7. Landing Gear

In this Section:
Making the Wheels
Making the Struts
Animating the Landing Gear
Steerable Gear and Link Constraints
Cutting Out the Wheelwells
Making the Gear Doors

Making the Wheels

I've found the easiest way to make wheels is simply to shape a Cylinder to you wheel. This should really be easy, because we've already used this method to make our fuselage. Refer to Adding a Cylinder to refresh your memory.

For each wheel I'm going to use a 12-sided cylinder with 8 height segments. This seems to be a good balance between detail (how "round" it looks) and the number of polygons (to save on Frame Rate hits in the sim). You can see in the screenshot I've made "long" to start with, then I'll "squish" it when I'm done shaping it.

You can see in the screenshot at the left: After making sure I had Use Selection Center enabled on the tool bar, I used the Select and Non-Uniform Scale tool to select vertices and Polygons and then manipulate them to produce a wheel shape (see also Sub-Object Modification). You'll also need to put the "hubs" into a separate Smoothing Group than the "tires" (see Some notes on Smoothing Groups).

How detailed you want to get is up to you. The Stock CFS3 aircraft (from the Aircraft, Vehicle & Building SDK available at the Combat Flight Simulator Insider website) don't even have "hubs" modeled; rather, they're just painted on with the textures. While these may not be as "pretty" they're a lot quicker to make and have few faces to "drag" the sim's frame rates down. I follow the theory that When in doubt, "less" is "more"!

For the nose wheel, use Edit/Clone to make a copy of the main wheel you just made, then move the new one into position ("zero" on the "X" axis, and then move it forward) then scale it with the Select and Non-Uniform Scale tool. The hub may not be where you want it, so you can select vertices, edges, and/or polygons to manipulate with the Select and Non-Uniform Scale tool until you get it right.

Finally, ensure the Pivot Point in the

Making the Struts

For the struts we'll use the same method we just did with the wheel: We'll created a cylinder, scale is with the Select and Non-Uniform Scale tool and Rotate (if required) it into position. Once that's done you can continue to use Select and Non-Uniform Scale to move the "cross sections" and scale parts of the strut into cylinders to represent the "compression oleos".

The "compression oleos" need to be a separate object from the rest of the strut, so go ahead and select those polygons and then Detatch them. Don't worry about the names; I'll cover that below in the part on "Animation".

Another simple six-sided cylinder will be the axle for the wheel, and then you're ready to do the nose gear. This is done the same way. Like the wheel, you're welcome to get as detailed as you want. I've kept the struts rather simple here, but that's because I want to get this part of the tutorial done!

For a good description of how this is done (and the animation also) download the following files from Free Flight Design/Tutorials by Chris File.

Landing Gear-gMax Part 1	GMAX	LGTUT1.zip	300K	Chris	15NOV01
Landing Gear-gMax Part 2	GMAX	LGTUT2.zip	97K	Chris	15NOV01
Landing Gear-gMax Extra	GMAX	LGTUTXTRA.zip	27K	Chris	15NOV01

Animating the Landing Gear

The next step I've going to take is animating the gear, and there's a very simple reason for that. I don't have view of the bottom of the Me334, and therefore I'm not sure what the gear doors and gear wells look like, so I've going to animate the landing gear, then use view how (and where) they fold into the wing so I know where I need to gut the gear doors out!

Unlike the control surfaces, we'll be using Keyframe Animation where we'll have to designate the position the gear starts in, the position it ends its movement in, and possible a few points in between.

Naming Parts: First we need to name all of out parts. So, let's start with the Left Main Gear. All the parts of the Strut will be named "l_gear_x", with the "X" being any name you want. I've used numbers. I just started at the top part of the strut and named it l_gear_1, the next lower part (the "oleo") l_gear_2, and the "axel" is l_gear_3. We need to have two wheels (for the "moving" and "still" textures) so we'll select the wheel, then Edit/Clone, and name one l_tire_still and the other l_tire_blurred. The sim will automatically switch from "l_tire_still" to "l_tire_blurred" as the aircraft begins to roll. Just Link both tires to l_gear_3 (see the screenshot at left).

Linking the Parts: The key to properly animating the landing gear is in Linking the objects together. Take a look at Some Notes on Part Hierarchy for more on this, and also Other Details and Linking Objects. In the case of the landing gear, we want to link everything to the part that will rotate (l_gear_1).

To do this, we'll select l_gear_2, then click on the Select and Link button on the main toolbar, then click on the Select by Name button. Choose l_gear_1 and press Link (you could "drag" the link without using Select by Name, but it's easy to make mistakes doing this, although they are also easy to fix!). Now link l_gear_3 to l_gear_2 using the same method (see the screenshot above/left).

Animating: As we learned about Rotation Animation in Animating the Control Surfaces, Keyframe Animation is based on the location of the Pivot Point, (see Moving, Hiding, and Pivot Point in Chapter 4). In this case we need to move the pivot point to the spot on l_gear_1 we want the gear to rotate around.

