I’ve been building RC airplanes for a number of years now. It all started back when I was in grade school and my dad started building a radio controlled glider. I was intrigued and as all little boys do I bugged him all the time about it asking questions every time he woudl work on it. Luckily for me (and an attempt to save his sanity) we went to the local hobby shop and picked up a Guillows free flight airplane kit for me to work on while he worked on his RC glider. Once we were finished we took them both out to a big grassy field and both airplanes took flight! From that first kit I was hooked!
Since then I have built and repaired many planes. I do enjoy the building side of the hobby which helps during what normally is 5 months of cold and snow up here in Minnesota. However what I have always toyed with doing was scratch building in the truest sense of the word. To me scratch building is starting from nothing more then an idea or a picture and creating the airframe yourself. While I have always had ideas rolling around in my head I could never seem to get them drawn out on paper or on the computer in CAD.
[Update Jan 2014] I have since started a tutorial series on using Sketchup for RC design work. Check out my first post and intro video here: Sketchup for RC Part 1
What finally pushed me to sit down and learn how to use a CAD program was seeing my friends CNC machine in action. After a brief overview of his machine and how he prepares files for cutting I sat down at my computer and started playing. I work at a community college and have access to many different versions of CAD and design software. While those are great at what they do they can also be loaded with so many tools that it can be intimidating for the newcomer to CAD drawing and design. For this reason and others I decided to work more with Google Sketchup. Sketchup is a very powerful design tool yet keeps itself simple for those just starting out. There are many videos online that can help you learn the software. In fact there are many out there that are specific to airplane design.
Google Sketchup is free to download for both Mac and PC: http://sketchup.google.com/
Mike “Crash” Handcock has some good tutorial videos on Vimeo here: Crash’s Sketchup Tutorials
But drawing the airplane in Google sketchup is only half the battle. Once done you have to take that drawing and make something useful out of it. Now you could just export the drawing and print out a full size plan to cut from by hand. But this is where my friends CNC machine comes into play. I was able to take all the parts I drew up in Sketchup and lay them out flat to create a cut file for his machine. Our friends at Phlatboyz have made this incredibly easy. They have created and sell kits for the PhlatPrinter. It is a compact CNC machine that is designed to cut foam, balsa and other sheet style material. I hope to own one in the near future but in the mean time I was able to use their Phlatboyz plugin for Google Sketchup to create Gcode that the CNC machine will read to make the cuts in the depron foam.
Having all the parts cut out by CNC means they are very precise and the build goes quickly. I also used tabs to help lock pieces into place and alignment. I only used CA on the spar as I wanted that to be very rigid. For the other joints I used UHU contact cement for foam. This holds the foam together very well but is not as brittle as a CA joint. There is just enough flex to prevent the foam from cracking under the normal forces put on a 3D foam airplane. I used blenderm for the hinges and threw on a quick paint scheme with some cheap acrylics and my airbrush. I cut up a quick ply motor mount on my bandsaw for the prototype but I have since added a CNC firewall to the design. After installing 3 4g servos, a Phoenix 10 amp esc, a trusty old Custom CDR single cool wind motor with a GWS 8×4.3 prop and a 2s 450 lipo it came in just a hair under 6 ounces. The build from a sheet of foam to ready to fly took me 12 hours including the time to drive to my friends house to cut out the parts on his CNC machine.
12 hours later and a little rest I was at the gym for a test flight. The test flight went very well. I had made some notes on the build and after flying I had a few more revisions to make. The plane was very stable in the air but I want to tweak the aileron response and make the wing a little less boxy. I have already finished the revisions and have new parts cut out. I’m loving working in Google Sketchup and having the CNC machine 5 minutes from my house is awesome. It would only be better with my own PhlatPrinter but that will have to wait for now. I plan to work on some more designs including some full fuse planes. Keep an eye out for more!