Introduction: Card Stock Twin-Boom Airplane
Enjoy this nifty little plane that resembles twin-boom aircraft of the 1930s and '40s. It is best suited for straight flights and gentle, sweeping turns.
This design takes several hours to build, and there are a few parts that are kind of tricky. If you have no experience with this kind of hobby/craft, you may want to start with a simpler design, such as the Pencil Eraser Popsicle Plane.
-Two sheets of card stock (65 lb.)
-Sheet of paper
-Chipboard (such as a cracker box)
-Two pencil eraser caps
-Two paper drinking straws (optional; 6 1/2" long and 5/16" diameter)
-Wood coffee stir sticks, popsicle sticks, basswood dowels, or some other wood to make wing spars
-Two small blocks of wood to make the canopy (approximately 2 1/2" x 3/8" x 3/8")
-Utility knife or hobby knife
-Metal ruler (or wood ruler with a metal edge)
-Craft glue (PVA glue) and glue stick
Step 1: Download and Print
Print or photocopy the first page onto card stock and the second page onto paper.
Step 2: Make Card Stock Tubes
If you found a pair of sturdy paper drinking straws, as seen in the photo of the purple plane, you can skip this step.
Cut out two rectangles of card stock, measuring 6 1/2" by 1 1/2". First give the rectangle a gentle curl by working it over a broomstick. Then get a chopstick or dowel and roll the card stock around it. When about 1/2" remains unrolled, apply glue and then finish. Hold it in place for a couple of minutes so the glue can dry.
Step 3: Cut Out the Pieces
Take your time. Try to be consistent with how you cut, whether that be on the inside or outside of the black lines.
Certain pieces will then need to be traced onto paper (I, J, K) and chipboard (L).
Step 4: Construct the Wings
On the dotted lines of all three pieces (A), fold the front segments down and under. Glue the layers together, so the front each wings is a double layer.
Use the small angle braces (B) to join the outer wings with the center section. In subsequent photos, you will see two white card stock braces behind the spars. The plans add two smaller braces in front of the spars. No strip is needed over the center spar.
Apply glue to the braces and attach them. I use a glue stick for this. Use the reference lines on the top of the wings for placement.
With the center section flat on the table, raise the wingtips by about 1/2". Allow the glue to dry for several minutes. Next, glue the large angle braces (C) onto the bottom of the wing joints, then place the wing to rest as it was before, with the wingtips raised.
Step 5: Attach the Booms
The booms will extend 1" beyond the leading edge of the wings. Cut out small rectangles where the booms will contact the wing spars, deep enough so that the booms rest flush with the wings. It helps to use a very sharp blade and to put the chopstick back into the boom before cutting. Glue the booms into place. Make sure they are parallel to each other and perpendicular to the wings.
Step 6: Construct the Tailplane
Cut out a strip of chip board (L) and use it to brace the end of the booms.
Use a ruler to establish mild creases on the dotted lines of the horizontal and vertical stabilizers (F, G), defining the elevator and rudders. Make stronger creases on the dotted lines of the braces (H) so they can bend at a right angle.
As with the wings, fold the front section of the horizontal stabilizer down and under, and glue the layers together. Glue the braces to the sides of the vertical stabilizers, and make sure they are well aligned. Then glue the vertical stabilizers to the horizontal stabilizer. Finally, glue the whole tailplane to the booms, making sure it overhangs the brace (L) enough for the elevator to move freely.
Step 7: Add Coverings
Apply stripes of glue about 1/4" wide on the leading and trailing edges of the two outer wing covers (I) and put them in place on the tops of the wings. Later, after the cockpit is it attached, you will do the same with the center wing cover (J).
Trim the wing covers at the ends, matching the curve of the wingtips, but leaving the tabs. Apply glue and fold the tabs down and under.
Next, attach the small covers on the outer sections of the horizontal stabilizer (K) and trim them with scissors if needed.
Step 8: Make the Nose
Use the grey profiles (M) in the plans. Use a somewhat dense wood, such as birch or maple; do not use balsa wood or foam, unless your going to embed some metal or clay for weight. If necessary, make the cockpit pieces out of layers of popsicle sticks or stir sticks. You could even make these structures by gluing many pieces of chipboard together; once dried into a solid piece, the chipboard can be carved and sanded.
Be careful! Carving small pieces of wood makes it very easy to stab or cut a finger. Do not use excessive force. Also, when sanding, go outdoors and wear a mask to protect yourself from toxic dust.
If desired, add color to the wood. I made an ink wash with a few drops of water and a felt-tip marker. I applied the wash, let it dry, applied it again, and so on, until the color was right.
Step 9: Finishing Touches
Attach the nose structures to the wing. Test fit the cover (J). If it is a poor fit, use scissors to make adjustments, or make a new piece with your extra paper. Glue the piece as you had done with other wing covers.
Glue the boom side pieces (D) in place. Test fit the pieces first to make sure the curves match the tops of the wing. Use scissors to make the curves deeper, if necessary. Depending on what material you used for wing spars, you may need to make new pieces with a shallower curve. Once you've used a small amount of glue to hold the pieces in place, apply thin beads of glue along the seams, where the pieces rest on the wing.
Wrap the engine cowls (E) around the booms, right in front of the leading edge of the wings. Curl them first, the tack one end on with a little glue and wait for it to dry. Once secure, wrap the piece around and use some glue on the last 1/2" or so to hold it all in place.
Put the pencil eraser caps onto the booms.
Test the fore-aft balance of the plane to see where the center of gravity is. If you are unfamiliar with this concept, there are many resources available online. The center of gravity should be about a third of the way back from the leading edge of the wing, about were the wing spar is.
If the aircraft is too tail heavy, you can put a bit of clay into each pencil eraser and/or add more strips of card stock to the engine cowls. Of course, you may also want to make a canopy, as I did, and that can add nose weight, depending on what you use to make it. I used balsa wood, carved and painted white.
If the aircraft is too nose heavy, add a strip of card stock across the horizontal stabilizer. Repeat, if needed (unlikely).
Step 10: Test Flights
Try to conduct the test flights when there is little or no breeze, or conduct them indoors if you have access to a large space. Make sure the elevator is in a neutral position or slightly raised.
Throw the plane gently and level with the ground. Do this a few times to see if there is a pattern.
If the plane drifts left or right, Try using a rudder (or both) to correct this. If it rolls to the left or right, check the wings for asymmetry, such as a slight twist, and try to gently correct it, little by little, without creasing the material. The card stock has a bit of memory and you may have to work out the twist several times. Breathing hot air onto it helps loosen up the material.
If the plane consistently pitches down, try correcting this by raising the elevator a few degrees. If it still pitches down, it may be nose heavy. If the plane consistently pitches up, it probably needs a little more nose weight. (Refer to the last step for tips on how to adjust the balance.) Note that throwing into a breeze often makes a plane pitch up a little.
WARNING! A flying plane can cause injury, especially to eyes. If there are people around when you fly the plane, allow a safe distance and inform them that you are throwing.