Lucky13
Forum Mascot
Exceptional work as always....and welcome back, I hope that you had a nice trip!
SBD Dauntless, from scratch
- Thread starter Witold Jaworski
- Start date
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Looking good so far!
- Thread starter
- #63
Witold Jaworski
Airman 1st Class
Wurger, Lucky13, Gnomey - thank you!
Let's continue. In this post I will create internal structure of the upper split flap. Structures of both flaps are similar, thus I started this job by copying stringers from the bottom flap, finished in the previous post:
Every copied stringer is a duplicate of its counterpart from the bottom flap (I just used the negative scale: -1). I had to rotate these objects, placing them on the internal side of the upper flap skin. I copied the internal ribs in the same way (see picture below). (All of them are clones, which use the same mesh):
As you can see in the side view (see in the picture above, upper left), there is just a small vertical distance between the last ribs of the upper and lower flap (i.e. at the aileron). This is the thinnest place of this structure.
At the trailing edge of the upper flap there is the profiled wedge (I described it in the previous post). The upper flap is little bit wider (it has longer chord length than the bottom flap). Because of this the ribs of the unified size used in these flaps are too short to reach the closing wedge (see picture above).
We can observe this effect on the photos. To make these ribs longer, designers added at their ends small "U"-shaped profiles (see picture below):
I recreated these elements in my model (see in the picture above, right).
The upper flap has a cutout in its inner edge. Thus there is "one and half" of the external rib here:
I recreated this structure in my model and modified the mesh of the upper skin:
These flaps were attached to the wing by two long hinges. I recreated them as two very long cylinders and placed between the flaps and the wing:
Now, when I rotate the hinge along its local Z axis, the whole flap rotates, like in the real aircraft:
This is a preparation for the future animation of this movement (during the detailing phase).
In this and the previous post I built the split flaps and their basic skeleton. I recreated these ribs and stringers because they are visible when the flaps are extended. The additional benefit of this work was the verification of my reference drawings. (Now I know that I have to shift a little the perforation and rivet seams on both flaps. I will do it when I prepare their textures). However, on this stage it is too early to finish all remaining details of these flaps. It still may happen that I will discover something which will force me to modify the geometry of this wing and its flaps. Thus in the picture below I marked what I prefer to postpone until the detailing phase:
As you can see in this picture, I will create the openings in the flap skin later. At this moment I am going to recreate them using the same technique as for the lightening holes: textures (the bump map and transparency map). However, if this idea fails, I will model these openings in the flap skin mesh. (This method requires much more time than the textures).
In addition to these openings I will also recreate all the minor details of the flap structure. For example — I will split the "L"-shaped auxiliary stringer between the ribs. I have also to split the flap forward reinforcements into separate segments.
The complex system of the flap actuators will be also a challenge for the detailing phase (however, I already analyzed how it works).
In this source *.blend file you can check all details of the model presented in this post. In the next post I will create the fixed slats and finish this outer wing panel for this "general modeling" stage of work. Of course, I will work on it again later, during texturing and detailing.
In the next post I will add fixed slats, completing this outer wing section.
Let's continue. In this post I will create internal structure of the upper split flap. Structures of both flaps are similar, thus I started this job by copying stringers from the bottom flap, finished in the previous post:
Every copied stringer is a duplicate of its counterpart from the bottom flap (I just used the negative scale: -1). I had to rotate these objects, placing them on the internal side of the upper flap skin. I copied the internal ribs in the same way (see picture below). (All of them are clones, which use the same mesh):
As you can see in the side view (see in the picture above, upper left), there is just a small vertical distance between the last ribs of the upper and lower flap (i.e. at the aileron). This is the thinnest place of this structure.
At the trailing edge of the upper flap there is the profiled wedge (I described it in the previous post). The upper flap is little bit wider (it has longer chord length than the bottom flap). Because of this the ribs of the unified size used in these flaps are too short to reach the closing wedge (see picture above).
We can observe this effect on the photos. To make these ribs longer, designers added at their ends small "U"-shaped profiles (see picture below):
I recreated these elements in my model (see in the picture above, right).
