Science Behind It: How Do Airplanes Fly?

In 1903, the Wright brothers, Orville and Wilbur, made the historic first flight, revolutionizing the way humans traveled around the world. Their biplane, the Flyer, stayed airborne for just 12 seconds, but that brief flight was the culmination of years of innovation, experimentation, and understanding of the fundamental laws of physics.

If you’ve ever wondered how giant aircraft (some weigh more than 661 tons) stay airborne, you’re not alone. It sounds like magic, but there’s actually science behind it.

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Aircraft fly through the air using air currents and uniquely designed wings to generate lift. Similar to birds, aircraft wings are designed so that air flows faster over the wing than under it, creating a critical imbalance that keeps the aircraft in flight.

In this article, we’ll break down the science of flight into easy-to-understand concepts to help you grasp the forces and mechanics behind airplane flight.

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The four forces of flight

Image: NASA

To understand how airplanes fly, we first need to examine the four main forces acting on an aircraft: lift, weight (gravity), thrust, and drag.

Lift: This is the upward force that lifts an aircraft off the ground and keeps it in the air. Without lift, flight would be impossible.

Drag: This is the air resistance that an aircraft faces as it flies forward. It acts in the opposite direction of thrust, slowing the aircraft down.

Weight (gravity): This is the downward force pulling the aircraft back toward the Earth. All objects, including aircraft, are affected by gravity.

Thrust: This is the forward force produced by the aircraft’s engines that propels the aircraft through the air.

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The role of lift: Bernoulli’s principle and Newton’s third law

The core force of an airplane’s flight is lift. But how is lift generated? The answer lies in Bernoulli’s principle and Newton’s third law of motion.

Bernoulli’s principle states that the greater the speed of a fluid (in this case, air), the less pressure it has. Airplane wings are designed as airfoils—flat at the bottom and curved at the top. As the plane flies forward, the air moves faster over the curved top surface, while the air moves slower over the flat bottom surface. The faster-moving air on top creates less pressure than the slower-moving air under the wing. This pressure difference creates an upward force—lift—that enables the plane to rise into the air.

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Newton’s third law of motion complements Bernoulli’s principle. It states that for every action, there is an equal and opposite reaction. When an airplane’s wing pushes the air down (action), the air pushes the wing up (reaction), further increasing lift.

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Airfoil: Shape is important

One of the most important factors in an aircraft’s ability to fly is the design of its wings. The shape of the wing (curved on top and flatter on the bottom) plays a key role in generating lift.

But why is this shape so effective? As mentioned earlier, Bernoulli’s principle tells us that the air over the curved top surface of the wing moves faster than the air beneath it. This speed difference reduces the pressure on the top surface, allowing the higher pressure under the wing to push it upward, thus creating lift.

Additionally, when an airplane tilts its wings (a motion called “pitch”), the angle at which the air hits the wing changes. This angle of attack increases lift, but if it’s too great, it can cause the airplane to suddenly lose lift—a condition called a stall.

Resistance: The Force to Overcome

Just as lift is necessary to counteract gravity, thrust is necessary to overcome drag. Drag is the aerodynamic resistance an aircraft encounters as it moves through the air. There are two main types of drag:

Parasite drag: includes all forces that resist the forward motion of an aircraft, such as friction between the aircraft surface and the air, and drag caused by the aircraft’s shape.

Induced Drag: This is directly related to lift. When wings generate lift, they also create small vortices of air at the wingtips which create drag and slow the aircraft down.

To reduce drag, airplanes are designed to be streamlined. This reduces air resistance and makes it easier for the engine to maintain speed and thrust.

Thrust: The driving force behind flight

Lift alone is not enough to make an aircraft fly. The aircraft also needs forward motion to generate the airflow necessary to produce lift. This is where thrust comes into play.

Thrust is produced by the aircraft’s engine, which can be either a propeller engine or a jet engine. Propeller engines work by spinning blades that cut through the air, pulling or pushing the aircraft forward. Jet engines, on the other hand, work by taking in air, compressing it, mixing it with fuel, igniting the mixture, and expelling it at high speed to create thrust.

In both cases, the engine’s job is to produce enough thrust to overcome drag and maintain forward motion. As the aircraft accelerates, the increased airflow over the wings increases lift, allowing the aircraft to take off and stay in the air.

Balance of power: balance in flight

Image: NASA

In order for an aircraft to fly straight and smoothly, lift and weight, as well as thrust and drag, must be balanced.

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Lift vs. Weight: Lift must counteract the weight of the aircraft. When lift equals the weight of the aircraft, the aircraft will maintain its altitude. If lift exceeds weight, the aircraft will climb. If weight exceeds lift, the aircraft will descend.

Thrust vs. Drag: An airplane must have thrust to maintain speed. If the thrust is greater than the drag, the airplane will speed up. If the drag is greater than the thrust, the airplane will slow down.

The pilot uses the aircraft’s controls to adjust these forces as needed to ensure a smooth takeoff, level flight, and safe landing.

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Stability and control: Keeping the plane in the air

Image: NASA

In addition to the basic flight forces, aircraft are equipped with control surfaces that allow the pilot to control the direction and stability of the aircraft. The three key control surfaces are:

Ailerons: Located on the trailing edge of the wing, they control roll and allow the aircraft to tilt left or right.

Elevator: The elevator is located at the tail and controls the pitch, making the aircraft climb or descend.

Rudder: Located on the vertical tail, the rudder controls yaw, helping the aircraft turn left or right.

Together, these controls help the pilot maintain balance, steer the aircraft, and ensure a smooth, controlled flight.

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Conclusion: A scientific masterpiece

Aircraft flight is a perfect demonstration of how the laws of physics come together to achieve what was once thought impossible. From the humble beginnings of the Wright brothers to modern supersonic jets, aircraft are a testament to human ingenuity and our understanding of the forces that govern our world. Lift, thrust, drag, and gravity all play a vital role in making flight possible, and by harnessing these forces, we have turned the skies into the highways of our modern world.

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Category: Optical Illusion