So, You Want to Build an Airplane...
Here is all the information required to design a balsa and tissue, or laminated paper airplane. The design equations and most of the other information were taken from the instruction book to a WhiteWings Paper Airplane kit. I highly recommend picking up one of these kits, The planes are great and the information well worth it.
Before we begin, let's discuss a few of the important terms we will be using...
- Aspect Ratio - The aspect ratio is the ratio of chord length to wingspan. Long duration gliders typically have a high aspect ratio wings, while long distance (high speed) planes have low aspect ratio wings.
- Center of Gravity - This is where the plane balances. Ideally this should be at about 1/3 of the chord length.
- Chord length - The chord length of a wing is simply the width of the wing.
- Dihedral - Dihedral is the angle the wing is offset from the horizontal. Dihedral allows the plane to make roll corrections in flight. If a wind gust causes the plane to roll, one wing will loose life, while the other gains lift, causing the plane to right itself.
- Fuselage - The fuselage is simply the body of the plane.
- Horizontal Stabilizer - The Horizontal Stabilizer is responsible for keeping the main wings at the proper angle of attack. Without the horizontal stabilizer the main wings would simply flip end over end. If the horizontal stabilizer is too small, the plane will tend to stall or dive without warning.
- Vertical Stabilizer - The vertical stabilizer is responsible for keeping the plane flying in a straight line. If the vertical stabilizer is too small the plane will wander left and right.
- Wing Span - Wings span is the length from wing tip to wing tip.
Desiging the Main Wing
The first step to designing an airplane is designing the main wings. There are several questions to ask yourself here:
- How large should my wing span be?
This depends on how big you want the plane to be overall. For laminated paper construction I would say no more than 12 inches. For Balsa, perhaps a maximum of 17.
- How wide should the wing be?
I usually pick a value that is aesthetically pleasing to me. You do need to be careful not to make the wing too wide or the design of the horizontal stabilizer will be unachievable. I used an aspect ratio of 4 in the ChopStick Flyer I. The ChopStick Flyer II used an aspect ratio of 6. I recommend an aspect ratio of no less than 4. An aspect ratio of 6 worked very well.
- Should I use a high or a low camber wing?
This depends on whether you are trying for long distance or long duration flights. Long distance planes should have a low camber wing, while long duration planes should have a high camber wing.
- What should the dihedral angle be?
This depends on whether this is a high wing or a low wing airplane. If the wings are attached to the top of the fuselage of the plane a dihedral angle of 5 - 15 degrees will be fine. Low wing airplanes will require a dihedral of 15 - 25 degrees.
Now that you have settled on the design of the main wings, it is time to crunch the numbers for the stabilizers. If the numbers you get are unachievable such as the stabilizers overlap the wings or have as much area as the wings, then go back and change a parameter or two. Experiment.
Designing the Horizontal Stabilizer
The following equation provides the surface area of the horizontal stabilizer. The shape doesn't really matter much, so long as it has the proper area. It is a good idea to keep the aspect ratio of the horizontal stabilizer the same as the main wings.
Designing the Vertical Stabilizer
The following equation provides the surface area of the vertical stabilizer. Again, the shape doesn't really matter much, so long as it has the proper area. The vertical stabilizer doesn't have to be directly over the horizontal stabilizer. It is possible for the vertical stabilizer to be ahead of, or behind the horizontal stabilizer. The important thing is that it is the right size.
Putting It All Together
Now that you have all the dimensions of your new plane calculated, it is time to build. Get out some graph paper big enough to hold a full size drawing of your plane and lay out the pieces. From here you can cut the paper to the proper sizes and shapes for a laminated paper airplane, or cut the balsa sticks and sheet to the right sizes for a stick and tissue plane. Glue all the parts together and let the glue dry.
Now it is time to trim the plane.
Carefully pick the plane up by the main wings about 1/3 of the way back from the leading edge.
Does the plane hang nose down? -- Add weight to the tail or shorten the nose until the plane hangs level. Does the tail hang down? -- Add weight to the nose until the plane balances.
Time for the test flight...
Find a large open place free of obstructions. Tall grass is a plus if you are outside. Carefully throw your plane and observe carefully. If it dives to the ground, warp the tail up slightly. If it noses up and then dives to the ground, Warp the tail down slightly. If it banks left, warp the right wing tip up slightly. If it banks right, warp the left wing tip up slightly. If it falls apart, either you 1) didn't wait for the glue to dry, 2) threw the plane too hard, or 3) need to design the plane better.
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Created by: Joseph M. Krzeszewski
Last updated: 6/12/1996