OK, here is part 3:
Now we come to a more challenging part: The canopy.
Some basics at first:
AFPD does calculate many physical values out of the actual geometry. For example the drag can be modified by the drag coefficient, but the front face is calculated out of the geometry.
For a realistic flight characteristic we should take care, that the aerodynamically important parts can be recognized as such. On a helicopter the canopy is the main producer of drag. Therefore we must define the canopy as “Fuselage-Object” and not as a “Chassis”.
This has also the side-effect that, if we intent to take our mechanic for a heli with scale fuselage, the new fuselage will automatically get the according aerodynamical attributes.
Another important point is the volume of the canopy. Because we can look inside the canopy from behind, we also have to think about the inside. The canopy will be a thin-walled volume with in- and outside.
Let’s start:
At first we need a nice side-view of the canopy that we can use in the background. I have used a composition of canopy and the rest of the heli because I couldn’t get a photo with the complete heli.
Then we draw the side-view of the canopy in the way that the poly-line is exactly on the symmetrical axis. Just take as much as needed polygons to get everything round.
The canopy is open at the upper- and bottom side. At first we only draw the part in front of the cuts.
Next we draw a poly-line with a few points on the symmetrical axis that should display the upper cut.
In the top-view we then the points to the outside to get an arc that accord the cut.
We only build the left side!
Do the same for the bottom cut.
Then join the endpoints of the upper and lower cut to build the trailing edge of the canopy in the side-view.
In the front-view we drag the polygons of the trailing edge to the outside. If necessary you can add some more points with the “Knife” function to get a nice shape.
In perspective view it looks like this:
To avoid surprises, overlay the rest of the heli to check if everything looks alright.
Looks fine so far!
With this we have created the base for our canopy.
A short comment: This procedure, to work from inside to outside is called “cageing”. A body is build at first as a rough grid on the striking positions and then filled with polygons.
Now we come to the “Window”.
We just draw a line around the border in the side-view. Use as little points as possible. Make the corners out of 3 points at maximum. You can use more but this doesn’t appreciably improve the visual effect.
The points of the window frame are still exactly on the mirror-line. To drag them outside according to the shape of the canopy, we need a reference.
Therefore we draw another line that connects the cone end with the trailing edge. I have placed it above the bulk. This makes it much easier.
On models with bigger bulks (like the Spirit Li) place it directly onto the bulk.
This line is kind of a longitudinal section. We modify it in the top-view to get the outer contour of the canopy.
It is recommended to place the points that are included according to the points of the window frame.
Then we drag the points of the window frame outwards until they match with the horizontal intersection in the top-view.
At the front- and upper edge of the window we must add some points to get a nice round shape in the front-view. It would be much easier if you have a proper photo of your heli.
Also here we use as less points as possible.
If you add points to the front- and upper window frame and move them to the correct position, check also in side-view if the contour is still ok. This is because points that are moved in front-view may also distort the photo in side-view.
Make sure that also in top-view everything is fine.
If we finally have finished the window frame, we check again if it still fits to our chassis. I recommend working very accurate here, because everything you miss now will come out with a lot of effort to be corrected later.
In my case the space between window frame and servo-arm was a little narrow and I have corrected it.
Afterwards you can already see how the canopy will look later on.
The further steps are easy, but need a little patience.
Let’s take core of the bulk on the side.
In the side-view we draw a line along the bulk. The line should be connected to the trailing edge of the canopy on one side and to the cut in the bottom on the other side.
This new line we modify in the front-view in a way that it goes along an “imagined” canopy shape. You will need a good sense of proportion here.
We add another line between the window and the upper edge of the canopy and adjust it in the top-view.
At the bulk we add some vertical lines that we use later as a support for the polygons.
It looks like this:
Below the horizontal “contour-line” we add another one the lays on the bulk from above. We need this to get a smooth intersection from the bulk to the rest of the canopy. Pull this line a little downward at the front.
