How Planes Fly

"Wow. How does it stay in the air?" Billy asked his dad. "It looks too heavy to fly. Is it safe?"

"Yes, it's safe." Billy's dad answered. "A lot of smart engineers made it safe."

Billy wasn't satisfied. "Yeah, but how did they figure it out? How can it stay in the air?"

Billy's question, is good. And before you say "wings make an airplane fly" and click on another article, you better keep reading. It's not just the wings that make a plane fly...

Thrust

Thrust is the force that pulls or pushes a plane forward. Thrust must be present to move the plane forward. Planes get their thrust from engines. Those engines either spin a propeller or push exhaust gases really, really hard, which then pushes the plane forward.

This forward motion makes the wing move through the air. And THAT's what makes a wing work...but why does a wing moving through the air make it work???

Lift

Wings have a very special shape. The top of the wing is curved. The bottom of the wing has a different shape. Most wings are flat on the bottom. This special shape, a curved top and flat bottom, are the keys to making lift.

As the air on the top of the wing moves along the curve, it speeds up! The faster air on the top and the slower air on the bottom create what's called a "pressure differential." This just means the pressure on the top and bottom are different. On a wing, when air moves faster, the pressure of the air decreases. So the pressure on the top of the wing is less than the pressure on the bottom of the wing. The difference in pressure creates a force on the wing that lifts the wing up into the air!

Each wing has a speed it must achieve to create lift. Planes cannot take off until they have reached this special speed. And that speed comes from the thrust of the engines.

Photo courtesy of NASA

Drag

Drag is simply the force that opposes the airplane's motion through the air. As the plane goes through the air, the air hitting it creates friction, which slows it down. Most of the time, less drag is better. Less drag means the plan can travel faster, burn less fuel and carry more weight like people or cargo.

A plane like the Concorde has very thin wings, and a pointy nose. This decreases drag. The Concorde is the fastest airliner ever made.

Weight/Gravity

Weight is how much the airplane weighs. Since a plane is tasked with defying gravity, its weight plays a crucial role in how well it flies. Every plane has a maximum weight it can fly at. If it's too heavy, it has to be lightened before it can fly. This might mean removing cargo, luggage, people or fuel.

Thrust, lift and drag all work together to counter the weight of the plane.

And those are the four forces that act on an airplane: Thrust, weight, drag and lift!

Want to dive deeper into the world of the four forces of flight? Check out the NASA document below.

four_forces_k-4.pdf

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