SBD Dauntless, from scratch
- Thread starter Witold Jaworski
- Start date
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Lucky13
Forum Mascot
Simply outstanding work!
- Thread starter
- #323
Witold Jaworski
Airman 1st Class
Thank you, guys!
Excuse me, I was out of this forum during winter, thus I my first answer is three months late :
.
Well, there is not any special "magic", you have to:
Excuse me, I was out of this forum during winter, thus I my first answer is three months late :
Of course! I will be honored, if you share this thread
.Well, there is not any special "magic", you have to:
- scan the drawings,
- check (and eventually correct) their horizontal and vertical axes (vertical axis => the axis that connects the wing tips),
- verify the length/span ratio of the top view. [BEWARE: the length of a historical aircraft can vary between the sources! For example - the length of the P-40D/E. It was NOT 4 inches shorter than the earlier P-40 versions, as you can find in many publications. The overall length of these versions was minimally (by a fraction of inch) shorter],
- check (and correct) the horizontal and vertical contours and panel lines. [Tip: you have to be familiar with this particular aircraft, to be sure which lines were horizontal and which were vertical],
- match the left side and bottom views to the corrected top view (stretching them a little, if needed),
- match the right side view to the left side view (flipping it for a while),
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SANCER
Senior Master Sergeant
Thanks for your reply Witold and it's nice to see you back.
Very few works (in all areas), can be appreciated with such a level of dedication, accuracy and clear way of explaining it.
In fact, it can be a source of inspiration to make a better effort in what each person has in their hands and the way they carry out.
Dziękuję bardzo, mój przyjacielu. Nadal będę cieszyć się twoim projektem.
Saludos hasta Polonia.
Very few works (in all areas), can be appreciated with such a level of dedication, accuracy and clear way of explaining it.
In fact, it can be a source of inspiration to make a better effort in what each person has in their hands and the way they carry out.
Dziękuję bardzo, mój przyjacielu. Nadal będę cieszyć się twoim projektem.
Saludos hasta Polonia.
I was hoping you had a special trick
Cool.
BTW: I'm honestly wondering if I'll end up having to measure the height and length of each component; and use the length of the misaligned "straight" line and apply the Pythagorean theorem to all of it and use that to establish the correct lengths
- Thread starter
- #327
Witold Jaworski
Airman 1st Class
I never did such a "piecewise approximation" (note that the overall error of such a multiple-step process, as you have described above, is the sum of the errors you can do in each step
). Fortunately, the popular graphic programs are powerful enough to fix most of the drawing deformations. (You can always rotate the picture or its fragment, aligning it to a guide line, instead of calculating its length with the math formula).Also note that the digitized scale plans may contain three classes of errors:
1. Author's errors (especially the older scale plans, made manually);
2. Overall deformations, caused by the book publishing process (printing);
3. Overall deformations, caused by the copying/scanning;
The group (1) of the errors is most difficult to find and fix (you have to use a lot of the photo resources). Remember: the scale plans do not contain the "ultimate truth" about the depicted object. It is just another approximation, prone to the human errors. It may happen that a good model better resembles the original aircraft than a poor plan.
- Thread starter
- #328
Witold Jaworski
Airman 1st Class
The engine is the heart of every powered aircraft. In the case of the SBD it was the Wright R-1820 "Cyclone 9" (the "G" model). In fact, this engine was one of the "workhorses" of the 1930s: designed in 1931, it was used in many aircraft, especially in the legendary DC-3. "Cyclone" was a reliable, fuel-saving unit for the Navy basic scout type. (Remember that the "Dauntless" was not only the bomber: it was also a scout airplane[1]). In general, the R-1820 is a classic nine-cylinder, single-row radial engine:
The R-1820 G had been produced for over two decades, not only by the Curtiss-Wright, but also (under license) by Lycoming, Pratt & Whitney Canada, and Studebaker Corporation. Thus various less important details of this engine "evolved" during this period. In this post I would like to highlight some of these differences. I will focus on the forward part of this engine, because at this moment I am going to create a simpler model of the "Cyclone", intended for the general, "outdoor" scenes. Inside the closed NACA cowling, you can see only its forward part. (Thanks to the air deflectors, placed between the cylinders - see picture above). In such an arrangement, the visible elements are: the front section of the crankcase, cylinders, ignition harness, and the variable-pitch propeller governor. While the front section of the R-1820 crankcase remained practically unchanged in all versions, and the governor depends on the propeller model, I could focus on the cylinders and their ignition harness.
Identification of the version differences is the basic step, because otherwise you can build a model of non-existing object that incorporates features from different engine variants.
While looking for the reference materials, I have also found an interesting article about the development of air-cooled aviation engines (more precisely, their most important parts: cylinders). I think that it provides a valuable "technical context" for the visual differences that I am describing below.
