SBD Dauntless (from scratch)

[Witold Jaworski]

In the previous post I formed horizontal tailplane of the SBD Dauntless. In this part I will describe how I created the fairing between this tailplane and the fuselage. It is an easier part than the wing root fairing, because it is smaller and most of its cross sections are not circular.

At the beginning I cut out from the stabilizer its middle segment, along the root rib:



Then I “draw” the outer contour of this fairing in the side view. I also checked it in the reference photo (as you can see in the figure above).

Then I projected this “sketched” outer contour onto the fuselage. I did it by extruding its polyline into a face strip that crosses fuselage surface (figure "a", below), then finding the intersection edge of this mesh with the fuselage (figure "b", below):



The intersection edge was calculated by one of my Blender add-ons (named Intersection — you can download it from here). In general, it would be easier to extrude this edge horizontally (because I sketched this contour in the side view). However, I was afraid that the add-on will lost the track of the upper rear part of this mesh (the part that crosses just the upper tip of the fuselage surface). That’s why I initially shifted this contour close to the fuselage, and extruded it in a more-or-less perpendicular direction to the fuselage surface.

All in all, after this operation I have the three edges, which is enough to create the first version of a smooth fairing:



Figure below shows the initial smooth, subdivided mesh based on these three edges:



It starts to resemble the original element. I created here the new row of faces, from the middle edge to the outer contour. Then, before creating this screenshot, I switched the display mode to the resulting subdivision surface.

To have better control over the shape of this fairing, I inserted two additional edge loops into this mesh



These additional vertices were extremely useful in shaping the bottom edge of this fairing, which had a semi-circular cross section:



In the most of the aircraft designs the fairing is just a piece of sheet metal bolted over the fuselage skin. In the SBD Dauntless it was an integral part of the fuselage skin (except the area around the stabilizer leading edge). Thus I had to extend the bottom part of this mesh, copying the fragment of the fuselage surface (as you can see in the figure above).

Figure below shows the finished fairing. As you can see, it smoothly fits the fuselage:



It was not necessary, but I also created the rear spar of this tailplane — just because I do not like to see a large empty space in a finished element (the fuselage is not finished, yet!).

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

In the next post I will create the fin and the rudder.

[Witold Jaworski]

This week I have worked on the SBD vertical tailplane. I started by forming its root airfoil (see the figure below). I had no description nor a direct photo of the airfoil used here. However, the reference photos reveal that it could have similar shape to the airfoil of the horizontal tailplane. Thus I copied that curve into this mesh.



Note that I used here a thin strip of the faces instead of a single curve (which I used in the case of the horizontal tailplane or the wing). The reason is simple: on the single subdivision curve I cannot mark a “sharp corner” at a control point (original mesh vertex). On the face “strip” I can mark the corresponding edge as sharp (increasing its Crease coefficient to 1). I marked in this way the edge at the split between the rudder and fin. Simultaneously I can form such a face strip in the top view as easily as a single curve. (I just have to remember to select its vertices using the group select commands (Border-select or Circle-select), instead of the simple mouse click). Why didn’t I use this method in the previous cases? Well, good ideas require some time to emerge…

Once the root airfoil was ready, I extruded it into the basic trapeze:



Then I split this mesh into the rudder and fin (i.e. into separate objects, as in figure below):



Note that I added additional “rib” edges to the mesh of the fin. They will be useful in forming the forward fragment of this part.

Initially, I extruded the first approximation of the dorsal fin from the bottom edges of the lower ribs:



However, I decided that the resulting topology of this mesh differs too much from the original layout of the panel seams (and the original ribs and spars). To make a better approximation, I used the fin shaped in the previous step as the reference object (in the figure below it is in red):



I cut out the forward part of the original fin, forming in this mesh the first vertical edge. Then I extruded it into next segment:



The next segments were extruded in similar way:



In each new segment the vertical cross section is significantly smaller than in the previous one. I had to compensate it by cutting out its bottom fragment (using the Knife tool — as in figure above) and reducing the number of remaining faces.

Figure below shows the resulting dorsal fin:



The tip of this fin was formed in an unusual way — it was stamped in the cover of a fuselage hatch (as you can see on the photo). I will form this cover later.

Figure below shows the objects created in this posts:



You can examine them in this source *.blend file.

In the next post I will describe my work on the fairing of this fin (it seems quite simple, but occurred more difficult than I expected!).

[Witold Jaworski]

In the SBD Dauntless the fillet along the fin and the fuselage was formed from the bent bottom edges of the fin panels. I am showing it in the figure below:



(To make some of these panel seams more visible on thee photos, I sketched along them thin lines). You can observe that each fin panel overlaps the next one, starting from the tip stamped as the part of one of the fuselage doors (see the second-last figure in the previous post). The outer contours of these panes are not perfectly aligned: you can see small overlaps on the photos (see the figure above). Surprisingly, such a detail makes the modeling more difficult. However, the most difficult part will be the seam between the fin and the horizontal tailplane fairings (as in the figure above). It runs along the fuselage longeron, across the fillet between the stabilizers and fuselage.

Well, I started this fillet by extruding some faces from the bottom edges of the fin mesh:



As you can see, I already recreated the sharp panel corners in these extruded faces. Then I lowered their outer edges and aligned them to their contours on the top view:



This is the first, rough approximation that fits these panels to the fuselage surface. In this process I discovered that I had to make some modifications to the upper part of the tailplane fairing. However, I was not entirely satisfied with the result: comparing to the photos, something was wrong at station 242 (see the figure above). The outer seam of the fin fillet should be a little bit wider here!

After some additional deliberations I decided that the fuselage under the fin was somewhat higher (by about 0.5”) than on my reference drawings, and the upper arc of these bulkheads had larger radius. Thus I had to modify this part of the fuselage:



I rotated a little this mesh fragment, then scaled up the upper part of each of its three bulkheads.

I had no photo of the SBD fuselage without the fin, taken from the side. In fact, the shape of this fragment on my scale plans is in 80% my assumption! Such small anomalies as this one helps me to discover the real shape of this airplane.

Basing on the corrected fuselage, I was able to fit better the outer edges of this fin to the fuselage and the tailplane fairing:



However, I was not satisfied with the forward part of the seam between these two fairings: despite all my efforts, it looked a little bit sharp!

Ultimately, I had to reshape a little bit the tailplane fairing and cut out the excess of its surface along this seam using a Boolean modifier:



This method produced results that resemble the smooth shape that I can see on the photos:

However, I do not like such a “Boolean – based” solution. It seems too complicated. In the next post I will try to eliminate such a “hard” seam between these two panels. I think that much better solution here will be a continuous, smooth surface. The seam can be recreated later, using textures.

Anyway, in this source *.blend file you can evaluate yourself the model from this post.

Edited April 2, 2016 by Witold Jaworski

[Witold Jaworski]

After the previous post I decided to simplify the empennage fairing. Originally I created it from two separate objects: the fin fairing and the tailplane fairing, split across their fillet. Now I decided to eliminate this troublesome seam by joining these two meshes into single object:



I will split it later, along the bottom rib of the fin (there was another panel seam in the real airplane). To simplify creation of the original overlapped panels, I simultaneously split the fin into the forward and the rear part, along one of the original seams.