Adding Animation Keys: Now we'll add some keys that will determine the location of the landing strut at a few positions along its movement path. For Combat Flight Simulator 3, the landing gear rotation is based on frames 0-100, while for Flight Simulator 2002 (and earlier MS sims) the gear rotation is based on a frame scale of 0-200.

Sim	Frame where Gear is 100% "Up"	Frame where Gear is 100% "Down"	Frame where Oleo is Compressed 50%	Frame where Oleo is Compressed 100%
CFS3	0	50	75	100
FS2002	0	100	150	200

Since I'm building this for CFS, I'll use 0-100 (if you're working for FS2002, then simply double the number for the key frame). Open the Motion Tab and select Rotation (under "PRS Parameters"). Drag the Time Slider all the way to the left to Frame Zero. Now click on the Rotation button under Create Key. You've created your first "Key Frame".

Next drag the Time Slider to Frame 50 (or type it in the Time window under Key Info) and Create another key. For this part of the strut, you only need to create a key at "0" and "50".

Animating the Strut: First, we'll Rotate the strut until it is in the 100% "Up" (retracted) position. Using the Rotate button on the main toolbar go ahead and rotate the strut l_gear_1 until it is in the retracted position (NOTE: Watching the Coordinate windows at the bottom of the screen you can see how many degrees you'll rotate the gear--Remember this. I rotated it 87°). You'll see that all your linked parts rotate along with it.

Now, click on the Toggle Animation Mode button on the bottom toolbar. You'll note that it turns red. The gear is now locked into this position at Frame 0. Now go to Frame 50 (you can either drag the Time Slider over to "50", or you can type "50" -or- you can "click" on the keyframe arrows under "Key Info" which will advance you to the next keyframe). Using the Rotate button again, rotate the gear until it is back in it's 100% "Down" (extended) position (simply rotate it back the same number of degrees you rotated it in the first place. In my case this was 87°).

You probably want to try it out, so check your animation by either dragging the Time Slider back and forth or pressing the Play Animation button at the bottom of the screen.

Animating the Oleo: Now we'll add the "compression" to the Oleo. For this we'll use a Position Key Frame, but otherwise this is nearly identical to the way we animated the strut. We'll create Position Keyframes at Frame 50 and Frame 100. Then, select Frame 50 with the Toggle Animation Mode button pushed, ensure the Oleo is in it's Fully Extended position. Then select Frame 100 and Moveand ensure the push the use the Move the Oleo to its fully compressed position. Now you should be finished with the main gear! Let's hit Play and see how it looks.

Steerable Gear and Link Constraints

We'll make the nose gear the same way but we'll have to add some other things in. For one, we'll want to make the nose gear Steerable. For the other, I want the nose gear to rotate 90° as it's retracting so the wheel lays flat against the fuselage. I don't know if this was the case with the gear on the planned Me334, but this was a common trait on WWII German aircraft with nose wheels.

To start with, first link everything together and create keyframes just as you did above with one exception: In this case we're going to start on Frame 1, not on Frame 0. Now, go ahead and animate your nose gear the same way you did your main gear. Don't worry about the position of the wheel for now (it'll stick out of the fuselage). Just have it linked to the Oleo the same way you did above, and make sure the upper strut is where it needs to be.

Link Constraints: To get the wheel to rotate 90° as the gear is retracting we'll have to use what's called a Link Constraint. The gMax help file says "A Link constraint causes an object to inherit the position, rotation, and scale of its target object..." In this case, we'll add a link constraint to the lower part of the strut (which the wheel is linked to) so that it will rotate independently of the rest of the gear while remaining linked to the gear. Otherwise the sim will attempt to rotate and retract the wheel at the same time, and it will be completely distorted. Note: I've not had any luck getting Link Constraints to work in FS2002. If they do, please let me know!

The 90° Rotation: To add a Link Constraint first ensure the Time Slider is at frame zero. Then selected the part you want to add the link constraint to, in this case c_gear_2 (the "Oleo") and then press the Unlink Selection on the main toolbar (we linked it originally only to "make sure" it was "lined up" with the rest of the strut in the retracted position). Now, with the Rotate button, rotate c_gear_2 (the "Oleo") 90° until it's in the "retracted" position. It should be completely "obscured" by the fuselage. If it's not, Undo and fix the animation of the upper strut--c_gear_1--until it's good.

Next go to the Motion Tab. In the Assign Controller rollout select the Transform: Position/Rotation/Scale controller, click the Assign Controller button and choose Link Constraint. Now, in the Link Params rollout you want to press the Link to World button which will allow you to animate the object independently of the rest of the gear (you should see "World: 0" in the Link Params window, meaning you are "linked to the world at Frame 0"). So, go ahead and add a Rotation Keyframe at Frame 1 and Frame 50 (the same positions as the upper strut), and then animate it so it rotates 90° between those frames. Now return the Time Slider to Frame 1 and under Link Params click Add Link then click on the upper strut--c_gear_1. Now test the animation. The gear should rotate smoothly as it extends from the retracted position until it's down.

