SBD Dauntless, from scratch

[SANCER]

Agree with W & Jan...!
IMPRESIONANTE trabajo ...

Greetings with affection to Poland

 

[Gnomey]

Lovely work so far!

 

[Witold Jaworski]

Wurger, Lucky13, SANCER, Gnomey - thank you!
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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:

As you can see in figure above, the final result does not differ from the openings modeled "in the mesh".

For this opacity map I used a 4096x4096px image, mapped with the same UV coordinates as the bump map (i.e. UVTech coordinates). Below you can see how it is connected to the material scheme:

I also used these black contours in the bump map (they create impression of "metal sheet thickness" around edges of these openings).
Of course, if you wish to make extreme close-ups of the model, you can generate from the source Inkscape drawing a raster picture of higher resolution (8192x8192px?). In the extreme cases you can even create a separate UV map for the opacity texture, enlarging the areas around holes and reducing all the others. (I do not need such an extremal solution in this model).

Working on this model, I am drawing the bump map and the opacity map in parallel.

In the previous post I showed how I recreated bump map details of a classic stressed skin: rivets, panel edges. However, the fabric-covered surfaces, like the aileron, require different elements:

As you can see, the background color of this image is darker than in the previous post (it is 75% black). I decided to use it, because most of the elements on the SBD skin is protruding (rivets, inspection doors). To recreate the protruding rib edges, I used a combination of linear and circular gradients (the latter for the circular endings of each rib). These gradients have a sharp, symmetric, parabolic profile. (For details of this solution, see "Virtual Airplane" guide, chapter about Inkscape, section titled "Mapping the fabric-covered surfaces").

I also used gradients to recreate flanges, stamped around the flap holes:

I set the opacity values in the subsequent nodes of this gradient so that they match the profile of this flange.

For another element I had to use a different solution. The fabric between ribs is tensed like a membrane, so in an aircraft standing on the ground it is flat. However, in the flight it is deformed by the airflow. To reproduce this deformation, I added another shape to the bump map:

First I sketched black shapes in the areas between ribs. Then I used a special so-called SVG filter to blur these areas. (SVG filters are "dynamic" modifiers: I still can turn it off to modify the original contour). Such a blurred shape creates gentle recesses on the rendering.

One note about implementation of these recesses in the bump maps textures. To obtain the effects depicted above I had to intensify the "black" components. The contrast between black areas and 75% black of the background is relatively low in the basic texture (see the fragment of nor_details.png image, presented below). To make these recesses deeper, I had to add another texture (nor_blur.png – see figure below):

Pixels from both images are merged in the material schema using Multiply node, thus all black areas in the result image are still black. Before the Multiply node, each texture has its own control node. These nodes control influences of their sources in the resulting bump map image (i.e. in the input delivered to the Displacement slot in the surface output node). The simpler Moderate node can make nor_blur.png darker, while the control node of nor_details.png makes it lighter (the Min value), but simultaneously it can "flatten" its grayscale Range. Comparing to altering the shades of the source image layers in Inkscape such a solution has two advantages:

1. You can easier to alter their intensity in the material schema, and you can instantly see the effect on the rendered picture;
2. Blender converts output from Image nodes to floating-point numbers, thus you will not lose any contrast from the source image. (In Inkscape every elementary color component is converted to a byte integer 0..255, thus when you decrease color intensity range, it can lose some of the image contrasts);

Of course, I can also decrease depth/height of a single element (for example – recesses of the fabric surface between the ribs) by reducing its opacity in Inkscape. However, to apply such a change, you have to export the new version of the texture image from Inkscape and refresh it in Blender. It requires more "clicks" than altering of a single slide in the material scheme. On the other hand, I did not want to use too many images in the material schema. Thus I decided that I will use two source bump maps in Blender. I expect that I will alter their intensities more often than the others.

