SBD Dauntless, from scratch

Good work so far!

I enjoy so much the perfection of your work as the excellent walkaround you spread thru the thread.

Wurger, Gnomey, VALENGO - thank you!

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As I described it in one of my previous posts, in parallel to the SBD-3 I build a SBD-1 model and a SBD-5 model. They are in the same Blender file, but in separate scenes. Since I completed the SBD-3 model for this project stage, now it is time to take care of these other versions. These models share all the common objects with the SBD-3, so I have to recreate a few different details. I already modified their NACA cowlings. In this post I will update the SBD-1, because there is just a single remaining difference: the ventilation slot in the side panel of the engine cowling.

The SBD-3 had this slot much wider than the SBD-1 and SBD-2:


(I used here an archival photo of the SBD-2, because it had the same side cowling as the SBD-1. There were only 57 SBD-1s ever built, so the photos of this version are not as numerous as the later ones).

Figure below reveals the reason of this difference in the cowling shapes:


The SBD-1 and SBD-2 had special emergency device: pneumatic balloons, which automatically opened when the aircraft ditched on the water. They had to keep the airframe on the surface, giving the pilot and gunner more time to evacuate. These balloons and their trigger installations were stowed in boxes behind the ventilation slots (figure "a", above).

In the SBD-3 the designers removed these balloons, creating more room for the air coming out from the oil radiator (figure "b", above). In this version these ventilation slots are completely integrated into the side cowling panels.

Because of the frame around the balloon compartments (as in figure "a", above), the side cowling of the engine had a slightly different shape in the SBD-1 and SBD-2. I modeled it by copying the corresponding cowling panel from the SBD-3, and inserting an additional edge loop in the middle (figure "a", below):


I marked this edge as sharp and used it for the minor modifications of the panel shape (figure "b", above).

It seems that the shape of the cutouts in the side view is identical in the SBD-1,-2 and SBD-3, thus I used the same auxiliary objects for its Boolean modifiers (figure "a", below):


However, I had to create anew the inner panel, located inside this cutout. I started with the edge copied from the firewall. I extruded it forward (figure "a", above), then inserted some additional edges in the middle (figure "b", above).

I shaped this inner panel forming it as a smooth continuation of the fuselage shape (figure "a", below):


Then I concentrated all the inner edges of this mesh at the ventilation slot (figure "b", above), and bent the forward edge of this panel toward this outlet (figure "c", above).

In the effect I obtained the shape that closely resembles the original cowling:


You can compare this photo with the first illustration in this post.

It was the last element that I had to modify in this model. Figure below shows the complete airframe of the SBD-1:


It is ready for the next stage of this project (applying materials and textures).

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

In the next post I will start updating the model of another Dauntless version: the SBD-5. (There will be more differences than between this SBD-1 and the SBD-3).

Looking good so far!

Wurger, Gnomey - thank you!

In this post I start finishing the SBD-5 model. It differs in more details from the SBD-3 than the SBD1. One of the most prominent differences is the propeller. I will create it in this post.

In the later Dauntless versions (starting from the SBD-4) Douglas used the new propeller: Hamilton Standard Hydromatic. The SBD-1,-2,-3 used the older constant speed propellers, which used counterweights to oppose the force generated by the oil pressure in the control cylinder. (I created the model of this propeller in this post). The Hydromatic propeller used the oil pressure on both sides of the piston that controlled the pitch. It eliminated the massive counterweights, creating a lighter, smaller, and more precise pitch control unit. Hamilton Standard Hydromatic propellers has been widely used since 40' (you can still encounter them in the various modern aircraft).

In the Dauntless, these Hydromatic propellers came with slightly modified blades:


I used some photos to copy the contour of this new blade into the reference drawing. Then I copied the "old", untwisted blade from the SBD-3 and modified its vertices so it fits the new shape (this is the view from the rear):


(It was quite similar to the las stages of shaping the SBD-3 propeller blade, described in this post. Thus I will not elaborate about it here).

The hub (Hamilton also refers this part as the "barrel") of this propeller had a quite complex shape:


This barrel splits into the front and rear halves. Because there is an oil under pressure inside, there are three bolts on each of the three flanges that keep these barrel halves together.