Searching for the reference photos, I have identified two basic variations of the "Cyclone" cylinder shape:
Figure "a" above shows the classic version, produced to the end of the WW2, while the cylinder from Figure "b" comes from the post-war production. I will refer this earlier one as the "classic" version. This is the engine used in all SBDs. You can quickly identify this version by the characteristic "L"-shaped fins on its cylinder head (Figure "a"). The "classic" head has also curved contours, while the head of the post-war version has different style, and its contour is based on the straight lines. Both heads are aluminum die-casts. The critical element in this design was the overall area of their fins. Greater cooling area of the cylinder head allows you to obtain more power from the same piston volume. Thus the fins of the "classic" head are small wonders of the 1930s metallurgy: they are evenly spaced at 0.2" (5mm) along the head, and the widths of their tips do not exceed 0.05" (1.2mm). The fin at its base is about 0.1" (2.5mm) wide. Die-casting of such an object is extremely difficult. It requires not only the "written down" engineering knowledge, but also individual artisanship of the key workers. Note that the spaces between the fins of the post-war head are two times wider than in the "classic" version. However, between each pair of these "full-size" fins there is a smaller, much shorter "inner" fin. It is much easier to die-cast such a head. I suppose that the post-war heads are cast from an aluminum alloy that has better heat transfer characteristics. It would allow their cylinders to maintain similar power output using somewhat smaller cooling area.
The cylinders of the last R-1820 versions had yet another, conical shape:
In this photo you can also see here the propeller governor (in the first photo in this post it is hidden behind the propeller blade), and another version of the ignition harness.
The "classic" and the "post-war" cylinder heads have different orientations of their intake openings, which results in different shape of the intake pipes:
The classic version has a simpler, L-shaped intake pipe, which fits to the oblique opening of the intake valve (Figure "a", above). In the post-war version planes of both valve openings (exhaust and intake) are parallel (Figure "b", above), thus the intake pipe has a more complex shape (resembling "S").
There are also minor differences in the rocker covers:
The classic version has simpler, four-bolt rocker cover (Figure "a", above), while the post-war covers uses two bolts more. The head of the post-war engine has some additional features (Figure "b", above), which do not exist in the classic head.
Finally, the ignition harness:
Classic ignition harness has a "collar" shape, smaller radius, and individual spark plug cables organized in pairs (Figure "a"). Post-war harness has a ring shape, somewhat greater radius, and evenly spaced spark plug cables (Figure "b"). Although each of these photos is taken from different side, it seems that both versions use the same propeller governor.
Having all these issues identified, I could select appropriate reference drawings. They came from "Cyclone 9GC Overhaul Manual", published in 1943. I expect that even the simplified model of such an engine can have many hundred thousand faces, thus I decided to build it in a separate Blender file. I use the same "scale" as in the SBD model: 1 unit = 1 inch. When it is ready, I will import it into the SBD model.
In this new Blender file I decided to give chance to the alternate method of setting up the blueprints: using Empty objects with the attached image:
First I placed on the perpendicular planes the four views of the original installation drawings (Figure "a", above). Note that they contain a lot of the explicit dimension values – such information is an invaluable help in recreating this engine.
I quickly realized that the Empty objects with the reference images allow you to use simultaneously several alternate sets of the blueprints. Just place each of them on a separate layer. It will be a great tool in the Blender 2.8, which has to have unlimited number of layers. While working in the actual Blender 2.7, I placed these planes on layers 7…10, practically reserving them for the reference pictures. The second blueprint set contains the images from the original "Limits and Lubrication Chart" (Figure "b", above). These two views (side and rear view) are much more detailed than the installation drawings (presented in Figure "a", above). Of course, these images do not match each other in a perfect way: there always are some differences. However, I did not fix them, as in the case of the SBD planes, because all the key dimensions of this engine are specified in the installation drawings. I will just use these explicit values.
Following the standard of my posts, I am enclosing the current state of the source *.blend file. While there is no model, yet, you look inside to check the arrangement of the reference pictures. Next week I will report the first stages of building this model: forming the central crankcase and the basic cylinder shape. (Cylinders of this engine are identical with each other. Once you prepare one of them, you can quickly "populate" the crankcase with its eight clones. However, as you will see in the next posts, the die-cast, air-cooled cylinder head is one of the most complex objects to model…).
_______________________________________________________________
[1]The SBD Dauntless was a new implementation of the US Navy carrier doctrine, worked out in the preceding decade: in the clash of the carriers always wins those, who first finds carriers of their opponent. In fact, the best option was to find, report, and immediately make the first attack – that's why all SBDs carried a 500-pound bomb on their scout missions
The R-1820 G had been produced for over two decades, not only by the Curtiss-Wright, but also (under license) by Lycoming, Pratt & Whitney Canada, and Studebaker Corporation. Thus various less important details of this engine "evolved" during this period. In this post I would like to highlight some of these differences. I will focus on the forward part of this engine, because at this moment I am going to create a simpler model of the "Cyclone", intended for the general, "outdoor" scenes. Inside the closed NACA cowling, you can see only its forward part. (Thanks to the air deflectors, placed between the cylinders - see picture above). In such an arrangement, the visible elements are: the front section of the crankcase, cylinders, ignition harness, and the variable-pitch propeller governor. While the front section of the R-1820 crankcase remained practically unchanged in all versions, and the governor depends on the propeller model, I could focus on the cylinders and their ignition harness.