Figure below shows the updates that I made in this post, on the model:

As I mentioned before, the rivets and panels seams created by the bump maps are visible from a relatively narrow field of view. The camera used to create the picture above was outside this area. They will become more visible when I apply other textures (reflectivity map, color map).

In this source *.blend file you can evaluate yourself the current version of the model. Note, that the enclosed texture images covers just the wing (BTW: it had a hell of inspection doors on its lower surface!). There is no image for the tailplane, nor for the fuselage, yet. I will finish these areas and describe in the next post, which will appear in two weeks.

 

[Wurger]

Great !!!

 

[Gnomey]

Good work so far!

 

[Witold Jaworski]

Wurger, Gnomey - thank you!
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In the middle of April I described the 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:

The wing on the left (see the picture above) 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 on the picture above 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.

I assume that the skin of the SBDs that were flying in 1940-44 resembled the skin of the wing from the left picture. Note that the leading edge and the central panels have no visible deformation. (However, their skin still could deform a little in the flight). This is because they were created from relatively thick (0.032") sheet metal. The buckling of the skin is more visible on the panel behind the rear spar, because it was made from a thinner (0.025") sheet.

It is quite easy to obtain this effect using textures:

To do it, I re-used the contents of the Rivets layers from the source Inkscape image. However, before I did it, I drew additional, thick gray lines below the rivet seams. I placed these lines on a separate layer, named Shadows:

Once this was done, I could compose the final texture image using these lines and clones of the Rivets sublayers:

First I altered the color of the white Rivets: Dome elements, using a simple SVG filter that blackens everything. Then I blurred this composition, using another SVG filter: cascading Gaussian blur. (For details of this solution, see "Virtual Airplane" guide, chapter about Inkscape, section titled "Using filters").

Finally, to decrease the influence of this texture on the forward part of the wing, I covered it with a gradient-filled shape:

As you have noticed, in this composition I re-used contents of the Rivets layers, using their clones. Using such clones in the final texture image allows me to easily modify contents of these pictures in the future. When you alter any element in the source layer, Inkscape immediately updates all its clones. Thus I rearranged the structure of the SVG file (see the layers pane in Figure 70‑5). I grouped all the source layers (Rivets, Panels, Covers, Bolts, etc.) into a layer group named Source. Then I created another layer group, named Result. Each of its sublayers contains the composition of one final texture image (Holes, Nor-Details, Nor-Blur). Their contents is composed from clones of the Source sublayers, with altered opacity and (sometimes) applied various SVG filters. (See the source Inkscape file).

When I work on such a drawing, I am drawing new elements (or modifying existing ones) on the Source sublayers. Then from time to time I export the final images generated by the Result sublayers to the raster files, used by Blender (holes.png, nor_details.png, nor_blur.png).

In the process of creating textures, the most troublesome areas are those along seams, especially when such a seam contains a corner. Some time ago I tried to avoid breaking the skin panel edge along such a UV seam (see this posts, Figure 67‑3). Now I can see that this was a bad idea:

The rivets in the line that runs along the UV seam are skewed. They also have different sizes. All of this has occurred because of the high shape distortion of the bottom faces that belong to the large wing fillet.

I placed the small part of the fuselage inside the UV seam at the center wing. This fragment is undistorted. The remaining triangle (marked in orange in the figure below) is an area where the mesh faces mapped onto UV surface have high distortion (see figure "a" below):

After some deliberations, I decided that it is much easier to join the few rivet lines that run across an UV seam, than to improve these skewed rivets produced by the current UV mapping. (Well, as you can see, the "improvement" of the seam line that I made some time ago was a bad idea). Thus I had to shift the UV seams to the outer edges (see figure "b", above), and "glue" some additional mesh faces to the center wing. This time I took care to minimize deformation of the faces that remained outside the mesh seam.

