Sig Mfg. CAP 231EX

State-of-the-art aerobatic ARF

It should come as no suprise to anyone who has been to the flying Meld lately that ARFs are more popular-and more abundant-than ever. What is surprising is just how good these kits are, and that they keep getting better. At the forefront of this trend in quality ARFs is Sig Mfg.* first with its Kadet LT-40 trainer and now with the fantastic CAP 231 EX. This high-performance, IMAA-legal aerobat comes completely built and is covered in dark yellow Ultracote, so all the hard work has been done by the time you open the box.

OPENING THE BOX

My first impression was "Wow! What a great-looking model!" When I removed the fuselage, wing panels and tail surfaces, I noticed how light everything was-atypical for an ARF. The kit contains a painted fiberglass cowl, wheel pants, a molded canopy tub and tail fairing, along with a crystal-clear canopy, a generous hardware package, lightweight wheels, steel axles, aluminum landing gear, a fuel tank, leafspring tailwheel assembly, comprehensive instructions and a magnificent set of decals. The hinge slots are cut and ready for hinge installation. All of this adds up to an excellent value.

The manual is excellent; it provides sound advice on radio equipment, engine selection, tools and supplies needed for assembly. Before beginning, go over the covering with an iron to remove any wrinkles and to seal any loose seams.

WING ASSEMBLY

The first step is to hinge the ailerons; the kit comes with Sig's double-X-pinned nylon hinges that must be epoxied. I decided to replace these with Sig's CA Easy Hinges to minimize the gap between the aileron and the wing. I have used these CA hinges in planes of this size for years, and they are very reliable.

After you've hinged the ailerons, remove the covering from the wingdowel-mounting holes and the servo hatches in the wing panels. Next, glue the plywood mounting pads in the servo bays to serve as screw anchor points for the hatches. When I began to mount the servos to the hatches, I encountered a problem: the hatches were warped. I tried heating them with a hot iron to pull the covering, without success. I ended up making new hatches using ply from my scrap box, and I covered them with dark yellow Ultracote to match the airframe. Mount the servos to the hatches, string the servo extensions through the wing panels and assemble the aileron linkages before you join the panels. The laminated plywood wing joiner fits well to the ends of the wing panels. I joined the panels using Anchor Bond* 2-hour epoxy.

Now it's time to add the two front wing hold-down dowels. I thought the supplied dowels were too short; they only engage the front wing plate. The rear of the dowels was not supported, so I made new, longer dowels and anchored them in the joiner brace by drilling a hole for each dowel using the front plate holes as a guide. Next, I mounted the wing to the fuselage as the manual instructed. The sharp threads in the metal blind nuts stripped the nylon bolts the very first time they were inserted, so I added hardwood blocks and tapped them for 1/4-20 nylon bolts.

FUSELAGE

The front and rear deck sheeting was loose along the center seam in a couple of spots, so I fixed it with thin CA. Also, some of the lite-ply had delaminated around the edges, so I soaked the areas in question with thin CA to prevent the delamination from spreading.

The engine mounts provided with this kit work well with a wide variety of engines; I chose a Saito* 1.50. To build the fuselage, first lay out the horizontal and vertical centerlines on the firewall using the existing marks, then measure the crankcase width (mine was 1.80 inches) and divide by two. Use this measurement to mark each side of the vertical centerline. These lines are the inside locaters for the engine mounts. I like to tack-glue the mounts (with thin CA) to the firewall so I can check their placement; this avoids drilling holes in the firewall in the wrong place. Next, mount the cowl and make the cutouts for the muffler, glow plug and needle valve. Then build the tailwheel assembly and plumb and install the fuel tank. Next, install the elevator, rudder and throttle servos, and set up the throttle linkage.

TAIL FEATHERS

Begin by accurately marking the centerline on the horizontal stabilizer and then placing the stab in the fuselage. Carefully center it and mark the bottom of the stab where it meets the fuselage. Remove the covering where you plan to epoxy the stab to the fuse-be careful not to cut into the balsa. Before I epoxied the stab into place, I checked the incidence to the wing and stab using a Robart* Incidence Meter. Mine read zero, so no adjustments were necessary.

Next, epoxy the vertical fin to the fuselage. When it has cured, hinge the rudder to the fin, attach the control horns for the pull/pull cables to the rudder and hook the cables to the rudder and the servo. Now epoxy the stab into place, trim the plastic tail fairing and glue it to the fuselage over the stab and the vertical fin. Hinge the elevators to the stab, then build and install the linkages. Instead of electronically mixing the two elevators together in the radio, I used an MPI* Miracle Y elevator splitter to produce "mirror-image" action.