-
Have you ever stuck your hand outside a car window while speeding down the road? If so, you've likely felt the wind forcefully pushing back against your hand, depending on its angle. That simple experience provides valuable insight into how airplanes fly. When four key forces—lift, weight, drag, and thrust—work together in harmony, they allow massive airplanes to rise and soar through the sky, sometimes speeding fast enough to break the sound barrier.
-
Let's examine these forces one at a time. Consider this: an airplane is a massive metal object that can weigh anywhere from a few hundred to half a million kilograms. The airplane's fuselage, its various components, onboard systems, equipment, payload, and fuel all contribute to its overall mass, which is directly related to its weight.
-
The weight is directed downwards, or in other words, toward the center of the Earth. To counteract this downward force, a force known as lift is required. Lift is primarily responsible for keeping an airplane, or any object, in flight. So how does an airplane generate lift? The airplane’s wings are primarily responsible. You may have noticed that most aircraft wings have a characteristic design—a flatter lower surface and a curved upper surface. This makes for a cross-sectional shape known as the airfoil.
-
As the aircraft moves through the sky at high speeds, the curved airfoil design allows the air above the wings to move faster than the air below them. This difference in air speed creates a difference in air pressure: the faster-moving air above the wing results in lower air pressure, while the relatively slower air beneath the wing has higher air pressure.
-
This pressure difference generates the force of lift, which allows the plane to ascend and remain airborne. You may recall Newton’s third law of motion: for every action, there is an equal and opposite reaction. As an airplane flies, it pushes through the air, and in response, the air pushes back against the airplane. This aerodynamic force is known as drag.
-
The direction of drag is always opposite to the direction of the plane's motion. Imagine swimming in a pool, where the faster you try to swim, the more the water resists your movement. This is another example of drag in action. The airplane's speed and shape significantly influence the drag it experiences during flight.
-
To overcome drag and maintain forward motion, another force called thrust is required. Without thrust, the plane cannot move forward; lift cannot be generated without forward movement, so flight would be impossible. An aircraft generates thrust through its engines. Commercial aircraft are typically powered by jet engines that expel air at high speeds from the back of the plane, propelling the plane forward.
-
Here, we see Newton’s third law in action again. The amount of thrust generated depends on several factors, including the number of engines, the types of engines, and the throttle setting. You may have noticed that commercial planes have their engines located under the wings, parallel to the body. Some aircraft, particularly military jets, have engines positioned in a way that allows for adjustments to change the direction of thrust; a prime example of this is the Harrier.
-
The tail wings and rudder help pilots control the airplane's direction and stabilize it while airborne. A variety of electrical and mechanical systems and components onboard work together harmoniously to achieve this elaborate airborne feat. It is this perfect combination of systems and physical forces that makes flying possible and safe.
-
These fundamental forces and engineering elements operate seamlessly behind the scenes of any flight, allowing us to sit back, relax, and enjoy the ride.