As you can see in figure above, there are the same number of spanwise edges on both fairing meshes. It is a matter of sheer luck, but it makes the process of joining these two parts much easier.

First, I modified these edges, bringing them closer to each other. (I did it by sliding their vertices along perpendicular edges — as you can see in figure "a", below):



Then I removed the unnecessary faces (as in figure "b", above).

Finally I filled this gap with new faces, effectively merging these two meshes (figure "a", below):



In the side view (as in figure "b", above) you can see that the forward part of the fin extends a little the panel line visible on the reference drawing. It will be overlapped by the forward part, which will end precisely along the original seam. (Such an overlap is visible on the photos). Note also that the seam along the fuselage upper panel (marked on the drawing by the dotted line) is somewhat higher than on my scale plans. This is the effect of the modification that I made in the upper part of the fuselage (described in my previous post). My reference drawings are simply wrong about its location in the side view.

I think that the empennage fairing looks much better after this modification:



It fits well all the three elements it joins: the fuselage, the fin and the tailplane. The fillets looks smooth and natural. As you can see, I split the fin and the fairing along the bottom rib edge, as I planned. (There was original panel seam). I think that this new arrangement of the model objects will facilitate further detailing of this assembly (for example, now the forward fin panel overlaps the other elements, as in the real airplane).

The last element of this assembly is the fin tip: in the real airplane it was stamped in one of the fuselage inspection doors. I started to form this part by creating a plain, rectangular cover placed over the fuselage, and separating the corresponding fragment of the fin tip (figure "a", below):



Then I joined these two object into a single mesh (figure "b", above).

In the next step I adjusted corresponding edges of both elements, and removed the unnecessary faces (figure "a", below):



Finally I filled this gap with new faces. Finally, after some rearrangements of the mesh topology, the resulting elements looks like in figure "b", above).

Figure below shows the final object, fitted to the fin and the fuselage:



The last element that I need to finish in this empennage is the rudder leading edge. I created it in the same way as the leading edge of the elevator: from a single circle (see my post from January 9th). I extruded it into a cone (figure "a", below), then removed the unnecessary faces and created new ones (figure "b", below):



Figure below shows the completed empennage (note that I also created the fin spar):



The last missing element is the tail tip. It has a rather complex shape, so I started modeling this part by copying its outer edges from the fuselage, fairing, rudder and elevator. You can see them in the picture above. I do so when I have no clear idea how to start. In the next post I will describe what I did next.

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

[Ex-FAAWAFU]

It's been a while since I caught up with this; amazing work. Your attention to detail & determination not to just settle for "close enough for Government work" is awesome.

[Witold Jaworski]

It's been a while since I caught up with this; amazing work. Your attention to detail & determination not to just settle for "close enough for Government work" is awesome.

Thank you very much! I will do my best (I am not especially quick, as you can see in this thread, but this is my "hobbyist" pace - I hope you will understand )

Edited April 9, 2016 by Witold Jaworski

[Witold Jaworski]

The tip of the SBD tail was a light fairing, attached to the last bulkhead (at station 271 — see figure "b" below). That’s why you can see “NO PUSH” label on the photo in figure "a". The tail wheel was attached to the bulkhead 271, which transferred the resulting loads forward, via the tail structure. The tail tip fairing was always free of any significant loads. However, the shape of this part is a combination of the empennage fairing and the last fuselage segment. What’s worse, there is a large opening at the bottom — for the eventual tail wheel deflection:

I had no initial idea about the mesh topology that I should use for such a part. Thus I started by copying all of its external edges from the adjacent objects (see figure "a" below):

Then I worked out an idea of its topology by sketching possible mesh edges on a scrap of paper. (I often do that before I start modeling a complex mesh). You can see the scan of my sketch of this tip in figure "b", above. I “think by drawing”, so this method helps me to better realize the shape that I have to create. These working sketches object do not have to perfect. The more important thing is the order of the individual edges and vertices (identified by the numerical IDs).

When the mesh topology on the sketch looked simple enough, I started building this mesh by extruding the trailing edges of the elevator fairing (see figure "a" below):

Then I extruded the upper edge of the elevator fairing into another rectangular “patch” (see figure "b", above). In the next step I extruded similar “patch” from the rudder contour (see figure "a", below):

Finally I filled the gaps between these three mesh “patches” by creating two rows of new faces (as in figure "b", above).

The resulting subdivision surface required some minor adjustments of the control mesh vertices. They formed the proper shape of the mesh behind the elevator trailing edge (figure "a", below):

While sketching this tip, I decided that it will be better to close it with a separate object — the “closing strip”. Such a strip reproduces the original piece of the sheet metal that contained the frame of the running light. (I thought that the side-view contour of this tail tip might require different edge distribution than the mesh of its sides). At this moment I created the initial segment of the “closing strip”: the part around the running light frame. Then I used it as the reference object for shaping the mesh of the tip sides (see figure "b", above)

I split the model surface into separate objects when I expect significant differences in their mesh topology. I “mask” outer edges of such objects by placing them along the original panel seams.

When the upper part of the tip was ready, I started forming its bottom part. As you can see in figure below, I did it in the same way as the upper fairing. First I extruded a part of the bulkhead contour (figure "a"), then I created new faces to incorporate this patch into the main mesh (figure "b"):

I extruded the side faces of this tip from the bulkhead edge (figure "a", below), then filled the gap in the resulting mesh by creating a row of new faces (figure "b", below):

(Note that I had to create more “bulkhead” edges in this mesh than I originally sketched (see the second figure in this post). Some of these edges came from the original vertices of the elevator edge, while the other were required by the shape of the bottom edge (around the tailwheel opening).

The ultimate number of edges in a mesh is often the sum of the vertices required to obtain appropriate shape on its opposite border edges.

Finally I extruded and merged the last part of this tip:

As you can see in figure "b" above, I added an additional, diagonal edge below the trailing edge. I did it to obtain a better shape of the elevator fairing

Figure below shows the smooth resulting shape:

I had no photo taken from the top or the bottom that would precisely reveal the vertical contours of this part. Thus I assumed that this tip is a smooth continuation of the tail cone (as I marked with the dashed line in Figure 38‑9). In the next post I will verify this assumption using available photos.

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

[Witold Jaworski]

In the previous post I formed the shape of the SBD Dauntless tail tip. In this post I will finish its “closing strip” that contains the running light frame. I will also verify the overall shape of the tail tip using the available photos.

