How wonderful it would be, if I could build planes exactly as I designed them with just a click of the button. No cutting of dozens of wing ribs and spars from balsa. No hours of sanding, aligning, gluing. That was sitting in my head for long long time.
I was dreaming about CNC machine and how it could help me. I was even dreaming that I could build composite planes with it.
There was nothing like 3D printer back then.
Sure there is something magical and satisfying about building something what is able to actually fly just from sheets of balsa. Perhaps I was newer patient enough to finalize what I started and new plane ideas kept rising in my head all the time while still building just one.
At first when 3D printers came on the market I didn't realize the potential. But one day when I was wandering in my mind
in world of new plane ideas it suddenly hit me. I could design whole plane in computer and then just print it. I could re-print
whatever I destroy when crashing (yes that happens to me from time to time) or harsh landing.
You can imagine how happy I was. But that was only beginning ...
Searching for the right construction
When I bought a 3D printer first thing that I printed was part of rc plane wing from thingiverse.
I was disappointed. No matter what I tried it kept breaking while printing. The wing surface always cracked or deformed from tension caused by material shrinkage when cooling down.
Although I finally managed to print it I realized that this is not the best way how to print RC plane, at least not easily and not with my printer. On top of that RC plane with such construction is prone to cracking every time you land it or just hit cars door when transporting it.
It took weeks until I found a solution, I tried almost 30 design ideas. Starting with balsa kit - like printed ribs,
carbon molecule - like inner structure, small bubbles touching each other and forming wing shape, classic design with many holes in it ...
Eventually I found it. I found a structure that can be printed on basic printer and on top of that can wonderfully absorb impact energy. Lets call it Kraga mesh.
When I start something I always try to do it as good as I can. And designing new plane is not different.
Having some knowledge from aerodynamics I started with flight envelop of the plane.
I was designing slope racer plane in the past so I knew typical speeds of such plane and forces acting on it in turns. But I never took seriously design of "normal" plane. So I put telemetry on couple of my "normal" RC planes and measured the speed. I was quite amazed with the results, I was expecting higher speeds than I measured.
Finding out flight speed envelope together with knowing approximate weight and dimension of the plane are basic things
when designing new plane. All that is needed to determine correct reynold numbers and required lift.
Then I spent dozens of hours searching for ideal airfoil. It is like a drug, you know that there is always something better so it is hard to stop and say this is the one I will use.
Airfoil is only the first step (actually it was more airfoils because of using aerodynamic twist), then I choosed
wing planform. The same I had to do for the tail. Some time spent with flow simulation and I was ready for cad design.
In reality it took much more time and effort but I will not go into details.
Having no experience with cad designing before, it was actually the hardest part for me. Kodo is not my first 3D printed RC plane. I was sure that first plane will have many design bugs. I was not sure how mesh structure will behave on bigger scale and I had many open questions.
I started with something more simple, I decided to build plank as my first plane. Although aerodynamically it is more demanding to design, it has less parts for printing having no tail. I was also not ready to deal with big fuselage. I knew that I will learn a lot by building it. Result was pleasant surprise from construction point of view, I knew where are the problems and how to solve them. Flight characteristic was poor though.
I redesigned and rebuild the plank with many design improvements and some aerodynamics improvements as well. From technical point of view I was quite satisfied but flying the plane was not as relaxing as I would like.
Finally I decided that plank plane design is perhaps not my niche and I should go back to what I'm sure will fly good.
I focused on aerodynamics design much more this time. I was already frustrated by spending so much time with planes
that are not giving me joy when flying.
Whole evolution of my planes took more than one year and final result is Kodo. I'm happy to say that it is really a joy to fly. Sure it can be improved in many ways but it is very good plane and excellent proof of concept.
I really enjoy designing and building RC planes. It is not one click build plane as I dreamed of. It takes time. But it is faster than building balsa plane while still giving me feeling of great achievement when the plane is done.
I have lots of new ideas. There is so much to try and improve...