The upper flap has a cutout in its inner edge. Thus there is "one and half" of the external rib here:
I recreated this structure in my model and modified the mesh of the upper skin:
These flaps were attached to the wing by two long hinges. I recreated them as two very long cylinders and placed between the flaps and the wing:
Now, when I rotate the hinge along its local Z axis, the whole flap rotates, like in the real aircraft:
This is a preparation for the future animation of this movement (during the detailing phase).
In this and the previous post I built the split flaps and their basic skeleton. I recreated these ribs and stringers because they are visible when the flaps are extended. The additional benefit of this work was the verification of my reference drawings. (Now I know that I have to shift a little the perforation and rivet seams on both flaps. I will do it when I prepare their textures). However, on this stage it is too early to finish all remaining details of these flaps. It still may happen that I will discover something which will force me to modify the geometry of this wing and its flaps. Thus in the picture below I marked what I prefer to postpone until the detailing phase:
As you can see in this picture, I will create the openings in the flap skin later. At this moment I am going to recreate them using the same technique as for the lightening holes: textures (the bump map and transparency map). However, if this idea fails, I will model these openings in the flap skin mesh. (This method requires much more time than the textures).
In addition to these openings I will also recreate all the minor details of the flap structure. For example — I will split the "L"-shaped auxiliary stringer between the ribs. I have also to split the flap forward reinforcements into separate segments.
The complex system of the flap actuators will be also a challenge for the detailing phase (however, I already analyzed how it works).
In this source *.blend file you can check all details of the model presented in this post. In the next post I will create the fixed slats and finish this outer wing panel for this "general modeling" stage of work. Of course, I will work on it again later, during texturing and detailing.
In the next post I will add fixed slats, completing this outer wing section.
Lovely work so far!
Lucky13
Forum Mascot
Outstanding work!
- Thread starter
- #67
Witold Jaworski
Airman 1st Class
Wurger, Gnomey, Lucky13 - thank you! In this post I finally finish with the outer wing panel. (The result still misses many details, which I will reporduce during the last phase of this project).
In one of the previous posts I showed the details of the aileron bay. Now I separated the corresponding wing mesh fragment into a new object. I bent its upper edge like it was depicted on the photo:
On some photos I could see that this wall was built of two pieces of sheet metal. Their seam was located below the aileron pushrod.
The reason for such split became obvious after the comment I received from one of the readers (thank you, Brian!). It happened that a few weeks ago he visited the Yanks Air Museum in Chino, and had an occasion to examine wings of their SBD-4. He reported that while the bottom edge of the aileron bay is a straight line, the upper edge has a break at the pushrod. The difference from the straight line at this point is about 0.1-0.2 inches. Checking this tip, I examined photos of this particular SBD-4, then I verified photos of the other SBD version:
This nuance of the aileron edge is hardly visible in a perspective view. It explains why I missed it studying the photos!
Finally I recreated this detail in my model:
(Doing it, I had to modify shapes of three objects: the wing, the rear wall of the aileron bay, and the aileron).
I could not resist the temptation to recreate the rounded corner of the wing skin at the aileron root:
Frankly speaking, I should model such a thing during the detailing phase. I allowed myself to use some n-gons (faces that have more than 4 vertices) here, because this surface is flat so these n-gons will not deform the smoothed result.
However, looking on the photo above I noticed that the aileron bay edge seems to lie on the same line as one of the rivet seams on the flap. (The seam that runs along the rear edge of the hinge reinforcements). So it was on the reference drawing. However, do you remember that I had to modify these flap reinforcements, shifting them forward (in this post)? So now I know that this rivet seam is in another place on this flap, different from the place where you can see it on my drawing. Now I have to update accordingly the location of the aileron edge!
To preserve its vertical shape, I did it by two rotations: first I rotated it along Z axis:
Then I had to make a small rotation along Y axis (along the same pivot point), elevating these faces back onto the wing surface.
The updated layout of the flap ribs and struts means that I will have to move forward not only the rivet seams, but also the rows of the circular openings placed on the flaps (I mentioned it in one of the previous posts). What's interesting, the auxiliary "L"-shaped stringers on the upper and lower flap have different chordwise locations. In the result, the last row of the holes in the upper flap does not match its counterpart on the bottom flap (see picture above).