There is one thing I didn’t mention in the previous post, just to keep the narration focused on the pure modeling. Before the modeling I carefully studied the reference photos. In the result I found differences in the shape of the curved trailing edges of the fairing behind the elevator. On the photos you can see a straight fragment of this edge (figure "a", below). Its presence means that the curve of the trailing edge was smaller, and the fuselage was somewhat thinner here. You can see the differences between the real shape and my reference drawing in figure "b", below:

I did not notice these detail before. As you can see, I applied this modification when I started to model this part.
When the mesh of the tail tip was formed, I worked on the “closing” strip. I created a part of it as a separate object in my post from 2016-02-13. Now I extruded it along the side contour (see figure "a", below), then extruded the side faces of this strip (figure "b", below):

I rounded the sharp edges of this element with a fillet. It is dynamically generated by a multiple-segment Bevel modifier — you can see the result in figure "a", below:

However, when I compared the bottom part of this tip to the photos, I saw that there are significant differences! Jut compare it in figure "a" and "b" above. The side edges of the tailwheel opening are less curved, and its rear edge is wider.

What is the reason of these differences? So far I tried to shape the bottom part of this tip as the smooth continuation of the previous tail segment (see figures "b" and "c", below). It seems that I was wrong: these lines were broken at station 271, where the tip fairing was attached to the last bulkhead of the tail (see figure "a", below):

To correct this shape, I first made the tailwheel opening wider by rotating the bottom part of the mesh:

Finally I adjusted the shape of the “closing” strip to this new opening (figure "b", above). Now it resembles the original in the photo.

When I fixed the shape of this opening, I noticed another difference, this time in the shape of the tip cross-section. It is revealed by the vertical panel seam behind the tailplane:

This vertical seam seems to be flat, especially in the restored SBD from figure "b", above. In my model this line is much more convex (figure "c", above).

The primary reason of all these differences between my model and the real airplane is the lack of the reference: I have no photos of this fuselage tip taken from above. Thus I have to determine its shape on the plans by various indirect means — and assumptions. In such cases, when you shape it as a 3D model, you will often find errors in the reference drawing.

Well, to make this section more “rectangular”, I have to make the fuselage even thinner in this area:

Yet the photos reveal another small difference, this time between the two different restorations of the SBD Dauntless: compare the photos "a" and "b" in the second-last figure above. The aircraft from photo "a" has the edges of the tailwheel opening bent inside, while in the SBD from photo "b" the tip cross-section contour is straight to the end. Which one is true? At this moment I do not know! However, it will be better to modify the mesh of this tip in a way that makes such a rounding possible. (You can always straighten a curved surface. However, bending a flat mesh requires additional edges). That’s why I modified the mesh topology around this opening, adding another “longeron” edge (figure "a", below):

Then I shifted two bottom edges a little (figure "b", above), forming such a cross section as you can see in photo "a" (compare it with the shape in figure "c", above).

Below you can see tip, finished for now:

I will recreate its internal reinforcements (bulkheads, stringers) later, during the detailing phase. At this moment I do not know whether I have to modify this part in the future. (It may happen when I find a better reference materials). Such a modification would require adjusting these internal structures, so it is better to postpone their creation as long as possible.

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

In the next post I will start to work on the engine cowling.

[Witold Jaworski]

SBD Dauntless had a radial engine hidden under typical NACA cowling. The Douglas designers placed its carburetor air intake on the top of this cowling, and the two Browning M2 guns behind it. In the result, the upper part of the SBD fuselage, up to the pilot’s windscreen, had a quite complex shape:

I am sure that I will tweak this shape multiple times before I reach the most probable compromise between all the reference photos I have. It will be much easier to do it by modifying a simple mesh instead of the complex topologies of the final cowling. Thus I decided to create first a simpler version of this fuselage section and adjust it to the all of the available photos. I will describe this process in this and the next post. Once this shape “stabilizes”, I will use it as the 3D reference in forming the ultimate cowling. Because I am going to recreate all the internal details of the engine compartment, I will create each cowling panel as a separate object.

I started by creating the three key contours of the NACA cowling:

Section 1 (see figure "b", above) was a perfect circle, while section 2 was a little bit higher than wider (see figure "a", above). Ultimately section 3 was a regular ellipse. Note that all these sections have the same number of the vertices (32).

Once I created these three edges, I connected them using three arrays of faces. Them I added in between (using the Loop Cut command) three additional edge loops. I needed them to form the curved forward part of this cowling:

As you can see above, I fit the silhouette of this NACA cowling to the reference photos. This is a photo of the SBD-5, so I moved this cowling forward by 3.5” (see in this post about differences between SBD-3 and SBD-5 cowlings Figure 4-6, for the explanation).

When I finished the NACA cowling, I formed the basic shape of the next fuselage section:

I created this part in the same way as the previous one. First I copied and shrunk the last NACA cowling edge, creating the gap for the outgoing air. Then I copied the firewall edge, and joined these two edges by an array of new faces.

In the next step I extruded the upper part of this surface, creating the section below the windscreen:

It is a “linear” continuation of the previous fuselage segment. I fitted its sides to the mid-fuselage, which I formed some months ago.

The next elements are the “bulges” that covered breeches of the Browning M2 guns. In this ‘quick and dirty’ approximation I formed them from a separate mesh patch (see figure "c", below):

Of course, I verified their shape on the available photos, as you can see in figure "c", above.

This comparison revealed, that the intersection lines between these “bulges” and the main fuselage require some improvements: they have to resemble straight lines:

To obtain such an effect, I had to decrease the upper radius of the last bulkhead (figure "b", above). In such a simple mesh it required just to move a few vertices. If I had to perform such an operation on the final panels, it would be much more difficult!

In the front of the gun barrels there were long recesses in the NACA cowling. The outer edges of such a feature are always a tough test for the model, because they depend on the proper shape of the both intersecting elements. First of these objects is the NACA cowling, the second is the shape of this recess — a cylinder in this case:

I cut these openings using a Boolean modifier. Figure below shows the result:

In figures "b" and "c", above, you can see the evaluation of the obtained contours. They seem to fit the borders of the recesses on the reference photos. (There are minor differences, but I suppose that they are results of the rounded edges of these features.

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

In the next post I will continue shaping this first approximation of the engine cowling.

[markleecarter]

Amazing stuff!

[Witold Jaworski]

Thank you, @markleecarter!

In this post I will continue my work on the engine cowling. I started it in the previous week by forming a “first approximation” of the forward part of the SBD Dauntless fuselage. Now I will create the last elements of this auxiliary object.

First of them are the covers around the M2 gun barrels. They were hinged around their inner edges, and their cross-section varies from a semi-circle at the NACA cowling to a flat line at the firewall:

I started forming this cover from a conic cylinder, created around the gun barrel:

Then I cut out its bottom part and flattened its end section along the side “bulge”:

I formed it to resemble the gun barrel covers as they were in the SBD-1..-4s. Studying the photos I identified that this detail looks a little bit different in the SBD-5 and -6:

As the last element of this auxiliary object I will form the windscreen. I need it for determining the ultimate slope of the “bulges” around the breeches of the M2 guns, and for checking the shape of its intersection with the fuselage. (If I did it later, it could reveal some unexpected surprises about the fuselage geometry, resulting in additional work).

I used the reference photos to determine the basic radii of the canopy hood and the windscreen cross sections:

(In this aircraft canopy hood slide under the windscreen, thus the radius of the windscreen cross-section was a little bit larger). As you can see in Figure "b", abve, the obtained contours differs a little to my reference drawings. (It seems that on these drawings the top of the cockpit canopy is a little bit lower than I have ultimately found it now on the photos).

