Stretching Airplanes

Introduction

Have you ever altered your shorter (or longer) variant of a particular airplane into another variant? Most of the time the conversion process is actually very straight forward and simple. All you need to do figure out two things:

  1. How much do you need to add or subtract in front of the wing?
  2. How much do you need to add or subtract behind the wing?

For the most part, the wings for a YSFlight Civilian aircraft are pretty close to the center of the 3D model. Additionally, there are lots of animations near the wing such as flaps, brakes, ailerons and the main landing gear. Trying to move them as well as nearly every other animation in the model after you stretch or shrink it can prove complicated, and as you have probably learned by now, I don't like complicated if I can avoid it.

Since we will leave our wings alone, knowing how much we need to add to or subtract from the fuselage in front of and behind the wing becomes important. This can actually be the hardest thing to determine. What you ideally want to do is find a side-by-side comparison of the two variants.

I have done three projects where I stretched or shrunk the aircraft (737, 727 & 757) and in all of them I generally had to use side view images where the aircraft drawn shared a common point, and I was able to use the windows as a length reference.

Unfortunately for me the 757 doesn't have many quality drawings, but after several searches, I found the image below. This is actually the best image I've found for stretching an aircraft because it overlaps the two aircraft and keeps the wings right on top of each other, just like we want to do in blender.

The Math

As the title of this section implies, we need to do some math in order to determine how much we need to add to the fuselage to stretch the 757-200 into a 757-300. To do this we will need to find the following information:

  1. How much longer is the stretch variant.
  2. Ratios of the lengths added in front of the wing and behind the wing to the total length to be added. (i.e. is the added fuselage length split 1/3 in front and 2/3 behind the wing? 50-50?)

The first piece of information can usually be found on Wikipedia or from any number of online aircraft resources. From the image above I can estimate that the lengths are approximately 50-50 in front of and behind the wing, so each of my ratios is 0.5 or 1/2.

I can find the difference between the two aircraft from this image by: 54.5 - 47.3 = 7.1 meters

From this I find that I need to add 3.55 meters to the fuselage both in front of and behind the wing.

Preparing to Stretch The Aircraft

Now that we know how much we need to add to the fuselage, it is time to take a closer look at the fuselage to see what we can move around. I like to break down the fuselage into 3 main sections:

  1. Nose Cone
  2. Fuselage Cylinder
  3. Tail Cone

What I have highlighted here in blender is what I would consider the nose cone section of the fuselage.The key with this is that directly behind it, there are no cross-sectional changes to the fuselage until we hit the wing-fuselage interface.

What I have highlighted here is what I consider the tail cone for this particular aircraft. Note how I do not select up to the wing-fuselage interface even though there is the tiniest amount of cross-section change. This is because we do not want to move the mesh at that point because it is part of the whole wing assembly and the change is incredibly small.

Stretching The Fuselage

Stretching the fuselage is very easy. Simply go into Edit Mode and select the nose cone section. Then type in the following keyboard shortcut:

g -> "x" -> ##

In this case, ## represents the length in front of the wing you need to add.

Note how the front door becomes slightly engulfed by the fuselage. This is okay, and we will edit this later.

Then we need to move tail cone backwards. In Edit mode deselect everything and then use the following shortcut:

g -> "x" -> "-" -> ###

Because we want the tail cone to move backwards we need have the negative sign in there. the ### represents the amount you need to add to the fuselage behind the wing.

Adjusting the Rest of the Aircraft

Now that the fuselage is the right length, we need to get the rest of the components and animation in the nose and tail to match up with the fuselage.

Matching The Doors

I like to start by working with the doors so that I can use them as a reference if I need to. By using the same shortcuts as when stretching the fuselage, you can move the leading and trailing doors into their new positions.

Matching Other Mesh Components

While moving the door may seem easy, it is very important to remember that whenever you move a mesh (non-animated component) in the process of stretching an aircraft, you want to directly edit the mesh in edit mode to avoid the potential for things to move around on you later on. If the object center never moves from (0,0,0) but the vertices and faces move relative to the object center, then blender is not likely to cause problems.

Let's start by moving the tail light backwards to demonstrate this.

As you can see here, the lights on the 757 have several components all within the same blender object and SRF. however we need to move the rear light only. If we moved the entire blender object, then the lights on the wings would be in the wrong place.

Therefore we simply select the component of the mesh we need and move it backwards 3.55 meters.

Moving Animations or Parented Objects

When we move animations or other stationary parent-child trees, we need to move them with the uppermost parent object or empty. We will use the tail light as another example here.

For animations that are in the same general vicinity we can move them all at the same time.

Then after you move the group of animations you can move the nearby meshes. In the tail, I like to leave the horizontal and vertical tail as separate pieces in the end, so I moved them separately, rather than joining them together and moving the one large mesh.

I do a similar process with the landing gear.

The one major problem with keeping every mesh separate and moving each mesh separately is when we get to the cockpit. In my case, I have upwards of 20 meshes for different components in the cockpit. Rather than trying to move them all separately, merging them together can be a great way to not only save time, but also reduce the complexity of the dnm file.

WARNING

While merging the cockpit can be a great way to simplify things, you DO NOT want to merge your windows or the window frame that is view-able from the outside. These should be left as separate SRFs. Essentially if a pilot could touch this from inside the cockpit (ignoring the glass) and the part is not animated, then you can merge these components into one large cockpit mesh.

The one downside to this is that if you have not painted the cockpit, it can be very difficult to select the faces that you want to paint if the cockpit is one large object in blender.

Final Touches

Now that you have all the major components of your aircraft completed, you can now focus on some of the smaller details that are unique to the stretched variant you just made. Typically this means adjusting the windows to match up with the new door locations and adding more windows to represent the more passengers the aircraft can carry. As you can see here, I also needed to add in another door behind the wing to match up with the real aircraft.

Questions?

If you have any questions or comments, you can PM me on YSFHQ.com.