Saturday, April 21st, 2012 10:38 am GMT -7 Saturday, April 21st, 2012 10:38 am GMT -7Saturday, April 21st, 2012 10:38 am GMT -7
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The third time around might just be the charm!




First Prototype

I started out with a pusher flying wing design. I wanted it to fit in a single sheet of foamboard (20×30 inches, 50×75 cm). I used a lot of sweep for stability, which led me to use a lot of taper so that it would still fit. Out of necessity, it had a very low aspect ratio.

Most of the wing area was in the center of the wing, which required the center of gravity to be pretty far forward. It did not have a large power system. Even mounting the motor on the nose would have not been enough to balance it all out.

In short, it was very tail heavy, with no hope for a quick fix.

Second Prototype

I figured I needed a lot of wing area towards the back of the airplane to make balancing easier. I looked at wings without taper, but quickly switched to a joined wing design.

A joined wing met my requirements. It has lots of wing area towards the back. It is very strong and easy to build. My half-size prototypes flew great. It also looks neat!

I started building another full-size prototype using these ideas. Halfway through the build, I realized I was not building quite the same airplane I thought I was building.

I stopped to think about how it was coming along. I was cheating on the constraint of fitting on a single sheet of foamboard by having extensions on the nose and wing tips. I really did not like these. The long nose (because of the high sweep angle) and large wing area in the front did not look good to me.

I decided to take the design in a new direction before I finished building the second prototype.

Third Prototype

I learned there was a fundamental trade-off involved. With a low sweep angle, I could have lots of wing area and the motor easily fit in between the two wings. With a high sweep angle, the nose was long for much easier balancing and the elevons were pushed back for better effectiveness.

A high sweep angle clearly became the only solution, because without it I needed a lot of weight on the nose. But how to make the motor fit? That is when I came upon the idea of cutting a notch for the motor.

Along the way, I decided to get rid of the raked wing tips. These looked great, but there was just no way of fitting the wing on the foamboard and still keep them.

All of a sudden, I could meet all of my constraints at once. I could fit it on a single sheet of foamboard, balancing it was easy, it had lots of wing area, it was very easy to build, it was very maneuverable, and it looked good. Time to build a third full-size prototype!

Video Summary

In this video, I am working on my third full-size prototype of the Pickerel RC model airplane design. I am constantly re-evaluating my decisions, so I talk about what I like and do not like about the build so far.

This prototype “feels right”. The half-size prototype flew great, so my expectations for this one are very high.

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