Fairchild 24 Argus

Model Airplane News, Jul 2002 by Kent, Phillip

A 1930s cabin plane with character

The Fairchild 24W Argus is an excellent choice for a scale subject, and it certainly is different from the typical Piper Cub and Taylorcraft. Though out of the ordinary, it retains smooth and undemanding flight characteristics. This version of the Argus was derived from my first version-a 36-inch rubberpowered model 1 built in 1949. The new RC model is built slightly larger than Ws scale, and this gives an impressive yet manageable wingspan of 90 inches. I powered the prototype model with a Laser 100 4-stroke engine that just fits within the radial cowl. You can also build the Ranger-powered inline engine version of the Argus, as I have included details for it on the plan. But be careful; the model could come out nose-heavy! I did not need to add any nose weight to the radial-engine version, so if you fit a lighter engine and rearrange the radio gear, you may be able to build the in-line version without difficulty; I have not built it this way, so you're on your own.

TAIL UNIT

The rudder and elevators have a 1A6-inch core sheet. You build them using half ribs glued on the top and bottom. Cut the elevator's core sheets to shape, then cut the Shs-inch sheet spars and glue them to the top of the core sheets. Add the 1/16-inch half ribs, the tips and the inboard sheet parts, and sand the unit to shape. Remove it from the work board and repeat the process on the second side. This technique produces a light, stiff structure that looks very scale when covered. Build the rudder in the same way, but use a the-inch core sheet and 1A-inch half ribs.

The horizontal stabilizer is built in two halves over the plan. Cut the 1/4-inch-thick balsa trailing-edge spars to size and pin them into place using the plan as a guide. Glue the ribs, tip parts and plywood braces into place, then add the 1/8-inch sheet subleading edge. Sand the structure to the cross-section shown on the plan, and then cover it with 1/16-inch balsa sheeting. To complete the structure, remove it from the building board and add the ribs to the underside, then add the 1/4-inch balsa leading edge. After the glue has dried, sand it to final shape. Build the vertical fin using the same technique. I find that balsa cement or aliphatic is the best glue to use with this building technique. It can be sanded easily and doesn't leave a ridge between parts. CA glue dries too hard and is difficult to sand smooth.

All the hinges on the model are Robart HingePoints. For a scale appearance, they are inset into notches in the trailing edge of the vertical fin and the leading edges of the elevator halves. Be sure to add balsa blocks to the hinge locations to provide adequate gluing surfaces. To connect the elevator halves, I used a 3/32-inch music-wire joiner to the center of which I silver-soldered a brass control horn. You may be able to find a commercially available joiner with the control horn attached, but note the forward angle required on the horn to clear the fuselage structure.

WINGS

To cut out the wing ribs, I made a full-rib template from plywood using the crosssection of the wing at R-3 as the master. I duplicated all the spar openings and notches, then I cut the 24 full ribs needed to complete the two wing panels from A-inch-thick balsa. These ribs can then be cut into shape to create the R-3 ribs (flap section) and the R-4 ribs (aileron section). The flap ribs that support the offset hinges require 1/16-inch plywood doublers. Bond the doublers to both sides of the ribs with epoxy. Note that the rib between the flap and the aileron also requires a plywood doubler to add rigidity. The root end of the wing panels is tapered sharply inward to align with the cabin and windshield structures. Finish the rib-cutting job by cutting out the smaller R-1, R-2 and root ribs, as well as the outer R-5 and R-6 tip ribs.

Pin the bottom main spar into place over the plan, and glue the ribs to the spar. Glue the sub-leading edge into place and then add the plywood trailing edge, the aileron and flap spars, the rear spar and the top main spar. Note that the aileron-attachment spar is made of two pieces of sheet balsa. I find it easier to carve the two-piece spar to shape before fitting it into place at the back of the ribs. Rib section R-4 on the plan shows the proper cross-section shape.

I made the laminated wingtip bows by wrapping four 1/16 x 1/4-inch balsa strips around a 1/4-- inch-thick plywood former. Cut the strips a little longer than needed to give yourself some room to work; then use a water-based glue to laminate them together. Tape the strips to the former at their midpoints and then work outward, bending them against the former; use more tape to hold them securely until the glue dries. Leave them overnight and then remove them from the former and cut them to the final shape. Remove the wing panel from the board, glue the tip bow into place, and fill in the areas between the ribs, spars and leading edge with 3/32-inch balsa sheet, where needed. This is a good time to install the 3/32-inch wing-joining wires at the root ends of the wing panels. Fill the area between the top and bottom main spars with 1/4-- inch balsa, then bend the wires to shape and position them as shown in the wing top view. Set up the wing panel so there is 1 7/8 inches dihedral under the last full rib, and position the wires so they are level with the building board. Secure the wires with grooved basswood blocks, and glue them into place against the front and rear spars.