Details of the Outer Wing Panel

In one of the previous posts I showed details of the aileron bay. Now I separated the corresponding wing mesh fragment into a new object. I bent its upper edge like it was depicted on the photo (Figure 17‑1):

Figure 17-1 Internal wall of the aileron bay

On some photos I could see that this wall was built of two pieces of sheet metal. Their seam was located below the aileron pushrod.

The reason for such split became obvious after the comment I received from one of the readers (thank you, Brian!). It happened that a few weeks ago he visited the Yanks Air Museum in Chino, and had an occasion to examine wings of their SBD-4. He reported that while the bottom edge of the aileron bay is a straight line, the upper edge has a break at the pushrod. The difference from the straight line at this point is about 0.1-0.2 inches. Checking this tip, I examined photos of this particular SBD-4, then I verified photos of the other SBD version (Figure 17‑2):

Figure 17-2 Broken line of the upper aileron edge (photo made on another aircraft)

This nuance of the aileron edge is hardly visible in a perspective view. It explains why I missed it studying the photos!

Finally I recreated this detail in my model (Figure 17‑3):

Figure 17-3 Modified upper edge of the aileron bay

(Doing it, I had to modify shapes of three objects: the wing, the rear wall of the aileron bay, and the aileron).

I could not resist the temptation to recreate the rounded corner of the wing skin at the aileron root (Figure 17‑4):

Figure 17-4 Details of the wing skin corner (at the aileron root rib)

Frankly speaking, I should model such a thing during the detailing phase. I allowed myself to use some n-gons (faces that have more than 4 vertices) here, because this surface is flat so these n-gons will not deform the smoothed result.

However, looking on the photo above I noticed that the aileron bay edge seems to lie on the same line as one of the rivet seams on the flap. (The seam that runs along the rear edge of the hinge reinforcements). So it was on the reference drawing. However, do you remember that I had to modify these flap reinforcements, shifting them forward (in this post)? So now I know that this rivet seam is in another place on this flap, different from the place where you can see it on my drawing. Now I have to update accordingly the location of the aileron edge!

To preserve its vertical shape, I did it by two rotations: first I rotated it along Z axis (Figure 17‑5):

Figure 17-5 Applying minor fix to the edge of aileron bay

Then I had to make a small rotation along Y axis (along the same pivot point), elevating these faces back onto the wing surface.

The updated layout of the flap ribs and struts means that I will have to move forward not only the rivet seams, but also the rows of the circular openings placed on the flaps (I mentioned it in one of the previous posts). What’s interesting, the auxiliary “L”-shaped stringers on the upper and lower flap have different chordwise locations. In the result, the last row of the holes in the upper flap does not match its counterpart on the bottom flap (Figure 17-5).

The last detail I will recreate during this stage of work is the fixed slat. It requires six openings in the wing skin: three on the upper surface and three on the bottom surface. I did not modify the wing mesh for this purpose, because additional edges around these openings would seriously complicate its topology. I decided to create them in another way: it may happen that ultimately I will make these holes using transparency textures, but for now I will do it using the Boolean modifier. First I prepared an auxiliary object — the “cutting tool” (Figure 17-6):

Figure 17-6 Preparing the fixed slats openings

I set the wing as its parent, and placed on a hidden layer. Then I used a Boolean modifier to dynamically cut out these openings in the wing (Figure 17‑7):

Figure 17-7 Cutting openings for the fixed slats in the wing skin (by the Boolean difference)

Note that I placed the Boolean modifier after the Subdivision Surface modifier, to cut these holes in the resulting, smooth wing surface. As an additional bonus, this modifier also creates their internal walls (they come from the auxiliary object).

Although the “rib” walls obtained in this way are OK, I decided to create the front and rear walls of this slat as a separate object. Why? Because it is easier to modify its shape when it is not split into three “boxes”, as the “cutting tool” object is (Figure 17‑8):

Figure 17-8 Adding internal walls of the fixed slats

I will join all these internal faces of the slats during the detailing phase. Currently I am leaving them in the current state, just in case I will have to modify the wingtip geometry.

This was the last element of the outer wing panel I wanted to create during the “general modeling” phase. I will recreate all of remaining parts (landing light, approaching light, Pitot tube, aileron axis arms, etc.) later, during the detailing phase.

In this source *.blend file you can check all details of the wing presented in this post.

Note: When you open this file, the Boolean modifier may not work properly. The slats will appear when you enter the Edit mode of the wing object, then switch back to the Object mode (i.e. select the wing panel and press twice the [Tab] key). It seems to be a minor bug in Blender: it happens when the object having the Boolean modifier is simultaneously the parent of the “cutting tool”. (More on various modeling issues you can find in Vol. II and Vol. IV of the “Virtual Airplane” guide).

In the next post I will start working on the center wing. It will be occasion to find another parent for the “cutting tool” object, resolving the issue of disappearing slats.