[Headline: It’s all about the details]
At this time last year, I was well into my Caudron project for last fall’s Northeast Electric Aircraft Technology (NEAT) Fair Air Racing Society demonstration. I barely got the model flying before our scheduled slot. I was frustrated enough to take a number of cosmetic shortcuts at the end of that project to ensure that it actually made it into the air. Once I returned home, I sat down with a pencil and paper and made a list of things I wanted to improve.
First and foremost, were its flying characteristics. It felt a touch unstable at the NEAT Fair. At the time I wasn’t able to tell if it was just a case of nerves, poor control setup, or if the small tail and side area of the long nose was conspiring against me. It actually felt a bit tail heavy, but not in the normal way.
I have found that a tail-heavy model is unstable in pitch, yet with the Caudron it primarily showed a divergence in yaw. Throughout those early initial flights, I felt like I was trying to herd it around the sky. It was certainly flyable, but it didn’t groove as I’d hoped. In short, it just wasn’t much fun to fly.
The initial results were definitely a disappointment, especially after spending most of the summer in the workshop. Throughout the build were months of back-and-forth emails with my friends and the anticipation about how much fun we were going to have carving up the course with our colorful racers. I knew it could be better, but other obligations forced me away from my workbench for a while after NEAT.
In early November I was fortunate to find a quiet midweek day with ideal weather and headed out to the field with a handful of batteries for some additional test flying. The primary goal was to explore the CG. Moving the battery forward brought the CG well ahead of the original design calculations, but it proved worth the try. The transformation was nothing short of miraculous.
I had first flown the Caudron with the CG at approximately 27% of the Mean Aerodynamic Chord (MAC). With the battery forward, the CG is now approximately 20% MAC. This change erased the tendency for the nose to hunt in the turns, and the sleek blue racer now flies like the arrow it resembles.
I flew 10 battery packs that day and also had time to fine-tune the control throws. On the drive home, I resolved to take some time and address the cosmetics ignored during the race to the starting line.
One of the primary targets that I wanted to address was the distinctive cowl louvers. The original Caudron featured inset louvers to minimize aerodynamic drag. This prevented me from carving pieces of balsa that I could just glue onto the cowl and cover with the same The World Models Lightex covering film that I used on the rest of the airframe.
I also wanted to form them as precisely as possible. Using a mechanical process to replicate the louvers instead of working them by hand made sense. Vacuum-forming thin styrene was the obvious path to success, but first I had to create the tooling.
I have had a desktop mill from A2Z CNC for a while and knew this would help me create the louver tooling. The mystery for this project was how to keep the inside corners sharp. In the end I realized that making a segmented tool would be the answer and handwrote a few simple lines of G code to profile a test blank on the mill. The test worked out well, so I got to work on the final tooling pieces.
First I milled several aluminum blanks to consistent dimensions, with the width matching the louver spacing. I then used a ball-end mill to relieve one side of each of these blanks while holding them in my Sherline vise. It only took a moment or so to profile each of the blanks and as they stacked up on the workbench I could see I was on the right path.
Pacer’s Zap-a-Gap CA made quick work of gluing the blanks together and I then added a generous coat of Bondo to provide additional support. This process gave me a master female mold, which I now needed to reverse to provide a male form to use on my vacuum former.
I think you will agree after looking over the photos, the final results were quite satisfactory. I have yet to actually install the louvers though, because I promised myself I would not rush these last few details.
I am also working on a dummy engine, radiator, instrument panel, and canopy frame. I hope the Caudron will be back in the air with renewed splendor by the time you read this.[dingbat]
The World Models