Lift

Gravity

Thrust

Drag

2.     Definition of the forces of flight:

Lift:

Lift is the upward force that counteracts gravity and enables airplanes to fly.

Lift keeps birds, gliders, and airplanes aloft as they move forward through the air. Lift is also generated by the spinning blades of a helicopter.

Aerodynamic lift is based on Daniel Bernoulli’s Principle, which states that the pressure of a flowing fluid or gas decreases as its velocity increases. To take advantage of this, an airplane wing, like a bird wing, is designed with a distinctive shape called an airfoil. This shape creates the greatest possible lift for the airplane.

The shape of an airplane wing, the angle at which the wing meets the airflow, and the speed of the airplane all affect the lift.

Gravity:

Gravity is the invisible force of attraction that exists between two objects.

Most of us think of gravity as the force that pulls objects toward Earth and gives us weight. In fact, gravity attracts all objects to one another. However, the force of gravity depends on the size or mass of the two objects. Because Earth is so large, its force of attraction is more noticeable. So the force of attraction that exists between your hand and a ball, for example, is far less apparent than the force that exists between the ball and Earth.

Many scientists have contributed to our knowledge of the law of gravity. Galileo Galilei and Sir Isaac Newton are two of the most famous. Today scientists continue to study gravity and its effects on vehicles, living things, and satellites of all kinds.

Thrust:

Thrust is the force of flight that opposes drag. The push or pull of an airplane’s engines propels it forward, generating lift and the ability to fly.

Without thrust, airplanes are just gliders, which can fly only under certain conditions and are not practical for transportation. The Wright Brothers made the first successful powered flight in 1903 in an airplane with two “pusher” propellers. The advent of powered flight made human air travel possible.

There are four main types of systems for producing thrust in modern aircraft: propellers, jet turbine engines, ramjet engines, and rocket engines. Each produces thrust in a different way.

Drag:

Drag is the force of resistance caused by air or liquid pressure. If you have ever put your hand out the window of a moving car and felt the wind pushing against it, or walked into the wind on a breezy day and noticed how hard it is to move forward, you have experienced drag.

Drag affects an object’s ability to travel through air or fluid in several ways. Drag slows an object down. It forces a powered object to use more fuel. Drag can even pull an object apart if it is not designed to withstand the force of drag.

Aerodynamic drag, which affects objects in flight, comes from two primary sources: form drag and friction drag.

* these definitions are based on Boeing Education’s  “Forces of Flight” lesson plans.

3.     How the forces counteract each other:

To fight drag, the airplane uses a propeller or jet engine to produce a forward force called thrust.

The airplane’s wings produce an upward force called lift that counteracts gravity.

4.     How the forces act on a wing.

Wing Shape

As an aircraft wing moves through the air, some of the air passes above the wing (purple bars) and some below (blue bars). The wing’s shape results in decreased air pressure above the wing. The air pressure below the wing is higher, which lifts the wing up.

Angle of Attack

Angle of attack is the angle at which a wing meets the airflow. As angle of attack changes, a wing generates more or less lift. This can result in a stall. Stalling occurs when the angle of the wing becomes too steep and disrupts the flow, causing a chaotic pattern that eliminates lift.

Speed

The faster an object flies forward, the more aerodynamic lift it creates. Flight occurs when the force of lift exceeds the weight of the object.