Modeling the Outer Wing Panel (1)

I started by setting up the initial scene in Blender (Figure 12‑1):

Figure 12-1 Initial setup of the reference images (in Blender)
Figure 12-1 Initial setup of the reference images (in Blender)

Although Blender allows for arranging the reference drawings on the three perpendicular planes like in the 3D Max, I prefer the alternate way: the Background images feature. Using them, I can assign appropriate image to the corresponding view, and simultaneously use all the six views (bottom, top, left, right, front, rear). They appear just when I set appropriate projection.

This is also the moment to determine the “scale” of this model. Because in the SBD drawings that I have all the dimensions are in inches, I decided to assume that 1 unit in this Blender scene = 1 inch on the real airplane. However, I have no experience with the Blender Units setting, so I left them set to None. If you want to check details of this setup, here is the original *.blend file.

I started modeling the wing by forming the contour of its root rib. (For this purpose I draw the shape NACA2415 airfoil on the reference drawing). I smooth most of the model meshes with Subdivision Surface modifier (it uses the classic Catmull-Clark scheme). The shape of a single edge loop smoothed by this scheme is a piecewise Bezier curve (or, if you wish, a NURBS curve – this is just an alternate math representation). The edge vertices are its control points, so I can easily shape this contour. You can see the result in Figure 12‑2. (In this image you can see that the vertices lie on the rib contour, because the mesh drawing mode there was switched to draw the resulting surface):

Figure 12-2 Shaping the wing root airfoil (NACA 2415)
Figure 12-2 Shaping the wing root airfoil (NACA 2415)

The theoretical shape of the NACA-2415 airfoil has a thin, sharp trailing edge. However, in the real airplane it was rounded because of the technological reasons. I tried to determine its radius from the photos. As you can see in the enlarged fragment of Figure 12‑2, it forms a small wedge with rounded corner. It is shaped using five vertices. (Their number corresponds the number of the leading edge vertices — I will explain the reason further in this text). The Dauntless inherited many solutions from its Northrop Delta lineage. For example — its wing spars are not perpendicular to the wing airfoil chord. Instead, they are perpendicular to the fuselage centerline. (In the SBD, like in the earlier Northrop designs, the center wing panel and the fuselage form a single unit. I suppose that it was easier to put together the wing spars and fuselage bulkheads when they shared the same technological bases).

To provide as many “technological bases” for my model as possible, the X axis of the wing object is parallel to the wing chord. I can set it “in the Northrop way” by setting the object incidence angle to 2.5⁰. In this position I can work with the wing mesh, moving vertices along the global coordinate axes (i.e. the axes of the fuselage), and then switch to the local wing object axes when needed.

In the next step I formed the basic wing trapeze. I did it by extruding the wing root edge, and shrinking the airfoil located at the wing tip (Figure 12‑3):

Figure 12-3 Forming the basic wing “trapeze”
Figure 12-3 Forming the basic wing “trapeze”

Now you can see why I draw this wing section on the plans without dihedral. This drawing would be useless if it depicted the wing “properly”! From the reference images and descriptions it seems that the wing tip had the NACA-2409 airfoil. In the first approximation I scaled down the rib of the tip, fitting it to the reference drawing. (To fit this mesh to the front view I temporarily rotated the wing by its dihedral angle — 10⁰ 8’ — as in Figure 12‑4). However, although scaling down the original NACA-2415 coordinates produces the NACA-2409, it does not work precisely for the airfoil shape recreated with the Bezier curves. To fix these small differences I prepared an auxiliary “guide” rib of the NACA-2409 airfoil and placed it in the tip. (see Figure 12‑3). Then I modified the wing tip airfoil, fitting the wing surface to the contour of this guide rib (you can see on the picture that it minimally protrudes from the wing – as a very thin line).

Then I rotated the root airfoil, adjusting it to the wing dihedral (Figure 12‑4):

Figure 12-4 Adjusting the wing dihedral
Figure 12-4 Adjusting the wing dihedral

In the SBD Dauntless all the wing ribs were perpendicular to the wing chord plane, except the root rib of the outer panel. To easily insert properly oriented ribs in the middle of this wing, I inserted another rib after the skewed wing root rib. It is perpendicular to the chord plane. I marked this rib edge as “sharp” (by increasing its Crease weight to 100% —you can recognize it on the picture by different edge color). In this way I ensured that the skewed root rib has no influence on the new edges I will add in the middle of this mesh.

In the Catmull-Clark subdivision surfaces, you can use the Crease weights to obtain a local sharp edge or to separate a mesh fragment from the influence of the outer mesh vertices. I learned this method from a Pixar paper, presented on SIGGRAPH 2000 by Tony DeRose. (Before I started my first model, I studied the subdivision surfaces math, to know better properties of the basic “material” used in the digital modeling).