In the next step I determined the radii of the cylindrical fragment of the windscreen:

It seems that it was not a regular cylinder — its radius at the top of the windscreen seems to be larger than the radius at the bottom (figure "a", above).

I created this cylinder as the first part of the windscreen surface (figure "a", below). I verified its shape using another reference photo (figure "b", below):

In the next step I removed the rear part of this cylinder and formed the flat, triangular side plates of the windscreen. As you can see in figure "b" above), they were hinged, providing the maintenance access to the M2 guns on the cockpit sides.

Then I extruded two additional rows of faces, forming the upper part of the windscreen (figure "a", below):

When the shape of the intersection between the windscreen and fuselage matched the reference photos, I also verified its side contour (figure "b", above).

Figure "a" below shows the complete object that approximates the shape of the SBD engine cowling. I set its color to red, as I do for all the reference objects in this model:

In figure "b" above you can see that it fits pretty well the reference photos. This is a picture of the SBD-5 from Chino Air Museum. The SBD-5 and -6 had their engines and the NACA cowlings shifted forward by about 4”, so did I in this model (see in this post Figure 4-6 for details).

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

Edited April 20, 2016 by Witold Jaworski

[Witold Jaworski]

In this post I describe a break in the modeling that I made this week, because I had to fix my reference photos before the further work. The reason for this fixing was simple: the NACA cowling of my model did fit only the long-lens photos. For the further work I needed more information. This information was available in the high-resolution photos made by the Pacific Aviation Museum Pearl Harbor. However, they are slightly distorted.

In the ‘mathematically ideal perspective’ calculated for the computer cameras all of the straight lines remains straight. Unfortunately, the real-world camera lens can slightly deform (bend) the straight contours. This is so-called ‘barrel’ (or ‘cushion’) distortion of a photo. Unless you are using a panoramic lens, this deformation is hardly noticeable for the naked eye. Unfortunately, these differences become evident when you place a photo behind a 3D model, projected by a computer camera.

In case of reference photos that I used to verify my SBD Dauntless, the differences caused by the barrel distortion are visible around the forward part of the engine cowling:

It is really difficult to find the precise shape of this airplane on such a deformed photo. Thus I started searching the Internet for a method that would allow me to revert this deformation. First I encountered some advanced tools, like Hugin software. However, it seems to require series of similar photos to make a really improved picture. None of my single photos met this criteria.

On the Internet I also found some general scientific/engineering papers about the barrel distortion, as well as the tutorials how to fix it (for the architectural visualizations). They advised to use some originally straight contours/lines visible on the photo to estimate the image distortion. Indeed, for the photos as above, I can use the splits between airstrip slabs as such a reference:

I marked these lines on the photo above using dashed line. To see better their deformation, I draw along them straight lines, in blue. Note that these straight lines are tangent to the dashed lines on the left side of this picture. On the right side of this picture you can see maximum deformation of these split lines. This is the evidence of the barrel distortion.

I tried to reverse barrel deformation of this image using these split lines as indicators. I used a simple Lens Distortion filter from GIMP 2-D graphic program. The idea was that when I apply a deformation that makes these lines straight. Maybe such an operation will reverse the whole barrel distortion in this photo?

Figure below shows the Lens Distortion filter dialog window (GIMP), which I used to find the proper “reverse deformation” for this photo:

As you can see I used only the first (Main) parameter of this filter. I decreased its value until the split between the airstrip slabs on the preview became straight.

Then I matched the projection of my 3D model to this photo:

This is really a rough, approximate method, but the obtained results look really promising! Now the whole cowling fits the modified photo!

If it worked well for this picture, I tried it on another one:

The SBD fuselage spans over the whole length of this photo, thus the barrel distortion is more visible here. You can see it in the fin and the last bulkhead (see figure "a", above), as well as in the engine cowling (see figure "b", above). However, the contour of the hangar roof was a great reference for the reverse deformation. What’s more, the GIMP dialog windows preserves the last used parameters. Thus I even did not have to adjust again the Lens Deformation filter! The same value of Main = -6.8 (as set in the filter dialog window - see the third figure in this post) made this hangar roof ideally straight. Both photos come from the same source, and their EXIF data reveal that they were made by the same camera. Thus I think that this deformation value is the “constant” property of this particular camera, which is repeated in each photo it made.

As you can see in figure above, after reverting the deformation, this picture perfectly matches the 3D model over the whole length, from the cowling to the fin.

During careful examination of all the nook and crannies of the fuselage, I encountered the difference at the root of the tailplane. In my model this rib seemed little bit shorter than in the photo (figure "a", below):

When all other element of this section fits the photo, such a gap means a real difference between my model and the original airplane. After some tweaks I decided that this rib was less deflected from the fuselage centerline (figure "b", above). (It seems that I made wrong estimation of its angle when I sketched these drawings). In fact, this rib run in parallel to the fuselage surface. Figure "c", above, shows that such a modified rib fits the reference photo pretty well.

As in the science: the theory is widely accepted, when it allows you to discover something previously unknown. These updated photos allowed me to find another error in my model!

I quickly converted most of the other photos from the same air museum. Unfortunately, I encountered the limits of this simplified method, when I tried it on the photos taken from a ¾ view:

I could not fit the model to the modified version of this photo! I had to revert to the original picture and its matching (using a slightly different lens length co compensate most of the barrel deformation).

It seems that the simple method of applying Lens Distortion deformation works only for the objects set in parallel to the picture plane.

For the consolation, I scanned again the Google image search (I have not done it for over four months). It was a fruitful idea, because I found two new reference photos, made by a long-lens (600 mm) camera. (They were published in this post from General Aviation News blog). The first of these pictures is even more banked aircraft than I have found before:

In spite of the same Navy blue camouflage, this is a different SBD-5 from Commemorative Air Force (note its '5' side number). It allows me to verify the important details of the vertical view: the width of the fuselage or the shape of the engine cowling. As you can see, the model fits this photo pretty well. In particular, I found here the confirmation of the new deflection angle of the tailplane root rib.

Another photo is an extremely high resolution (5400 x 3600 px) picture of the same aircraft, taken during landing. It allows me to check better the side view details:

Ultimately, on such a detailed picture I was able to find the dynamic deformation of the wing: it is slightly bent upward, so its tip is no more than an inch above its non-loaded location. The Dauntless wings were as stiff as in the fighters!

In this source *.blend file you can find one of these updated photos.

In the next post I will start to work on the NACA cowling details, using the reference objects formed in the two previous posts.

[hendie]

5 pages in and I'm still astounded by the quality and depth of your research and also your software skills

[Witold Jaworski]

Thank you hendie, I will do my best!