Figure "a" below shows, that I was able to precisely match the rivet lines across this new seam. It was not as difficult as I thought. Figure "b" below shows the UV map of this area and the original image of the panel seams and rivet lines:

Note that this time only small number of rivets occur in the highly deformed area. On the other hand, because the degree of deformation is lower than in the previous case, these rivets are not ideal, but look "acceptable", at least.

Figure below shows both bump map images, that I mix to obtain the texture of the technical details:

At this moment, I filled with appropriate details all the common surfaces, and the elements belonging to the SBD-3. As you can also see, I already drew some asymmetric elements on these textures. However, before I map them, I have to apply the Mirror modifiers to the appropriate meshes of my model. I will do in the next post. (I delayed this operation as long as I could, because presence of the Mirror modifiers allowed me easily alternate the model shape. (I had to modify its left side only. Blender took care on updating of the right side). However, after so many months of various checks I can only hope that the shape of this model "seasoned" enough, so I will not have to modify it in the future).

Figure below shows my model. (To make the effect of the bump textures more visible, I significantly increased their intensity):

Strangely enough, I obtained such an intensity increase by setting control nodes of these two textures to negative values: Moderate:Range = -1 (nor_blur.png) and Range From Min:Min = -3 (nor_details.png).

Actually, the textures of this model are symmetric, which means that there are many missing/wrong details on the fuselage right side. In the next post I will introduce asymmetry to these meshes.

In this source *.blend file you can evaluate yourself the current version of the model, and here is the source Inkscape file of its textures.

 

[Wurger]

Great, just great !!!

 

[Gnomey]

Lovely work so far!

 

[Witold Jaworski]

Wurger, Gnomey - thank you!
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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 below 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.

Let's see how it works in practice. I created the right side of the center wing by mirroring its left side (see figure "a", below). Initially, the texture image is symmetric, because mesh faces from both sides are mapped onto the same areas in the UV space:

Then I drew the asymmetric elements of the center wing on the image, and "flipped" an L-shaped selection of the corresponding UV faces onto this area (figure "b", above). However, when I looked at the effect in the 3D space, I saw a huge texture deformation (figure "c", above). Why did it occurr?

The reason of this deformation is the Subdivision Surface modifier that I used to smooth this mesh (as well as most of the other meshes in this model). To preserve proportions of the texture image, I enabled its Subdivide UVs option. When I turned on in the UV/Image Editor the preview of the modified (ultimate) UV faces, I saw the pattern as in figure "a", below):

Edges of the ultimate, subdivided UV mesh faces are marked in yellow. As you can see, the Subdivide UVs option "smooths" all inner corners of the original UV layout! Well, I cannot disable this option, ibecause it would deform the texture details, on all mesh faces. Still, it is possible to counter this "inner corner" effect by sharping selected seam edges (i.e. by increasing their Crease coefficent to 1.0). As you can see in figure "b", above), I was able to fix most of the original deformation in this way. However, while I could mark as sharp any of the "rib" edges, I could not do the same for the perpendicular "stringer" edge, because it would change the wing shape. (It would alter the side view profile of the center wing).

All in all, the solution for the wings was to "cut out" from their UV layout "stripes" of the faces that span across whole wing chord. Such a stripe has no inner corners (figure "a", below):

As you can see in figure "b", above, it produces the desired effect. The drawback is that it occupies more precious UV space, and I had to replicate more details on this drawing (for the whole span of such a "stripe").

There are also few differences between the left and the right outer wing:

Strangely enough, aircraft designers usually place all additional stuff like the aileron tab or landing light on the left wing. At this moment I just marked on the wing the contours of these two lights. During the next, "detailing" phase of this project, I will create all of these three details shown in the figure above as separate objects. However, I still have to modify the bump map texture, because of the different rivet pattern around these lights and frame around aileron trim tab. (When there is an element without influence on the rivets/panels pattern, I skip it at this moment. For example: in the left leading edge of the center wing there is small round inlet of the cockpit ventilation air. It does not alter the rivet seams, thus I will recreate it completely during the detailed phase).