Beware: it seems that these classic Hydromatic propellers are rare, and some of the restored SBDs use different, non-original models. As a quick indicator you can use the number of the bolts around the barrel. The original propellers had a single bolt in the middle of each flange (as the propeller from the figure above).

Click to expand...

The propeller from the figure above was used in the flyable SBD-5 ("white 39") from Chino Planes of Fame air museum. It seems OK, just misses a small detail: the cap on the tip of the dome. Another example: in the flyable "white 5" from the Commemorative Air Force you can find a larger hub with two bolts in the middle of each barrel flange. What's more, the blades of this aircraft have non-original shape. To further increase the confusion, there is a non-flyable SBD at the Palm Springs Air Museum, ("white 25") which combines a non-original, larger Hydromatic barrel and the propeller blades from an earlier SBD version (SBD-3?).

In fact, the aircraft from Palm Springs is a real trap for the modelers: its engine cowling combines panels from various Dauntless versions! (You can see in this photo that it has the carburetor air scoop from the SBD-3 and the side panels with narrow ventilation cutouts from the SBD-5).

Click to expand...

The halves of this hub barrel were forged (or casted?), thus all of its edges and corners are rounded. It makes modeling of this element much more difficult, at least in Blender (you will see it in a moment).

To better understand this shape, I started with its conceptual model, without all these fillets and flanges:


Studying the photos and available drawings of this control pitch mechanism, I decided that this "barrel" is a combination of three cylinders (the bases of the propeller blades) and a solid of revolution resembling a jug (as in the figure above). Using this conceptual model, I quickly determined the exact shape of this central "jug" that produces the same intersection edges as you can see in the photos.

In a CAD system the next steps would be easy: I would create the basic flange shape by adding some plates and small cylinders. Then I would rounded all their edges using various fillets, and the barrel would be ready.

Unfortunately, Blender has no such a powerful fillet feature: it only has a multi-segment Bevel command, which can create a fillet between two elementary faces. It is usually sufficient for architects. However, If I joined the conceptual model from the figure above into a single mesh (using Boolean union operator), I would to be able to create the appropriate fillet along its edges. (Boolean operation produces in Blender a lot of small elementary faces along the intersection edge. Their size determine the maximum radius of a fillet). I started to think about following pzzf7s' suggestion about using the free AutoCAD 123D as an auxiliary tool for such parts. Ultimately I decided that before I do it, it is a good idea to create at least one of such difficult shapes using Blender tools. Later it will allow me to make a fair comparison between making complex mechanical parts in Blender and AutoCad 123D.

So I started modeling the propeller barrel in Blender. During this process I used the conceptual model as the reference object (I marked it in red):


I decided to take the advantage of the internal symmetries of this shape, and prepared the mesh for 1/6th​ of the barrel — just half of a single blade base and one and half of the flange bolts. Thus I initially created two cylinders for these bolts (figure "a", above). Then I joined these two cylinders into a single object, which is rotated along Y axis by 60⁰ (to create the local symmetry axis along the flange). I removed the half of the inner cylinder, because it is dynamically recreated by the Mirror modifier. In the next step I created the basic flange that connects these two cylinders (figure "b", above). Then I added two inner edges, to bend the side faces of this mesh along the rounded sides of the reference surface (figure "c", above).

Once I formed this flange, I started to shape the remaining part of this mesh. I added an arc that lies on the surface of the central solid of the barrel (figure "a", below):


The number of the arc vertices is extremely important here. It had to be similar to the distance between vertices of the flange edges that connects the bolt cylinders. In similar way I added another arc around the blade base cylinder, then extruded both these edges into two intersecting surfaces (figure "b", above). Finally I generated in this mesh the intersection edge of these two surfaces (using my Intersection add-on). I used this edge as the base for forming two new rows of faces that replaced the original ones (figure 'c", above).

Now the shape of this object starts to resemble the barrel. I improved the shape of its fillet by adding additional edge (figure "a", below):


Finally I shaped the inner part of the blade base (figure "b", above) and filled the gap in the front of flange cylinders (figure "c", above).

The rear half of the barrel was easier, because I started it from a mirror copy of the forward part (figure "a", below):


Then I removed some of its faces and modified the shape of remaining key edges (figure "b", above). Finally I connected these edges with new faces, and added additional edges along the fillets (figure "c", above).