The last detail I will recreate during this stage of work is the fixed slat. It requires six openings in the wing skin: three on the upper surface and three on the bottom surface. I did not modify the wing mesh for this purpose, because additional edges around these openings would seriously complicate its topology. I decided to create them in another way: it may happen that ultimately I will make these holes using transparency textures, but for now I will do it using the Boolean modifier. First I prepared an auxiliary object — the "cutting tool"
I set the wing as its parent, and placed on a hidden layer. Then I used a Boolean modifier to dynamically cut out these openings in the wing:
Note that I placed the Boolean modifier after the Subdivision Surface modifier, to cut these holes in the resulting, smooth wing surface. As an additional bonus, this modifier also creates their internal walls (they come from the auxiliary object).
Although the "rib" walls obtained in this way are OK, I decided to create the front and rear walls of this slat as a separate object. Why? Because it is easier to modify its shape when it is not split into three "boxes", as the "cutting tool" object is:
I will join all these internal faces of the slats during the detailing phase. Currently I am leaving them in the current state, just in case I will have to modify the wingtip geometry.
This was the last element of the outer wing panel I wanted to create during the "general modeling" phase. I will recreate all of remaining parts (landing light, approaching light, Pitot tube, aileron axis arms, etc.) later, during the detailing phase.
In this source *.blend file you can check all details of the wing presented in this post.
In the next post I will start working on the centerwing. It will be occasion to find another parent for the "cutting tool" object, resolving the issue of disappearing slats.
In one of the previous posts I showed the details of the aileron bay. Now I separated the corresponding wing mesh fragment into a new object. I bent its upper edge like it was depicted on the photo:
On some photos I could see that this wall was built of two pieces of sheet metal. Their seam was located below the aileron pushrod.
The reason for such split became obvious after the comment I received from one of the readers (thank you, Brian!). It happened that a few weeks ago he visited the Yanks Air Museum in Chino, and had an occasion to examine wings of their SBD-4. He reported that while the bottom edge of the aileron bay is a straight line, the upper edge has a break at the pushrod. The difference from the straight line at this point is about 0.1-0.2 inches. Checking this tip, I examined photos of this particular SBD-4, then I verified photos of the other SBD version:
This nuance of the aileron edge is hardly visible in a perspective view. It explains why I missed it studying the photos!
Finally I recreated this detail in my model:
(Doing it, I had to modify shapes of three objects: the wing, the rear wall of the aileron bay, and the aileron).
I could not resist the temptation to recreate the rounded corner of the wing skin at the aileron root:
Frankly speaking, I should model such a thing during the detailing phase. I allowed myself to use some n-gons (faces that have more than 4 vertices) here, because this surface is flat so these n-gons will not deform the smoothed result.
However, looking on the photo above I noticed that the aileron bay edge seems to lie on the same line as one of the rivet seams on the flap. (The seam that runs along the rear edge of the hinge reinforcements). So it was on the reference drawing. However, do you remember that I had to modify these flap reinforcements, shifting them forward (in this post)? So now I know that this rivet seam is in another place on this flap, different from the place where you can see it on my drawing. Now I have to update accordingly the location of the aileron edge!
To preserve its vertical shape, I did it by two rotations: first I rotated it along Z axis:
Then I had to make a small rotation along Y axis (along the same pivot point), elevating these faces back onto the wing surface.
The updated layout of the flap ribs and struts means that I will have to move forward not only the rivet seams, but also the rows of the circular openings placed on the flaps (I mentioned it in one of the previous posts). What's interesting, the auxiliary "L"-shaped stringers on the upper and lower flap have different chordwise locations. In the result, the last row of the holes in the upper flap does not match its counterpart on the bottom flap (see picture above).
The last detail I will recreate during this stage of work is the fixed slat. It requires six openings in the wing skin: three on the upper surface and three on the bottom surface. I did not modify the wing mesh for this purpose, because additional edges around these openings would seriously complicate its topology. I decided to create them in another way: it may happen that ultimately I will make these holes using transparency textures, but for now I will do it using the Boolean modifier. First I prepared an auxiliary object — the "cutting tool"
I set the wing as its parent, and placed on a hidden layer. Then I used a Boolean modifier to dynamically cut out these openings in the wing:
Note that I placed the Boolean modifier after the Subdivision Surface modifier, to cut these holes in the resulting, smooth wing surface. As an additional bonus, this modifier also creates their internal walls (they come from the auxiliary object).
