FOUR FORCES OF FLIGHT

Today we will learn about the the four forces of flight and how aircraft move!

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Before we start, let’s reflect on these questions:

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• What are the four forces of flight?
• How do the forces of flight act on a moving object?
• How does the design of an aircraft help it fly?

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What are the four forces of flight?

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The four forces of flight are gravity, lift, thrust, and drag.

Gravity is the force that pulls all things toward the center of the Earth.

Lift is the upward-acting force on an airfoil.

Thrust is a force that pushes something forward.

Drag is the resistance offered by a fluid, like air or water.

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Collection of the Intrepid Museum. Gift of the family of Forrest Masters. P2021.29.05

How do the forces of flight act on a moving object?

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Drag acts opposite to the direction of motion. As a bird moves forward, for example, it will face drag from the air around it. Drag is caused by friction and changing air pressure.

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Gravity pulls all things toward the center of the Earth. It acts in a downward direction on all objects. It creates weight.

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Collection of the Intrepid Museum. Gift of Robert and Sue Ann Dilts. P2011.48.27

How do the forces of flight act on a moving object?

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Lift and thrust work against drag and gravity to move a vehicle through the air.

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Lift is created when the pressure on top of an airfoil is less than the pressure below the airfoil. It is the force that holds an aircraft in the air.

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Thrust moves an object in the direction of motion. When air is moved in one direction, the object is moved in the opposite direction.

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Let’s Visit Intrepid!

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Press play on the next slide to travel to the Intrepid Sea, Air & Space Museum and learn how the four forces of flight affect aircraft and spacecraft.

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How does the design of an aircraft help it fly?

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An aircraft or spacecraft must move air in order to create thrust. They may use a propeller, jet engine, or rocket. Air is pulled in and then pushed out in an opposite direction. Helicopters and some styles of airplanes use propellers. Newer airplanes use jet engines. Spacecraft use rockets.

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Collection of the Intrepid Museum. Gift of Robert and Sue Ann Dilts. P2013.30.08

How does the design of an aircraft help it fly?

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To create lift, an airplane’s wings are in the shape of an airfoil. The blades of a propeller are also airfoils, which is how a helicopter rises in the air. An aircraft’s tail may also be shaped like an airfoil.

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Collection of the Intrepid Museum. Gift of Robert Wayne Osburn and family. P2013.149.18

Let’s Explore: Gravity

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What happens when you drop a pencil on the ground? Where does it go? Why?

• Gravity is a downward acting force, pulling everything toward the center of the Earth.
• Anything that has mass also has gravity, and gravity gets weaker with distance.

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Let’s Explore: Gravity

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• How does gravity affect aircraft and spacecraft?

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• How do engineers make sure their flying vehicles can resist gravity?

NASA

Let’s Explore: Lift

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Lift is created by air moving on the top and bottom of an airfoil. Airfoils are not always the exact same shape. The image on the right illustrates the “family of airfoils,” as described by the National Advisory Committee for Aeronautics in 1929. Describe the shapes that you see!

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NASA

Let’s Explore: Lift

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Lift relies on Bernoulli’s principle.

• Bernoulli’s principle states that the faster air leads to lower pressure. Because there is higher pressure on the bottom of a wing than on the top, the wings are lifted into the air and the airplane is able to fly.

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Collection of the Intrepid Museum

Let’s Explore: Lift

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• Where did engineers get the idea for the shape of an airfoil?
• Where might we see the airfoil shape in nature?
• What types of vehicles have the airfoil shape on them?

National Archives

Let’s Explore: Drag

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Drag acts opposite to the direction of motion. As a bird moves forward, for example, it will face air resistance. Drag is caused by friction and changing air pressure.

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NASA

Let’s Explore: Drag

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There are two main types of drag: parasite and induced.

• Parasite drag increases as the speed of the vehicle increases. Induced drag decreases as the speed of the vehicle increases.

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• Is there ever a time when drag could be helpful?

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Collection of the Intrepid Museum

Let’s Explore: Thrust

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Thrust moves aircraft and spacecraft toward the direction of motion. It relies on Newton’s third law of motion.

• Newton’s third law of motion says that for every action there is an equal and opposite reaction.
• Thrust relies on Newton’s third law.

Collection of the Intrepid Museum

Let’s Explore: Thrust

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Propellers, jet engines and rockets push air or exhaust backward, which moves the vehicle forward.

• Everything that moves relies on thrust. What creates thrust in a car or bus? A train? A bicycle?
• What is the difference between thrust and lift?

NASA

Let’s Make a Rotocopter!

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A rotocopter is like a mini helicopter. Using one exemplifies the forces of thrust, lift, gravity, and drag.

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Decorate the rotocopter template.

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Use visual instructions to cut and fold rotocopter template.

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Toss the rotocopter as far and high as you can. Watch what happens!

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Let’s Make a Rotocopter!

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To make your rotocopter, you will need a template and one paper clip.

Start by folding the X panel back along the dotted line.

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Then, fold the Y panel back along the dotted line. Press down on the creases.

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Let’s Make a Rotocopter!

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Fold the Z panel up along the dotted line and press down.

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Next, fold Wing A down along the dotted line and press down.

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Then, fold Wing B back in the opposite direction and press down.

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Let’s Make a Rotocopter!

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Lift the two wings up so that they stick out.

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Finally, put a paperclip on the bottom of your rotocopter, on top of Z.

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Your rotocopter is ready to fly. Drop it and see what happens!

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Reflection

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• How is a rotocopter affected by the four forces of flight?
• How do the forces of flight affect aircraft and spacecraft differently?
• What do you want to learn more about?

For More Information

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Explore the Museum’s Photographs

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Intrepid Sea Air & Space Museum