Soon after I started using FSDS I decided any aircraft I designed that had retractable landing gear would have 3D gear bays. My first attempts at this were pitiful to say the least. I found it was almost impossible to line up a gear bay "box" I designed to the wing without bleed through. After trial and error I had a system that was easy to design with no bleed through. Here is my tutorial on how to build 3D gear bays or any other type of recessed area such as cockpits etc. The following is only an example of the process. The wing and gear are not to scale for any aircraft.

First is the planning stage of the gear bay. This starts with the wing template. Make sure that the fore and aft placement of the bay is between 2 points on your template (figure 1).

Figure 1

After your wing is made you will have to make sure that the bay is positioned between 2 sections. Don't move a section right or left as it will distort the wing. You can add sections between sections and then delete the ones you don't need. Figure 2 shows the wing before and after I have added and deleted the sections to get the area where I want to place the gear bay. Sometimes when adding and deleting sections some polygons are flipped for some reason. Go to polygon mode and flip any polygons that are not pointing out on the whole wing.

Figure 2

Now that we have a general area to build the bay, it is time to define the shape of the bay on the wing and cut it out. This example bay will have a 2 door cover much like a P51D. We could just move the vertex points around to define the shape but distortion of the wing will occur. Instead we will add 4 vertex points inside the polygon and move them to define the gear door shapes. Here is how you do that. Select - Part/Add/Polygon and create a 4 sided polygon on the Y axis. Go to polygon view and flip the new polygon if necessary. Now rotate and size it as necessary and move it to the area shown in figure 3. You will need to position it within the same plane as the polygon shown. An easy way to tell is to change it to a different color and view in perspective to get your bearings as to where it is.

Figure 3

The next step while in part mode, Select -Edit/Select All. Then Select - Part/Join Selected. The wing and the polygon should be one part now. Now go to polygon mode and select the new polygon you just made (figure 4) then delete it. Don't worry all that work wasn't in vain. The polygon is gone but the vertex points are still there.

Figure 4

Now select the lower wing polygon the new polygon was in (figure 5) and delete it also.

Figure 5

You should end up with a nice hole in the wing (figure 6).

Figure 6

Now go to point mode. You should have 4 vertex points inside the empty wing space where the polygon was (figure 7).

Figure 7

Now it's connecting the dots time. While in point mode, Select - Mouse Select icon and select 4 vertex points, 2 on the wing and 2 from the newly deleted polygon vertex points (figure 8). Make sure if any points were selected on the upper part of the wing to unselect them before proceeding.

Figure 8

Now Select - Polygon/Make Poly From Select Points. You should have a new polygon (figure 9). If necessary flip the polygon to correspond with the other wing polygons.

Figure 9

Continue on and create 3 other polygons in the same manner to end up with something that looks like (figure 10).

Figure 10

Now we have a hole in the wing we need to fill in. Select the center 4 vertex points and Select - Polygon/Make Poly From Select Points. All the polygons should now be visible. Lets move the points around to define the shape of the bay and 2 gear doors. Go to Point Mode, select your points and move them around to define the bay shape. My shape looks like (figure 11).

Figure 11

The hard part is done. Now it is time to cut out the bay and build it to the wing. The parts we are going to cut out are to be saved. These parts are used by Aircraft Animator to cover the gear bay when the gear is up. The actual doors we will be making won't be used when the gear is retracted. The reason for this is as many know the gear is usually raked forward and in this retracting gear setup one gear door is attached to the gear strut. Making a seamless fit is almost impossible when the gear is retracted. OK here we go...

Go to polygon mode. Select the 2 polygons as in (figure 12). Then Select - Part/Split part. Go to part mode. Save the part (I used gearbay closed) as the filename. While in Part Mode Select the next entity icon and select the wing. Select - Edit/Check Parts/No to check the current part. This lets FSDS fix any polygons. Depending on the project and results from this step you might or not want to do this. On this project it worked fine.

Figure 12

Now to build the bay. While still in part mode Select the gearbay closed part. Select move mode and select constrain X and Z. Move the part down as in figure 13. This will be the upper part of the gear bay. Next select the gearbay part and the wing then Select - Part/Join Selected. The gearbay part and the wing should now be one part.

Figure 13

The next phase in building the gear bay we have to join the gearbay part to the wing. These joining polygons will be the gear bay sides. Go to Point Mode and Select - Mouse Select. Select 4 vertex points, 2 from the wing and 2 from the gearbay part (figure 14).

Figure 14

Now Select - Polygon/Make Poly From Selected Points. If the polygons are split, meaning part is showing and part is not, you will have to select 2 points from the polygon and flip it to get it to display properly. A procedure for this is in the FSDS help files under advanced exercises/creating polygons from existing points. You should have a polygon connecting the wing to the gearbay part (figure 15).

Figure 15

During this time I apply a texture to each polygon as I go. It seems easier to see what I'm doing. So while in polygon mode and the polygon selected, right click your mouse. Click Textures/Custom Texture/Texture Properties and apply the texture to the polygon. Continue on around the gearbay part connecting the part to the wing with polygons until a complete box is built (figure 16).

Figure 16

Now that the gear bay is built let's put it in the wing. Go to point mode and select all the lower points (figure 17).

Figure 17

While still in point mode Select - Move Mode, Constrain X and Z. Move the gearbay part up into the wing as far as it will go without coming out the top side of the wing (figure 18). This is the completed gear bay. Next is to build the doors for the bay.

Figure 18

Save the wing and either hide it or delete it from view. Now load the previously saved gearbay closed part. Select polygon mode, select one of the gearbay door polygons, then Select - Part/Split Part. Save one part as geardoor1 and the other part as geardoor2. Hide or delete one of the gear doors. Select - Edit/Copy, then Select - Edit/Paste. Select Move Mode and Select Constrain X and Z. Move the copied part down as in (figure 19).

Figure 19

Now check each of the 2 parts and make sure the polygons are each facing out. Correct if needed. Select all the parts, then Select - Part/Join Selected. Now we have to build the edges of the gear door. This is done the same way we built the sides of the gear bay for the wing (figure 20).

Figure 20

In point mode select all the bottom points. Select Move Mode and Constrain X and Z. Move the lower portion up to get the desired thickness of the gear bay door (figure 21). Save this part and complete the same procedure for the other door.

Figure 21

This completes the 3D gear bay tutorial. Here are the sequences for the gear bay using Aircraft Animator.

For the larger gear door attached to the gear struts is 1-25:0;25-75:+2;75-100:0

For the smaller gear door 1-25:+4;25-75:0;75-100:-4

For the gear bay closed part 0-1G

Using the sequences above the gear bay doors and landing gear is visible until they are fully retracted. When fully retracted the doors and gear are hidden and the gear bay closed part becomes visible and covers the landing bay recess.

Any comments are welcome I hope this helps it has worked great for me.

Mike Crosthwaite
m431c@gbis.com