Learn to Use Blender - Part 6

This tutorial is currently a Work In Progress

Introduction

Once you create a decal, you now need to apply this decal to your aircraft. If you were working with a physical model you would by applying a sticker or paint using a stencil. In blender we need to do the digital equivalent to this.

The method I will show you here is called shrinkwrapping. There are many different options that blender gives us, but in the end, the method I show you here will take care of all of your needs. If you decide to experiment with this method (which I always recommend that you do to learn more about blender) you will get widely different results. This can sometimes lead you to finding these results more useful for different applications in the future.

When you made your decal you were primarily concerned with how the shape matched the reference images and trying to keep the vertex count low. In this step of the shrinkwrapping process, you may feel that we are taking a step backwards, but stick with it, and you will get a wonderfully applied decal.

The process for applying a decal to an aircraft is as follows:

  1. Sizing & Positioning - You need to to take your 2-D srf decal and import it into your aircraft blender file. Then re-size and position it so that you are prepared for the shrink-wrap process.
  2. Creasing - To prepare for the shink-wrap, we need to put 'creases' into the mesh to tell it where to bend around the aircraft.
  3. Separation - If the decal needs to be split between different blender objects, this is where you do it.
  4. Shrink-Wrap Modifier - Setup the shrink-wrap modifier for the particular application you wish to use it for. If you had to split the decal to cover multiple objects, you will need to repeat this step for each segment of the decal.
  5. Verification - Double check to make sure the decal is looking as you expect it to. You may need to put a crease in an unanticipated location to ensure everything looks good.
  6. Apply Shrink-Wrap Modifier - When everything looks good, you will apply the shrink-wrap modifier applied to each of the decal segments.
  7. Parenting & Recombination - When the decals have been shrink-wrapped now you need to ensure they follow the animated parts they are wrapped around (eg. Rudder) or combining multiple segments together (eg. non-animated Vertical Tail and Rear Fuselage) so that you minimize the number of blender objects and lock in the shape and position of the decal

I will show you the process of applying a decal, by shrink-wrapping a decal to the side of our fuselage, and then later show how to apply this concept to more complicated arrangements.

Step #1 - Sizing & Positioning

When you import the decal you made, or one from my decal packs, it will never be the right shape, size or even in the correct orientation you want it to be.

For this example I want to have the decal just behind the cockpit on both sides of the fuselage. Because there is text in the decal, we want to be able to read the text from both sides of the aircraft, which will impact how we proceed in the next steps.

Typically I like to position my decals about 3 to 5 meters away from the aircraft, so that when I look in the side view (number pad 1) or its reverse, I can see the decal in front of the aircraft. This allows me to position it in the correct spot and finalize any sizing changes that I need to make. The process I follow is as such:

  1. Import SRF file of decal into my blender file.
  2. Move decal to the right side of the aircraft, about 3 - 5 meters away from the fuselage.
  3. Rotate the decal in object mode about the x-axis such that the decal is now aligned vertically with the aircraft.
  4. Switch to side view
  5. Scale down the decal and position it in the x-z plane.

Once you have completed these steps we are ready to begin preparing the decal for shrink wrapping. If the decal you are using has text or otherwise needs to appear on both sides of the aircraft, duplicate the decal, move it to the other side of the fuselage and rotate it 180 degrees around the z-axis. Merge the two meshes together with:

ctrl -> j

Now you are ready to begin the process of shrink-wrapping the decal to the aircraft. Just in case, duplicate your properly sized and mirrored decal and move it to the third layer of your blender file using:

m -> 3 -> Return

You will need to select the decal in object mode in order for the above command to know which object to move. This will serve as a backup incase you make an un-recoverable error with your decal. It is better to create duplicates as a backup method at critical points in the shrink-wrapping process than to re-start from importing the SRF file.

One thing you will wish to do is make sure that your decal on the far side of the aircraft lines up with the original decal. All to often they will not be the same when you rotate the decal to the other side, so enter edit mode and fix it up!

Rotating Options

To rotate our decal, we have two main options. The first is simply to rotate the decal while in object mode. The downside of this is that we introduce a second step of clearing the rotation transformations from the object data. If you look in the Transformation Properties window, you will see non-zero values for some of the rotation and/or scaling values. In order to ensure proper dnm exporting when we are finished with our aircraft, we need to reset the transformation information to zero while not changing the physical transformations. Luckily there is a blender tool specifically for this process and it is only a few button clicks!

While you have the decal selected in object mode, follow the menu path below:

Object -> Clear/Apply -> Apply Scale/Rotation to ObData

This will change the Transformation Properties window as shown below:

The second method of rotating the decal into the proper place is to enter edit mode so that you can directly control the faces and vertices of the decal mesh. Select everything and apply the rotations to the mesh directly. The advantage of this method is that you do not have to fiddle with the Object Data, but it can sometimes be confusing to edit the mesh directly.

Step #2 - Creasing

When you first start shrink-wrapping, this step is possibly the most counter-intuitive of them all, but has the largest impact on how well your shrink-wrap will appear in the end. The easiest way to explain the idea is you wish to replicate the geometry of the surface you are wrapping around as closely as possible to avoid distortion in the final shrink-wrap.