In this post I will shape panels of the Dauntless NACA cowling. Working on the scale plans a couple months ago I came to the conclusion that the basic shape of this cowling was the same in all the SBD versions (see Figure 4.6 in this post). You can find the differences in their ‘ornaments’, like the sizes and locations of the carburetor air intake, or the number of their cowling flaps. Thus I used the high-resolution, long-lens photo of the SBD-5 (described in the previous post), to determine the ultimate shape of this cowling, and the split lines of its panels (figure "a", below):

Basically, the SBD Dauntless NACA cowling was split into a single upper panel and two symmetric side panels. I started by copying corresponding part of the reference shape (created in this post) into the single side panel (figure "b", above). The subdivision surface of such a 120⁰ mesh ‘arc’ is somewhat flat at both ends. Thus I had to tweak a little mesh edges in these areas, fitting them to the reference contour.

In the next step I extruded the ‘strip’ that overlapped the upper panel (figure "a", below):

I also marked the bottom edge of this panel as sharp (figure "b", above). In fact, the right panel overlapped the left panel along this line (they were similar, but not identical).

What’s more, in the SBD-5 and -6 the split line between these panels was shifted left by about one inch. Nevertheless I decided that I will split these two panels later, during the detailing phase. At this moment I just dynamically mirrored the left panel using modifiers. It will be easier to unwrap in the UV space this single element, then copy its unwrapped mesh and form the right panel during the detailing phase.

To keep the topology of this mesh as simple as possible, I decided to cut out the exhaust stacks openings using a Boolean modifier:

The high-resolution photo was a very useful reference for the ultimate check of the shape of this opening. (Its contour contains two arches connected by short straight lines).

In a similar way I cut out the space for the cowling flaps:

Actually, I am preparing the three-flaps sections, as used in the SBD-1.. -4. Note that I used the same auxiliary object to cut the upper cowling panel.

The overlapping ‘strip’ along the upper edges of the side panels was chamfered just on the cowling leading edge (figure "a", below):

It would be very difficult to shape such an effect ‘in the mesh’ here, because of the two-dimensional curvature of this area. That’s why I created it using two auxiliary objects and another Boolean modifier (as in figure "b", above). This was the last detail of this panel, for the modeling phase.

The next element are the cowling flaps. Initially I created them as a three-segment ‘strip’ (one quad face per each flap). I marked all edges of this initial mesh as ‘sharp’ (Crease = 1). Once I determined the size and shape of these basic faces, I added new, internal edges and started to bend this ‘strip’ along the reference shape (red object in the figure below):

When this ‘strip’ was fitted to the reference cowling panel, I added temporary edges connecting their opposite vertices. These auxiliary lines helped me to determine direction of individual rotation axes of these flaps, as well as their origins (figure "a", below):

Then I separated appropriate fragments of this mesh into three cowling flaps (figure "b", above).

Finally I cloned and mirrored the three left cowling flaps into the three right cowling flaps (figure "a", below):

At this moment the right flaps objects have a negative scale, thus for the movement test I have to rotate these left and right flaps separately (along their local Z axes, using the Individual Centers pivot point mode — as in figure "b", above).

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

In the next post I will form the gun recesses in the upper cowling panel. It will be a quite difficult detail!

[Witold Jaworski]

The gun troughs in the aircraft usually are tricky elements. Their edges depends on the shape of two curved surfaces: the fuselage around the recess and the tubular inner surface. When you make mistake in any of these two shapes you have to remodel the whole thing.

In the SBD there are two symmetric gun troughs in the upper part of the NACA cowling. Figure below shows the left one:

As you can see on the photo, these recesses were formed in a separate metal sheet. It was riveted afterwards to the main body of the NACA cowling. I will repeat such an arrangement in my model, because using a separate object for such a feature simplifies its mesh. (I can make this mesh denser than the NACA cowling around it, and still I do not have to worry about the topological implications). The sheet metal around these recesses seems to be relatively thick, which ultimately makes the fitting of this panel to the NACA cowling surface easier. To make some space for this dedicated panel, I created initial openings for the gun troughs in the upper panel of the NACA cowling. They are generated by a Boolean modifier, and are a little bit larger than the final recesses.

The most difficult part of the gun trough in this aircraft is the fillet around its edge. To obtain a high-quality shape, I decided to start this panel as two separate objects. The first of them is the tubular inner surface (copied from the cutting object used in the Boolean modifier). The second object is just a small cylinder, which radius is close to the fillet radius. I will deform it along a 3D curve, which follows the border of the gun recess opening:

When I started to extrude subsequent segments of the fillet cylinder, it automatically follows the assigned curve. (The curve allows me to do it without worrying about preserving the circular cross-section along the whole length of the opening border). Technically, this is the effect of a Curve Deform modifier that I assigned to the cylinder object. This is the first modifier in the stack, and it precedes the smoothing (Subdivision Surface) modifier. Such an arrangement allows me freely slide the circular cylinder sections around the opening border, finding the proper locations for these key vertices:

Then I shifted this resulting contour down, and adjusted its spine curve so that the fillet cylinder barely touches the opening edge.

When the basic cylinder was shaped, I removed (applied) the curve modifier, as well as the unnecessary ¾ of the cylinder surface. The result is a regular fillet, formed around the opening (figure "a", below):

Now I started prepare the inner part of this recess for joining with this fillet. I had to add some additional sections. They are placed at the corresponding sections in the fillet mesh (figure "b", above).

When all the edges of the inner recess mesh were verified and adjusted to match the filet, I joined these two objects and removed the unnecessary faces (figure "a", below):

Then I created new faces that join these two meshes (figure "b", above).

Once the inner part of the recess panel was completed, I started to form its outer part by extruding its outer edge (figure "a", below):

I placed its vertices on the outer edges of this panel (figure "b", above). Then I added another edge loop in the middle and started to elevate the sunken part of this surface above the cowling panel (figure "c", above).

Figure "a" below shows the outer surface neatly fitted to the cowling. As you can see, it requires not one, but two inner edge loops outside the fillet, to reproduce circular cross section of the NACA cowling around this recess:

Finally I used the same auxiliary object as for the underlying panel to cut out the space for the topmost cowling flap (figure "b", above). (It is made using the Boolean modifier).

The gun trough in figure "b", above, looks good enough. However, when I looked onto another reference photo, and then onto another, I slowly started to discover that these recesses had different cross sections! I assumed that it was an arc, while the more I study the photos, the more I came to a conclusion that it had narrower, U-shape cross-section!

Such surprises are common, when you are making a precise model. Thus, do not assume that the progress of your work will go as a "waterfall". It is more similar to a "spiral": you often come back to the completed parts and adjust some of their details. Just keep the objects ready for such situations: they are normal part of the work.

Thats why I still keep as much features as possible implemented as the modifiers applied to relatively simple meshes. Thanks to such an arrangement, the adjustment of the recess shape does not require a lot of work:

First I created a simple auxiliary object as the reference of the correct cross-section shape (white contour in figure "a", above). Then I placed the panel being modified over the reference shape of the NACA cowling (in red). Then I started to shift the complete fillet sections and the near lengthwise edges in the front view, placing them on the new contour. When it was done, I made minor adjustments along the recess edge, shifting the fillet sections until they fit the red surface of the NACA cowling.