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Stearable Gear: Now it's time to make the gear "steerable". There are two types of steerable gear. One that moves with the rudder, and one that moves on it's own as the aircraft is moving. Which one you use is as simple as a naming different in of a single object that we'll link the gear to. If this object is named rudder_1 (or another name starting with rudder_) then the wheel will move with the rudder. If the object is names c_wheel it will steer as the aircraft is steered (either using brakes or rudder). In other words, it won't move until the aircraft does.

In this case I'll have to use a Link Constraint because I've already used one "further down" in the Object Hierarchy (see Some Notes on Part Hierarchy). If the nose gear didn't have a Link Constraint in it's animation, then we could link directly to the c_wheel (or rudder_) object.

Cutting Out the Wheelwells

Note: You may want to Texture the Fuselage & Wings before detatching the polygons that will become your gear doors.

Now that we've got the gear animations working, it's time to cut out the wheelwells. If you're using an aircraft that was actually entered production (unlike the Me334) then you probably have some drawings including the other side from which to pattern you wheelwells and doors from. In that case, you'll want to load these drawing as a backdrop into gMax as a pattern for the doors (as we'll do below). Because I don't have any drawing depicting the underside of the Me334, I've use photos on the Me262 and Do334 (both German fighters with nose gear of about the same timeframe) to pattern my gear after.

Getting the gear to fit: Either way you do it, there's a good chance the landing gear won't fit into your wheelwell with the animation it has now. In that case you'll have to add some more keyframes in the first part of the animation so the gear starts "in" the wheelwell, then "extends" as it comes out, and is fulle extended at frame 50. You can see in the screenshot at the right how I did this: I added keyframes at Frame 0 and Frame 10 c_gear_2 is partially "compressed" at Frame 0, and therefore "fits" in the wheelwell. You can see the stock P-47 in the Aircraft SDK does this.

Cutting out the Wheelwell: Because I don't have any guide as to how the wheelwells of the Me334 looked, I'm going to use the wheels themselves as the guide. I'm going to make the main wheels first. In the Perspective viewport, I'm going to move the Animation Time Slider back until the wheels are about halfway imbedded in the wing and fuselage. Now I'll use Edge/Cut to cut out the wheelwell around the outline of the landing gear.

Extruding the Wheelwell: Now we'll select the polygons that make up the Wheelwell and Detach them, naming then "door1". Because my gearwell extends across both the wing and the fuselage, I'll detach the polygons on the fuselage and name them "door2". With these new objects we'll make both the wheelwell and the baydoors, so go ahead and Edit/Clone them so you have two sets. Hide one set (right click/Hide Selection). We won't need it until we get to the gear doors.

Attach the two halves of the ("door1" and "door2") together and Select all the polygons. Go ahead and Extrude them up until they don't overlap the gear (in the retracted position). Also see Creating and Extruding Polygons for more info. NOTE: If the extrusion is "separated" you may need to Undo, Select all the Vertices, and Weld Selected to about 0.005m. Then Extrude the polygons again.

Now, with the Polygons still selected go to the top viewport and click on View Align. Now using the Move tool adjust the polygons until you've happy with them. Now Name this object l_wheelwell. Your wheelwell is now complete!

Making the Gear Doors

Making the gear doors will actually be quite similar to making the wheelwell. We'll Unhide by Name the set of doors we cloned earlier (go to the Display Tab and click on Unhide by Name. I have joined the two door halves we had earlier, and now I need to make a further cut, because I've going to divide these into two objects again, but now here I currently have an Edge.

Now, Edit/Clone the doors (Yes, again!). Select one of the clones and Select the polygons just as you did for the wheelwell, and Extrude the polygons upwards just a bit to add "thickness" to the gear doors. Once that is done click on Elementin the "Editable Ploy" window, select all of them, and then click on Flip Normals. This will turn the object inside-out. Then you can go back to Poly and using the Select and Non-Uniform Scale tool you can resize them a little to give the doors taper.

Now we'll attach the Clone door back to this object, Weld Selected Vertices, and then can Select and Detach the Polys of the "inner door" from the "outer door". To finish the construction phase of the doors you simply need to use Polygon/Create to add the "ends" to the doors where you just detached them, then give them a name (I named then l_gear_dout and l_gear_din.

Animating the Doors: Compared to the animations we've done on the landing gear above this will be quite simple. For the l_gear_dout we only need to Link it to l_gear_1 (the upper strut on the Landing gear). l_gear_din has it's pivot point positioned along the inner hinge and is Keyframe Animated to open fully between Frame 0 and Frame 11.

I made and animated the Nose Gear using the same techniques as I used above. In the interest of time, I've not going to walk you through the details. After I made the Edge/Cuts for the gear doors in one half of the fuselage, I then applied a Mirror Modifier and Completed the fuselage as shown written in xxxxx. After the fuselage halves were joined I then Detached the "door polys", made the wheelwell, the Doors, and completed the Animation.

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