Although the "rib" walls obtained in this way are OK, I decided to create the front and rear walls of this slat as a separate object. Why? Because it is easier to modify its shape when it is not split into three "boxes", as the "cutting tool" object is:
I will join all these internal faces of the slats during the detailing phase. Currently I am leaving them in the current state, just in case I will have to modify the wingtip geometry.
This was the last element of the outer wing panel I wanted to create during the "general modeling" phase. I will recreate all of remaining parts (landing light, approaching light, Pitot tube, aileron axis arms, etc.) later, during the detailing phase.
In this source *.blend file you can check all details of the wing presented in this post.
In the next post I will start working on the centerwing. It will be occasion to find another parent for the "cutting tool" object, resolving the issue of disappearing slats.
Lucky13
Forum Mascot
Looking good so far!
fubar57
General
I understand nothing but it looks great.
Geo
Geo
SANCER
Senior Master Sergeant
Excellent and impressive work Witold!!! 
You have a formidable photos and computer images ... I do not even imagine what following in your tremendous project !!
Saludos y estoy atento al proceso
SANCER
You have a formidable photos and computer images ... I do not even imagine what following in your tremendous project !!
Saludos y estoy atento al proceso
SANCER
- Thread starter
- #73
Witold Jaworski
Airman 1st Class
Wurger, Gnomey, Lucky13, fubar57, SANCER - thank you!
fubar57 - well, this is a new branch of our hobby - digital models of historical airplanes. If you are interesting how to start, there are various materials at airplanes3d.net portal. For example - see the Finished Models section there. I share my models, and each of them is accompanied by the step-by-step introduction which shows how to start (and play with the included model)...
SANCER - on thing is sure: this project will require a lot of work (an time), because I am going to recreate as much details as I can (not only the cockpit and other visible elements, but also the engine compartment. It may happen that the complete skeleton, including all the ribs and spars hidden under the aircraft skin will follow
.
OK, below the next step of my (relatively slow) progress.
On the first glance the SBD center wing section seems to be a simple rectangular (i.e. constant chord) wing, with modified leading edge:
However, the landing gear openings visible on the photo can be difficult to recreate in a mesh smoothed by the subdivision surface modifier.
Additional photos from one of the SBD restorations made by Vulture Aviation in 2012-2013 reveal that the fuselage was mounted on the top of the wing (see the a) picture below):
A part of the upper wing surface was simultaneously the cockpit floor. Note the rectangular cutout in the middle of the leading edge. The SBD had a small window on the bottom of the fuselage, in the space between the two root ribs.
On the photo of the bottom of this wing (as in the b) picture, above) you can see that these root ribs had a modified airfoil shape: it bottom contour has a straight edge from the leading edge to the main spar.
I started to form the center wing section by preparing the single curve of its external rib. (I copied it from the root rib of the wing reference object, which I used during modeling of the outer wing panel):
I think that creation of these large landing gear bays (as the first picture in this post) will require a lot of modification in the wing mesh. Thus I decided to separate the mesh fragment that contains these openings (from the leading edge to the main spar) into a separate object. (It is always easier to modify topology of such a medium-size mesh part, than the whole wing). To ensure a smooth, invisible seam between this forward and the rear part of the wing, I had to accordingly prepare the control polygon of the initial airfoil. I added an additional point on each side of the vertices located above and below the spar line:
What's important, such three points have to be collinear. The resulting subdivision surface "touches" the middle point of such a fragment of the control polygon, and it is tangent in this point to these two adjacent control polygon segments. (This is just one of the mathematical properties of the Catmull-Clark subdivision surfaces, which are implemented in Blender).
However, these four new control points altered the shape of the airfoil curve. Now I have to fit this shape to the original NACA-2415 airfoil of the outer wing panel:
Fortunately, the Catmull-Clark curves/surfaces have another property similar to the NURBS: so-called local change. Their formula ensures that influence of a single control point does not exceeds two subsequent segments of the control polygon (two segments in both directions — see picture above, right). It is easier to focus on the modified mesh fragment, when you know this rule.
