Author: Thayer Syme
Edition: Model Aviation - 2014/09
Page Numbers: 101,102
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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 and was frustrated enough to take a number of cosmetic shortcuts at the end of the project just to ensure it actually made it into the air. Once I returned home I sat down with 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 couldn't tell if it was just nerves, poor control setup, or if the small tail and the long nose's limited side area were conspiring against me. It actually felt a bit tail‑heavy, but not in the usual way. A tail‑heavy model is typically unstable in pitch, yet with the Caudron the primary symptom was a divergence in yaw. During those early 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 a disappointment, especially after spending most of the summer in the workshop. The build had involved months of back‑and‑forth emails with friends and a lot of anticipation about how much fun we'd have carving up the course with our colorful racers. I knew it could be better, but other obligations forced me away from the workbench for a while after NEAT.

In early November I was fortunate to find a quiet midweek day with ideal weather and headed to the field with a handful of batteries for additional test flying. The primary goal was to explore the center of gravity (CG). Moving the battery forward put 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 moved 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 ten 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 I had ignored during the race to the starting line.

Tooling Up

One of the primary targets I wanted to address was the distinctive cowl louvers. The original Caudron featured inset louvers to minimize aerodynamic drag. That prevented me from carving pieces of balsa that I could simply glue onto the cowl and cover with the same The World Models Lightex covering film 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 it 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 set 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 blank 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 needed to reverse to provide a male form for use on my vacuum former.

I think you will agree, after looking over the photos, that 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.

SOURCES:

Transcribed from original scans by AI. Minor OCR errors may remain.