This
knowledge was fundamental while modeling that beautiful pair of
ducted fan nacelles for the SoloTrek™ aircraft. If you pay
attention to their renderization you will notice that they seem
to be hollow when looked from the front/up but that they are closed
when looked from the back/rear.
It
was a design decision because the way X-Plane renders each part.
I had to choose one side to be visible (hence to seem closed,
but nothing that a good blue-sky colored texture could not disguise).
Each
plane part is rendered just on one side of its polygons, so if
you find a way to look from the other side (let's say from the
interior of the body) you will not see the polygon texture; it
will be transparent.
The
key is to learn how to fold that "tube" shape (which
is the starting shape for any new plane) in ways that you have
control of what will be visible and what will be transparent.
It will be useful while doing engine nacelles, usually for their
intakes.
Here
you see SoloTrek™'s nacelles from both directions:
I
would like the central engine core been painted all black but
that is other issue related to the texturization process of X-Plane's
engine preventing this. The engine core shown above is been rendered
with the same texture pattern of the external duct, not by my
desire but as a kind of overrun of the textures. Now you can guess
why there is a blue ribbon painted over the duct's perimeter:
that is for getting the visible rear of the circle disguised as
a blue-sky, but that is another story...
Back
to the main subject of how to displace the sections (ribs) and
then how to control their behavior, you must understand that starting
from the first section (station #1) in the part been modeled,
anytime you put the next section at a lesser coordinate than the
previous section, the skin (polygons) that goes from that previous
section to this one will be rendered by the inside, and while
placing it at a greater coordinate the skin will be rendered by
the outside.
Well,
it is easier to illustrate than to explain, so take a look at
this following image assuming that if you were placed at the cyan
side of skin (or "wall") it would appear transparent
to you, and when placed at the red side of skin you would see
its texture.