Following the experiences with the UV mapping of the center wing, I stripped two full-span bands of the UV faces from the left wing and the right aileron:

Frankly speaking, drawing details of these additional strips in a way that they seamlessly fit the rest of the wing was quite difficult. As you can see, I also made small adjustment on the leading edge seam, on both wings. (It removed the deformation described some time ago in this post, Figure 64-9).

The UV layout depicted above contains three inner corners, all located on the leading edge. This is a kind of a compromise: I used sharp "rib" edges (Crease = 1.0) to minimize the overall deformation of the mesh UV faces around these points. They still bend the texture along their "stringer" edges (as in the case of the center wing, depicted previously in this post). However, in these two particular cases I managed to "hide" this unwanted effect. Figures below show how I did such a thing:

Figure "a", above, shows the fragment around the landing attitude light indicator and its faces in the UV space. This is a simple quad, without inner corners. As you can see, I mapped the inner wing edge as a straight line, to facilitate drawing of the multiple rivets and panel seams that run along it. Figure "b", above, shows the details of the corresponding inner corner in the main part of the mesh. I used a sharp "rib" edge along this seam. Still there is deformation along the perpendicular "stringer" seams, but it is practically invisible. There are two factors that "hide" it:

1. The edges adjacent to the seam edge are relatively close to each other, which minimizes the deformation size;
2. The seam edge runs in "safe" distance between nearest visible element of the texture image (a rivet seam), so the deformation in the UV mapping disappears before it reaches this image;

The possibility to "cut out" such a small part from the main body of the UV faces preserved precious UV space. It also allowed me to avoid duplicating on the texture picture of all the details along the inner edge of the left wing. (It would require a few hours, to fit such a separate fragment to the rest of the picture).

Apart the differences on the bottom of the fuselage, depicted in the first figure of this post, there are also differences between its left and right side:

The circular door of the life raft compartment was located on the port side (you can see it in the last picture from the previous post - Figure 70‑10). The raft was packed in a tube riveted to the starboard skin, creating characteristic circular rivet pattern (visible in the figure above). The door to the baggage compartment was also located on the starboard. There were also differences in the locations of the steps to pilot's cockpit.

The shape of this fuselage is much more complex than the wing. I cannot mark any of its edges as sharp, because it would change the shape of this element. Thus, after the experiences with the wing, I decided that I need to map in the UV space the whole fuselage right side. Fortunately, I preserved some spare space on the original UVTech layout. Now I used it to fit this part:

On the picture above, I marked the newly added objects in orange. The main dilemma was how to fit another fuselage silhouette by replacing as few drawing elements as possible. As you can see, I finally decided to "shuffle" the cowling panels from the left side of the original image into the spare area. It created enough space for the fuselage on the left. Note that I also added the right sides of the cowling panels (because they also were asymmetric: there were two inspection doors on the left side of the cowling).

Figure below shows the source image of the bump textures adapted to this new layout:

My experience tells me that in the future I will have to update some details of this picture, following new findings in the photo material (it is just a matter of time). Avoiding applying the same modification twice, I decided to join into a group all the originally drawn elements that are identical for both sides of the fuselage and belong to the same layer. Then I created a mirrored clone of such a group and placed it over the right side of the fuselage. After I "filled" this contour with all the required clones, I drew the asymmetric details. In the future, when I change contents of any of these groups on the fuselage port side, they will be automatically updated on the starboard.

I drew the other side of the elevator in the same way. In this case, the whole difference is a plate mounted between two ribs. It contains the hole for the trim tab actuator. Of course, I could "cut out" this very mesh fragment, as I did in the case of the aileron. However, in the SBD the elevator is smaller than the aileron, thus I decided to make the "full size" copy of its opposite side. (Just to make the eventual future modifications easier).

In this source *.blend file you can evaluate yourself the current version of the model, and here is the source Inkscape file of its textures.

 

[Wurger]

 

[Gnomey]

Great work so far!