All in all, forming this element in Blender was not easy. On the next occasion I will try the AutoCAD 123. (I have to learn it).

In figure "a", below, you can see the finished hub barrel. I also added the cap on the dome tip:


Figure "b", above, shows the finished assembly. I suppose that I will reuse this hub in many other models. A lot of the various aircraft which used the Hamilton Standard Hydromatic propellers. (At least those, which used the tree-blade model with the single bolt in the middle of their barrel flanges. I know that such a specific conditions sound strange, but it is a quite common model).

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

In the next post I will recreate other SBD-5 details that differ from the SBD-3.

Lovely work so far!

Wurger, Gnomey - thank you!

I continue updating the Dauntless versions that I am building in parallel to the basic SBD-3. In the previous post I updated the one important element of the SBD-5 model: its propeller (SBD-3 used an older version of the Hamilton Standard propeller). In this post I will continue this update.

While I already recreated the SBD-5 NACA cowling (see Figure 46-8 in this post), now it is time to adapt the panels behind it. I started by copying the corresponding cowling from the SBD-3. When it appeared in the place, I discovered a 1" gap between this cowling and the SBD-5 inner cowling panel (see figure "a"), below:


I immediately verified these cowling panels in the reference photos (figure "b", above). It does not look like my mistake: the side panels perfectly fit the firewall and the upper and lower fuselage contour. It seems that this segment of the engine cowling really was in the SBD-5 and SBD-6 longer by 1"! (It seems quite probable: if the designers shifted the whole engine forward by about 3", they could also modify this segment).

Following this finding, I modified all the panels of this cowling segment. I also modified the auxiliary "boxes" used by the Boolean modifier, to obtain thinner and higher air ventilation outlets. (This is another difference between the SBD-3 and SBD-5):


I shaped the inner surface of these outlets starting from a rectangular plane, as I did in the SBD-1 model:


When the side cowling panels were finished, I modified the oil radiator air scoop, located in the bottom panel:


The photos reveal that this panel was in the SBD-5 wider than it was in the SBD-3 by about 2", because it housed a larger (wider) air scoop. (I suppose that they mounted in the SBD-5 a larger oil radiator, because it had a more powerful engine – 1200 HP instead of 1000 HP in the SBD-1…4).

When I finished the bottom panel, I started shaping the upper panels that cover the pilot's gun barrels:


It seems that they have slightly different shape than in the SBD-3. What's more, the protruding upper edge of the side panel (as in the figure above) indicates that the designers remodeled (simplified) this area altering both shapes: of the side panel and of the upper panel.

I compared these elements with all available photos, then remodeled both of them:


Note that in this SBD-5 the upper border of the side panel is not a straight line, like in the previous versions. The last mesh face that contains this edge has 5 edges, while all the other faces in this mesh have four edges. This is an intended effect — it seems that such a n-gon creates in this place the desired shape.

There is yet another difference, which you can hardly find on any scale plans: the windscreen frame:


In the older versions (from SBD-1 to SBD-4) it was built from the upper part and two rectangular plates on the sides. It seems that in the SBD-5 they simplified its technology, and created it from two metal stripes. The thinner, forward strip runs around the windshield, while the much wider rear strip forms its trailing edge. The pilot's canopy hood slid under this rear strip — I suppose it better sealed this canopy edge.

I used a copy of the SBD-3 windscreen frame as the starting point. I modified most of its inner edges, recreating the "two-strip" shape:


Finally the whole front of this SBD-5 was ready (as in figure "a", below):


In the last minute I discovered that in the SBD-5 they also simplified the upper cowling panel. In the earlier versions it consisted two hinged covers above the gun barrels and a central panel (see this post). In the SBD-5 it was just a single panel (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 recreate the last remaining details for this project stage: the cutouts behind the gunner's cockpit.

Looks good so far!

Fantastic work my friend.
Muchas felicidades!!!

Luis Carlos

Wurger, Gnomey, SANCER - thank you!
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The last details that I create in this project stage are the gun doors behind the gunner's cockpit. In the SBD-1 they covered a single Browning gun. Fortunately, they were wide enough for stowing the double guns, which were mounted in the SBD-2 and SBD-3 by the Navy workshops:


Note that stowing the ammunition belts of this double gun required additional cutouts in the cockpit rear border. They were covered by slide plates on both sides of the gun doors (see figure above). In this post I will recreate these details.

