mini Kaos, The

How many of you remember the pattern competition models of the 1970s? It was a period of rapid change, and the models were fairly simple. Designed and flown competitively by Joe Bridi, the Kaos became an icon that represented pattern flying of the time. By today's standards, with a mild engine, the Kaos makes a fine advanced trainer or sport model even though, in the right hands, it can fly pattern aerobatics.

Because I am a dyed-in-the-wool small-model enthusiast, I chose the Kaos design scaled down to 1/2A size as a mini project. With today's powerful new small engines from Norvel* and Thunder Tiger*, many suitable power options are available. It also doesn't hurt that the available RC gear is now smaller and lighter.

I did make one significant change, and that was to the wing airfoil. From experience, I have learned that on small wings, thick, symmetrical airfoils are not the best performers. I substituted an airfoil that had served me well in previous projects. Because I had a Norvel BigMig .061 engine, I used it, though the Thunder Tiger .074 would be a fine alternative.

Nobody can accuse me of playing favorites! My RC installation is a real mixed bag. The receiver is a Berg* 6-channel, the 1l0mAh battery came from FMA*, two micro servos are from JR* while the others are a micro Cannon* and a Hitec* HS-50. Just to round things out, my switch harness is a small Futaba* unit. On the original, I used a Hitec Prism 7X TX and Williams Bros.* smooth contour wheels, but Dave Brown* Electra Lite wheels are much lighter. Finding a small fuel tank is a challenge: I chose a 1-ounce plastic contact-lens-cleaner bottle. The plumbing is made of K&S* ifis-inch-- outside-diameter metal tubes and thin silicone fuel line from Si* or Du-Bro*.

I covered the Mini Kaos with MonoKote*, bonding it completely to the wood. This ensures a tougher model with fewer wrinkles, and it helps the thin tail to resist warping. Wanting to keep things simple, I opted for a fixed nose gear; the huge rudder provides ample control for takeoff steering and landing control. If you prefer, with little extra effort, you could make the nose gear steerable.

CONSTRUCTION

Let's assume that you have a few kits under your belt and maybe even a plan-- built model or two. I don't want to cop out on this phase but rather to pass on only the information that may be unique to one of my 1/2A designs.

My prototype weighed 14 ounces all up; to achieve this weight, you must choose your materials and RC gear carefully. Make up a shopping list; note that you will need fairly light balsa throughout (except for the wing spars). By that, I mean wood that has a density of 6 to 8 pounds per cubic foot-a sheet of 3/32x3x36 inches weighing no more than 18 grams (3/4 ounce), for example.

You can make it through this project with a single bottle of medium CA; please leave the heavy epoxy on the shelf!

Before you start assembling, make a "kit" of parts to ensure that you have the crucial materials on hand; you'll also be able to check the parts fit before you make things permanent. Make patterns-copies of all the parts that need to be cut out-and use a glue stick to attach them temporarily to the wood (but do peel them off fairly soon after you've cut the parts). This method may also be applied to the wing ribs: use the glue stick to temporarily laminate two pieces of sheet under the pattern, and you'll be able to cut the ribs in half the time.

On the tail, just cut the parts out and sand them smooth; see the bevel on the hinge line? This is important to smooth control. Install the elevator joiner, and set these parts aside.

The fuselage is basically two joined side assemblies; refer to the plan to get all the parts in the right places. Work over the top view and install the two center bulkheads and then the firewall (the nose gear should be on the firewall now), and pull the tail panels together. Plank the top and bottom, and you've nearly finished. Finally, take the carving knife and sanding block and trim the corners to a nice rounded shape. The fille are very much a part of thi design, so shame on you if you leave them off! They not only improve the appearance, but they also enhance flight performance.

Either hunt down a formed-plastic canopy, or shape a balsa block as I did (yes, I hollowed it out).

THE WING

The wing really is pretty simple, especially if you did a good job of cutting out the ribs. If you haven't already done so, strip the leading edges (LEs) out of 1/4-inch-thick balsa sheet (note the depth of its taper) along with the trailing edges (TEs) and ailerons, I used little spots of glue to hold the ailerons to the TE strips and then carved and sanded them to shape as a unit. Protect the plan with wax paper while you assemble the wing's halves. I pinned the bottom spar and the TE to the surface, and then I glued in the ribs and the spar webbing. Now glue on the LE and the top spars.

At this point, I lifted my wing panels off the board and added the center sheeting. Take a good look at the wing cross-sections and maybe make templates that will help you carve the LE to the correct taper. Compare the two halves closely to verify that they match. Sand a tiny angle into the ends of the wing roots where they join, and make sure they make full contact. Glue the two halves together as a butt joint, adding slight dihedral, and do what's necessary to avoid twisting the wing. Decide whether you want to add the fiberglass band around the center (I left it off), and then make the aileron-servo cutout.