Modeling the Empennage (2)

After some verification of the reference contours that I described in the previous week, I am coming back to modeling of the horizontal tailplane.

In the previous post I created the reference airfoil of its root rib. Now I copied it into a new object, straighten along the fuselage centerline, and finally extruded spanwise (Figure 33‑1):

Figure 33-1 Forming the basic contour of the horizontal tailplane

I checked the resulting shape, ensuring that the thickness of the tip ribs matches their counterparts on the photos (Figure 33‑2):

Figure 33-2 Checking the shape against the photo reference

When this base shape was verified, I started to form the curved contour of the tip. Basically, it was an arc, thus I shaped it by extruding and rotating subsequent mesh segments (Figure 33‑3):

Figure 33-3 Shaping the circular tips

Preparing the horizontal tailplane for such a mesh topology, I used the same number of rib vertices to form the leading and trailing edges of its root airfoil.

In the next step I created an additional gap in this mesh, at the point where it will be split between the stabilizer and the elevator (Figure 33‑4a):

Figure 33-4 Further modifications of the tip mesh (1)

Such a gap deforms the original circular contour of the tip. To restore its shape, I had to move a little two nearest vertices on each side of the gap. Facilitating this task, I used an auxiliary circle as the reference shape.

To fill the empty space inside the tip, I extruded the internal edges of the last rib (as in Figure 33‑4b).

I slid the last vertex of the edge that runs along the elevator leading edge, forming in this way the angle visible on the reference drawings (Figure 33‑5a). In fact, its location was re-checked on the reference photos, thus it lies in a slightly different place than you can see on the underlying scale plans.

Figure 33-5 Shaping the internal faces of the tip mesh

Of course, I also scaled the thickness of this newly formed “rib” (Figure 33‑5b), aligning it to the slope of the previous, trapezoidal segment of this tailplane.

In the next step I started to build different topologies in each part of this tip mesh. In the “stabilizer” part I joined the “tab” of the internal faces and the leading edge (Figure 33‑6a). In the “elevator” part, I removed the first and the last face of this tab, and shifted the vertices of the middle face, forming a thinner trapeze. Then I extruded the outer edge of this face several times, rotating them around the “corner” of the elevator leading edge. Note that each of these faces corresponds to a single mesh segment on the tip external contour (Figure 33‑6a):

Figure 33-6 Further mesh faces, added to the tip

I also joined the “gap” in the tip contour into a single, “sharp” (Crease = 1) edge. (In fact, I should create it as a single sharp edge in the beginning). Such an arrangement allows me to quickly create an array of new faces that closed the tip of the elevator (Figure 33‑6b). Note that I filled the gap in the “corner” using two quad faces.

To match the topology of the elevator tip, I had to add additional “rib” to the stabilizer mesh. I did it in three steps. First, I created edges that joined the corresponding vertices of the tip external contour and the internal faces (Figure 33‑7a). Then I split them by half (using the Subdivide command). Finally I used all these vertices to create new faces (Figure 33‑7b):

Figure 33-7 Filling the internal faces of the tip

Note that I had to create a single triangular face near the leading edge (Figure 33‑7b). Fortunately, the mesh curvature in this place is low enough that it does not disturb the resulting, smooth shape of the tip.

When the overall shape of the tailplane was ready, I split it into the stabilizer and elevator objects. I did it by copying the original object and then removing the “elevator” part of its mesh faces (Figure 33‑8a):

Figure 33-8 Separation of the stabilizer and elevator

Similarly, I removed the “stabilizer” faces from the elevator object (Figure 33‑8b). Ultimately I also simplified this mesh by removing one of its “longeron” edges. (It seems that the tip contour in the front view requires just a three-point curve).

The elevator of the SBD Dauntless had an oval leading edge (it was the aerodynamic compensation, an area shifted in the front of the hinge line). I started to form this element by inserting on the symmetry plane a circle (consisting 12 vertices) (Figure 33‑9):

Figure 33-9 Beginning of the elevator leading edge

Then I extruded it spanwise, adapting its radius to the local airfoil thickness (Figure 33‑10a):

Figure 33-10 Shaping and joining of the leading edge

In the next step I removed the rear faces from the leading edge cone, and joined it with the rest of the elevator mesh (Figure 33‑10b).

The presence of a single middle edge in the elevator tip allowed me to remove similar edge from the stabilizer tip (Figure 33‑11a):

Figure 33-11 Finishing touches

Of course, it would be even easier to not create this edge at all — but this is typical situation, when I modify the initial concept of the mesh topology during the progress of the work. Figure 33‑11b) displays the resulting tailplane assembly.

In this source *.blend file you can evaluate yourself the model from this post.

In the next post I will describe my work on tailplane fairing.







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