For this step, you will almost entirely be in the wireframe view-mode in order to see the geometry lines of the fuselage. In more complicated aircraft, this may not be enough, however for our simple aircraft from OWL, the geometry is coarse enough to let us work easily enough.

As you look at the image below, the colors of the lines indicate what order they should be done in. The order you cut each color should not matter, but with your back up stored on layer 3, if you make a mistake here, there is nothing to worry about.

I ALWAYS cut the vertical lines first. If you reverse the order, and do the horizontal lines first, IT WILL NOT WORK WELL. Speaking from experience it is much better to cut the red, vertical lines, followed by the green horizontal lines.

Make sure to follow these steps for creating each cut:

  1. Enter Edit Mode
  2. Deselect everything to make sure there is nothing left out
  3. Select everything
  4. Perform an exact cut
  5. Deselect Everything

You should pick up on the fact that selecting and deselecting everything to make sure that you are not missing any faces is vitally important to this process.

Step #3 - Seperation

Because this decal is not wrapped around more than one object in blender. If it were, you would need to sepearte the decal mesh and perform two shrinkwraps. For now, we will skip this step, but if you are interested in learning about it now, you may look at my video tutorial about wrapping decals around 'complex geometries'.

Step #4 - Shrinkwrap Modifier

Modifiers are powerful tools in blender that we can use to manipulate objects and meshes in such a manner that would either be impossible to do by hand or take an extreme amount of time. The shrinkwrap modifier takes a decal and wraps it around another object in blender. Similar to how a sticker might look after applied to a water bottle, we will be wrapping the decal around the fuselage mesh of the aircraft.

To begin, select the decal in Object Mode and select the shrinkwrap modifier as shown to the right.

This will open a sub-menu in the button window where we will have to provide several inputs.

The Ob text box is where you enter the name of the blender object you wish to wrap the decal around. You can find out the name several ways but the easiest way is to select the fuselage in object mode and open the Transform Properties window and look at the title box on the upper left corner of the box..

After you enter the object name, your decal will start to wrap around the fuselage, however it might look very strange!

This is perfectly normal, because we have not finished setting up the shrinkwrap modifier. You will see this preview in Object Mode when you have defined a target object to wrap the decal around, however in Edit Mode, you will see where the mesh really is. It is important to understand that until a modfier is applied, it does not physically alter the mesh. If the modifier you are trying to setup starts to look bad, and you are not sure how to fix it, you can simply delete the un-applied modifier.

WARNING: Once you apply a modifier, you cannot undo it unless you use the undo shortcut: Ctrl -> z. As long as you do not apply the modifier, the change will remain in limbo, waiting for your command. If you export your model before applying the modifier, it will not appear in YSFlight.

To fix the odd preview from our initial shrinkwrap preview, we need to tell the modifier several factors. First, we want to have the decal separated from the surface of the fuselage just a little bit. If you look at the modifier sub-window above, the offset box has a value of 0.01. This means that the decal will be 0.01 meters (1 centimeter) from the surface of the fuselage. You may think that it should be on the fuselage, but YSFlight will render that as interference and not know whether to show the fuselage or the decal on top of the other. By adding in the offset, we force the decal to be displayed before the rest of the fuselage. Unless you are looking at the aircraft at some extreme angle, you will not be able to tell the difference.

Finally, we need to tell the modifier how to overlay the decal over the fuselage. 100% of the time, I use the projection option. This is what is used in real life, and looks the best when used for a decal in YSFlight. The important thing to know about the projection method is that it will be as if a movie projector was displaying the decal on whatever object you are targeting. You can have this method applied in any of the othogonal directions, both positive and negative, and as we will see, the negative is important because we have a decal on both sides of the fuselage.

As you can see in the images above, we select projection in the menu right underneath the offset box. Then we click on y, because that is the direction the decal should be projected, and finally make sure that Negative and Positive are both selected as shown to the right. This will produce an excellent decal that is tightly wrapped around the fuselage of the aircraft as shown below.

Step #5 - Verification

As with any operation you perform with a computer, you need to double check and make sure that this is what you desired from the beginning. When you have windows and other decal-like elements in the same area as pictured above, you may need to fiddle with the offset values for the different components of the aircraft.

Step #6 - Apply Shrink-Wrap Modifier

When you have everything as you want it, and are completely satisfied with the shrink-wrap modifier, it is now time to apply the modifier. If you have multiple modifiers applied to a single object, only the top modifier can be applied. To re-arrange the order, click the arrow keys next to the apply button to re-arrange the modifiers. Then when you are ready, click the apply button. When you have applied the modifier, it will disappear from the modifier sub-menu, and now the mesh of the object will be changed.

Step #7 - Parenting & Recombination

If you had to separate the decal to wrap it around multiple objects, or you need to parent it to an animated part, this is the time to do it. I typically do not parent any decals that will not be moving, however you may parent it to the fuselage if you desire.