Identification of the version differences is the basic step, because otherwise you can build a model of non-existing object that incorporates features from different engine variants.
While looking for the reference materials, I have also found an interesting article about the development of air-cooled aviation engines (more precisely, their most important parts: cylinders). I think that it provides a valuable "technical context" for the visual differences that I am describing below.
Searching for the reference photos, I have identified two basic variations of the "Cyclone" cylinder shape:
Figure "a" above shows the classic version, produced to the end of the WW2, while the cylinder from Figure "b" comes from the post-war production. I will refer this earlier one as the "classic" version. This is the engine used in all SBDs. You can quickly identify this version by the characteristic "L"-shaped fins on its cylinder head (Figure "a"). The "classic" head has also curved contours, while the head of the post-war version has different style, and its contour is based on the straight lines. Both heads are aluminum die-casts. The critical element in this design was the overall area of their fins. Greater cooling area of the cylinder head allows you to obtain more power from the same piston volume. Thus the fins of the "classic" head are small wonders of the 1930s metallurgy: they are evenly spaced at 0.2" (5mm) along the head, and the widths of their tips do not exceed 0.05" (1.2mm). The fin at its base is about 0.1" (2.5mm) wide. Die-casting of such an object is extremely difficult. It requires not only the "written down" engineering knowledge, but also individual artisanship of the key workers. Note that the spaces between the fins of the post-war head are two times wider than in the "classic" version. However, between each pair of these "full-size" fins there is a smaller, much shorter "inner" fin. It is much easier to die-cast such a head. I suppose that the post-war heads are cast from an aluminum alloy that has better heat transfer characteristics. It would allow their cylinders to maintain similar power output using somewhat smaller cooling area.
The cylinders of the last R-1820 versions had yet another, conical shape:
In this photo you can also see here the propeller governor (in the first photo in this post it is hidden behind the propeller blade), and another version of the ignition harness.
The "classic" and the "post-war" cylinder heads have different orientations of their intake openings, which results in different shape of the intake pipes:
The classic version has a simpler, L-shaped intake pipe, which fits to the oblique opening of the intake valve (Figure "a", above). In the post-war version planes of both valve openings (exhaust and intake) are parallel (Figure "b", above), thus the intake pipe has a more complex shape (resembling "S").
There are also minor differences in the rocker covers:
The classic version has simpler, four-bolt rocker cover (Figure "a", above), while the post-war covers uses two bolts more. The head of the post-war engine has some additional features (Figure "b", above), which do not exist in the classic head.
Finally, the ignition harness:
Classic ignition harness has a "collar" shape, smaller radius, and individual spark plug cables organized in pairs (Figure "a"). Post-war harness has a ring shape, somewhat greater radius, and evenly spaced spark plug cables (Figure "b"). Although each of these photos is taken from different side, it seems that both versions use the same propeller governor.
Having all these issues identified, I could select appropriate reference drawings. They came from "Cyclone 9GC Overhaul Manual", published in 1943. I expect that even the simplified model of such an engine can have many hundred thousand faces, thus I decided to build it in a separate Blender file. I use the same "scale" as in the SBD model: 1 unit = 1 inch. When it is ready, I will import it into the SBD model.
In this new Blender file I decided to give chance to the alternate method of setting up the blueprints: using Empty objects with the attached image:
First I placed on the perpendicular planes the four views of the original installation drawings (Figure "a", above). Note that they contain a lot of the explicit dimension values – such information is an invaluable help in recreating this engine.
I quickly realized that the Empty objects with the reference images allow you to use simultaneously several alternate sets of the blueprints. Just place each of them on a separate layer. It will be a great tool in the Blender 2.8, which has to have unlimited number of layers. While working in the actual Blender 2.7, I placed these planes on layers 7…10, practically reserving them for the reference pictures. The second blueprint set contains the images from the original "Limits and Lubrication Chart" (Figure "b", above). These two views (side and rear view) are much more detailed than the installation drawings (presented in Figure "a", above). Of course, these images do not match each other in a perfect way: there always are some differences. However, I did not fix them, as in the case of the SBD planes, because all the key dimensions of this engine are specified in the installation drawings. I will just use these explicit values.
Following the standard of my posts, I am enclosing the current state of the source *.blend file. While there is no model, yet, you look inside to check the arrangement of the reference pictures. Next week I will report the first stages of building this model: forming the central crankcase and the basic cylinder shape. (Cylinders of this engine are identical with each other. Once you prepare one of them, you can quickly "populate" the crankcase with its eight clones. However, as you will see in the next posts, the die-cast, air-cooled cylinder head is one of the most complex objects to model…).
_______________________________________________________________
[1]The SBD Dauntless was a new implementation of the US Navy carrier doctrine, worked out in the preceding decade: in the clash of the carriers always wins those, who first finds carriers of their opponent. In fact, the best option was to find, report, and immediately make the first attack – that's why all SBDs carried a 500-pound bomb on their scout missions
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Lovely work so far!
Lucky13
Forum Mascot
Fantastic work, as always!! 