 

[Wayne Little]

Wow...

 

[SANCER]

Hermoso y laborioso trabajo!!
... just great.

Saludos

 

[Lucky13]

Phenomenal work!

 

[Rogi]

Amazing work wow :O

 

[Witold Jaworski]

Wurger, Gnomey, Wayne Little, SANCER, Lucky 13, Rogi - thank you!
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This post is a small digression about a modeling technique that may be useful for those, who would like to build their own 3D models.

There is a detail on the bottom surfaces of the SBD center wing: an opening, made partially in the cover of the fuselage belly:

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.

I had an idea of shaping this recession using so-called displacement modifier. (I used it for a certain purposes in my previous model). It displaces mesh faces along given direction, on the distance determined by the color intensity of assigned texture. (That's why I waited with this detail for the texturing phase). The displacement modifier requires plenty of small mesh faces. I thought that I will generate them by increasing the number of mesh subdivisions in the Subdivision Surface modifier assigned to this cover. Preparing for this, I split the mesh of bottom fuselage in the middle. This operation created two objects, representing the forward and rear part of the Dauntless "bomb bay". I was going to increase the subdivision level in the rear part, which contains the flange.

However, after initial trials I went to the conclusion that the displacement modifier is not optimal solution for such a circular shape with rounded edges. It would require relatively high subdivision level, to obtain this shape with appropriate precision. (It would generate hundreds thousands of additional elementary faces). Too much troubles for such a small detail. Thus I decided to find another method that requires less resources.

Finally I modeled it using a technique that resembles me methods used by dentists. First I cut out in the belly cover circular area around the flange:

To not complicate the mesh of this cover, I did it dynamically, using additional Boolean modifier and an auxiliary cone (the latter as the "cutting tool").

Then I formed around the opening a small ring of faces, and extruded them, creating the basic shape of the flange:

In the next step, I trimmed the extent of this mesh faces using the Boolean modifier and the same auxiliary cone that I used for the belly cover. Then I fitted external edges of this flange to the edges of the belly cover:

Note that, thanks to the Boolean modifiers, I only had to fit these edges along the normal direction of the joined surfaces. It required less work. To further facilitate this task, I assigned a contrasting red color to the rim of the belly cover.

Finally I mapped this small detail on the general UV map (figures "a", "b" below):

The UV map of this patch is a simple projection from the vertical view. So far it looks good – there are no visible seams between the patch and the belly cover (figure "c", above).

Figure below shows the final result on the rendered picture:

You cannot recognize here that this fuselage cover is created from two separated objects – it looks like a single one. This is the effect I wanted to achieve.

Of course, this method of using shared Boolean "tool" for trimming both involved objects is useful for modeling single features stamped in a sheet metal. It would require too much work for modeling more than two or three such objects. (Fortunately, they do not occur too often).

You can examine the details of this mesh in this source *.blend file (this the same file that I attached to the previous post).

 

[Lucky13]

Outstanding work, as always!

 

[Wurger]

 

[Gnomey]

Lovely work so far!

 

[Witold Jaworski]

Lucky13, Wurger, Gnomey - thank you!

Today I will add some basic "weathering" to this bird:
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I already finished the bump map (in the second-last post), so it's time to introduce another texture: the reflection (ref) map. It alters the basic reflectivity (gloss) assigned to the material. In addition, it also alters the material "roughness". (In the typical CG materials the roughness and reflectivity are coupled in an inverse proportion). These two parameters are important, when you have to paint an oil streak or a soot streak. Both are black – the difference between them lies in their reflectivity.

The effects of the ref map are most visible inside these areas of the model that actually reflect the light:

Figure above shows two renders of the same model: the upper one was created without any reflectivity map, the lower one uses a basic ref map. (I created this texture around the technical details of the aircraft skin).