The difference in colors helps me to estimate the remaining deviations from the reference surface. I usually shift the modified section downward, until the resulting gray surface around it sinks in the red reference surface. Then I move it minimally upward, so that the resulting surface appears just above the reference object.

Figure below shows the final result: gun troughs in the upper panel of the NACA cowling:

For convenient handling, the gun trough panels are attached to their cowling panel by the parent relation in the internal hierarchy of this model.

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

In the next post I will form another element of the upper cowling panel: the carburetor scoop.

[Witold Jaworski]

This week I have worked on the carburetor air scoop. This scoop passed significant evolution in the subsequent Dauntless versions. In the SBD-1 there was a rather large air duct placed on the top of the NACA cowling (see figure "a", below):

However, it was quickly discovered that it obscures one of the most important spots in the pilot’s field of view: straight ahead and slightly below the flight path. That’s why it was somewhat corrected in the next version (SBD-2). In this aircraft the designers lowered the scoop, increasing the field of view from the cockpit (see figure "b", above). Such a solution persisted in the SBD-3 and -4. In the SBD-5 they completely redesigned it, placing the carburetor scoops inside the NACA cowling (more about this — see in this post the paragraphs around Figure 11-6).

Close examination of the various reference photos led me to the conclusion that in the SBD-1 the air duct ran between the inner surfaces of the scoop and the top of the NACA cowling (figure "a", below):

There was a rectangular opening in the rear part of the cowling, located just above the Bendix-Stromberg carburetor of the R-1820 engine. (There was a short, vertical duct inside the NACA cowling from this opening to the carburetor intake. I will model it later, together with the engine).

The later scoop version (from the SBD-2, through SBD-3, up to SBD-4) was a typical “quick and dirty” solution for the identified problem. The designers could not split the upper panel to place the lowered air duct there, because it would hinder the stiffness of the whole NACA cowling. Instead, they cut out another rectangular opening in its leading edge (figure "b", above). In this way a half of the incoming air went to the engine as before, over the NACA cowling. However, the bottom part of the air stream was directed below the cowling surface. Both streams were joining inside the rear opening, before they went into the carburetor.

I created both openings using Boolean modifiers:

Then I started by forming the lower part of the air intake. I started with a single strip fitted to the side edges of the frontal opening (figure "a", below):

Then I extruded this edge and flatten the subsequent segments, forming the characteristic shape of the inner inlet, as in the reference photos (figure 'b", above).

When this first part of the bottom air duct was ready, I extruded its subsequent segments, forming the rear part (figure "a", below):

Finally I reduced the roundings along the duct side edges by adding there a multi-segment Bevel modifier. It not only diminished their size, but also made its cross section more circular (figure "b", above).

When the bottom part of the scoop was ready, I started the upper part. It begins in the same way: from a single strip, fitted to the cowling surface (figure "a", below):

Then I extruded the vertical faces (figure "b", above).

In the next step I extruded their upper edge into the horizontal surface (figure "a", below):

Finally I extruded the subsequent segments of the rear part of this mesh (figure "b", above).

Initially I kept the lengthwise edges of this object sharp, because I intended to create their fillets using the Bevel modifiers. However, a careful study of the reference photos revealed that the radii of the upper and bottom edge vary along the length of the scoop. Thus I created them by adding two additional lengthwise edgeloops to this mesh:

Figure below shows the real scoop (on the left) and the final version of the same scoop my model (on the right):

Although I did not managed to set up the picture on the right precisely as in the left photo, the carburetor scoop looks quite similar on both images. I can leave it “as it is” and start the work on the next cowling element. I can always fix its shape during the next stages of this project.

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

[Jamie @ Sovereign Hobbies]

It will be sad if this model does not end up being translated into injection moulds!

Witold, how much additional work would it be to replicate the surface rippling of the stressed skin construction? That is the sort of thing that would move plastic model kits to the next generation in my opinion.

[Witold Jaworski]

Witold, how much additional work would it be to replicate the surface rippling of the stressed skin construction? That is the sort of thing that would move plastic model kits to the next generation in my opinion.

Well, surprisingly it is quite easy: in the next, "texturing" stage of this project I will paint the "height map" of the skin of this aircraft. (Technically - this is a grayscale picture, which darker regions correspond to lowered areas, while lighter regions - to elevated details). One of the components of this image are the "bulges" between the bulkheads and longerons that appear on the stressed skin. I will use it as so-called "bump map", to create impression of the various aircraft skin details (panels, rivets, bolt heads). It plays with the light reflections, so on the final render there small details look like "cut" in the model.

It is possible to use the same image as so-called "displacement map". I would have to subdivide all the existing elementary faces of this model several times (no problem - I can just do it by moving a single scroll bar). When the resulting mesh is dense enough - I would apply the image, which displaces these mesh faces up and down according the mapped pixel gray scale. (Still it preserves the continuity of these faces). In the result - I would get a 3D object that recreates everything I painted on it, including the stressed skin details. It could be recreated as a "physical" object on a 3D printer

Such a model is mathematically described as hundred thousand of very small flat quads connected to each other. While it perfectly suits the 3D printers, I do not know if it will be useful for most of the CNC mills that cut the mould forms. (I can imagine that their software requires industry standard models, described by NURBS surfaces - but I can be wrong and they can easily operate on the same input as the 3D printers).

[Witold Jaworski]

In this post I will finish the engine cowling of the Dauntless (of course, for this stage of the project). In the previous posts I formed its outer panels. In the case of the air-cooled radial engines like the one used in the SBD, there is always another, inner panel: the central part of the cowling. It is located behind the cylinders and exhaust stacks. In the classic arrangement of the NACA cowling it is nearly invisible. In the SBD-1..-4 you could see only its outer rim. That’s why I had to use all available pictures of the Dauntless engine maintenance or the wrecks, to learn about its general shape:

This panel had two variants. The first one (let’s call it “flat”) is visible on the photo above. It was used in the SBD-1..-4. In the SBD-5 and -6 the engine was shifted forward by 4”, so the central panel became a little bit longer (“deeper”).

Frankly speaking, I still need more photos and drawings to better determine the shape of this part, especially the details of its earlier, “flat” version! Let me know if you have one — I am especially interested in the upper area, around the carburetor, in the SBD-1…-4. (The few photos that I have reveal that behind the upper cylinders of the R-1820 engine there was a vertical air duct from the air scoop to the carburetor. I still need to determine its shape, as well as the shape of the inner cowling around it).

That’s why I decided to determine the exact shape of this hidden panel later, when I fit the engine and its mounts. (I count on the indirect information coming from the geometry of the engine mount and the exhaust stack shape). At this moment I am leaving this area “as it is”, because too much of its geometry is based on my assumptions.

However, I can precisely shape the recesses around the gun barrels, because they are better visible on the photos. I have to make these details easily adaptable when I have to alter the shape of this panel. (I expect that in the future I will tweak the area around the carburetor multiple times, before it “stabilizes” in the most probable state).

