In last month’s article we talked about the wide variety of opportunities available with 3-D printing. In this article, we want to talk about the process of creating those 3-D models. Within, literally, years of the initial offering of personal computers that software engineers started creating software for generating mechanical engineering drawings. And just like the computer industry itself, the exponential growth of CAD (computer-aided drafting) programs has blossomed into some of the most amazing collection of capabilities which only years ago were relegated to organizations such as NASA and Boeing. These capabilities have now become available to the average experimental aircraft builder/designer. If your aspirations revolve around being a component or aircraft designer, it is imperative that you recognize and embrace these new CAD technologies. For those holdouts, who do not wish to undergo the difficulty of learning to use a CAD program but still wish to be an aircraft designer, the only advice that we can offer is to lock yourself in the closet until you change your mind. Of course, we jest, but the capabilities of solid modeling software put the designer at such an advantage that the difficulties associated with learning the software are far outweighed by the results and capabilities that can be achieved.
|Figure 1: 3D Solid Modeling Software Learning Curve|
There are literally hundreds of CAD programs available to choose from. The software capabilities, as well as the price, vary dramatically. Giving advice to the average person on which software to utilize is fraught with peril. Among the many considerations, price seems to be one of the most critical elements. Most of the more advanced software programs require a painful initial investment only to be followed along with an unreasonably high yearly licensing fee that continually rubs salt into the initial wound. These companies also use hostage like tactics to ensure that you pay the yearly licensing fees by applying delinquent yearly fees when you try to upgrade to the current version of the software. There are also many CAD programs that can be used for free and many others that fall somewhere in the middle. It’s very difficult to justify the cost of the advanced software unless you can somehow justify its usefulness. If you’re new to CAD programs in general, starting off with any software will start you down the path to learning. There are cloud-based 3-D modeling programs with a great deal of capability that you can start using for free. At Rainbow Aviation, we use one of the more popular advanced software programs called Solidworks. Solidworks is one of the commercial programs with amazing capabilities with a cost structure for the basic program that is tangible (but still painful). Keep in mind that this is the same software that is used by many major aircraft manufacturers. When you get into the more advanced capabilities and software packages from Solidworks you will need to be at the level where you are generating revenue from the software in order to justify its cost. One of our recommendations for those interested in starting to use a more advanced program like Solidworks is to start off with one of Solidworks many introductory programs. For example, taking a college extension class on Solidworks will provide you with the opportunity to buy a student version of the software at a very low cost. Although this student software does have some limitations in terms of using it commercially, it is basically unfettered software in terms of its capabilities. This provides a low-cost jumping off point which will allow you to begin the learning process. The learning curve on a program such as Solidworks can be fairly substantial. If you’ve been a 2-D CAD user, you have a leg up in terms of just understanding the basic drawing principles. However, to get your brain to shift into 3-D mode can be a challenge. If you have been proficient enough to be drawing isometric views of models using depth and perspective on a 2-D CAD system, you will have to undergo a complete transformation of your thinking to transfer to a 3-D modeling software program. Once you have made the transition, you will look back upon 2-D CAD systems as a drawing method used by cavemen. This learning curve is indicative of any new technologies which you are unfamiliar with. Initially, the difficulty level can be overwhelming and the amount of productivity will be virtually stagnant. (Figure: 1) If you stick with the program, you will eventually hit the point where you can start to leverage the amazing capabilities of the software into your day-to-day usage. At this point, you will find yourself addicted to the software as if it were crack cocaine. Solidworks knows this. The more you use it, the more addictive it becomes. With the power of Solidworks at your fingertips, you figuratively become Superman. You will gladly continue to give up your lunch money if the bullies will just leave you alone on the playground with your software. As time progresses, and you become more proficient with the program, the amount of difficulty in using the software completely diminishes, and the amount of productivity increases exponentially making you a designing and creating machine. In conjunction with Solidworks, we use an additional program called Solid Cam which allows us to seamlessly export machine code into our CNC machines for manufacturing parts. It has literally become easier to cut a sheet of plywood in half by generating code using Solidworks/Solid Cam and our CNC router, than it is to wrestle a piece of plywood on to the table saw to accomplish the same task. All we can say is “that’s pathetic,” but it’s true.
