Few experiences are as satisfying as watching a model airplane you have built soar through the summer sky. A balsa wood glider is easy to build and serves as the perfect primer to flying model airplanes, introducing the builder to building techniques, aerodynamics and flight trimming. Be prepared to spend a few sessions building your model. Each step is fairly simple, but thorough sanding and careful gluing will pay off when your bird takes wing.
Building the Model
Print an outline of your glider plan to scale.
Place the plan over the wood and, pressing gently with a ball point pen, follow the outlines. The soft balsa will take the impression of the pen and provide you with a line to cut on. The grain of the wood should run along the longest dimension of the piece, as it will be much more difficult to cut across the grain.
Cut along the impressions with a modeling knife, taking multiple passes if you need to. The wood should cut or split easily along the grain.
Sand the pieces into their final shape. Start with the edges, but avoid the inner edge of the two wing halves, the bottom of the vertical stabilizer, and the places on the fuselage where the wing and horizontal stabilizer will be mounted; these will be glued together later. Hold identical pieces together as you sand, like the two halves of the wing, so they maintain an identical shape. Once the edges are sanded, sand the fuselage and the tail pieces until they are smooth to the touch.
Use sandpaper to create an airfoil in the wings. The airfoil shape should make the wing rounded along the leading edge, widening toward the center and then tapering almost to a point at the trailing edge.
Shape the inner edge of each of the wings using sandpaper to create a dihedral angle when the two halves are glued together. The amount of dihedral is measured as the distance each wingtip is from where it would be if the wing were parallel to the ground. With the wing’s leading edge facing away from you, prop up one half of the wing with a small block so the wingtip is at the proper height. Take a sanding block and place it vertically against the inner edge. Sand until the edge is perfectly flat and perpendicular to the work surface. Repeat with the other wing half.
Glue the two wing halves together. Using blocks under both wingtips to create the proper dihedral, apply a bead of glue to the inner edge of each of the wing halves. Press the two halves together. Remove the excess glue. Place a light weight on the wing near the center joint to hold it in place. Measure the dihedral again and make any necessary adjustments. Let the glue dry for a couple of hours.
Assemble the plane by fitting and gluing the remaining parts together. Check your parts against the plan to be sure the proper angles are maintained as you build. Let the glue dry for a couple of hours.
Trimming and Test Flying
Place a finger on the bottom of each wing half, roughly in the middle of the width of the wing. Balanced this way, the plane will tip toward the tail. Add modeling clay for weight on the nose of the plane until you achieve a level balance.
Hold the plane at shoulder height, with the nose angled slightly downward. Gently push the plane as you release it into the air. Do not throw it or toss it. The glider should fly fairly straight on a smooth, steady path.
Trim or add clay to the nose as needed. If the plane dives out of your hand, remove some nose weight. If it flies sharply upward, then stalls and flips downward into a dive, add more nose weight. If the plane veers sharply to the right or left, gently bend the back edge of the vertical stabilizer to compensate for the turn until the glider flies fairly straight.
Balsa can be purchased from most craft stores, but better quality and a wider selection of sizes will be available at a hobby shop. Some plans may call for spruce. You can use basswood if spruce is unavailable. The plane can be thrown hard almost vertically into the wind for the longest possible flight. However, this type of flying requires special trimming.
Be patient while trimming the model and change only one thing at a time until it flies the way you want.
When assembling the plane, pay special attention to the angle of the horizontal stabilizer relative to the angle of the wing. This is called the wing incidence. If it is incorrect, the model will fly poorly.