Compare the rivets seams in these two pictures, especially in areas (1) and (3). As you can see, ref map "emphasizes" these elements. In the lower picture the rivets and panel seams look more weathered than in the upper picture. The same applies to the bolts (2). In general, I use the reflectivity map to recreate the weathering and dirt that accumulates on the aircraft. Of course, the dirt pattern of this texture has to be tightly coupled with the corresponding pattern on the color map. (I will describe it in the next post).

I composed the basic reflectivity map in Inkscape, using three overlapped pictures. I briefly describe this composition below, on a representative fragment of the texture: the wing tip. (This fragment is small enough to make visible the minor details of this image. You can also examine the source Inkscape file for the further details). The first component of this texture is a blurred image of the basic rivet seams:

It contains clones of three source layers: Rivets: Dome (turned black), Rivets:Flush, and Shadows. To alter the color of the Rivets: Dome layer clone to black, I used an auxiliary SVG filter that contains just a single ColorMatrix component. Similarly, to blur the contents of this Ref-Details:Blur layer, I used another SVG filter, that contains a GaussianBlur component.

The other component of this texture emulates the small, random dirt and scratches that accumulate around all seams. I named it Grunge:

I composed this picture from clones of the Lines, Contours, Bumps:Bolt and Covers layers. Their contents is "dispersed" here using a special SVG filter. (For details of this solution, see "Virtual Airplane" guide, chapter about Inkscape, section about the dirt effect). I used here a new layer Contours, which I have not mentioned in previous posts. It contains just outer outlines of some selected elements (for example – cowling panels), drawn using thicker black line. (Such a line adds additional dirt along their edges).

I placed the dirt image (Ref-Details:Grunge layer) over the blurred panel lines (Ref-Details:Blur layer), and placed on top of them another layer named Ref-Details:Other. It contains clones of the Rivets, Fabric:Stripes, Covers, and Bolts layers. The idea is that this layer "clears the dirt" off the protruding skin elements (that's why the clone of originally black Rivets:Flush layer is white here). Figure below shows the final composition of the Ref-Details texture:

The basic elements of this image – clones of the source layers – will update automatically, when I change one of the original layers. This feature is important for me, because I often have to introduce small corrections to the model, even during the last, detailing phase of the project. (You never know, when you find a new picture or drawing, which reveals that a particular detail in your aircraft had a different shape). Some of these corrections require corresponding changes in the textures. The automatic update of the three basic textures (two bump maps, and this reflectivity map) is a great help in such a case.

I exported contents of the Ref-Details layer into a file named ref_details.png, and connected it to the material scheme:

Because this Inkscape image re-uses the same components as in the bump maps, the reflectivity texture uses the same UV layout (UVTech). I connected this texture to two sockets: Ref Image and Dirt Image. The max. (i.e. basic) reflectivity is controlled by the Reflectivity parameter, while the contents of the ref texture decreases this value locally, in appropriate areas. The intensity of this effect is controlled by the Range parameter in the auxiliary Range To Max control node. To control the dirt effect I use the Dirt Intensity parameter (there is no need for another Range To Max control node on this line, because the basic Dirt Intensity = 0). (For explanation of the inner details of the X.Textured Skin group, see "Virtual Airplane" guide, chapter "Texturing the Model", section "Summary").

The dirt is hardly visible on the metal surface kept in the "natural finish". (You can see the effect of this reflectivity map on such a surface in the first figure in this post). Om this example I switched the material to the non-specular Navy Blue-Gray color (see figure above). The U.S. Navy and Marines used this color to paint the upper and side surfaces of their aircraft in 1941, 1942 and 1943. This is just the first approximation – a solid color for all surfaces. (I will create the proper color texture in the next post).

Figure below shows the result of applying the reflectivity/dirt map (connected as in figure above) to a low-specular surface:

Still, the aircraft depicted in the figure above seems "too clean".

