Ingram Foster Biplane

Model Airplane News, Feb 2005 by Tritle, Pat

A pioneering pusher design for electrics

I HAVE ALWAYS THOUGHT that the Ingram Foster pusher biplane would make an excellent model. Builders will notice that I've used several out-of-the-ordinary materials. All the components are easily obtained, and you'll find most of the hardware at hobby shops, online, or in mail-order catalogs. In spite of its unusual nature, this biplane is really a lot easier to build than you might think.

BUILDING THE MODEL

* The fuselage Begin with the fuselage; cut the upper and lower carbon-fiber tail-boom tubes to length. Mark and drill the holes for the vertical bracing and the retention pins. I used bamboo skewers for the uprights and CA'd them into place. Before you glue the assemblies together, sand an angle at the rear for the horizontal stabilizer, and paint the booms a light tan "bamboo" color. Then, to represent scale metal clamps, wrap strips of aluminum duct tape around the booms as shown on the plans. Reassemble the booms over the plans and glue them together. Mark the booms for proper orientation during final assembly.

Build the forward fuselage frame with basswood. Stack, cut and drill the upper longerons for the bamboo cross-bracing, and glue them together over the plans. Build the bamboo V-braces, and glue the rest of the fuselage assembly together.

Make the brass nosewheel brackets, and then drill the holes for the toothpick pins that will hold them to the frame. Once you've drilled the brackets, roughen them with sandpaper, glue them to the frame, and drill the toothpick-pin holes. Secure the pins with a drop of thin CA on both ends. Finish the job by wrapping two layers of aluminum tape around all the attachment points.

To complete the basic fuselage assembly, apply three coats of varnish to the frame, and brush all the uprights, metal bands, brackets and braces with Testers Model Master Steel Metalizer paint.

*Flying surfaces Build the rudder and horizontal stabilizer over the plans, and then sand the edges round. Hinge the elevators using thin strips of CA hinge material. Build both wing assemblies over the same wing view on the plans. The upper and lower wings are slightly different, so study the plans carefully.

Remove the wing from the plans, add all the gussets and blocks, and then sand the wing to its final shape. Repeat the process for the next wing, and then mark and drill the holes for the motor-mount struts.Build the two ailerons, and sand their edges round. Use the aileron side view to build the actuator frames using toothpicks and brass deadeyes from Model Expo, but don't glue them into place yet.

*The seat and landing gear. The seat moves with aileron input; make sure that its framework moves without binding. I made the seat cushion out of an old leather wallet.

The main landing gear is built using lengths of aluminum tube and dowel. Cut all the lower fitting tubes to length, squeeze the ends flat, drill the wire axle holes and bend the tubes to the appropriate angles. The upper main gear frames are also made of aluminum tube and are drilled for the attachment pins that will secure them to the wing. Cut the dowels to length, and assemble the wheel brackets, but don't glue anything until final assembly.

*Covering I used silk, but iron-on finishes such as Nelson Litefilm, Black Barron Coverlite and Litespan will also do nicely. The structures are too delicate for MonoKote or any of the other thicker Mylar films. Once you have covered the flying surfaces, add the aluminum-ducttape "brackets" and forward "tip caps" to the horizontal stabilizer, and then add the "hinge brackets" around the aileron hinge notches on the IS-3 struts.

*Final assembly To join the upper and lower wings, place the top wing on its leading edge (trailing edge pointing upward), and use a square or a triangle to ensure that its lower surface is perpendicular to the building board. Shim the IS-1 struts 1/8 inch above the building board, and glue them to the top wing with medium CA or 5-minute epoxy. To ensure a good glue bond, trim the covering away from the wooden structures. Place the bottom wing against the struts and position it in the same fashion. When you're happy with the alignment, glue the wing to the struts. Glue all the struts into place to complete the basic assembly.

Place 1/8-inch shims under the main spar, and pin the lower wing to the building board. Cut the motor-mount beams to length, and drill them for the bamboo vertical mount struts. Slip them into the holes you drilled in the wing and secure them with thin CA. Adjust their height at the rear strut, and secure them with thin CA. Use a small level to set the beams to zero degrees, and secure the front ends to the struts. Add the side and rear diagonal bracing (bamboo skewers).

Rig the wings with 40-pound-test Kevlar fishing line (I use Spider Line). Start at the top front motor-mount strut, and zigzag the line from top to bottom and front to back until you end up where you started. Then repeat the process until all the front, back and side strut bays are rigged in an "X" fashion. Rig the rear motor-mount struts to the innermost struts in the same way. Secure the line only at the ends until all the rigging is in place; then apply a drop of medium CA at each attachment point. The control-surface rigging uses one continuous piece of thread.