House of Balsa: Super Decathlon

Model Airplane News, Oct 2000 by Randolph, Randy

The Aeronca Champion was always one of my favorite airplanes. It was comfortable and roomy on the inside and a very nice airplane to fly. The Aeronca Super Decathlon is a direct descendant of the Champ, and its influence is still visible. The Super Decathlon inherited a certain friendliness from its "great granddad."

The House of Balsa* .061 to .10 kit of the Super Decathlon produces a friendly airplane, too. It is more "reminder" scale than a true rendition, but the flavor is there. The laser-cut parts are excellent, and the parts that are die-cut are of top quality. The wood is good and fairly well matched to its intended use. The hardware package, though not complete for a full-- house radio installation, is fine for 2-channel operations and is of good quality. A well-illustrated manual is included, and the plan does its job.

In building the kit, I followed the sequence in the instruction manual as closely as possible with only a few out-of-sequence steps--usually small jobs that could be done while I waited for glue to cure.

WING CONSTRUCTION

Whenever I build an airplane, I start with the wing; the Super Decathlon instruction manual agreed with me and suggested starting with that piece. The trailing edge (TE) is pinned over the plan on the building board, followed by the laser-cut main spar and the ribs. The main spar has deep notches that receive the ribs. When the ribs have been installed and the top main spar is in place, the result is a full-- depth spar that is light and strong. The TE is built of three pieces and is very warp-resistant. The leading edge (LE) is a cedar dowel that fits perfectly into the ribs. Although the dowel is on the heavy side, it makes the wing easy to finish and smells good when sanded. Before you know it, the wing halves are on the bench ready to receive the tips, bottom LE spar and center sheeting. It would have been a real help if the manufacturer had beveled the center joint of the main spar to the dihedral angle.

You need to make a groove for the aileron torque rods in the aileron stock that forms the center of the TE. The servo location is offset to miss the joint where the wing panels meet, so one torque rod must be longer than the other. Before you cement the TE and hardware into place, it is a good idea to smooth some petroleum jelly along the length of the torque rods that are covered by the balsa. That will help to keep the rods from being cemented along with the TE stock.

Next, you butt-join the wing halves and secure them with tape cemented around the joint. This attachment method is a common practice, but I also added a plywood dihedral brace to the center of the main spar before applying the sheeting. This may not have been necessary, but it made me feel better.

I then trimmed the ailerons to shape and set them aside for installation after the airplane had been covered.

BUILDING THE FUSELAGE

Each fuselage side is made by gluing a top and bottom piece together, then adding a plywood nose piece. The two sides are not the same and are labeled "left" and "right"; it is important that you pay attention to these designations during assembly. The cabin formers are glued to the inside of one fuselage side. A gauge that's included in the kit allows you to accurately position the formers. When the glue has set, add the second side. The next step is to pull the tail together and glue the laser-cut bottom sheet from the aft cabin former, between the fuselage sides and all the way to the tail. This almost guarantees a straight fuselage!

The next step is to add the aft cabin formers and the firewall. Because I intended to use the dandy JK Aerotech* Slickmount for a tank as well as an engine mount, I drilled a 1 1/4-inch hole in the firewall at the proper location. Because I used the Slickmount, I didn't need to make a hatch above the tank, thus simplifying the sheeting that was to follow.

Because I intended 4-channel operation, I added additional Nyrods for the rudder and throttle. After I added the landing-gear mount and the Nyrod guides, I added the laser-cut bottom sheeting between the fuselage sides in the same way as the top sheeting. Cross-grain sheeting above and below the firewall finishes the fuselage, which is now ready for sanding.

TAIL CONSTRUCTION

Because the tail assembly is entirely laser-cut from sheet balsa, the only actual building is to cement the tips on the fin and stab and join the elevator halves via a hardwood carry-through.

When all the glue has set, a light sanding removes any glue residue around the joints. Some time ago, I made some tools by drilling holes of various sizes in pine blocks, sawing them down the center and lining the half-moon holes with sandpaper. A few quick passes with one of these tools generated nice, round leading and trailing edges in no time at all.

RADIO INSTALLATION

Plywood bearers are supplied, and radio installation was straightforward. I had to use a few extra Nyrods for throttle and rudder control. I used 15-year-old Kraft miniservos (KPS-18s) that still worked flawlessly! The aileron servo is mounted on the side of the wing center--a practice I do not prefer, but I did promise to follow the instructions! With four RC channels, a Norvel* BigMig .061 on a Slickmount and a 500mAh battery pack, the finished weight was 27 ounces ready to fly--a tad heavier than I expected.