Putting Wings to Work
by Kathiann M. Kowalski
What makes an airplane fly? Before the Wright brothers ever flew their airplane, scientists figured out what makes flight possible.
LiftTo get off the ground, airplanes must overcome gravity. Gravity is the force of Earth's mass pulling things down. So airplanes need an upward force—lift.
To get lift, airplanes use the Bernoulli principle. Back in the 1700s, Swiss scientist Daniel Bernoulli learned that the faster gases travel, the lower their pressure becomes.
Today, airplane wings are built with an airfoil shape. They are curved on the top and pretty flat on the bottom. The curved shape forces the air moving on top to go farther and travel faster than the air moving underneath the wing. Greater air pressure underneath the wing pushes against the lower air pressure above. That lifts the wing—and the “attached” airplane—up.
Airplanes also need thrust, or forward force. Thrust moves air around the wings to get lift. It also lets the airplane travel to where it's going.
On smaller airplanes, engines power propellers that push the plane through the air. Bigger airplanes get their thrust from jet engines. Jet engines burn fuel with compressed (tightly packed) air. The reaction produces hot expanding gases. As gases shoot out from the back of the engine, they push the airplane forward.
The more friction, or rubbing, between the airplane and surrounding air, the more drag there is. Drag slows airplanes down. Thus, the less drag there is, the better. Airplanes' streamlined shape reduces drag.
At the Controls
Airplanes are safe and practical only if pilots can control where they're going. Pilots must master all of an airplane's controls and fly it successfully to get a license. Different types of airplanes have different controls. Thus, pilots must pass separate tests for each type of aircraft they fly.
- What kind of a force is created by a jet engine?
[anno: A forward, or push, force is created by a jet engine.]
- What are two forces that work against keeping an airplane in flight?
[anno: Gravity and friction work against keeping an airplane in flight.]
- What are three things that are done or used to overcome these two forces?
[anno: Gravity and friction are overcome by creating more push force from a jet engine or a propeller than the pull force of gravity or friction. Putting curved wings on planes also helps to keep a plane aloft. Streamlining the body of a plane helps to reduce drag.]
- What is the Bernoulli principle?
[anno: The Bernoulli principle states that the faster gases travel, the lower their pressure becomes.]
- Why are a plane's wing flaps extended during takeoff and landing? Why do you think the wing flaps are pulled in during flight?
[anno: Answers may vary but could include that wing flaps are extended during takeoff and landing to create more lift at low speeds. The wing flaps are pulled in during flight because there is not as much need for lift once the plane is up in the air. The passage of air over the wings at high speeds provides enough lift.]