiosity, are those ribs concave? because in the picture they look convex.

Cheers

Hi Jean-Paul, sorry I did not realize you were going to STL it instead of render it.

So yes, render-only stuff would not work for you, but a sub-d or brush based modeling program would work for that since they can generate polygon output.

Once you get into this realm of small bumpy details, you are just probably going to be better off with one of those tools that is oriented towards making organic shapes with small sculpted features in it. That kind of a target is just not generally a great fit with NURBS modeling only.

For adding details in a brush-based system you can use MoI as part of the workflow to generate a base initial shape, like the smooth wing before applying bumps to it. That can be a good combination.


re: achieving seamless continuity for small details in STL - yeah since your final STL model is made up of small flat facets anyway, it probably does not do you much good to worry about perfect continuity in very small features of the shape like in each individual rib...

If you did want to focus on that, a sub-d modeler is much more oriented towards that goal.

- Michael

How about this?

Hi Danny,

The ribs stand out of the overall profile of the wing. The effect to achieve is one of stretched canvas, like in this photo of a Fairey Swordfish torpedo plane. WWI aircraft had fewer, more prominent ribs. Even so, it would be easy to get overboard and overstate them. It is just only stretched canvas over wooden ribs, not mini-fins.

Hi BurrMan,

Yes, I guess you generated the ribbed surface and then blended the leading edge and under wing. I came up with that much too. It works fine like that, although it still does not quite look like stretched canvas yet. This is probably due to the profile of the ribs that should be a bit more complex (i.e. with a few more control points).

Hi Michael,

I normally do ships, but now I am stuck with a bunch of warplane masters to deliver. Airplanes are more organic in nature than ships. I have bumped into NURBS limitations much more now than ever before, although generating complex modern hulls for warships is sometimes a challenge too. I would really like to avoid having to go into Zbrush territory, but I can see that MoI (or Rhino for those stunts that MoI does not yet do) can be a good first step. It has to be much less painful to generate the overall shapes of an airplane using NURBS than with a sub-d approach, although the MilitaryMesh.com community swears of the contrary, but they have mastered 3DMax and the like long ago.

I’d like to stick to a MoI only workflow also because the STL guys want 3dm files only. They seem religious about that, for some reason.

Thanks a lot for your input anyway.

Jean-Paul

Hi Jean-Paul, I wouldn't say that sub-d is "easy" at all, really - it definitely takes plenty time and practice to get accustomed to how its toolset works.

But the overall mechanism for how sub-d works tends to work better for sculpting or deforming localized areas of a shape.

You do end up dealing with a lot of points in sub-d since you basically do your work on a 3D point cage all the time. That's also one reason why it can take some time to refine the techniques, because you have to use various tools to help you manage and manipulate a larger number of points to work with.

But it does have a lot more freedom to kind of add a ring of additional points in one area, inflate some points to make a bulge, etc...


NURBS on the other hand tends to work best when the shapes involved are well defined by a set of profile curves. When that's the case then NURBS can build the shape much more accurately and also much more quickly than trying to manipulate a big bunch of points.

But as you get more into shapes with bumps in them and things like cloth, faces, etc... those kinds of shapes become more difficult to define clearly by using only a few profile curves.

That's kind of the territory that you're getting into with this one.


- Michael

I think the key is that the ribs are actually the intended shape and the canvas deflects/sags down into the valleys of the span due to gravity and downward force from the laminar flow in flight stretching the canvas.

See if this helps

Thats very cool stuff grendel.

Interesting how that point back tracking on each other works. That was not in my toolset but is now!

Thanks again.

No problem, kind of a Sub-D aproach to it.

Hi Grendel
The Canvas is actually layed out over the wing and sewn together at trailing etch and wingtip. then
painted with something called "dope". That makes the canvas shrink and the ribs stick out.
Hope that helps.
Andy

I thought that last one from grendel pretty much nailed it!

Indeed. I believe that Grendel's suggestion does it. Well done, gang ! And thanks a lot. Your help is much appreciated.

Jean-Paul

Andy - That makes sense..you would want some sort of waterproofing to prevent the wings from retaining water and some way of pulling it taut over the frame.

Grendel - that dope or, taughtning dope, as they called it did all that. Some celluloses based compound.
Awfully smelling stuff. That why the name.
Andy