SANCER
Senior Master Sergeant
I am impressed by the images you get, the quality of the photographs and the clear description you give us.
I am sure that the engine process will be another part to learn and enjoy your work.
Admiro tu trabajo, saludos
I am sure that the engine process will be another part to learn and enjoy your work.
Admiro tu trabajo, saludos
- Thread starter
- #333
Witold Jaworski
Airman 1st Class
Wurger, Gnomey, Lucky13, SANCER: thank you!
Today, we will start with relatively simple parts, the cylinder head will be a real headache (you will see it in further posts).
_______________________________________________________
In this post I will recreate the main and the front sections of the R-1820 crankcase, and the cylinder basic shape. Let's start this model by forming the main crankcase:
This section is always obscured by the cylinders, so you cannot see it clearly on any photo. That's why I used here the original drawing from the manual. Generally, this barrel-like shape contains nine cylinder bases. It is formed by two steel castings, bolted to each other. (These bolts are hidden inside the crankcase, between the cylinder openings).
It is always a good idea to start with a simplified model. It allows us to check all constrains of the geometry that are not obvious at the first glance from the reference drawings. In this case started by forming a symmetric half of the crankcase:
This is a simple barrel, smoothed with a Subdivision Surface modifier. Then I placed the flat piston bases along the circumference of this crankcase. I quickly realized that the side contour of this barrel depends entirely on the size and shape of these piston bases. After a few quick adjustments of the control edge loops, the barrel surface "touched" the outer edges of the piston bases along their whole length (as in figure above).
Note that these piston bases are so tightly packed around the crankcase, that they nearly join each other along a short, straight edge:
This means, that the crankcase barrel contains a cylindrical strip in the middle, which matches this straight edges on the piston bases. In fact, the sharp corners of these edges forced similar sharp edge on the barrel side contour.
When the general shape of the crankcase barrel looked right, it was time to create the final mesh. I decided that I will not use the dynamic effects of the subdivision surfaces for such a complex objects as the engine parts. (Because I want to keep the polygon count of this engine model below 1 million). Thus I "fixed" this subdivision effect, converting it into the normal faces (by "applying" the modifier). Then I took take the advantage of the "repeatability" of this shape. I deleted all the faces of the original "barrel", leaving just the 20⁰ "slice" (as in figure "a", below):
The opposite 20⁰ of this "slice" is generated by the Mirror modifier. Then I made further modification to this mesh, removing all the faces from above the piston base (figure "b", above). I also copied and inserted into this mesh a quarter of the piston base contour. Then I started to join this contour and the mesh around it with new faces. You can see the result in figure "a", below):
As you can see, I also recreated the rear part of this crankcase section, just adding another symmetry axis to its Mirror modifier. The whole body of this crankcase can be built from 9 clones of such an object (as you can see in figure "b", above).
The shading of the crankcase faces is set as Smooth, except the faces around the piston base (which are marked as Flat).
I would like to mention a little "trick", which can be useful in many other cases. To obtain a seamless join between the crankcase "slices" (as in figure "a", below), I added an additional, thin "strip" of the faces around the slice edge. These faces are parallel to the faces of similar strip in the adjacent slice (as in figures "b" and "c", below):
Once the middle section of the crankcase is ready, I started working on its front section. Generally speaking, this part looks like a combination of a cone and a cylinder, with many "protrusions" of additional details:
Actually, I recreated the basic shape of this section. (I will recreate the remaining details later). I did it using the same workflow as in the case of the previous section. First, I made a simple, "conceptual" model of this part. It was smoothed using a Subdivision Surface modifier. When the shape seemed to be OK, I converted the result of this modifier into normal mesh faces. Then I removed all the unnecessary edge loops and created the basic 20⁰ "slice" of this section:
To obtain the smooth shading between slices, I also created the additional thin strips of parallel faces along their adjacent edges. The basic slice of this section was easier to form than the one from the middle section, because it did not contain any opening.
Just to make the front of the engine more complete, I created the front disk (in a classic way, no "slicing" here) and the propeller shaft.
Finally I started working on the cylinder. Because all cylinders of this engine are uniform, I will complete a single (the topmost) one. The complete cylinder will be an assembly of many objects. Then, when it is finished, I will clone it around the crankcase.
As the first object in this assembly I created the simple, basic cylinder (i.e. the cylinder and its head without the fins and rocker covers):
It will be the parent object of all further elements of the cylinder assembly. As in the case of the crankcase, it does not use any Subdivision Surface modifier, just the "fixed" mesh faces with the Shade Smooth option (and Mirror and Bevel modifiers).
You can check details of this model in the source *.blend file. In the next post I will model the rocker covers and the covers of the intake/exhaust valves. (In the R-1820 they are just fragments of a single-piece cylinder head).
Today, we will start with relatively simple parts, the cylinder head will be a real headache (you will see it in further posts).
_______________________________________________________
In this post I will recreate the main and the front sections of the R-1820 crankcase, and the cylinder basic shape. Let's start this model by forming the main crankcase:
This section is always obscured by the cylinders, so you cannot see it clearly on any photo. That's why I used here the original drawing from the manual. Generally, this barrel-like shape contains nine cylinder bases. It is formed by two steel castings, bolted to each other. (These bolts are hidden inside the crankcase, between the cylinder openings).
