Dynaflite: Super decathlon

Model Airplane News, Sep 2001 by Bell, Rick

Easy to build, fun to fly, giant-scale aerobat

Dynaflite is well known for producing fun-scale, IMAA-size aircraft kits that are easy to build and fly great. The Super Decathlon is no exception; in fact, it's probably Dynaflite's best effort to date.

This sharp-looking, 89-inch aerobatic trainer has all the attributes sought by the first-time giant-scale builder; it's easy to build, has great visual appeal, and like its full-scale counterparts, it has wonderful flight performance. The two-piece wing is a welcome feature that provides convenient transportation and storage. In short, this plane has everything that a first-timer could ask for in giant-scale acrobatic trainer.

THE KIT

The Decathlon comes in a smaller box than most large planes. It is well packed and includes lots of balsa, hardware, a threepiece ABS cowl, ABS wheel pants, a windscreen, one-piece aluminum landing gear, a rolled plan and a detailed, easy-to-understand instruction manual. The edges of the die-cut wood are sharp and cleanly cut.

The manual includes an inventory of kit contents and a list of items needed to complete the plan. It also has a building-notes section and patterns of the die-cut sheets. The plan comes rolled, and you must cut and tape two sheets together to make the fuselage. The windshield on my kit was warped, but a call to Great Planes put a new one in my hands within a couple of days.

CONSTRUCTION

Begin with the tail feathers; they are constructed of balsa sticks and fit together easily. The elevator tips and trailing edges (TEs) are laminated from five strips of 1/16x24-inch balsa. Old-timers will remember this type of construction; it produces a strong, light frame.

I placed pins where the instructions indicated, wet a balsa strip and pulled it around the pins to form the tip and TE. I then wet the other strips and glued them in place on the first strip using aliphatic resin instead of the recommended medium CA; it makes them easier to sand later. When the glue dried, I lifted the structures from the plan, rounded the leading edges (hEs) and TEs, added the hinges and installed the hard points for the tail bracing.

SUPER DECATHLON

* Wing. Construction is easy and straightforward, but because of its two-piece design, the lite-ply rib reinforcement subassemblies for the aluminum wing tube and the basswood main spars must be completed before actual wing construction begins. The airfoil is semisymmetrical, so be sure that the top and bottom of the ribs are correctly oriented. I also jumped ahead and joined the sheeting before I started the wing.

First, I pinned a spar in place and used a 1/4x3/8x42-inch balsa wing jig to set the correct amount of washout. Next, I added the ribs, the top spar, shear webs, remaining spars, the wing tube and the sub-LE. I then shaped the sub-LE to the rib contour and framed up the aileron bay. Last, I added the wing top sheeting and the capstrips where the directions indicated.

At this point, you can remove the wing panel from the plan, flip it over and realign it on the plan; make sure to properly place it over the wing jig to preserve the washout. Add the wing-strut-attachment blocks and the wing-mounting-bolt blocks, taper the TE sheeting, and sheet the bottom of the wing. After you have built the other wing panel, glue the LEs in place and shape them using the provided gauge to complete the airfoil.

The wingtips are made from large balsa blocks that need to be carved and sanded to shape. (I'd like to see Dynaflite use vacuum-formed parts here to save the builder a lot of carving, sanding and construction time.) After the tips have been completed, build the ailerons, hinge them to the wing, and fit the servos and pushrods.

Fuselage. The first step is to build the firewall. You can use many engines in the Decathlon, so the instructions show two firewall assemblies, depending on whether you select a gas or glow engine.

After you've built the firewall, build the three main bulkheads using balsa sticks and assemble the fuselage sides directly over the plan. True up the fuselage sides and place them on the fuselage top view. Install the bulkheads and firewall, then join the fuselage at the rear according to the instructions. Using the plan is a good idea because it helps keep the fuselage straight during assembly. The rest of the assembly goes along quickly without any problems.

To give the fuselage a little more shape, I added 1/4-inch-square balsa strips to the longerons on the side of the fuselage from the rear to the cabin windows. This eliminated the flatness on the fuselage's aft portion. I then fit the wing panels to the fuselage, squared them up, and drilled and tapped the holes for the wing-mounting bolts. I installed the fuel tank, added the forward bulkheads, and sheeted the front deck with 3/32-inch sheeting. Finally, I flipped the fuselage over to complete the built-up bottom. While the angles on the fuselage bottom look challenging, they actually go together very easily.

Next, add the tail feathers and true them to the wing. The instructions call for you to epoxy them in place at this point, but to make the covering job easier, I waited until after I had covered the plane. Because I wanted to use the starburst scheme, I'm glad that I went this route.