Once the initial rib shape fits the outer panel, I can extrude it forming the center wing section:
To shape the leading edge I had to stretch a little bit the forward part of this mesh. As you can see (in the picture above), I placed this new edge loop in the place of the wing root rib.
However, comparing the resulting object with the photos I discovered that the leading edge of the center wing section should have constant radius (at least approximately):
In this way I have found another error in my reference drawing: the wrong shape of the root airfoil:
The tangent direction at the wing spar differs from the direction estimated on the drawing, thus the bottom, straight segment of the root airfoil has a slightly different slope. The leading edge is much thicker than I draw on these plans.
I created a first approximation of the main wheel (it lacks the details) to check if it fits into the space between the leading edge and the main spar:
When I was sure that the shape of the wing is OK, I separated the forward part of this mesh (by splitting it along the main spar). As you can see (in picture above, right) these two parts join in a seamless way. It was quite simple to prepare such an effect in the initial curve by adding additional control points (as I described in the beginning of this post). It would be much more difficult to introduce similar modifications into the extruded mesh.
In this source *.blend file you can check all details of the wing presented in this post.
In the next post I will create the opening for the landing gear.
fubar57 - well, this is a new branch of our hobby - digital models of historical airplanes. If you are interesting how to start, there are various materials at airplanes3d.net portal. For example - see the Finished Models section there. I share my models, and each of them is accompanied by the step-by-step introduction which shows how to start (and play with the included model)...
SANCER - on thing is sure: this project will require a lot of work (an time), because I am going to recreate as much details as I can (not only the cockpit and other visible elements, but also the engine compartment. It may happen that the complete skeleton, including all the ribs and spars hidden under the aircraft skin will follow
.OK, below the next step of my (relatively slow) progress
.On the first glance the SBD center wing section seems to be a simple rectangular (i.e. constant chord) wing, with modified leading edge:
However, the landing gear openings visible on the photo can be difficult to recreate in a mesh smoothed by the subdivision surface modifier.
Additional photos from one of the SBD restorations made by Vulture Aviation in 2012-2013 reveal that the fuselage was mounted on the top of the wing (see the a) picture below):
A part of the upper wing surface was simultaneously the cockpit floor. Note the rectangular cutout in the middle of the leading edge. The SBD had a small window on the bottom of the fuselage, in the space between the two root ribs.
On the photo of the bottom of this wing (as in the b) picture, above) you can see that these root ribs had a modified airfoil shape: it bottom contour has a straight edge from the leading edge to the main spar.
I started to form the center wing section by preparing the single curve of its external rib. (I copied it from the root rib of the wing reference object, which I used during modeling of the outer wing panel):
I think that creation of these large landing gear bays (as the first picture in this post) will require a lot of modification in the wing mesh. Thus I decided to separate the mesh fragment that contains these openings (from the leading edge to the main spar) into a separate object. (It is always easier to modify topology of such a medium-size mesh part, than the whole wing). To ensure a smooth, invisible seam between this forward and the rear part of the wing, I had to accordingly prepare the control polygon of the initial airfoil. I added an additional point on each side of the vertices located above and below the spar line:
What's important, such three points have to be collinear. The resulting subdivision surface "touches" the middle point of such a fragment of the control polygon, and it is tangent in this point to these two adjacent control polygon segments. (This is just one of the mathematical properties of the Catmull-Clark subdivision surfaces, which are implemented in Blender).
However, these four new control points altered the shape of the airfoil curve. Now I have to fit this shape to the original NACA-2415 airfoil of the outer wing panel:
Fortunately, the Catmull-Clark curves/surfaces have another property similar to the NURBS: so-called local change. Their formula ensures that influence of a single control point does not exceeds two subsequent segments of the control polygon (two segments in both directions — see picture above, right). It is easier to focus on the modified mesh fragment, when you know this rule.
Once the initial rib shape fits the outer panel, I can extrude it forming the center wing section:
To shape the leading edge I had to stretch a little bit the forward part of this mesh. As you can see (in the picture above), I placed this new edge loop in the place of the wing root rib.
However, comparing the resulting object with the photos I discovered that the leading edge of the center wing section should have constant radius (at least approximately):
In this way I have found another error in my reference drawing: the wrong shape of the root airfoil:
The tangent direction at the wing spar differs from the direction estimated on the drawing, thus the bottom, straight segment of the root airfoil has a slightly different slope. The leading edge is much thicker than I draw on these plans.