It is always a good idea to start with a simplified model. It allows us to check all constrains of the geometry that are not obvious at the first glance from the reference drawings. In this case started by forming a symmetric half of the crankcase:
This is a simple barrel, smoothed with a Subdivision Surface modifier. Then I placed the flat piston bases along the circumference of this crankcase. I quickly realized that the side contour of this barrel depends entirely on the size and shape of these piston bases. After a few quick adjustments of the control edge loops, the barrel surface "touched" the outer edges of the piston bases along their whole length (as in figure above).
Note that these piston bases are so tightly packed around the crankcase, that they nearly join each other along a short, straight edge:
This means, that the crankcase barrel contains a cylindrical strip in the middle, which matches this straight edges on the piston bases. In fact, the sharp corners of these edges forced similar sharp edge on the barrel side contour.
When the general shape of the crankcase barrel looked right, it was time to create the final mesh. I decided that I will not use the dynamic effects of the subdivision surfaces for such a complex objects as the engine parts. (Because I want to keep the polygon count of this engine model below 1 million). Thus I "fixed" this subdivision effect, converting it into the normal faces (by "applying" the modifier). Then I took take the advantage of the "repeatability" of this shape. I deleted all the faces of the original "barrel", leaving just the 20⁰ "slice" (as in figure "a", below):
The opposite 20⁰ of this "slice" is generated by the Mirror modifier. Then I made further modification to this mesh, removing all the faces from above the piston base (figure "b", above). I also copied and inserted into this mesh a quarter of the piston base contour. Then I started to join this contour and the mesh around it with new faces. You can see the result in figure "a", below):
As you can see, I also recreated the rear part of this crankcase section, just adding another symmetry axis to its Mirror modifier. The whole body of this crankcase can be built from 9 clones of such an object (as you can see in figure "b", above).
The shading of the crankcase faces is set as Smooth, except the faces around the piston base (which are marked as Flat).
I would like to mention a little "trick", which can be useful in many other cases. To obtain a seamless join between the crankcase "slices" (as in figure "a", below), I added an additional, thin "strip" of the faces around the slice edge. These faces are parallel to the faces of similar strip in the adjacent slice (as in figures "b" and "c", below):
Once the middle section of the crankcase is ready, I started working on its front section. Generally speaking, this part looks like a combination of a cone and a cylinder, with many "protrusions" of additional details:
Actually, I recreated the basic shape of this section. (I will recreate the remaining details later). I did it using the same workflow as in the case of the previous section. First, I made a simple, "conceptual" model of this part. It was smoothed using a Subdivision Surface modifier. When the shape seemed to be OK, I converted the result of this modifier into normal mesh faces. Then I removed all the unnecessary edge loops and created the basic 20⁰ "slice" of this section:
To obtain the smooth shading between slices, I also created the additional thin strips of parallel faces along their adjacent edges. The basic slice of this section was easier to form than the one from the middle section, because it did not contain any opening.
Just to make the front of the engine more complete, I created the front disk (in a classic way, no "slicing" here) and the propeller shaft.
Finally I started working on the cylinder. Because all cylinders of this engine are uniform, I will complete a single (the topmost) one. The complete cylinder will be an assembly of many objects. Then, when it is finished, I will clone it around the crankcase.
As the first object in this assembly I created the simple, basic cylinder (i.e. the cylinder and its head without the fins and rocker covers):
It will be the parent object of all further elements of the cylinder assembly. As in the case of the crankcase, it does not use any Subdivision Surface modifier, just the "fixed" mesh faces with the Shade Smooth option (and Mirror and Bevel modifiers).
You can check details of this model in the source *.blend file. In the next post I will model the rocker covers and the covers of the intake/exhaust valves. (In the R-1820 they are just fragments of a single-piece cylinder head).
SANCER
Senior Master Sergeant
...
Lovely work so far!
T Bolt
Colonel
Wow!
- Thread starter
- #338
Witold Jaworski
Airman 1st Class
Wurger, SANCER, Gnomey, T Bolt - thank you!
In this post I am wrestling with the partially hidden shape of the cylinder head:
___________________________________________________________________________
One of the most prominent features of the R-1820 engine cylinders are their rockers. More precisely – their covers, cast as the part of the cylinder head:
The R-1820 was a classic four-stroke engine. Its cylinders had two valves: single intake valve, connected to the supercharger via a wide pipe, and single exhaust valve. Movements of these valves were controlled by cams, via pushrods and rocker arms mounted in the cylinder heads. The covers housing these valves and rocker mechanisms were placed on the right and left side of the cylinder head.
To simplify my model, I decided to separate the cylinder fins from its "solid" body (i.e. to create them as separate objects). However, because in the reality the cylinder head was cast as the single piece, it is very difficult to precisely determine its shape hidden between these fins:
While you can see the upper parts of the rocker covers on the reference photos, you can only guess their contours below the "fin surface".
