by Boston Public Library

The first flight in 1903 by the Wright brothers was hard to comprehend at the time, and almost no one believed that the two brothers had actually successfully reached the sky. They did in fact conquer the sky and they changed the way the world travels.

There are many factors that go into successfully flying a plane, and some of the most important have to do with aerodynamic forces. These include lift, weight, thrust, and drag.

Thrust is a force that must be created by a plane in order to overcome the effects of drag. This thrust is created by propellers, jet engines, or rockets that pull or force air past the vehicle.

Drag resists the motion of an object moving through air or water. You can experience the effects of drag by holding your hand out of the car window while the vehicle is moving.

The amount of drag that your hand creates depends on the size of your hand, the speed of the car, and the density of the air. If you were to slow down, you would notice that the drag on your hand would decrease.

Another example of drag reduction is when we watch downhill skiers in the Olympics. You will notice that they will squeeze down into a tight crouch as often as they can.

By making themselves more compact they decrease the drag they create, which allows them to move faster down the mountain. This same concept is displayed when planes retract their landing gear after take-off.

The amount of drag produced by the landing gear of a jet is so great that, at cruising speeds, the gear would be ripped right off of the plane. Pulling the wheels into the belly of the plane makes for a smoother right through the air.

Weight is the easiest concept for people do grasp because they are familiar with the concepts of gravity. Every object has weight, which is pulled down toward the earth because of gravitational forces.

Lift is the aerodynamic force that holds an airplane in the air and counteracts the effects of weight. The vast majority of lift that is produced while flying an airplane comes from the wings.

The principal concept of fluid is essential to understanding how it is a jet is able to fly through the sky. Keep in mind that like water, air is also considered a fluid because it is a gas.

Like all gases, air flows and behaves in a similar manner to water and other liquids. Even though air, water, and pancake syrup may seem like very different substances, they all conform to the same set of mathematical relationships.

Because of this fact, many aerodynamic tests can be performed in water so that researchers and engineers may evaluate how machines will react. Another important concept is the fact that lift can exist only in the presence of a moving fluid.

That means that either the air or the vehicle must be constantly moving in order for a jet to fly through it. This is also true for drag to work.

It does not matter if the object is stationary and the fluid is moving, or if the fluid is still and the object is moving through it. What really matters is the relative difference in speeds between the object and the fluid.

Neither lift nor drag can be created in space because there is no fluid there, so spaceships cannot use these same principles to travel. This also explains why spacecrafts do not have wings.

The space shuttle is a good example of a spacecraft that spends most of its time in space, where there is no air that can be used to create lift. However, when the shuttle re-enters the earth’s atmosphere, its stubby wings on the tail end of the craft produce enough lift to allow the shuttle to glide to a graceful landing.

In order to have a straight and balanced flight, thrust and drag need to be equal, as do lift and weight. If drag is larger than thrust then the plane will slow down; and if weight is greater than lift the plane will descend.