It is important to constantly check the proportion of the whole canopy in different views. The canopy is nearly finished now and we can add the first polygons.
In case you have drawn the lines accurately and have taken care that neighboured lines have the same number of points you can easily draw the polygons between them. With a proper preparation this is like “drawing by numbers”.
We begin in the upper, middle part.
Then we draw in the same way some lines at the front and take care that neighboured lines have the same number of points.
After the front is filled with polygons you can switch on the automatic mirroring.
I have found that the foursquare polygons at the upper edge of the canopy do have ugly dents. They are caused by too hard stretching and bending of the polygons. This purely optical effect can be solved by “Triangulation”.
Therefore I have exchanged (manually) a few of the foursquare polygons by two triangular polygons and the dents are gone.
We add another line in the lower part of the canopy, adjust it and draw the polygons.
After we have drawn the last line into the remaining gap, we can “close” the canopy completely.
If we overlay the rest of the heli, it already looks quite fine.
The method of cageing needs some effort, but it has the big advantage that almost each form can be built very precisely. Especially for parts like the distinctive window there is almost no other chance.
Disadvantage is that all points that you have drawn must be touched and moved to the correct place. Therefore you should try to use not too many points.
The window itself we build in the same way.
At the moment the complete canopy including the window is one object.
At first we draw again some lines…..
… and form them accordingly. You should work very accurately here and make sure that the points show exactly the shape of the window.
The window will later get a reflecting surface (Shiny-value). Each dent will derogate this effect.
Then again you join the points to polygons. The biggest part is done!!
But we are not finished yet:
With “Freeze” we mirror the polygons to the other side and make sure that the points are connected on the symmetry-axis. The joining of the points is EXTREMELY IMPORTANT.
If you have worked accurately before, you will see that after “Freezing” the points at the mirror-level are already joined.
Anyway you should check this manually by using “join vertices” (Ctrl.+J) or each point. If you get an error message the points are already joined and everything is fine.
The joining of the points has 2 effects:
1. The polygons are “planed” via the centre
2. The “Extruding” will not create a vertical area there.
This is the point where you can make some final adjustments. Have a look at the canopy from all directions and “fine adjust” some points.
Now we come to the inside of the canopy. Some background information:
Polygons do have a front-and a back-side. In AFPD (and most of the other 3D Programs) only the front-side is displayed because of performance reasons. If you look through the window to the opposite inside of the canopy it is normally not displayed and our model does look a little poor.
To change this we need polygons that are in the inverse direction, with the front to the inside. This could be done by making them double sided, but I generally disadvice this.
There are several reasons not to work with double-sided polygons:
1. This figure is not a volume; it does not have a wall-thickness. If you look at it from the back-side it looks accordingly poor.
2. Double sided polygons are actually two polygons that are inversely overlayed. In many programs this makes problem with the display (“Flicker”.)
We will make it correctly and build the canopy as a thin-walled volume (it’s not too difficult)
Therefore we separate the window from the rest of the canopy.
We select the polygons of the window and move them with “Selected > Move face to a new object” into a new object.
Then we duplicate both objects.
I have named them as following:
-Fuselage (the original canopy without the window)
-FuselageInner (the copy of the canopy)
-Glass (the original window)
-GlassInner (the copy of the window)
Then we switch off the function “CObj” in the “Edit Option” Panel, select the two copied objects (FuselageInner, GlassInner) and invert them with “Selected > Invert”.
Now there front looks to the inside.
We keep both objects selected and move them with the “Extrd” function a little to the INSIDE.
With this procedure all necessary faces are created; on the back of the trailing edge of the canopy as well as on the border of the window.
If you overly the original canopy and the new inner part it looks like this:
Both glass-objects (Glass and GlassInner) can be joined to one object (select both, then “Selected > Cut >“Selected > Paste”).
We DON’T do this with the rest of the canopy (I will tell you later why)
We overlay the rest of the heli and we have a very nice canopy!!
