This post is a small digression about a modeling technique that you may find useful.
There is a detail on the bottom surfaces of the SBD center wing: an opening, made partially in the cover of the fuselage belly (Figure 72‑1):
The difficult part of this detail is its flange, stamped in the fuselage cover. I just have two photos of this element, both of average resolution. On both of them you can see a typical circular recession, made around the opening in the belly cover. In fact, such a feature is quite common in the sheet metal design (you can see plenty of such stamped flanges in various places inside your car). This is a minor detail, too small for any serious modeling, but too large for recreating it with the textures.
Although the technical details of aircraft skin are symmetric in general, there are always exceptions. For example, look at the bottom surfaces of the SBD (Figure 71‑1 shows them on my model):
As you can see, there are several details that are not symmetric. (In addition, let’s do not forget about the asymmetric opening under bottom covers of the fuselage, visible on this picture – see Figure 70‑9 in my previous post).
So far I mapped only the symmetric half of the wing on the UVTech texture layout. It occupies a significant portion of the space. Such a size allowed me to draw all the technical details in higher resolution. The plan was that both wings will be mapped in the same points of the UV space, because most of their structure is symmetric. For the few asymmetric details, I was going to prepare additional areas, intended for the UV mesh faces that contain these elements.
In previous post I have enhanced the bump map texture effect, using two different images. This is the continuation on this subject.
Have you ever noticed that the classic stressed skin of a real aircraft is not ideally smooth? It is more visible in the areas where the skin is thinner, especially on an old, “weary” aircraft (Figure 70‑1):
The wing on the left (Figure 70‑1a) belongs to a SBD-4 (BuNo 10518) from Yanks Air Museum in Chino. This wing was recovered separately from Guadalcanal (circa 1980), and restored a few years later. This aircraft is in flyable condition (registered as N4864J), but has not flown since its restoration.
The wing on the right (Figure 70‑1b) belongs to a SBD-5 (BuNo 28536) from Planes of Fame, also in Chino. This wing was also recovered from Guadalcanal, in the same time as for BuNo 10518. This aircraft was restored, registered as N670AM, and made its first flight in 1987. Since that time it has been flying during various air shows.
Originally I was going to describe the finished bump map in this post. However, when I started writing it, I discovered that I have enough materials for at least two subsequent posts. Thus I decided to split this text into this and the next article.
There are many small openings in the aircraft skin. For example – perforation of the SBD Dauntless wing flaps, or small slots for control surfaces actuators. It would require a lot work to model each of such details “in the mesh”. What’s more – it would make the model meshes much more complex, which would hinder the UV mapping, and so on.
Fortunately, there is a much simpler solution for all these small openings. Just draw their shapes as black objects on white background, then use this picture as so-called opacity map (Figure 69‑1):
As you can see in figure above, the final result does not differ from the openings modeled “in the mesh”.
In this and the next post I will describe my work on the first of the textures required for the SBD Dauntless model. It is called bump (height) map. I use it for recreating all of the minor details that are visible on the aircraft skin.
However, before I begin this work, I had to put my model into more “natural” surroundings. I imported the environment (World) and the material settings from my previous model (the P-40). You can see the initial results below (Figure 68‑1):
Of course, the propeller of this aircraft is static, and there is nothing in the cockpit and under the engine cowling. Do not worry, this is just the first approximation! The principle is that you should work with the materials in the final environment. Otherwise the final result may not look as you want. In this case there is an outdoor scene, full of the sunlight. (Every painter will tell you, that everything on the picture depends on the light: many details would look quite different in the indoor lights and their soft shadows).
As you can see, I decided to start this work with an ideal, smooth and shiny material. Each new texture that I will apply will make it more realistic.
In every creative process, after each “big step forward” you have to stop and carefully examine the results. Usually you have to make various corrections (sometimes minor, sometimes major), before taking the next step. This post describes such minor corrections that I had to make after mapping the key texture of the panel lines.
In my first post published in October, I drew the panel lines on the model, then compared them with the photos. Sometimes a minor difference between their layouts can lead to a discovery of an error in the fuselage shape. I in that post already found and fixed an issue in the shape of the tailplane fillet.
I also mentioned (see Figure 65‑9 in previous post) that I can see a difference in the bottom part of the wing fillet. Now I would like to resume my analysis at this point (Figure 67‑1):
This post is a small digression from the main thread – I will write here about a new method for recreating geometry of historical airplanes.
In one of my previous posts I complained that it is hard to find any reliable drawings of the historical propeller blades from the middle of 20th century. In particular, the geometry of various popular Hamilton Standard propellers from WWII era is unavailable. I have found in a discussion on one of the aviation forums that Hamilton Standard Company still keeps this data as their “business secret” – even their design from 1936!
So far, all we had were the photos – but it is really difficult to precisely recreate from a few pictures such a twisted, complex shape as the propeller blade. However, it seems that there is a new hope! Two years ago I encountered on Blender Artists forum an interesting project. The Author of this thread (nick: NRK) used one of the general photo-based 3D scanning methods to obtain a spatial reference of a C-47 aircraft. Although this is not the SBD Dauntless, it seems that its Hamilton Standard propeller blades are similar to the blades used in the earlier Dauntless versions (SBD-1 .. SBD-3). Thus I asked NRK for the part of his 3D scan that contains the propeller. He sent me it within a few weeks (thank you very much, Nick!). Below you can see the picture of this blade and the contents of the 3D scan (Figure 66‑1):
This week I continue mapping the SBD-5 Dauntless skin panels onto my model. After tracing the outer wing sections, described in the previous post, I traced the center wing section (Figure 65‑1):
As you can see in the picture, I also traced the contours of the wheel bay on the wing surfaces. (These openings disappear, when you enter mesh edit mode, because they are dynamically created by Boolean modifiers. Thus such contours will be useful during further work, because in this way you can see these edges while editing the mesh).
I always start drawing the image of the aircraft skin by tracing the lines of the main panel seams. They will form a kind of reference “grid”, which later I will fill with other details: rivet seams, inspection doors, etc.
I will draw all these technical details in Inkscape, because it is much easier to modify such shapes in this vector-based program than in GIMP, which is mainly intended for the raster images. What’s more, I can export this scalable vector graphic from Inkscape to a raster image of any resolution.
Initially I prepared in Inkscape an empty drawing, set up its layer structure, and placed the appropriate links to reference drawings on the UV and Reference layers (Figure 64‑1):
I duplicated here the basic structure for the detailed bump map, which I worked out during my P-40B project. It is explained in all details in the “Virtual Airplane” guide (chapters 3 and 4 in Vol III, or chapters 6 and 7 in the complete edition). In this case I just used the hierarchical layers feature for grouping the related layers (in Panels, Fabric) together. (This feature was introduced in the latest Inkscape 0.9x, while the guide was written earlier, using older versions of this software).
The progress of my work in this month will be relatively slow, because I still have some additional activities linked to my “daily” job. Nevertheless, it is going on.
The original texture map (UV map) finished in the previous post (Figure 63‑1) is appropriate for the color textures (camouflage, national insignia and other markings). In this mapping various parts of the airplane overlap each other, so the pattern of the test image remains continuous:
While such an arrangement makes the camouflage painting easier, it would be impossible to use such a map with overlapping elements for another important texture: the image of the aircraft skin details. In this post I will shortly describe, how I prepared an alternate UV map for this purpose.