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Stable paper airplanes fly farther and faster. Paper airplanes typically benefit from adding what’s known as up elevator. Take the back end of the airplane, which on a standard dart-shaped plane is the wing tips, and use your finger to bend them upwards a little. This counterbalances the weight in the nose of your plane. Most planes also benefit from a little weight in the nose. This helps balance the plane so it doesn’t have a tendency to fly straight up. Cover the nose in a layer or two of tape or add a paper clip. Test out out the plane and make adjustments as necessary.  Most airplanes are better off being slightly nose heavy rather than slightly tail heavy. Heavier planes are better at withstanding outdoor flight. Bending the wing tips downwards is only useful for planes that try to fly upwards when launched. Use your fingers to bend them down slightly. Try throwing the plane again. If this isn’t enough to balance it, you can try adding more weight to the nose of the plane. Slightly bend the end of the tail to the left. If your tail has two sides, bend the left side up and the right side down. When the air hits the bends, the plane will change the plane’s direction. If your plane has a single, vertical edge for a tail, bend it to the right. Otherwise, pull the right side up and the left side down. These bends will correct the airflow to cause a more stable flight.

Summary:
Bend the back end of nosediving planes upwards. Weigh down the nose on stalling planes. Bend the back ends downwards on stalling planes. Bend right-leaning planes to the left. Bend left-leaning planes to the right.