To further enhance this dirt pattern, I combined the original image with a random "noise" pattern (see figure "a", below). This random pattern is composed from two different Noise Texture nodes of different size. One of them creates big darker and lighter "clouds". I set the intensity of the General Noise texture (in the accompanying Range To Max node) so that its darker "clouds" have similar shade to the elements of the of the ref_details.png image. It makes the resulting dirt/ref pattern less regular (see figure "b", below):

The other component of the General Noise pattern creates a "white noise" of small darker and lighter spots (see figure "c", above). It resembles the real micro-dirt, dispersed evenly on the whole aircraft surface.

On all SBDs you can see anti-slip stripes running along both sides of their fuselages. Its surface was painted in the factory with a special "rough" paint. It seems to have much lower light reflection than the rest of the aircraft surface. I will recreate this reduced reflectivity of this strip on the ref texture, while I will paint it in black later, on the color texture.

It seems that the anti-slip strip is longer on the restored aircraft than on the photos of the original SBDs. To determine its true (i.e. original) size and location, I used the archival photos, as well as the contemporary photos of the few SBD wrecks (taken before their reconstruction). Below you can see two of these photos:

Figure "a", above, shows the original state of the SBD-5 restored by the Pacific Aviation Museum, while figure "b", above, shows the SBD-3s on the deck of USS "Enterprise", on April 4th​, 1942. It is a good photo, because it shows multiple aircraft belonging to the same squadron. You can see on these bombers that the anti-slip stripes extend from the trailing edge to the main spar of the wing. Precisely the same span you can see in the original SBD-5 from figure "a", above. However, on some airplanes that I saw on the photos the anti-slip strip is extended over the main spar, into the area that I marked in figure "a" with white outline. I suppose that this forward part of the strip could be painted in black by the local crews. It seems that they used various paints for this purpose, sometimes even the glossy ones.

At this moment I recreated this strip in its standard shape: from the trailing edge to the main spar. For this (and other, similar) purpose I made an auxiliary reflectivity map, and named it ref_aux.png (see figure "a", below):

You can see that I drew the anti-slip stripe in black there – this means that this area will have the minimal reflectivity (and maximum roughness). Thinking about the eventual glossy fragment at the end of this strip, as well as the oil streaks that I will paint in the next post, I set its background color to neutral gray (50% black). All the glossy elements will be lighter than this color. In addition to the strip, I decided to decrease the reflectivity of the fabric-covered control surfaces. (The fabric surface is rougher the metal surface, even when you paint them using the same paint). Because this difference in material reflectivity is not as intensive as on the anti-slip strip, I filled the aileron, elevator and rudder outlines with a dark gray instead of black.

Figure "b", above, shows that I mixed these auxiliary and basic ref maps using a Multiple node. This means, that now the background color of the resulting image is close to the neutral gray (it was 92% white, before). To compensate this difference, I had to increase the basic Reflectivity (the parameter in the X.Textured Skin group) to the maximum.

Below you can see the results of applying this additional ref map:

In figure "a", above, you can clearly see the anti-slip strip as a dark area on the center wing. Similarly, the fabric-covered aileron is also somewhat darker than the rest of the wing tip surface. However, this effect depends on the incoming light angle. When you look at this model from the opposite direction (as in figure "b", above), you will notice that these areas are lighter! In the real world, you can find the same effect on the photos of the aircraft painted with non-specular paints.

Figure "c", above, shows the final effect of the reflectivity maps, created in this post. In fact, this is just a beginning: this texture represents an "overall dirt", evenly dispersed on the whole aircraft. Now I have to add the soot and oil streaks that appear on every real piston-engine airplane. The radial R-1820 engine (and especially its exhaust stacks) provided plenty of interesting patterns on the SBDs fuselages and center wings. However, I want to paint this dirt simultaneously on the reflectivity map and the color map. Thus in the next post I will prepare the basic color (diffuse) texture, then we will return to the "dirt painting".

In this source *.blend file you can evaluate yourself the current version of the model, and here is the source Inkscape file of its textures.