Build a cardboard combat model

Model Airplane News, Jun 2000 by Raskin, Jef

Not your ordinary paper airplane!

My son Aza and I had long wanted to make an RC model that looks like a conventional paper airplane, but neither of us knew of the other's interest. I had hesitated to design one because most paper airplanes are "flying wings," which usually require an electronic or mechanical mixer to control elevons that move up and down together to control pitch and in opposite directions to control roll. Even though affordable Hitec* transmitters with mixers are available, it seemed to run against the simplicity of the airplane to build it with elevons. One day, as I was sketching a paper plane on my shop blackboard, I realized that because the hypothetical rudder was nearly as long as each of the wing halves and was on the bottom of the wing, it would act as both an aileron and a rudder working in the same direction. I call it a "rudderon." A conventional rudder is too short to have much of an aileron effect and, if it is above the center of gravity, the moderate aileron effect it does have in producing roll works against its yawing effect.

A conventional flying wing uses elevons (Figure 1-A). To bank to the right, the right elevon goes up and the left elevon goes down (1-B). To pull up, the two elevons move up together (1-C).

With a rudderon system (1-D), to bank to the right, you move the rudderon over to the right (1-E). To pull up, the full-width elevator moves up (1-F).

The synergetic turning and banking effect of large, underslung rudders was known long before I was born, but it has seldom been used in models or full-size aircraft. In the WARP 9, it makes the airplane very easy to fly, even for beginners and gives the airplane a very tight turning radius.

As soon as I told Aza about this idea, he told me he had the same dream, and we immediately started building and flying planes we called "WARP 9s." With two of us building and test-flying, progress was rapid.

THE PAPER AIRPLANE GROWS UP

There are four parts to a WARP 9 airframe: the wing, the keel, the elevator and the rudderon. Typical spans and lengths range from 20 to 27 inches when using small (but not really tiny) RC gear.

After building a few WARP 9s (each one a little different, but all having the same pleasant flight characteristics), we learned that the design had some advantages we hadn't anticipated: the keel is easy to grasp for launching, and it provides a point to attach a hook for bungee launches; it also protects the radio equipment when landing.

Before you print out computer-- drawn plans, add some graphics. There are colorful triangles on my plane, and Aza chose a dragon that we found on the Web. Talk about wowing them at the slope with your color scheme!

For inland flying, attach a rocket motor or a small glow engine to a WARP 9. On the slope, we learned that our soarer is nearly indestructible, which makes it ideal for contact combat. No fussy streamers; just knock the other guy out of the air-if you can.

Since WARP 9s are meant to look like paper airplanes, we build them out of one of our favorite modeling materials: corrugated cardboard. This stuff is just two flat sheets of paper glued together with a wiggly sheet of paper in between. Cardboard is surprisingly light, very inexpensive and strong and tough (which is the reason model planes usually come in cardboard boxes). Most shipping and packaging shops sell sheets of corrugated cardboard, but it is obviously less expensive to cannibalize a discarded cardboard box.

Wherever you get your cardboard, try

for the kind that is 1/8 inch (3mm) thick. In the trade it's called "B-flute." The "flutes" are the tube-like openings that run through inside the cardboard. With balsa, it is important to determine how the grain runs; similarly, with cardboard, we are careful about how the flutes run. Incidentally, Aflute is thicker and C-- flute thinner than B (the thinnest cardboard I've seen is F-- flute). You could build a WARP 9 out of foamboard, plastic corrugated material, or even balsa. We've found that foam-core board is relatively fragile, plastic is really too heavy and balsa too expensive, but this is a hobby, so your way is just as good as ours. B-flute cardboard comes in three weights. The best for flying is rated "125-pound test." We called around to local box makers and located cardboard in this weight, even though the heavier 175- and 200-pound-test cardboards are more common.

If you use cardboard with different surface materials on each side (such as a white finish on one side and brown craft paper on the other), or if you leave the finished model in a closed automobile on a hot day, the cardboard wing will take on a distinct spanwise curve-one reason why we call this model WARP 9. Though the plane theoretically would fly perfectly well with a curved wing, the elevator won't work with a curved hinge line. To "Star Trek" fans (which we are), "WARP 9" is the normal top speed of a Federation starship, and that's how fast these models look in the air-even though they are not, in fact, speedy flyers.