Before I do it, I have to fix a certain error that I have recently found: the shape of the tail cross-section, near the cockpit edge. When I formed it, I relied on the photos from a certain restoration project (as in figure "a", below):


The upper part of the first bulkhead behind the cockpit (at station 140) in figure "a", above was shaped along a single, gentle arc/curve. Looking on the other photos I assumed that in the front view the gun doors formed an arc, and this arc smoothly joins the curve of the bulkhead contour at the hinge line. Basing on these assumptions (marked in figure "a", above) in blue), I prepared appropriate mesh topology (as in figure "a". below). I created a "sharp" edge along the future gun doors hinge line, which enables me to cut out the inner area for the gun doors (as you can see in this post, Figure 24-9).

However, since that time I still had an impression that something is wrong with this tail shape. Finally, when I started to look at the sliding panels behind the gunner's cockpit, I found that their cross-sections are different than I expected. I have found the ultimate confirmation in the picture from SBD-1 manual (figure "b", above). The top arc of this contour had larger radius, and its endpoints were outside the hinge lines. It was smoothly combined with a straight contour segment, spanning from the topmost longeron of the fuselage (the same that runs along the canopy side border).

Well, great! This means that I have to modify the concept of the mesh topology for this area in my model! Figure "a", below, shows the original layout, while figure "b" shows the modified mesh:


The enlarged arc of the tail cross-sections forced me to shift the mesh edges away from the gun door hinge line. In the effect, I had to switch to the "plan B" for this opening: I will create it using a Boolean modifier. (Never mind, I was going to use it anyway during the detailed phase, for the other openings in the fuselage).

To better fit the fuselage to the straight edges of the gun doors, I already placed their hinges on the tail upper surface (figure "a", below):


I tweaked the mesh edges around the cockpit rear border, obtaining the shape that closely resembles the original part in the reference photos (figure "b", above). However, I do not like their complex topology: such a thing can be an obstacle for eventual further modifications.

After this, I decided to verify how the last cockpit canopy slides under the previous segment. (This is another test before I start to work on the cutouts in the tail surface). In general, the gunner had to rotate it first into horizontal position, then slide it under the previous canopy (figure "a", below):


However, when I started sliding it, I had to stop: its rear edge was too wide (figure "b", above)! It seems that its radius is exaggerated: it was larger than the radius in the forward section of this canopy (figure "a", below):


Well, I adjusted the size of this last section, so that in the rotated position the last canopy segment fits the previous one (figure "b", above). Of course, then I also had to adjust the corresponding frame object to this new glass shape. I definitely should check it earlier! On the other hand, after this modification the gunner's cockpit of my model better resembles the original photos.

The decision of using the Boolean operator for the gunner's opening allows me to simplify the fuselage mesh (figure "a", below):


As I mentioned earlier in this post, I was not satisfied with the complex topology of the cockpit rear border. Now I decided to create it as a separate panel (i.e. separate object). It will differ between the SBD-1 and the later SBD versions, because in the SBD-1 (and SBD-2) the fuselage did not have the side cutouts (compare the first figure from this post and figure "a", below). That's why the auxiliary "cutting object" for the Boolean operation has a shape that resembles the "T" letter (figure "b", above). In this way I created the main fuselage part that fits all the SBD versions. The topologies of both meshes — the fuselage and the rear panel around the gunner's cockpit — became simpler. It means that it will be easier to introduce eventual further modifications.


There was an issue with the internal hierarchy of this model: the fuselage could not be the parent of the auxiliary "T"-like object, because it "cuts" its shape. (Such an arrangement causes problems with displaying the model — I already encountered it in the case of the wing fixed slats). The obvious solution was to assign both objects used by the Boolean modifier to a common parent. In the case of the wing it was its root rib. However, so far this main part of the fuselage was the root object of the whole model hierarchy. To resolve this problem I decided to create a new root: an Empty object. Because I will need it for posing the airplane in an eventual final scene, thus I placed it on layer 19, among other auxiliary handles (figure "b", above).