There is a blueprint that provides some additional clues:
However, I have some doubts about details of the contour that you can see on the rear view above. (I marked it with thick dashed lines in the picture). Look at the lowest part of this top contour: it should correspond to the upper (outer) surface of the combustion chamber. According other drawings, the shape of this chamber resembled a regular dome. If so, why the fragment of its contour visible in this drawing seems to be (a little) oblique? In the cutaway depicted in the first photo in this post I cannot see such an oblique shape. And why the side contours of this heads (the vertical dashed lines below the valve openings) are not symmetric? Thinking about it, I concluded that this drawing was not focused on the precise representation of the cylinder geometry: its main goal was to show the lubrication areas. Thus all these details, which we can see here, were drawn thanks to a "good will" of its draughtsman. They were hand-made, ink-traced drawings, and we can be just thankful to this technician for such a detailed piece of work. Still, I assumed that these lines can differ a little from the real contours – just because of the plain human error.
I formed the basic shape of the rocker cover using two clones of the same mesh: I placed one instance on the auxiliary drawing, while the second instance is located in its proper position on the cylinder (Figure "a", below):
Modeling this cover as a separate object allowed me to switch between its local (along the valve axis) and global coordinate systems. I could also modify this mesh switching between its clones. I used the instance, located on the cylinder, to fit its base into the combustion chamber dome. The other instance of this cover, placed over the auxiliary drawing, allowed me to follow the shape of this element. (In fact, I could also put another instance of this mesh over the top view of the rocker cover. However, I did not do it - just because I used this view only during the initial phases of the modeling, and it was relatively easy to rotate the modeled object and move it over the side view).
This is the initial, "conceptual" model of the cylinder head, so I split it into the key "solids" and formed the semi-spherical cover of the exhaust valve as another object (the red one in figure above). Such an arrangement allows for easy manipulating of these parts. During this phase I have to determine their most probable sizes and locations. For example – following the precise location of the exhaust opening, I discovered that for the size as in the "Lubrication Chart", it has to be placed in a slightly different position (as in Figure "b", above). Otherwise, the right-bottom corner of the rim around exhaust opening would "sink" into the combustion chamber dome. (Of course, I also checked multiple times the most probable radius of this dome!).
When the whole thing seemed to match the photos, I made the rocker cover asymmetric (by "applying" its Mirror modifier and modifying the resulting faces). Then I modeled the oblique pushrod base (Figure "a", below):
To avoid some potential errors in the future, I started with placing the pushrod (another object) in the proper position, then formed the base around it. Figure "b", above) shows the resulting mesh. Note the sharp edges in its upper part. In the next step I rounded them, using a multi-segment Bevel modifier (Figure "a", below):
To have more control over these fillets, I used the weight-based version of the Bevel. Figure "a", above, shows the mesh edges that have a non-zero bevel weight marked in yellow. However, even in such a case, I could not avoid an artificial sharp edge between two fillets that were too close to each other (Figure "b", above). Well, in this situation I had to "apply" this modifier, and manually introduce small fixes to the resulting faces (Figure "c", above). I also dynamically created a "rim" around the upper edge of this cover. It is generated by the Solidify modifier, assigned to the thin face strip around this edge. Figure "d", above) shows the final result of these modifications.
While working on these parts, I simultaneously "scanned" the Internet, searching for more reference photos. Sometimes they just expose details, which were obscured in the reference materials that I already have. In this case – it was a protrusion on the rocker cover around the first and the last bolt (Figure "a", below):
I just had missed this tiny detail while forming the upper part of the rocker cover! Now I had a headache, how to fix it in a quick way. Ultimately I prepared two reference "cylinders" (I marked them in red, as you can see in Figure "b", above. Fortunately, there were many faces around the area that I had to modify. I placed these faces on the corresponding reference cylinders using the Blender Sculpt tool. (It allows me to push/pull multiple faces at once in a gradual manner).
You can see the final result of this modification in Figure "a", below:
Frankly speaking, I can see now that this protrusion had somewhat smaller radius. Ultimately I decided that it is "good enough" for the assumed level of details.
In the next step I cloned the rocker and valve covers onto the opposite side of the cylinder head: over the intake valve (Figure "b", above). In this first approximation of these parts, I rotated the intake valve cover (marked in red in the picture above), trying to find the proper location and angle of the intake opening. To fit it better, I also placed in this model the intake pipe. I knew, that in the future I will adjust its shape multiple times. That's why I crated it initially as a simple cylinder, smoothed by the Subdivision Surface and bent along a parent curve using Curve Deform modifier. By controlling the location, rotation and shape of the parent curve I had full control over this pipe.
The intake rocker cover had also a unique feature: two bolts on its front and rear walls (Figure "a", below). They were intended for mounting around the engine an eventual NACA cowling. (Wright added these bolts on the Army request). For this "conceptual" stage of the modeling, I decided to add the bases of these bolts as a separate part. (Because I expect that I will move/modify shape of this element many times, before I reach the result that matches the reference photos). I will eventually join it with the cover (and add appropriate fillets around its edges) when it fits well.