Adapting the well-known von Moltke's sentence: "no plan survives contact with the enemy" to this situation, we can say that "no scale plans survive contact with their 3D model".
I created a first approximation of the main wheel (it lacks the details) to check if it fits into the space between the leading edge and the main spar:
When I was sure that the shape of the wing is OK, I separated the forward part of this mesh (by splitting it along the main spar). As you can see (in picture above, right) these two parts join in a seamless way. It was quite simple to prepare such an effect in the initial curve by adding additional control points (as I described in the beginning of this post). It would be much more difficult to introduce similar modifications into the extruded mesh.
In this source *.blend file you can check all details of the wing presented in this post.
In the next post I will create the opening for the landing gear.
Lucky13
Forum Mascot
Outstanding work as always!
Lovely work so far!
vikingBerserker
Lieutenant General
Very cool!
- Thread starter
- #78
Witold Jaworski
Airman 1st Class
Wurger, Lucky13, Gnomey, vikingBerserker - thank you!
In this post I will cut out the opening of the landing gear bay in the wing. In the SBD Dauntless its shape consists a rectangle and a circle:
However, when you look closer, you will notice that the contour of the main wheel bay is not perfectly circular. There is a small deformation of its shape on the leading edge (see picture above). I think that it looks in this way because of the technological reasons. Another feature of this opening is the fragment "cut out" in the bottom part of the fuselage, below the wing. (We will make it when we will form the fuselage).
I started by applying all the information that was confirmed by the general arrangement drawing and various technical descriptions: the main wheel used 30"x7" tire. Its center was placed 18.5" from the firewall (measured along the global Y axis)
The X coordinate of the wheel center can be determined by the location of the root rib (10") + small gap + tire radius (30"/2) ≈ 26".
Then I tried to put around the main wheel a test contour of the opening in the wing:
Initially I thought that I will recreate this opening by embedding a subdivided octagonal hole in the wing mesh, as I did in my P-40 model (see Vol. II of the "Virtual Airplane" guide).
However, when I created an appropriate octagon around the wheel, I discovered that one of its vertices lies outside the wing mesh (see figure a), above). You cannot compose such a contour into the wing. Therefore I decided to create this opening using another Boolean modifier, as I did in the case of the fixed slats (described in one of the previous posts). I prepared the basic contour of the "cutting tool" — a smooth circle based on a 16-vertex polygon (as in figure b), above).
The fragment of the main wheel opening that "touches" the wing leading edge seems to be flatten a little (see the first picture in this post). To obtain such an effect I rotated the "cutting tool" object (the ring) by a few degrees so its Y axis was perpendicular to the leading edge. Then I shifted a little the single edge of this ring along the Y axis, fitting it into the wing:
By small movement of these two vertices I was able to precisely recreate the shape of this opening visible on the photos:
If I do not want to get the inner part of the "cutting ring" inside the resulting opening, I have to assign to this wing mesh a sheet metal thickness (using the Solidify modifier – as in picture below):
Because the forward and rear part of the wing are separated, I can use this Solidify modifier only in the front part. In this way I do not increase the polygon count of this model with unnecessary faces.
As you can see in the picture above, I also created a second "cutting object" — a box. I will use it to recreate the rectangular opening around the landing gear leg. Both of these tool objects are located on a single layer (9) which will be hidden during rendering. Their parent is the rear part of the center wing section (to avoid dependency conflict with the front part of the wing).
Finally I assigned both of these "cutting" objects to the Boolean (Difference) modifiers of the wing skin (The same method as used for the fixed slats). You can see the result in picture below:
It would be quite difficult to recreate such an opening by altering the control mesh of the wing skin. It also would make its shape more complex, and difficult to unwrap in the UV space (for the textures).
The openings created by Boolean modifiers have another advantage: it is very easy to modify their contours. I had to do this just after I created these holes. I discovered that I made minor error in the reference drawing: the landing gear leg opening should lie a little bit back. (Its centerline should pass through the landing gear wheel center
All what I had to do was to shift back the auxiliary box object, which creates this opening. So easy!