After these preparations I was finally able to make the sliding panels and their rails:


I used the reference photos to precisely recreate these elements. (The picture of a SBD-5 wreck in the figure above comes from Pacific Aviation Museum Pearl Harbor. I decided that when I work with the details, I can more trust the wrecks than the restored aircraft). The cutout for the ammunition belt was made between two fuselage stringers and the bulkhead at station 140 (see figure "a", above). Note that it creates a triangular hole between the sliding plate and the canopy rear frame (figure "c", above). Ultimately it was covered by a rubber band, attached to the canopy. (I will recreate it during the detailing stage of this project).

I created the sliding panel from a rectangle, which received the oblique forward edge. Initially I created the shapes embossed on its surface from separate cylinder halves. Then I recreated the faces around their edges, integrating these shapes with the base plate.

The "rails" of this sliding panel were made from simple duralumin stripes, folded inside. They were riveted to the fuselage stringers. Because these rails had to be parallel to each other, the axis of the fold in the bottom rail was deflected from the stringer axis (figure "b", above). That's why this element had a wedge-like shape.

The archival photos revealed that there was also an alternate version of the sliding plates, which appeared in the SBD-3s. You can see it in the figure below:


I think that the photo in figure "a", above, was taken during operation "Torch" (November 1942), because the star on this picture has a wide light outline, most probably in yellow. Note that the gun has no armor plates there, and the sliding panel has no embossed stiffener along its rear edge. Figure "c", above, shows such a panel in a restored aircraft. (I have found it in the photos from the Kalamazoo Air Museum). We can see clearly here that the lower rail strip is not folded like in the previous figure, but just bent upward, and it is riveted to the stringer along its lower edge. This means that this sliding panel is somewhat narrower than the one from the SBD-5. (Why? Because the lower edge of this panel lies above the stringer axis, while in the SBD-5 it is slightly below the stringer axis). I suppose that it can be a field modification of an original SBD-3, adapting it for the double gun. However, I am not sure that all the SBD-3s had such sliding plates. Anyway, I recreated it in my SBD-3 model. The other version of the sliding panel, as in the previous figure, you can find in the SBD-5 model.

In this source *.blend file you can evaluate yourself the SBD-1, SBD-3 and SBD-5 models from this post.

Good work so far!

Wurger, Gnomey - thank you!

While working on the cowling details, I discovered that the SBD-5 from the Commemorative Air Force ("white 5") uses a non-original Hamilton Standard propeller. It has larger hub and a pair of bolts in the middle of the hub barrel edges. (As I wrote in this post, the original Hamilton Standard hubs used in the SBDs were smaller, thus they had a single bolt in the middle of each barrel edge). What's more, I also noticed that the centerline of my model does not precisely pass through the tip of the propeller dome visible in this photo. When I corrected this mistake, I also noticed that the edges of certain cowling panels in my model are minimally below their counterparts on the photo. I examined this difference and decided that I should fix it by rotating the camera of this projection around the fuselage centerline. It was really a "cosmetic" adjustment — the rotation angle was about 0.7⁰. However, suddenly everything in this model matched better the reference photo — except the horizontal tailplane:


When I previously matched my model to this photo (see Figure 42-9 in this post), I aligned it along its horizontal stabilizer. (I assumed that it is not deformed by any significant load). It seems that I was wrong: the Dauntless on this picture is taking off (its wing flaps are retracted). What's more, its elevator is slightly rotated upward, what means that this airplane has already gained enough speed and currently the pilot is lifting its nose to leave the ground. Thus there is an aerodynamic force which bends the tailplane downward, while the lift force tries to bend the wingtips upward:


I think that I would obtain a perfect match between the fuselages of my model and in the photo by placing the viewpoint of this projection between its previous and the current location. (In its previous location it matched the deformed tailplane, while in the current one — it matches the deformed wing).

However, both of these tailplane and wing deformations are small. Thus aligning the wing of my model to the wing in this photo delivers me much more useful information, than a "geometrically pure" match somewhere between these two points. The influence of viewport rotation of 0.7⁰/2 = 0.35⁰ on the fuselage can be neglected, and now the only part of my model that does not fit the photo is the tailplane. It's OK, because in this projection I cannot see any special details on this element. On the other hand, now I can use this high-resolution photo to check various details on the bottom side of the wing.

