This article describes the design, construction, and flying of the easiest to build, cheapest little RC glider for schoolyard thermal hunting I’ve ever tried. You can follow along by downloading the free plans.

The Inspiration

While living in North Carolina I had the privilege of flying with the great Carl Dowdy (SFA:bugsoaring). His knowledge of RC & free flight gliders and his penchant for great craftsmanship are difficult to compete against. It can be embarrassing and frustrating to watch how well his airplanes – always simpler than mine – seem to fly.

So far, Carl’s most famous contribution to aeromodelling has been the remarkable 30” RC glider called The Bug. This model landed Carl on the cover of RCM, and has generated what is perhaps the highest form of recognition in the information age – a Yahoo! Group dedicated to the design. Many modified versions have been built.

The Bug is very simple and attractive. It combines cheap, everyday materials (balsa, dowel, and pultrusion carbon tube) in a simple, structurally sound and elegant balance. It looks like it wants to fly and just begs for any number of modifications – conventional tail, setup for discus launching, electric power, etc.

The Bug also happens to be ideal for my needs for an RC glider – small size, easy building and flying, durability. So I built one, right? Of course not. I had to try to design – with my inferior experience and questionable IQ – some thing even simpler, even quicker and cheaper to build.

The Design: the Candy Wrapper

My airplane is built around the wings from the “Skyraider” Styrofoam glider molded by Guillows and marketed to children at craft and toy stores. You can find it online through The Guillow’s website. The stabilizer from the toy is also cut down, hinged, and used as the stab on the Candy Wrapper. The “Skyraider” usually costs about $5.

The other unique element is the Blue Arrow receiver and servo equipment. It is very light and small, functional, and costs about $70 for everything. You can view Blue Arrow’s products at the Blue Arrow Website, and you can purchase Blue Arrow receiver and servo equipment at various online hobby retailers.

All other materials are completely ordinary: light, stiff 1/8” and 1/16” balsa, 1/32” ply, 20.25” of 1/8” pultruded carbon tube, cellophane tape, CA, and – that’s right – a wrapper from a granola bar.

Construction (Free plans available)

Wings first: I cut the plugs off the molded Styrofoam wings in a single stroke that goes at a right angle to the trailing edge. I angled the blade slightly to induce the 1” of dihedral. Putting the two wing halves together was simple…a butt joint with aliphatic resin, then cellophane tape spanwise from tip to tip, top and bottom, 1.5” from the trailing edge, and a 2.5” piece top and bottom 3” from the trailing edge. The left wing features 1/32” ply discs, glued with foam-safe CA, as reinforcement for the discus launching peg.

The wing mount was the most difficult part of the build. I built up a ¼ x 3/8” triangle fillet on each side of the wing half. This is a fragile piece as the grain runs spanwise. I’m not sure, but I sense that it might work better with grain running fore-aft like typical triangle stock. Unlike triangle stock, however, the fillets are not right triangles in cross section. Their angles fit the wing and wing pylon exactly. The wing pylon is light 1/8” balsa with grain running up-down.

The forward fuselage uses light 1/8” balsa with grain running fore-aft. The front piece is an expendable piece of 1/8” balsa. This is like a car bumper. It is smooshed in a crash, reducing damage to the rest of the airplane, and easily replaced. The battery and received are taped to the forward fuselage using double-sided foam tape. The granola bar wrapper, trimmed to the shape shown on plan, is slipped over this and taped to the top of the wing. The fuselage behind the wing is a servo tray built from very stiff 1/8” square balsa. It must be very securely assembled and tightly taped down to the carbon tube. I secured the tape with CA.

I cut the rudder from 1/16 balsa and the stab from the Skyraider’s Depron stab. All edges were sanded round. I would recommend doping or otherwise finishing the rudder. A smooth finish reduces drag. There are many ways to hinge an airplane like this; the simplest that I could think of was to use tape on the stab (glued with foam-safe CA) and tissue (glued with plain CA) on the rudder. I drew the plan with cellophane tape on both surfaces; no reason to mess with the tissue.

The control linkages used the horns provided with the Blue Arrow servos and a pull-pull system with 2-lb test fishing line from Bass Pro Shops (link). The control lines pass through ¼” of 1/16” alu tube near the servos and just before the stab. The control surface horns have the same basic dimensions as the servo horns. I used 1/32 ply.

Flying the Candy Wrapper

The Candy Wrapper prototype flew with virtually no trim adjustments but, because of fairly rearward CG and the Skyraider’s primitive airfoil, it tended to loop on a discus launch. In the end I trimmed it for down elevator, and just hold in some up on the glide.

Some controlled crashes (and one really violent altercation with a manhole cover) proved that the Candy Wrapper design is essentially extremely durable. The wing often popped off on less than perfect landings. I think this is a good thing, and I recommend using very little glue to keep the wing in place.

The tail of the model — a major weak point on small RC gliders — stayed put even on the worst landings. The servo tray(shown on the plan has also held up perfectly.

Unfortunately, the elevator shown on the plan is not big enough! After flying the Wrapper, Carl Dowdy recommends that it should be doubled in size. This is the next thing I will try.

Moving On

I feel that the Candy Wrapper is a design ripe for modification. With more accurately cut wings from blue foam and smooth finishes on all surfaces, performance of this little airplane could go up by 50% if not more. Simply cutting off the bottom 3/32” of the wing – the extra foam doesn’t really do anything – could have a similar effect. It would be very easy and take little time to build a sturdy balsa fuselage pod. The Skyraider parts could also carry electric power.

If you build the Candy Wrapper, or something like it, please drop in the Small Flying Arts Discussion Forum and let us know. We would love to hear from you.

-Andy Mitas, August 22, 2006

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