you know that paper was not square. Similarly, when you open a ream of office paper, turn a few sheets from the center around 180 degrees and align one end with a tap on the table. Look at the top edge to see if the rotated sheets are even along the top, or if they stick out at either side.
You can also try the following folding experiment. Take a sheet of letter paper and fold it in half, long edge to long edge. Are the edges and corners of the top layer matching those of the layer beneath?
Next, unfold the paper and form a simple “airplane point” at one end of the sheet by folding the two halves of a short edge to meet at the center crease. Do the two square corners meet?
Unfold the paper and try the same thing at the other end. It is not uncommon for a sheet to fail these tests for trueness. In most cases, trim discrepancies are slight and can be accommodated for folded paper airplanes. However, when the trim error is off by several millimeters you should consider re-trimming the paper to true it up. This will be especially important for performance-critical contest entries.
To learn if your store-bought origami paper is acceptably symmetrical simply fold the sheet in half diagonally, corner to corner. The edges and the free corner of the top layer should match those of the bottom layer.
Thickness
The planes in this book were designed to be folded from many common types and sizes of paper—either origami paper or 20-pound letter bond—but a general guide will be to use thinner papers on the complex models and thicker on the simplest ones.
There is also the issue of relative thickness, which can be expressed as a ratio of thickness to area. You can use a thicker paper if the area is increased, but thinner stock must be used if you decrease the area of the sheet.
If you were to graph the variables of the acceptable planes, you would determine the designs’ acceptable range of relative thickness. Each paper airplane design will have an optimum size for a given thickness. When designing new paper planes it is wise to keep the technical handling of the folds well within the doable limits of the paper with which you are experimenting. Some paper folding design plans may accumulate many layers in certain places, such as the nose or the leading edge of the wings. Choose paper thin enough to accommodate the folding in the thickest places of the model. If an airplane folded from thick paper does not perform well, perhaps that design should be folded from a larger sheet, in order to bring the design back into the “doable range” (or window of acceptability).
Weight
Most office and printing stocks fall into one of two types: “Bond,” and “Offset.” Each type has different weights, sold in packs, or reams, of 500 sheets. The ream is marked with a number indicating the weight, such as 20-pound (abbreviated 20 #, 20 lb, etc.). When you lift a 500-sheet ream of 20-pound bond, the first thing you notice is that it cannot possibly weigh 20 pounds. That is because all grades of bond are labeled with the weight, in pounds, of a much larger ream measuring 11 by 22 inches—which is called the basis size for bond papers.
It’s confusing, but reams of so-called “offset” paper stocks (including “book,” “text” and “coated” stock) used in professional printing presses are made by different machinery, so their weight is described by a different basic size sheet: 25 by 38 inches. You can’t compare the two types by only considering the area. The 50-pound offset stock is slightly lighter than 20-pound bond because the machinery that makes the offset paper uses a process that makes it thinner and denser.
The system is useful when comparing the weights of the same types of paper: 24-pound bond is 20% heavier than 20-pound bond (24-20=4; 4/20= 20%), and 60-pound offset is 20% heavier than 50-pound offset paper (60-50=10; 10/50=20%).
Metric units are more direct. When paper “weight” is described in grams per square meter, this removes confusion, but we are probably stuck with knowing and using at least a few different systems for a while.
Only simple, large models can be folded from heavy papers. When you fold the same design from different weights of papers with the same area, those from heavier papers will glide farther, but are less likely to look neat because of bunching caused by the increased thickness. When you lift an airplane and launch it, your arm is imparting a force on the mass of the plane. Those folded from heavier papers have greater mass, but essentially the same area and resistance to air molecules. Other variables being equal, increased mass translates to increased potential energy, and greater distance.
Foldability
How well does the paper take a crease? How many times can the paper be folded back and forth before it splits or cracks? How long does that crease stay crisp? Many papers today are coated with plastic, paint, clay, varnish, wax or even silicone. Some are fused to metal or plastic films. Heavily coated papers and foils are unforgiving of poor technique, so it is important to choose papers that fit your folding skills. At the very least, it is fun and instructive to test an origami airplane on many kinds of papers. This is when the paper is your best teacher.
Rigidity
Rigid paper planes are generally more efficient and fly better than floppy planes. The rigidity can come from the weight and size of the paper, but also the folding method. Compare a paper towel to a sheet of letter paper. Each was formulated and manufactured differently to best suit a particular need. A soft paper towel does not make a good paper airplane: it would be too floppy. However, a paper plane that is folded from a very large sheet of office paper, say four times its typical size, could be so heavy, that the shape of the flaps and wings would distort.
Moisture in the air changes from day to day and also affects paper’s rigidity. On very humid days, you may have noticed that fins flutter and wings droop—this change of shape affects motion. As a deformation propagates along the surface, it results in extra wind resistance and unwanted drag. Energy expended to flex the structure is energy drained from the momentum (forward path of force), shortening or even stalling a flight. Unequal distortions to wing or fin can also result in an erratic path. Using slightly smaller sheets of paper can improve rigidity, as can choosing models that have multi-layered wings with several folded edges.
Special planes intended for photography or display often benefit from the use of crisp tracing paper, which really shows off the intricate folds and precise workmanship.
Rigid wings of balsa or from composites of paper card will always perform better than pure origami planes. Nevertheless, origami airplanes can produce some impressive and very satisfying performances.
Aesthetics Impact Performance
Color pigments, printing inks, and toners on the paper may have a small, but measurable impact on a paper airplane’s mass (and therefore density), surface roughness and symmetry. Besides these technical aspects, the aesthetics of a paper airplane’s appearance may influence the crowd and psych-out the competition. Do drivers of bright red cars receive more speeding tickets? Does the car’s color somehow motivate the driver to hit the gas pedal harder? Do people who are more likely to speed select car colors of the more aggressive hues? Use plain white paper if you subscribe to the maxims “Beauty is only skin-deep,” or “Don’t judge a book by its cover.” This lets you appreciate the elegance of the plane’s lines and geometry. Aesthetics can also be a function of age and culture, so you must decide how to play this card.
Putting It All Together
Paper selection depends upon why you are folding the model. If you are just practicing, use anything available. If you have plenty of used copier paper handy in a recycle bin, begin by learning the models that work well from
