In addition to understanding the forces that affect flight, it is helpful to know some of the properties good airplanes share.Most important is the property we call STABILITY, which helps an airplane return to steady flight after a bad throw or a strong gust of wind.An unstable plane will tumble out of control or go into a tight, spiralling dive.
There are three basic types of stability: pitch, directional, and spiral.
Pitch stability keeps the airplane is nose from pointing too far up or down.
Directional stability keeps an airplane is nose from veering to the right or left.
Spiral stability keeps the airplane from spinning or rolling about it is body or fuselage The first of these, PITCH STABILITY, keeps the airplane flying at a constant speed.
If the nose of the plane “pitches” up, it will slow down. If it pitches down, it will speed up. There is a small distance along the length of the airplane where it must balance to have the optimum pitch stability. On full-size airplane, this area ranges from a couple of inches (on a two-seater) to a couple of feet (for, say, a 747).
On a paper airplane, this range is less than an inch long. If the balance point is forward of this region, the plane will dive at the ground. If it is behind this range, the plane will stall and tumble out of control. The best way to tell if your airplane is “pitch stable” is to give it a toss and see if it dives, swoops up and down, or glides smoothly.
If you put a paper clip on the nose of your plane, it will become more stable. However, if you move the paper clip back, it will become less and less stable the farther you move it. Therefore, it would seem that to be on the safe side, you should put a lot of weight on the nose. Unfortunately, this does not work because if there is too much weight on the nose, the airplane will become overly stable and it will dive to the ground. (Lawn darts, for example, are extremely stable. ) Even if you have an airplane with pitch stability, your plane will not necessarily fly in a straight line.
It also needs DIRECTIONAL STABILITY, or it will spin around and fly backward. Having a fin on the back of the airplane will counteract it is tendency to spin (just as the feathers on the back of arrows help them fly straight). On most paper airplanes, the body acts as the fin. If most of the plane is body is behind the balance point, it is a good bet it will be directionally stable.Bending the wing tips (fins) up or down will also contribute to the plane is directional stability.
The third type of stability is called SPIRAL STABILITY, if an airplane is spirally stable, it will fly in a straight line or a slow constant curve. A spirally unstable plane will begin to circle, turning tighter and tighter, until it spins down in a vertical dive. This is a very common problem, but it is easily corrected. When looking at the plane from the nose, bend the wings up slightly so they form a “Y” shape with the body, and make sure they are symmetrical.
Originally posted 2012-05-19 15:06:48.