B-26 MARAUDER

Model Airplane News, Dec 2004 by Rittinger, Mark, Davisson, Budd

A hot electric WW II bomber

With its sleek, powerful looks and big, twin Pratt & Whitney radiais, the Martin B-26 Marauder has always been a favorite of mine. I decided to build the model after I had several conversations with Roy Siewert, a B-26 tail gunner during WW II. After hearing his stories, I thought it fitting to design, build and fly this electric-powered version of Roy's old bird, "Miss Arkansas."

For the fuselage, I used foam-core construction covered with fiberglass cloth and resin and a fully sheeted, built-up balsa wing structure. Since this design can hardly be considered a beginner's project, I'll cover only the building techniques specific to this model. It's best to avoid adding excessive detail, as this model has a relatively small wing area. Don't add retracts or flaps; they'll make the model too heavy.

THE FUSELAGE

Because the fuselage and nacelles have complex compound curves, I decided to build them out of pink insulation foam. Cut the cross-section templates from the plans, and then cut the various fuselage sections out of blocks of 2-inch pink foam. Using the templates as a guide, cut the foam blocks into tubular shapes with a hot-wire cutter. Cut each section slightly oversize and sand the blocks to shape. After all the sections have been cut, glue them to the 3/32-inch balsa spine. To keep the structure straight, glue the blocks onto one side of the spine while it's pinned to your workbench. When the glue dries, unpin it and glue the blocks to the other side. Sand the foam to shape.

Mark the wing's cutout area and cut it out carefully. Mark and cut out the stabilizer area. You will also need to cut an opening for the elevator linkages to fit through, and carve out the cockpit area, the waist-gunner positions and the top turret position. After a final smoothing with fine sandpaper, the foam can be finished with 0.75-ounce glass cloth and Zap Z-Poxy resin. Add a second layer of cloth and resin to the bottom of the fuselage because the model will land on its belly. Sand the cured resin with 400-grit paper until it's smooth. Face the nose bulkhead section with Ve4-inch ply, and do the same to the wing's cutout section and the overthe-wing section. You can now add the cockpit detail. I applied a layer of cloth and resin inside the radio equipment and battery compartment. As shown in the plans, make the wing hold-downs using plywood plates held in place by sections of triangular balsa.

Carve the aft tail block out of balsa, and glue it into place after the stabilizer and control linkages have been installed. You will be surprised by how quickly the fuselage goes together. The canopy, top turret bubble, nose-gunner bubble and tail-gunner blister must be molded. I made my molds out of balsa and simply primed them to produce a smooth finish. Use 0.030-inch clear plastic to form them. (I told you this wasn't a beginner's model!)

THE WING

The wing is a simple, flat-bottom affair, It has a few spars and basic 1/16-inch top and bottom sheeting. Begin by gluing 1/16-inch balsa sheets together to make the bottom sheeting. Transfer the rib and spar locations to the bottom sheeting by placing the plans face down over the wood and rubbing acetone over the back of the plans. Glue the leading-edge stock and the spars into place and then glue in the ribs. Add the aileron facings, and sand a taper into the bottom sheeting's trailing edge. Then sand the leading edge to match the curve of the ribs. Glue the left and right bottom-wing sheeting together with 1 �-inch dihedral under each tip, and then add the 1/8-inch spar doublers. Cut out the openings for the motor wires to run through and mark the corners of the aileron cutouts by sticking pinholes through the bottom sheeting. This will make the aileron cutouts easy to find after the top sheeting has been added. Pin the wing panel to the building board, and prop up the trailing edge at the wingtip using the washout guide shown on the plans. Cut the top sheeting a bit oversize, and glue it into place with slow CA or aliphatic resin. After the adhesive has dried, remove the panel from the board and do the same thing to the other half of the wing. Wrap the wing's center section with nylon or glass cloth and resin to add strength.

You can now cut the ailerons free of the wing. Bevel the ailerons' leading edges to allow free movement when they are hinged back into place, glue on the wingtip blocks and sand them to shape. Sand the leading edges to a nice, round contour and cut a slot in the bottom of the wing panels for the aileron torque rods; small Du-Bro �A aileron torque rods work well. I used 2 Hitec HS-55 servos (one in each motor nacelle) and connected them with a Y-harness. Attach the servos with double-sided foam mounting tape; for a stronger bond, apply a layer of epoxy to the wing surface and let it dry to form a smooth attachment area.

I hinged the ailerons with strips of film covering (using an over-and-under technique) after I had covered the wings. You can use CA hinges or pin-type hinges, if you prefer.