Paper airplane gliding performance is not usually very important. We usually want a plane that does a good job of flying across the room, and aren't too concerned if another paper airplane design (which would be more difficult to build) could have made the same flight more gracefully. Notice that for my world record paper airplane gliding performance is extremely important, but a low aspect ratio wing is needed to withstand the high launch speed (more on the specifics of the world record plane later). The airfoil of the plane also affects the launch. I have tried using highly cambered airfoils optimized for slow gliding, but they tend to degrade the ascent. I wrote a computer program to reproduce the flight of the world record paper airplane to learn what parameters were most important for a long flight. One of the most important things I learned was that Cdo, zero lift wing drag, is more important in the ascent than it is in the descent. The airfoil optimized for slow gliding is not optimized for zero lift, and produces extra drag during the ascent. What is needed is an airfoil which produces low drag during slow, high lift flight, but more importantly has low drag during the ascent. I believe a nearly flat, uncambered airfoil does this. Certainly a flat airfoil is ideal for low drag at zero lift, but it can work at higher lift coefficients also. The flat wing at high lift results in a steep pressure gradient near the front of the wing on the upper surface, which likely aids transition to a turbulent boundary layer which is needed for low drag at high lift. I plan to do more airfoil tests during the spring of '97 to help find the best airfoil for long flight.

As I mentioned above, not all my world record planes can set a record. Most have flight times from 10-14 seconds. Maybe 10% can get to 15-17 seconds, and about 1% can get to 20 seconds. One of the goals of my research and testing is to be able to make the "good" planes on a repeatable basis. The best way I know to do this is to understand the physics involved, and then work on solutions. I have found that the physics involved can get quite complex, and it is difficult to get definite answers from my tests. I do think I am making progress, and hope to continue to improve my understanding and ability to consistently make good planes.As mentioned in section 2.2, where a paper airplane balances is called the Center of Gravity (CG), and there is a specific CG position known as the Neutral Point which provides neutral pitch stability. If the airplane has a CG ahead of this point, the plane is stable, if its behind this point its unstable. Naturally all airplanes without computer assisted flight controls need a CG ahead of their neutral point. For rectangular wings the neutral point is ¼ of the distance from the nose to the tail. For delta wings (such as the common dart paper airplane) the neutral point is ½ of the distance from the nose to the tail.

The goal for gliding flight is to descend vertically as slowly as possible. This represents the lowest rate of change of potential energy(power) which is the minimum product of drag times velocity. Generally the minimum sink rate for gliders is just above stall, and that's true for paper airplanes as well. For those interested in the details and math, finding the minimum power required involves taking the equation for powered required, differentiating with respect to velocity, and setting this equal to zero (standard calculus procedure for finding the minimum or maximum of a function. Starting with the basic parabolic drag curve; Fold the top two corners down so they meet the center crease. This is the classic way to start a paper airplane, and probably what you first learned as a kid. This wasn't going to be easy. If successful, it would be my forth time at setting the record. Each time was the absolute I could achieve, with improvements resulting from improving my planes and from working on a faster throw. My best unofficial time, 20.88 seconds, was the product of months of working out and well over 100 airplanes constructed. And I have another enemy sneaking up on me as well - time. I am 35 years old, and soon I know my arm speed is likely to decrease. M.M. O'Meara and T.J.Mueller, "Experimental Determination of the Laminar Separation Bubble Characteristics of an Airfoil at Low Reynolds Numbers", AIAA-86-1065, May 1986

In addition, paper planes resemble flight itself! As early as 500 BC, they found the first folding paper airplane that came from China. The popularity of these paper airplane flying toys is the same as the paper-folding craft of origami, which grew in Japan around the same time in China.