In the next step I transformed the clone of the intake cover into a completely separate object (marked in blue in Figure "b", above). I also added the bolt bases around the exhaust and intake openings. (As you can see in the figure above, there are four of them on the exhaust cover, and three on the intake cover). Initially I created these bases as separate objects.
Once I verified their location, I joined these bolt bases with the cover mesh (Figure "a", below):
I joined these objects by applying a Boolean (Union) modifier. However, after such an operation the resulting edges required some manual "cleaning" (removing doubled vertices and edges).
I also formed an initial approximation of the rocker upper cover (Figure "b", above). I just placed it over the left rocker. The front contour of this part had to fit the circular contour of this engine (dimensioned on the original installation drawing). I also rounded its upper edge using a multi-segment Bevel modifier, but I can see that this part will require further modifications.
While working with these rocker covers, I discovered that I made a mistake in reading the original blueprints! I thought that one of the exhaust rocker cover elements was a cross-section, while it was oblique view of one of its fins (Figure "a", below):
On the reference photos I can also see that the bottom pushrod base plane was bent, with sharp side edges (Figure "b", above). Thus I had to modify accordingly the bottom part of this cover (Figure "c", above).
Well, such "discoveries" slow down the overall progress of the work, but they are inevitable, if you want to build a close copy of the real object. They happen all the time, as I am collecting growing number of the reference photos. In fact, I have measured that I spend at least half of the overall time on analyzing the photos. (Sometimes I also sketch on a paper the most complex shapes, before I start to model them in Blender. These sketches help me to better "understand" the objects that I want to recreate). The complex details of the cylinder head are often obscured by the fins, which makes this element an extremely difficult case. I am sure that I will identify and fix many of similar mistakes in the nearest future. For example: I will shift and rotate the cover of the intake valve multiple times, and then have to adjust the intake pipe after each of these updates. That's why I prefer keeping this cylinder as an assembly of multiple, relatively simple objects. It would be much more difficult to modify this head, if it was a single, complex mesh. (In such a case you would have to care about all of its intersection edges!).
You can check details of this model in the source *.blend file. In the next post I will model the cylinder head fins.
In this post I am wrestling with the partially hidden shape of the cylinder head:
___________________________________________________________________________
One of the most prominent features of the R-1820 engine cylinders are their rockers. More precisely – their covers, cast as the part of the cylinder head:
The R-1820 was a classic four-stroke engine. Its cylinders had two valves: single intake valve, connected to the supercharger via a wide pipe, and single exhaust valve. Movements of these valves were controlled by cams, via pushrods and rocker arms mounted in the cylinder heads. The covers housing these valves and rocker mechanisms were placed on the right and left side of the cylinder head.
To simplify my model, I decided to separate the cylinder fins from its "solid" body (i.e. to create them as separate objects). However, because in the reality the cylinder head was cast as the single piece, it is very difficult to precisely determine its shape hidden between these fins:
While you can see the upper parts of the rocker covers on the reference photos, you can only guess their contours below the "fin surface".
There is a blueprint that provides some additional clues:
However, I have some doubts about details of the contour that you can see on the rear view above. (I marked it with thick dashed lines in the picture). Look at the lowest part of this top contour: it should correspond to the upper (outer) surface of the combustion chamber. According other drawings, the shape of this chamber resembled a regular dome. If so, why the fragment of its contour visible in this drawing seems to be (a little) oblique? In the cutaway depicted in the first photo in this post I cannot see such an oblique shape. And why the side contours of this heads (the vertical dashed lines below the valve openings) are not symmetric? Thinking about it, I concluded that this drawing was not focused on the precise representation of the cylinder geometry: its main goal was to show the lubrication areas. Thus all these details, which we can see here, were drawn thanks to a "good will" of its draughtsman. They were hand-made, ink-traced drawings, and we can be just thankful to this technician for such a detailed piece of work. Still, I assumed that these lines can differ a little from the real contours – just because of the plain human error.
I formed the basic shape of the rocker cover using two clones of the same mesh: I placed one instance on the auxiliary drawing, while the second instance is located in its proper position on the cylinder (Figure "a", below):
Modeling this cover as a separate object allowed me to switch between its local (along the valve axis) and global coordinate systems. I could also modify this mesh switching between its clones. I used the instance, located on the cylinder, to fit its base into the combustion chamber dome. The other instance of this cover, placed over the auxiliary drawing, allowed me to follow the shape of this element. (In fact, I could also put another instance of this mesh over the top view of the rocker cover. However, I did not do it - just because I used this view only during the initial phases of the modeling, and it was relatively easy to rotate the modeled object and move it over the side view).
This is the initial, "conceptual" model of the cylinder head, so I split it into the key "solids" and formed the semi-spherical cover of the exhaust valve as another object (the red one in figure above). Such an arrangement allows for easy manipulating of these parts. During this phase I have to determine their most probable sizes and locations. For example – following the precise location of the exhaust opening, I discovered that for the size as in the "Lubrication Chart", it has to be placed in a slightly different position (as in Figure "b", above). Otherwise, the right-bottom corner of the rim around exhaust opening would "sink" into the combustion chamber dome. (Of course, I also checked multiple times the most probable radius of this dome!).