I had an occasion to learn that it works as expected in the next step: forming of the rounded wing tip. First I inserted into the tip area a few new ribs (using the Loop Cut command). Then I started bending their trailing and leading edges, to finally join them into an arch (Figure 12‑5):

Figure 12-5 Shaping the rounded wing tip
Figure 12-5 Shaping the rounded wing tip

As you can see in this picture, I also removed some of the internal mesh faces. I did it because I had to alter the topology of this area. (It is easier for me to determine the new faces when the old ones are removed).

Note that it was a good idea to have the same number of vertices on the trailing and leading edge. Now I can easily join them at the wing tip.

Figure 12‑6 shows the resulting surface:

Figure 12-6 Wing tip — the intermediate result
Figure 12-6 Wing tip — the intermediate result

Note that the wing tip edge lies on the wing chord plane. As we can see from the reference drawing, in the real airplane the wing tips were slightly bent upward. We can easily obtain such an effect by moving upward (and slightly rotating) last vertices of the tip (Figure 12‑7):

Figure 12-7 Wing tip — the final touches
Figure 12-7 Wing tip — the final touches

Figure 12‑8 shows the control (i.e. not subdivided) mesh of this wing:

Figure 12-8 Wing mesh topology
Figure 12-8 Wing mesh topology

Note that I tried to align as many “longitudinal” mesh edges as possible to the stringers and spars visible on the reference drawing. This will be extremely useful when I draw skin details on the wing surface unwrapped in the UV space (for texturing).

In this source *.blend file you can check any detail of the mesh presented in this post. The next post will describe further steps of the wing modeling: separation of the aileron and forming its bay in the wing.

This blog provides just an overall picture of the process. If you want to learn more about Blender, digital aircraft modeling and subdivision surfaces, see this guide: “Virtual Airplane” (vol. II).

Advertisements

7 thoughts on “Modeling the Outer Wing Panel (1)

  1. Great to see a start on the modelling Witold.

    The wing tip geometry is very neat- mine normally ends up quite cluttered and messy with a few triangles as well- although I use much the same procedure as you. It generally smooths out well enough though. I’ll try your method when I rebuild the KI 43 wing today.

    I look forward to seeing how you get sharp edges on the ailerons etc, this is one of the reasons I have stopped using subdivisions- I have had to add to much geometry to sharpen the edges, and I haven’t seen much difference when using crease and other edge tools- but I probably didn’t do it right.

    I have had a blender background set up for the Dauntless for quite some time- its a nice looking plane that punched way above its weight, but the thing that put me off modelling it was the dive brakes- do you plan on using geometry or alpha textures to cut out all those holes?

    I look forward to the next instalment.

    Like

    1. Thank you!
      It seems that we like this airplane for the same reasons 🙂
      – about the sharp trailing edge: I will preserve the rounding of 0.15″ I have created here during further modeling of the aileron. In the case of flaps I will have to split it , but I will recreate the original solution: the upper part preserve rounded edge (there was a profiled beam along it) while the bottom part will be a simple rectangular sheet metal, reinforced by internal formers.
      – about the holes in these flaps: I am going to recreate them using bump maps and transparency (alpha) textures. There is always an option to model them (a hexagon + Subdivide Surface modifier will produce satisfactory, circular hole), but I want to try the easier way first.

      Like

    1. Thank you very much!

      I read this article and set up the appropriate scale in my drawing. However, after few quick experiments I decided that:
      – when I switch to the Imperial system, all distances appear in feet. I can turn on the “Separate Units” option, so I can see the dimensions as [3′ 10″]. However I cannot find an option which would allow me to switch the default unit to inch;
      – most of the Dauntless dimensions are expressed in inches with decimal point (for example: 66.80″). I am too accustomed to the metric base! Switching to feet and inches makes these dimension less readable (for me);

      It seems that these systems were created mainly for the architects. All in all I will stay in the neutral (“None”) system. 🙂

      Like

      1. Setting up your units preferences really isn’t that important unless you are modelling for a Flight sim, in which case it is a major concern- your ultralight model could dwarf a Jumbo if you didn’t get it right.

        I’m like you- I don’t worry about it at all when modelling for renders.

        Like

  2. Witold,

    At last the modeling starts. I’ve been looking forward to this ever since you announced you were doing a new model, and your first modeling post doesn’t disappoint. There’s a lot to learn here. Blender is an excellent tool for modeling irregular shapes like people and animals and cartoon characters, and rectilinear objects like boards and bricks and buildings, but it’s very tricky to model things like airplanes that lie between these two extremes.

    I’ve been modeling in imperial units in inches. What makes it tolerable is that you can enter decimal values for inches directly into any numerical input field by adding the suffix “in” to the end of the value string.

    -Brian-

    Like

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s