Why Paper Airplanes Fly?

Despite my degree in aerospace engineering and many years work in the field, explaining why a paper airplane stays in the air is not easy.

I’ll begin by saying that paper airplane fly using the game general principles as real airplanes, both are controlled by four basic forces: weight, lift, thrust, and drag.

Think of it as two teams each playing tug-of-war with the airplane attached to a rope in the middle.

Weight vs.

lift The first team, weight and lift, play a vertical game of tug-of-war.

Because gravity is constantly trying to pull the airplane to the ground, WEIGHT is obviously on the downward side of the rope.

LIFT exerts an upward pull.

As an airplane flies, it is wings are angled with the front edges higher than the back edges.

This causes the air going over the top of the wings to speed up slightly as it gets sucked downward across the wing.

The air travelling under the wing slows down a bit a it gets shoved by the bottom of the wing.

The speeding up and slowing down of the air is what creates lift.



As eighteenth-century Swiss scientist Daniel Bernoulli discovered, when air speed up it is pressure is reduced, and when the air slows down it is pressure is increased.

Therefore the air that speeds up over the top of the wing creates a slight suction which pulls upward on the wing.

At the same time, the air below the wing creates extra pressure which pushes upward on the wing.

Lift is the combination of these two forces.

During straight level flight both lift and weight are pulling equally.

If lift pulls harder than weight, the plane begins to accelerate up, if weight pulls harder, the plane accelerates down.

Drag vs.

Thrust While lift and weight are tugging up and down on our airplane, thrust and drag are pulling forward and aft.

Let is look at DRAG first.

When you fly a paper airplane level across a room, drag is what pulls back on your airplane and slows it down.

Most of drag comes from air resistance.

Thin and insubstantial as air may seem, it does have mass and in some ways is like runny maple syrup.

As a plane flies, the air is viscosity makes it stick to the plane, creating resistance to motion.

Another source of drag comes from lift never pulls directly up, but rather tugs up and a little back, and that backward pull contributes to brag.

THRUST is on the opposite end of our imaginary rope forward.

Real airplanes get their thrust from a propeller or a jet engine.

Paper airplanes get it from your arm, then from gravity.

A throw gives them their initial speed, and then they fly a title downward, letting gravity pull them along (like a bicycle coasting down a hill).

When you throw a paper airplane from a building or hill, the plane descends at an angle that lets gravity balance the pull of drag so the plane won’t slow down.

A typical paper airplane is drag is about one fifth it is weight.

This requires the paper airplane to fly at an angle approximately 11 degrees below level in order for gravity (weight) to pull forward enough to counteract drag.



Print this Article