The cross-section of these gun recesses have the same shape as their troughs in the NACA cowling. Thus I started by copying the control polygon of this “U”-like cross-section shape (five control vertices) and extruding it into an auxiliary “trough” (see figure "a", below):

I examined the interesection edge of this auxiliary object with the central panel. The goal was to place its vertices as close as possible to the existing mesh edges. I could easily check it in the front view, because the “trough” in this projection is reduced to a single contour (figure "b", above). While the both of its side vertices are very close to one of the elliptical edge loops, the middle vertex was too far from the nearest radial edge loop. I had to adjust the mesh of the central panel by rotating a little all of its upper radial edges.

After these preparations, I generated in the panel mesh the intersection edge with the auxiliary “trough” (I used my Interesct add-on for this purpose):

I removed the three vertices that were inside the contour of this intersection. It also deleted all the mesh faces around these points. Then I created new faces in this place, merging the intersection contour with the rest of the mesh of this panel (as in the figure above).

Figure below shows how I created the inner surface of this gun trough:

I started by creating a new face that “bridged” the opposite edges of the opening. Then I split it twice, obtaining three inner edges. I placed these edges directly behind the corresponding vertices of the opening contour. Then I closed this opening, creating the four remaining faces. (Now I can see that I could do the same in a simpler way, by extruding the bottom part of the opening contour. Never mind, both methods lead to the same result). At this moment the edges of this recess are too smooth. To reduce the radius of this rounding, and make it similar to a regular fillet, I assigned these edges the full Bevel Weight (=1.0). Then I added to this object a multi-segment Bevel modifier (before the smoothing Subdivision Surface modifier). The last picture from figure above shows the faces generated by this Bevel, before they were smoothed.

Finally I compared the shape of the resulting gun trough to the corresponding troughs in the upper cowling panel:

(I made it transparent, to better see the eventual differences in their shapes). Indeed, there were some deviations. I quickly fixed them, adjusting in the front view the whole edges of this recess. (In this view these edges are reduced to a single point).

Now I have to trim ends of the troughs in the NACA cowling, creating the space for the central cowling panel. I could do it by modifying their mesh. However, because the shape of this panel may be altered in the future, I decided to use another Boolean modifier for this purpose. I just created an appropriate auxiliary object, and applied it to the gun trough panel:

This was the last element of the NACA cowling. Figure "a", below, shows the recesses in the central panel that I formed in this post, while figure "b" shows details of the whole assembly:

As you have probably noticed in the course of the few previous posts, I had often to move the location of the NACA cowling, switching between the SBD-5 and the SBD-3 versions. To avoid such endless movements in the future, I decided to split the Bledner file of this project into several separate scenes for each Dauntless version that I need. For the beginning I created two additional scenes, for the SBD-1 and SBD-5. They are named after the Dauntless version they contain, thus I renamed the current scene to “SBD-3”.

Figure below shows the SBD-5 scene (and the scene selection menu):

When I created the scene for this Dauntless variant, I chose the option that created it as a copy of the original scene. Initially both scenes share the same objects (the same fuselage object or the wing objects are “linked” to SBD-3 and SBD-5 scenes). In the effect, I can edit these shared objects in any of these scenes. Every change I apply to their meshes, modifier stacks, or general positions/scales/rotations is visible everywhere.

Because the NACA cowling in the SBD-5 was shifted forward by 4”, I had to make in its scene local copies of the panel objects. However, they still share with the SBD-3 their meshes. In the effect, they became “clones” of their counterparts from the SBD-3 scene. Clones share the common meshes, thus they have the same basic shape, but they can have different general transformation (location/rotation/scale). Thanks to this, in the SBD-5 scene the bottom panels of the NACA cowling have the same shape as in the SBD-3, but their location is different. What’s more, the clones can have different modifier stacks. Thus in this SBD-5 model I was able to remove the carburetor scoop openings from the upper NACA panel, and modify the cutouts for the different cowling flaps (see figure above) because they were generated dynamically, by a Boolean modifier.

Ultimately — there are a few objects specific for the SBD-5, which exist only in this scene: the central cowling panel and the panels around the gun troughs. I copied their meshes from the SBD-3 and then modified them according the SBD-5 reference drawings. In the SBD-5 the central cowling panel, placed behind the engine cylinders, was longer by 3.5” than in the previous versions. I had to scale and reshape this mesh. Fortunately, its gun recesses (formed at beginning of this post) are easily adjustable, thanks to their simple topology.

In similar way I created a separate scene for the SBD-1:

At this moment the only difference between the SBD-1 and SBD-3 is the carburetor scoop on the top of the NACA cowling. However, there will be another minor differences in the next row of cowling panels.

In the future I will also create the SBD-2 scene (combining the NACA cowling from the SBD-3 and further cowling panels from the SBD-1), and the SBD-4 scene (basically – it is the SBD-3 with the SBD-5 Hamilton Standard Hydromatic propeller). As you can see, the SBD-2 and SBD-4 will be just combinations of various parts from the “key” versions (SBD-1, SBD-3, SBD-5), thus I will create them at the end of this build.

In this source *.blend file you can evaluate yourself these SBD-1, SBD-3 and SBD-5 scenes and their initial contents. In the next posts I will continue my work on the SBD-3, then update the SBD-1 and SBD-5.

[helios16v]

Most excellent work as always.

[Witold Jaworski]

helios16v, thank you fo following !

This relatively short post contains a digression about the aircraft shape. It was sparked by a suggestion that I received. Some time ago Alan from SOARING Simulator.com pointed me that the SBD NACA cowling was not as smooth as in my model (thanks, Alan!). He suggested that its contour was created from a combination of two or three arcs and a straight segment:

I thought about it and decided that this is a highly probable hypothesis. For most of the 20th century aircraft engineers did not have CAD systems. During that “BC” (“Before Computers” :)/>) era the typical problem in the ship, aircraft, or car industry was: “how to precisely recreate in the workshops the shapes sketched — usually in scale — on the designers’ drawing boards”. The most important shape — the wing airfoil — was recreated using a “cloud” of data points. However, it was a time-consuming (i.e. costly) method. That’s why for the less important areas, as the fuselage, designers used simpler solutions. The most obvious method to define a specific contour was a curve composed from two or three arc segments. It is relatively easy to recreate such a contour, because you need only to know the radii and the center point coordinates of the subsequent arcs. For example, there are many cases of such curves in the P-36 and P-40. There was also another drawing method for obtaining more “fancy” shapes (like the rudder contours) which was based on a general conic curves. To overcome this problem in a more advanced way the design team of the P-51 “Mustang” described all key contours of this aircraft using polynomial (2D) functions. Still the resulting points of the “Mustang” curves had to be calculated by hand!

The modern, computer-generated curves and surfaces (Bezier, NURBS, subdivision) have continuous curvature (as in figure "a", above). Thus it requires some effort to recreate in a computer model such a contour like the one sketched in figure "b", above), where the curvature continuity is broken between each segment. (BTW: the air flow “likes” the shapes that have continuous curvature. That’s why designers always tried to preserve it in the airfoil contours).