Currently we are close to the end of the modeling stage of this project. All the elements of this model that I am going to 'unwrap' for the image textures are already in place. Now I will use this high-resolution reference photo to re-examine the model shape and fix all the remaining differences. I started from the empennage:


I fixed it working directly on this picture (I restricted the movement of the mesh vertices to the global YZ planes).

Then I shifted forward, fixing the dorsal fin:


There still was a difference in the tail bottom contour. This time I had to alternate the lower part of the tailplane bulkheads:


I did it by scaling these parts of the bulkheads downward. The most difficult part of this operation was the preservation of the straight lengthwise ("longeron") edges in the rear part of the tail.

Of course, I also used other photos for this check. In the figure below you can see matching the wing against a "semi-vertical" shot of a Dauntless in a steep bank (most probably in a tight turn):


I can see here a difference in the wingtip shape. However, I already verified it against other photos, several months ago (see Figure 31-8 in this post). What's more, I discovered that when I slightly rotate the wing tip around the wing span axis, it perfectly fits the photo (figure "b", above). Thus I again started to think about the forces — this time acting on these wings in such a turn. The lift force has to counter the centrifugal force here. For such a steep bank it can be several times greater than the weight of the aircraft. Thus the wing in this photo is under extremely heavy load, and it wing tips can be twisted as severely, as those in figure "b", above). Ultimately I assumed that this is an effect of dynamic deformation, and I should not modify the wingtip. (The photos of this wing in static conditions do not confirm this shape).

However, in figure "c" above you can see another difference that has haunted me for a long time: the gap between the wing flaps and the aileron. On the various photos, both static and in-flight, it seems that the trailing edge of the wing flap was a little bit shorter than in my model.

First I checked if in this photo the flap is not shifted nor rotated:


I placed auxiliary lines on the flap surface of my model. They go along the last row of holes in each of the 6 segments of this flap (figures "a", "b" above). These lines reveal the "natural" direction of the flap ribs. At the outer end of this flap I put a polyline, which upper edge matches the flap upper. (I wanted to check if this edge is parallel do the flap ribs).

Then I put the wing and these auxiliary lines flat on my reference drawings (i.e. I set the wing dihedral and incidence angles to 0). You can the result in figure "c", above). It seems that the middle sections match my reference drawings (and my model). However, the most inner section (containing the four rows of three holes in each row) should be slightly wider, while the most outer section was shorter (although it contains the same number of holes!). This result was a little surprise, because when I drew these scale plans, I assumed that the spacing between the flap holes was constant. (It would be easier to machine such a perforation). Now it seems that this distance varies in different segments of this flap! Finally, the polygon on the outer end of the flap clearly indicates that its outer edge is oblique (as in figure "c", above).

Of course, I verified these findings in other reference materials:


The close-up photos of various aircraft confirmed that the outer edge of the upper flap was slightly oblique (figure 'a", above). I can also see that the distances between the rows of holes in the last flap segment were shorter than in the segments in the middle. (It implies that the spacing between these rows in the most inner segment could be also a little bit wider). What's more, I could see these differences in one of the original Douglas drawings (figure 'b", above). However, I neglected them before, because this is not a regular, orthogonal view. (Such a drawings can be often deformed in various ways).

Thus I modified the aileron and the flap according these findings (figure "a", below). When I attached wing to the centerplane (i.e. when I set its incidence and dihedral angles) I discovered that the corresponding aileron and flap edges became vertical in the rear view (figure "b", below):


An additional headache was the outer edge of the bottom flap, which was parallel to the last rib (figure "c", above). Ultimately I decided that most probably the outer corners of the upper and lower flaps overlaps as in figure "b", above).

Of course, I reviewed the whole model and made much more minor adjustments. I will not bother you describing them all. Fortunately, most of them did not require as much work as this small gap!

Figure below shows the resulting SBD-5 model:


In this source *.blend file you can evaluate yourself the current version, described in this post.

In the next post I will start the "painting" stage of this project. I begins with mapping of the texture coordinates (UV) onto the model surfaces (so-called UV-unwrapping).

Lovely work so far!

Phenomenal work!