The landing gear on this aircraft is just one small piece of a very large project. I’m re-creating the entire aircraft, but for a fiction I’ve been writing for some time, so I will be taking some creative liberties with the aircraft. I’m hoping to keep much of the mechanical functionality faithful to the real-world airplane. Once this 3D aircraft is in its final form, it will help me tell a story of globe-trotting adventures. That finished aircraft model will be used for rendered illustrations and, hopefully, cinematics.
But for now, I’d like to talk about some of the work I’ve done so far in putting together a complex part of this aircraft - the rear landing gear, which deploys from inside the hull of this amphibious aircraft.
Please Note: The works in this article are in progress. All of the models and materials you see in these renderings and animations are approximate, and are subject to change.
Deforming tires, multiple piston rigs, rotating fairings, deforming brake lines & tires, all working off of a single control parameter.
Based on a real-life aircraft, I’m re-creating a PBY-5A, an amphibious WW2 submarine hunter. I’m working closely with reliable references such as historical books and even a generous local museum.
The Project:
PBY-5A Catalina Landing Gear Illustrations
Staying motivated when working on large personal projects can be challenging. Generally it’s best to stick to smaller projects to avoid this. However when I find myself working on a larger scale project, I find it’s best to set milestone goals which lead to a result that can be published, maybe even a product.
Right now, I find myself re-creating a historic World War II airplane in 3D, exterior and interior. It’s for a fiction, so I will be taking some creative liberties, but the aircraft in the fiction is a PBY-5A nonetheless. To keep from burning out in this big undertaking, I decided to create a small project out of a larger one. To create a multi-picture illustration which demonstrates the PBY’s working landing gear system. Why? Because it’s cool, and I would hang pictures like that in my house. And if I will, maybe others will want to buy copies from me to do the same.
The Subject
The PBY’s rear landing gear is unconventional. When the aircraft was originally designed, by a now defunct aviation company called Consolidated, it was only capable of landing on water - it had no landing gear for conventional paved landing strips. But very soon after delivering the first iteration of the aircraft, Consolidated re-visited the design, modifying it so the rear landing gear would tuck into the sides of the aircraft hull and effectively turning the boat-plane into an amphibious submarine-hunting war machine.
For this multi-print illustration I’m working on, and the 3D PBY’s future use, I’ll need landing gear that functions just like the real plane. For the prints, I’ll be rendering a few images of the stages of deployment of the landing gear:
Collapsed and flying,
starting to deploy,
completely extended,
touch-down and rolling,
at rest on the ground.
I’d like to describe what technical work goes on behind an animation like this.
The Rig
When creating complex mechanical elements that will animate in 3D, it’s important to consult accurate references. Considerations for animation need to be made upstream from the very start when you begin modeling.
In the 3D application I’m using called Modo, the user has many options for creating a rig for mechanical animation. For most of the models in this rig, I’m simply using a parent-child hierarchy to animate the landing gear. But I’m also mixing some other rigging methods for some pieces including; constraints and different geometry deformer types.
Hierarchy
When modeling the landing gear, it will need to be broken up into individual pieces so they can be animated separately. To do this, each piece of the model will belong to a hierarchical structure. This hierarchy is a tree of parent-child relationships which allow for various 3D models (children) to be translated and rotated in 3D space by the transformation axis of another object (the parent). So the most ideal time to start planning your rig is in the modeling stage, otherwise you may find yourself redoing a lot of work downstream.
Constraints
In addition to the parent-child hierarchy, there can be special animation relationships between objects called constraints. These constraints can live inside and outside of the hierarchy structure, but their placement in or out of that structure is not arbitrary. If not setup correctly, errors can be created like double-transformations and other animation phenomena.
In the animated image above, you’re actually seeing two constraints at work: Direction constraints for the main piston and forward & aft wishbone suspension, and a position constraint for the brake-line organizer. And the two triangles are ‘upvectors’ for the direction constraints on the wishbones - because the entire rig rotates into the aircraft hull, the rotation can confuse the constraint if these upvectors do not exist.
Deformation
For the ‘organic’ type of objects on this model, such as the tires and the brake lines, I’m using a couple of geometry deformation tools:
For the tires, I’m using a lattice deformer to create the inflated ‘swollen’ state of the tire when it comes to a rest on the ground. Since the tire has to roll along the ground or completely lift off of the ground, I don’t always want the mesh to be deformed, and I also only want it to deform in one spot. To limit the lattice deformer to only deform an isolated part of the tire, I’m using one of Modo’s useful linear falloffs, which allow the tire to deform only when it touches the ground. Falloffs essentially act as a mask for effector influences in 3D space, and they’re one of the tools that make Modo the best 3D application on the market.
For the brake lines, I’m simply using a skeletal rig with an inverse kinematics (IK) chain, which is bound to the brake line mesh with skin weights. Inverse kinematics works fundamentally different than forward kinematics. Instead of animating from the root of the chain to the end, you animate first from the end, using a ‘goal’ object to animate the rig in combination with twist and orientation parameters. And with the brake lines on this landing gear, the goals are parented to the appropriate places in the hierarchy, and so are the IK roots. This allows the brake lines to deform while staying attached to various parts of the landing gear, just as they would in reality.
References
Where to get references is an interesting subject to me these days. With the internet being the easy way to get to anything you need immediately, including images, it feels like many have forgotten about books. For references, I still find them a very important resource. The information inside of them are specifically and carefully curated around an intentional subject by the author(s); images are detailed and accurate, history is thoroughly researched, and interviews with subject matter experts can often be found.
In addition to books, I also value going places and looking at your references in person. For military machinery, museums are some of the best resources available to so many around the world. And a few of the best military museums are located in my current residence of Washington state.
Books
80 Years, A Tribute to the PBY Catalina
By Hans Wiesman
For information around the subject of my passion project, Hans Wiesman has done the work to publish a very high quality photo-illustrated book that goes through the entire history of this aircraft. In it, the plane’s origins are covered, its years of service in militaries in the USA and across the globe. Also covered in the book is other uses it found once it was retired from most militaries and found use in the civilian market, as well as information on Catalina’s that are still operational.
Museums
Pacific Northwest Naval Air Museum
PBY Memorial Foundation
Living in Washington state actually turned out to be a good coincidence for this project. Just over an hour north of Seattle is the Naval Air Museum of the Pacific Northwest which owns and is restoring its very own PBY-5A Catalina.
The museum staff was generous enough to give me a tour of their PBY, exterior and interior. I was able to take photos and measurements throughout. They’ve also kindly provided some useful documents on the aircraft which contains information for their aircraft, with measurements and all. I highly recommend anyone who may be in Washington state to visit the museum. I’m aiming to continue my relationship with the museum all the way through this project, perhaps contributing to the museum exhibits with the 3D assets I create and helping with illustrations they may need.
More to Come
With the rear landing gear mostly complete, I still have much more to go on this airplane model. Even with just the rear landing gear, there are some minor bugs and features left to do; an additional flap left to model and rig, and an overall final modeling pass needs to be performed. But this rear landing gear was set to be one of the most complex and challenging parts of this airplane’s animation rig. In regards to rigging, the rest of the aircraft is comparatively simpler; the front landing gear will be much simpler to setup, the engine and propellers are simple but will require some particle effect work, the rudder and ailerons are also simple, and finally the plane’s unique wing-tip floats that deploy when landing on water need to be modeled and rigged.
In between small rigging tasks on the airplane will be just modeling and material work - making the plane look amazing. Of course I’ll be updating my personal website and social networking accounts as I progress on this fun passion project. I hope you’ll follow along!