On the other hand, I observed small shadows caused by triangular faces created by the Boolean modifiers along edges of this opening. It was impossible to remove them in the typical way — using the Auto Smooth option or the Edge Split modifier. The only solution was to increase (from 2 to 4) the level of the Subdivision Surface modifier assigned to the wing surface object. It increased 16 times the number of resulting smooth faces created from this mesh. Fortunately, I split the wing into two parts, so I could set keep such a dense mesh only around the area where it is needed.
In this source *.blend file you can check all details of the wing presented in this post.
In the next post I will create main spars and ribs, visible inside this opening.
In this post I will cut out the opening of the landing gear bay in the wing. In the SBD Dauntless its shape consists a rectangle and a circle:
However, when you look closer, you will notice that the contour of the main wheel bay is not perfectly circular. There is a small deformation of its shape on the leading edge (see picture above). I think that it looks in this way because of the technological reasons. Another feature of this opening is the fragment "cut out" in the bottom part of the fuselage, below the wing. (We will make it when we will form the fuselage).
I started by applying all the information that was confirmed by the general arrangement drawing and various technical descriptions: the main wheel used 30"x7" tire. Its center was placed 18.5" from the firewall (measured along the global Y axis)
The X coordinate of the wheel center can be determined by the location of the root rib (10") + small gap + tire radius (30"/2) ≈ 26".
Then I tried to put around the main wheel a test contour of the opening in the wing:
Initially I thought that I will recreate this opening by embedding a subdivided octagonal hole in the wing mesh, as I did in my P-40 model (see Vol. II of the "Virtual Airplane" guide).
However, when I created an appropriate octagon around the wheel, I discovered that one of its vertices lies outside the wing mesh (see figure a), above). You cannot compose such a contour into the wing. Therefore I decided to create this opening using another Boolean modifier, as I did in the case of the fixed slats (described in one of the previous posts). I prepared the basic contour of the "cutting tool" — a smooth circle based on a 16-vertex polygon (as in figure b), above).
The fragment of the main wheel opening that "touches" the wing leading edge seems to be flatten a little (see the first picture in this post). To obtain such an effect I rotated the "cutting tool" object (the ring) by a few degrees so its Y axis was perpendicular to the leading edge. Then I shifted a little the single edge of this ring along the Y axis, fitting it into the wing:
By small movement of these two vertices I was able to precisely recreate the shape of this opening visible on the photos:
If I do not want to get the inner part of the "cutting ring" inside the resulting opening, I have to assign to this wing mesh a sheet metal thickness (using the Solidify modifier – as in picture below):
Because the forward and rear part of the wing are separated, I can use this Solidify modifier only in the front part. In this way I do not increase the polygon count of this model with unnecessary faces.
As you can see in the picture above, I also created a second "cutting object" — a box. I will use it to recreate the rectangular opening around the landing gear leg. Both of these tool objects are located on a single layer (9) which will be hidden during rendering. Their parent is the rear part of the center wing section (to avoid dependency conflict with the front part of the wing).
Finally I assigned both of these "cutting" objects to the Boolean (Difference) modifiers of the wing skin (The same method as used for the fixed slats). You can see the result in picture below:
It would be quite difficult to recreate such an opening by altering the control mesh of the wing skin. It also would make its shape more complex, and difficult to unwrap in the UV space (for the textures).
The openings created by Boolean modifiers have another advantage: it is very easy to modify their contours. I had to do this just after I created these holes. I discovered that I made minor error in the reference drawing: the landing gear leg opening should lie a little bit back. (Its centerline should pass through the landing gear wheel center
All what I had to do was to shift back the auxiliary box object, which creates this opening. So easy!
On the other hand, I observed small shadows caused by triangular faces created by the Boolean modifiers along edges of this opening. It was impossible to remove them in the typical way — using the Auto Smooth option or the Edge Split modifier. The only solution was to increase (from 2 to 4) the level of the Subdivision Surface modifier assigned to the wing surface object. It increased 16 times the number of resulting smooth faces created from this mesh. Fortunately, I split the wing into two parts, so I could set keep such a dense mesh only around the area where it is needed.
In this source *.blend file you can check all details of the wing presented in this post.
In the next post I will create main spars and ribs, visible inside this opening.
Nicely done so far!
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