Zephyr (oz8726)

About this Plan

Zephyr. Radio control glider model.

Quote: "An ultra-light RC Glider that's great for hand-launching, slope soaring, or mini hi-starting. With this glider, virtually any empty lot or public park becomes a flying site. Zephyr by Bob Owens.

THE IDEA of this Glider is certainly not original with me, for I have been hand-tossing Wanderers (oz4100) and the like for some time. Small RC Gliders are such a logical evolution.

Zephyr brings together many aspects of modeling. The light-weight construction is similar to that of Free Flight models. It can be hand-launched into thermals like solid-balsa gliders. It soars like a high-performance sailplane. It slope-soars from a ridge in light-to-moderate wind. it can do aerobatics. It also can be hand-towed or launched with a hi-start. Best of all, it is RC and fun to fly!

I enjoy flying most types of RC models, but the more elaborate they are, the more up-tight I get while flying. Not so with Zephyr. There is no anxiety, because there is not so much time and money invested. If it sounds like I am sold on this phase of modeling, you are right.

Advantages of the small silent flier are the absence of noise and the small space requirements. Any empty parking lot or public park can become a flying site - no need to drive miles to the regular flying field. You even can get in a few pitches after work. This is especially true, since there is no engine gunk to clean up. But Glider folks knew that all along.

Design Considerations. Because I don't own a super-small, ultra-light, micro-mini radio, initially I didn't think too seriously about hand-launch Gliders. Then, one day at the drawing board, I was laying out a new Two-Meter Slope-Soarer with all the radio components in tandem alignment to minimize fuselage cross section for reduced drag. Suddenly, it occurred to me that the widest item was my Kraft KPR-3C receiver. That's about the same as my index finger used in hand-launching. So, I borrowed two KPS-18 servos and a 225 mAh battery from my son's 1/2A Pylon Racer, and I was in business.

But I would need to minimize the structural weight to achieve a desirable 10 oz maximum weight and a wing loading of 4 oz/sq ft. Keeping in mind that I might have to go back to my own radio during Pylon Racing season, I made sure that Bantam-size servos would fit.

The airfoil is an Eppler 387, which has a slight undercamber. On other Sailplanes this airfoil has proved to have a good speed range. It lifts well at slow thermalling speeds, yet moves fast and penetrates well at low angles of attack. That seems to be just what is needed for hand-launching at a fast speed, then for gliding slowly.

Tail areas and moments are similar to other popular gliders, but are kept small to reduce weight. The name Zephyr was selected for this model based on Webster's definition: Something light and airy. How true it is.

Weight Control. My philosophy about weight: if it isn't breaking, it is too heavy and overly strong. However, I must exempt those who insist on circling telephone poles, and looping around the wires. Also exempt would be those with throwing arms like Don Drysdale's.

Selection of balsa for this project is vital to achieving the 10 oz flying weight. My Zephyrs are weighing in, without radio, at 5 oz. That's 1-1/2 oz for fuselage and tail, 1-1/2 oz for wings, and 2 oz for MonoKote. Follow the plans closely, and use lightweight balsa..."

Zephyr, Model Aviation, May 1981.

Direct submission to Outerzone.

Supplementary file notes

Article pages, thanks to RFJ.

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