All in all, I turned to the reference photos, trying to identify a kind of the contour like the one depicted in figure "b", above). Ultimately I discovered a more severe break than the lack of the continuous curvature: a minor difference in the tangent directions along the panel seam (i.e. the contour of this NACA cowling does not preserve even the tangent continuity!):

I marked the tangent directions along the panel seam in blue. This is a modern, high-resolution picture of a restored SBD-5. To exclude the possibility that this is an accidental inaccuracy made during restoration, I started to search for this break in all other photos. Surprisingly, I think that I was able to identify this “bulge” in the others SBD-5s. In the previous versions (SBD-1 to -4) it was hidden under the carburetor air scoop. But even there I think that I can trace it in the lines of the nearby panel seams (the gun troughs panels, side edges of the air scoop). Such a small deviations are usually a “side effects” of the technology applied to the particular element. Finally I used the reference photo to recreate this “bulge” in the side view:

What’s interesting: previously the contour of this NACA cowling had a small convex break in the top view. (When I shaped it for the first time, without the additional section, I was not able to eliminate such a break in the tangent directions. It had to occur somewhere along this panel seam. I had only the choice where to place it, and I decided to leave it on the vertical contour). Now this contour is smooth, and there is a concave break in the side view.

I suppose that initially the forward ring of this NACA cowling was formed as a perfect solid of revolution. Then it was slightly deformed while fitting to the rear, “flat” part of the cowling. The cross section along the seam between these parts is not a perfect circle: it is somewhat higher than wider. Thus the rear edge of the forward cowling sheet had to follow this shape. It altered the tangent dimensions along this panel seam. In the top view it improved the fitting between these two panels of the NACA cowling. In the side view it only decreased the initial difference in the tangent directions.

Well, I hope that this post gives you a better insight, how we can deliberate on each small detail of the recreated airplane. In the overall picture of this aircraft the differences between the shapes before and after modification described above are hardly noticeable. However, I am a hobbyist, and sometimes we are the only ones who have the time to care about such minor things.

In this source *.blend file you can find this modified NACA cowling. (The change in its shape required some adjustments in the other panels).

[Witold Jaworski]

In this post I will create the next section of the engine cowling. I copied its forward edge from the rear edge of the inner cowling panel. Then I extruded it toward the firewall:

I am going to split this object into individual panels, thus I already marked their future edges as “sharp” (as you can see in the figure above). It allowed me to preserve continuity of the tangent directions around these future panel borders from the very beginning.

In the next step I created the space necessary for the covers of the gun barrels:

Then I split this object into separate cowling panels:

I also used auxiliary “boxes” and the Boolean modifiers to cut out various openings in the side and bottom panel.

To keep the mesh topologies as simple as possible, I decided to model the inner part of the air outlet in the side cowling as a separate object:

(In the real SBD-3 it was also a separate piece of sheet metal). Its vertical contour was rounded to fit the fuselage behind the firewall (as you can see in Figure 48‑4), thus to shape it in this way I added three additional edge loops in the middle of this mesh.

The initial version of the gun cover was copied from the reference object, then I adjusted its shape fitting it to the adjacent panels (at least to their contours — see figure below):

Note that it is possible to have a corner in the middle of the border of a 3D surface that was carefully fit at its front and the rear contour (see the figure above)! In this case this is an intended effect, recreating the effect visible on the reference photos.

The last element of this cowling is the adjustable scoop (see the figure below), directing the air into the oil radiator (hidden inside engine compartment). It seems to have thick walls, but I suppose that they were empty inside (however, I am not sure — I cannot see any seams there):

I started forming this element by fitting its bottom surface into the fuselage contour:

Then I formed the side walls of this object. As the reference I used an auxiliary circle, centered at the scoop pivot point (as in figure "a", below):

Then I created the thick walls of this scoop using a Solidify modifier (see figure "b", above)

Initially I was going to round the edges of this object using a multi-segment Bevel modifier, placed after the Solid modifier. However it occurred that the Solid modifier created in some corners of this mesh dynamic faces that cause problems in the result generated by the Bevel modifier. Thus I had to “fix” the results of the Solid modifier before using the Bevel tool. You can see the rounded, thick edges of this scoop in figure "a", below, while figure "b" demonstrates the complete cowling panels:

Figure below shows the complete engine cowling, compared to an original aircraft:

Note that the model in the picture above uses different lighting than in the photo. It results in different shadows and reflections from the curved surfaces of the fuselage.

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

In the next post I will create the last panel of this fuselage: the hinged doors in the front of the windscreen.

[(ex)Sgtrafman]

This has to be modelling in its purest form - simply stunning research and execution.

Bravo!

Iain

[Pete in Lincs]

I'm amazed at the level of detail.

Beautiful work.

[Witold Jaworski]

This has to be modelling in its purest form - simply stunning research and execution.

Well, these "virtual materials" are much easier to form than the real ones . Thank you!

I'm amazed at the level of detail.

Beautiful work.

Thanks a lot! I will do my best!

OK, in this post I will form the fuselage panels in the front of the windscreen. In the SBD there were two hinged cowlings, split in the middle. They allowed for quick and easy access to the M2 gun breeches and the internal cabling behind the instrument panels:

The parts of the fuselage around the cockpit are always tricky to model. It especially applies to the panel around the windscreen. When you obtain the intersection edge of these two objects, it can reveal every error in the windscreen or the fuselage shape. To be better prepared for this task, I created an auxiliary, simplified model of this fuselage section (see this post and the next one). Now I copied a part of it as the initial mesh of this panel:

In the next step I used my Intersection add-on to obtain the intersection edge between this mesh and the windscreen object (see figure "a", below):

Initially this edge is not connected to any of the mesh faces. To fit this panel to the windscreen I removed some of the original faces and created in their place the new ones. They incorporated the intersection edge into this mesh (see figure "b", above).

The resulting curve that I obtained in this way required just a few minor adjustments (see figure "a", below):

It is always good idea to check this shape in the reference photo (see figure "b", above). Fortunately, it seems that my edge between the windscreen and the fuselage fits its real counterpart.

When I verified the basic shape of this panel, I extruded it into the “frame” strip that spans around the windscreen:

To obtain a shape that resembles the real part, I assigned to the intersection edge a multi-segment Bevel modifier. It produces a fillet that forces the Subdivision Surface modifier (applied later) to generate a more regular rounding along this windscreen bottom frame.

Finally I created the armor plates that were attached to this hinged cowling. It was an easy part: I copied corresponding fragment of the cowling mesh, then I used a Solidify modifier to make it thick enough (on the photos it seems to have just a few millimeters):

I think that in this armor I will use textures (bump texture, ref texture) to recreate the bolts and the circular recesses around their heads (as visible in the photos). However, I will do it during the next stage of this project.

The last element that I modeled in this mesh was the seam along the bottom border of this panel. It was stamped in the sheet metal to overlap the upper longeron of the fuselage (see figure "a", below):

I also thought about recreating this detail in the textures, but ultimately I decided that it needs a more pronounced appearance. It is an easy effect (see figure "b", above) that required just a few additional edges (as in figure "c", above).

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

In the next post I will form the multiple segments of the SBD “greenhouse” cockpit canopy.

Edited May 20, 2016 by Witold Jaworski