When the whole thing seemed to match the photos, I made the rocker cover asymmetric (by "applying" its Mirror modifier and modifying the resulting faces). Then I modeled the oblique pushrod base (Figure "a", below):
To avoid some potential errors in the future, I started with placing the pushrod (another object) in the proper position, then formed the base around it. Figure "b", above) shows the resulting mesh. Note the sharp edges in its upper part. In the next step I rounded them, using a multi-segment Bevel modifier (Figure "a", below):
To have more control over these fillets, I used the weight-based version of the Bevel. Figure "a", above, shows the mesh edges that have a non-zero bevel weight marked in yellow. However, even in such a case, I could not avoid an artificial sharp edge between two fillets that were too close to each other (Figure "b", above). Well, in this situation I had to "apply" this modifier, and manually introduce small fixes to the resulting faces (Figure "c", above). I also dynamically created a "rim" around the upper edge of this cover. It is generated by the Solidify modifier, assigned to the thin face strip around this edge. Figure "d", above) shows the final result of these modifications.
While working on these parts, I simultaneously "scanned" the Internet, searching for more reference photos. Sometimes they just expose details, which were obscured in the reference materials that I already have. In this case – it was a protrusion on the rocker cover around the first and the last bolt (Figure "a", below):
I just had missed this tiny detail while forming the upper part of the rocker cover! Now I had a headache, how to fix it in a quick way. Ultimately I prepared two reference "cylinders" (I marked them in red, as you can see in Figure "b", above. Fortunately, there were many faces around the area that I had to modify. I placed these faces on the corresponding reference cylinders using the Blender Sculpt tool. (It allows me to push/pull multiple faces at once in a gradual manner).
You can see the final result of this modification in Figure "a", below:
Frankly speaking, I can see now that this protrusion had somewhat smaller radius. Ultimately I decided that it is "good enough" for the assumed level of details.
In the next step I cloned the rocker and valve covers onto the opposite side of the cylinder head: over the intake valve (Figure "b", above). In this first approximation of these parts, I rotated the intake valve cover (marked in red in the picture above), trying to find the proper location and angle of the intake opening. To fit it better, I also placed in this model the intake pipe. I knew, that in the future I will adjust its shape multiple times. That's why I crated it initially as a simple cylinder, smoothed by the Subdivision Surface and bent along a parent curve using Curve Deform modifier. By controlling the location, rotation and shape of the parent curve I had full control over this pipe.
The intake rocker cover had also a unique feature: two bolts on its front and rear walls (Figure "a", below). They were intended for mounting around the engine an eventual NACA cowling. (Wright added these bolts on the Army request). For this "conceptual" stage of the modeling, I decided to add the bases of these bolts as a separate part. (Because I expect that I will move/modify shape of this element many times, before I reach the result that matches the reference photos). I will eventually join it with the cover (and add appropriate fillets around its edges) when it fits well.
In the next step I transformed the clone of the intake cover into a completely separate object (marked in blue in Figure "b", above). I also added the bolt bases around the exhaust and intake openings. (As you can see in the figure above, there are four of them on the exhaust cover, and three on the intake cover). Initially I created these bases as separate objects.
Once I verified their location, I joined these bolt bases with the cover mesh (Figure "a", below):
I joined these objects by applying a Boolean (Union) modifier. However, after such an operation the resulting edges required some manual "cleaning" (removing doubled vertices and edges).
I also formed an initial approximation of the rocker upper cover (Figure "b", above). I just placed it over the left rocker. The front contour of this part had to fit the circular contour of this engine (dimensioned on the original installation drawing). I also rounded its upper edge using a multi-segment Bevel modifier, but I can see that this part will require further modifications.
While working with these rocker covers, I discovered that I made a mistake in reading the original blueprints! I thought that one of the exhaust rocker cover elements was a cross-section, while it was oblique view of one of its fins (Figure "a", below):
On the reference photos I can also see that the bottom pushrod base plane was bent, with sharp side edges (Figure "b", above). Thus I had to modify accordingly the bottom part of this cover (Figure "c", above).
Well, such "discoveries" slow down the overall progress of the work, but they are inevitable, if you want to build a close copy of the real object. They happen all the time, as I am collecting growing number of the reference photos. In fact, I have measured that I spend at least half of the overall time on analyzing the photos. (Sometimes I also sketch on a paper the most complex shapes, before I start to model them in Blender. These sketches help me to better "understand" the objects that I want to recreate). The complex details of the cylinder head are often obscured by the fins, which makes this element an extremely difficult case. I am sure that I will identify and fix many of similar mistakes in the nearest future. For example: I will shift and rotate the cover of the intake valve multiple times, and then have to adjust the intake pipe after each of these updates. That's why I prefer keeping this cylinder as an assembly of multiple, relatively simple objects. It would be much more difficult to modify this head, if it was a single, complex mesh. (In such a case you would have to care about all of its intersection edges!).
You can check details of this model in the source *.blend file. In the next post I will model the cylinder head fins.
Great work so far!
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