How can airplanes fly like birds?
For the most part, gliding birds and airplanes fly for the same reasons. If we looked at the shape of a bird's wings, we would see they are curved the same way airfoils on airplanes are. When a bird glides during level flight, it stays in the air just like airplanes do -- wings provide the lift.
Four forces -- weight, lift, drag, and thrust -- affect flight. They push an object down, up, slow it down and move it forward. There's a constant "tug-of-war" between these forces.
Weight (a result of the force of gravity)
pulls a plane toward the ground. To fly, things need to be light. Balloons oppose this downward pull with buoyancy and rockets do it with thrust. Wings help birds and airplanes oppose this force, creating most of the lift used by airplanes as they move through the air. The details of why a particular wing has lift are complex and aeronautical engineers spend considerable effort understanding and calculating lift for different wing shapes. Modern aeronautical engineers design better planes from how birds fly and how fish swim.
Lift works to overcome gravity's downward pull. An airplane or bird can fly when lift is greater than or equal to gravity's pull and thrust is stronger than drag. Stick your hand out of a moving car window and you can feel these forces. The wind's force hits the flat surface of your palm, making your hand move up or down. Change the angle of your hand and you change the movement. Your hand has lift. Tilt your hand in different ways and you also feel drag force due to air resistance.
Moving through the air generates lift, but also creates drag. All the
things that make lift also make drag. Drag is resistance to motion through
the air and it eventually slows you down which stops lift. The bouncing of air molecules off an object causes drag. We call this air resistance.
To overcome drag you need the force called thrust. Thrust pushes the plane forward. It is a force that moves an aircraft in the direction of the motion. It is created with a propeller, jet engine, or rocket. Air is pulled in and then pushed out in an opposite direction. One example is a household fan.
Once the plane is flying and the forces are balanced, a plane continues in a level direction. The plane goes up if the force of lift is greater than the weight. If the weight is greater than lift, the plane goes down. If the thrust is greater than the air drag, the plane speeds up. If the air drag is greater than the thrust, the plane slows down.
What do you think?
How do the four forces of flight - gravity, lift, thrust, and drag - compare?
How would these forces be changed if there was no air?
How does nature use these forces to its advantage?
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