|Figure 2: Extrude and Revolve Commands|
So let’s look at some of the basic principles around using this 3-D modeling software. Individual parts are created using simple 2-D sketches on selected planes. These 2-D sketches can then be converted to a 3-D component through a selection of basic commands like extrude and revolve. (Figure: 2) and just like the extrude and revolve commands, there are also extrude and revolve cuts. This allows us to create a 2-D geometry drawing on any face or plane and remove material from the solid part in the same fashion. You can continue to stack these types of commands, one on top of another, creating a basic part, selecting a face on that part, creating an additional 2-D sketch, and once again extruding from or cutting into your existing model. And although these are the most widely used commands which can generate a tremendous amount of 3-D modeling, there remains a host of other commands which allow us to modify and manipulate 2-D drawings into 3-D components. Other commands like “sweep” allow us to create a 2-D model along with a secondary 2-D drawing that provides a path for the extruded 2-D model to follow. This is used extensively when we are trying to create a path for fluid lines or hoses. Another command is the “loft” command. Here we use multiple 2-D drawings placed on individual “planes” and then loft them together creating a very nonlinear shape such as a propeller blade. (Figure: 3)
|Figure 3: Using the Loft Command to Generate a Propeller Blade|
All of these and the other commands combined together allow us to generate individual “parts.” And, in the case of designing an aircraft, the sum of the aircraft is made up of sub assemblies. These sub assemblies are made up of these individual parts or other smaller sub assemblies. Similar to the process of building an aircraft, we take these virtual 3D parts which we have created, and assemble them into a subassembly by creating “mates” between the individual parts. (Figure: 4)
|Figure 4: Sub Assemblies Created from Individual Parts|
It’s just like building an airplane. We take our individual components and we define relationships between each one of those parts. We may tell a part that it needs to become coincident with another part, and then we may tell the holes within the parts to become concentric. We can even insert fasteners or Cleco’s in the same fashion. This is helpful in generating 3-D renderings for instruction manuals. Once we have generated a single part, we can use that part over and over again within an assembly, significantly reducing the time to create a large assembly. The mating process of the individual components has nearly limitless possibilities. In addition to basic mating commands like coincident, tangent, parallel, collinear, concentric, there are also advanced commands which allow a part to be positioned while allowing the individual part to move through specified parameters. Perhaps you have flight controls that move in the 3-D model. These control surfaces can have their deflections limited in the 3D assembly to provide a more realistic representation of actual conditions that act on the aircraft. If you can visualize a component on an aircraft, and how it relates to the rest of the structure, you can represent that interaction in a virtual environment using the Solidworks software.
|Figure 5: Mass Properties Dialog Box|
One of the most useful features within solid works, for us aircraft designers, is the “mass properties dialog box.” During the creation of a part, we can assign material properties to the part. This will allow us to pull up the mass properties dialog box and obtain information about the weight of the part as well as other useful information. (Figure 5) The dialog box will also create a triad arrow showing the center of gravity on the individual part. When we assemble these parts into and assembly, the software will calculate the combined weight of all of the individual parts, as well as the center of gravity of each part, to generate a center of gravity for the completed assembly. We use the surface area function on a regular basis to calculate the amount of time that a part will have to stay in the anodizing booth at a given voltage.
Also contained within the basic entry-level version of solid works is the ability to use what is called simulation express. (Figure: 6) This is basically a finite element analysis (stress analysis) program that allows us to simulate the material reactions to simple loads applied to a single component. More advanced capabilities, which allow the analysis of complete assemblies, are available for upgraded versions of the software.
|Figure 6 “Simulation Express” Stress Analysis.|
And even the professional level software, which we use, allows for the creation of some amazing realistic photo renderings using the render tools add-in module. In our office, in hangar 7 at the Corning Municipal Airport, we have a myriad of rendered photos of the EMG-6 electric motor glider posted on the bulletin board. I’m constantly surprised by the number of people who think that these renderings, created in solid works, are actual photographs of the aircraft. (Figure: 7)
One of the greatest advantages of working in a 3-D modeling software program, such as Solidworks, is it allows you to build your design “virtually” before you cut your first piece of material. This allows you to check the interaction of individual components, check for clearances, get a visual representation of the aesthetics of a assembly, check the weights of components along with the weight of the total assembly, and even check center of gravity.
|Figure 7: Photo Realistic Rendering of the EMG-6 Electric Motor Glider|
If you are the inventor/creator type, you should put away any apprehension you may have about approaching 3-D modeling software. This is the future. You just need to get started. If you have a restricted budget, we recommend that you start off with some budget software. Much of the software out there will do the majority of what you need to do in designing your own aircraft or component. Transitioning from one 3-D modeling program to another is much easier than starting from scratch. Even if you want to jump in with both feet and start working with something like Solidworks, do your homework. Check the compatibility of your computer with the requirements of the software you are considering. Our Dell T5500 desktop computer with an 8 core processor and a $2000 video card finds itself challenged on a regular basis. Creating a 5 minute HD video at 30 frames per second with each frame fully rendered often takes as much is 60 hours of computing time. The results are spectacular and the computational gymnastics, which the Solidworks software is capable of, is nothing short of amazing. The use of 3-D solid modeling software is quickly becoming the norm rather than the exception, especially when dealing with experimental aircraft. We encourage you to embrace the technology and begin the learning process. The rewards are beyond imagination.