How Do Airplanes Work?
- Science Holic
- Jul 6
- 3 min read
Author: Shuhan Yu
Editor: Jonathan Chen
Artist: Becky Li
Planes can fly due to the exact ratios of four aerodynamic forces (thrust, drag, gravity, and lift) that balance the airplane in the aerodynamic phases of takeoff, cruise, maneuver, and landing. To understand the science behind the airplane, one of the foremost designs of contemporary transportation, we need to identify the four forces acting on it and how engineers and pilots manage them.
The first force to be considered is lift, as this is what causes the airplane to ascend into the air. Lift is generated primarily by the wings, which are airfoil-shaped. An airfoil has a curved upper surface and an almost flat lower surface. When the airplane moves forward, air moves over the upper and lower surfaces of the wing. Due to the shape of the wing, air travels faster over the curved surface than over the flat surface, so less pressure is present above the wing compared to below it. This pressure imbalance creates a force pushing upwards on the wing, or lift. This is an oversimplified explanation of how lift is created using Bernoulli's Principle, which discusses air pressure and air speed. Lift is also produced according to Newton's Third Law of Motion. Since the wing applies a force on the air downward, the air applies an equal force onto the wing upward.
At the same time, the airplane is also being drawn downward by weight, caused by the force of gravity pulling on the mass of the plane. Weight changes with whatever the plane weighs, through cargo, passengers, fuel, and even the aircraft itself. For the airplane to take off from the ground, the lift has to be greater than the weight. Under steady level flight, or cruising, lift and weight are equal and in opposite directions. When the magnitude of weight is greater than lift, perhaps due to a loss of thrust or due to a descent, the airplane will descend in altitude.
To move forward, an airplane uses thrust, and all thrust comes from engines. In a jet engine, air is sucked in at the front, compressed, combined with fuel, and ignited. The high-temperature gases that come out the back, at very high speed, move the airplane forward due to Newton's third law (equal and opposite reactions). There are aircraft that use propeller engines rather than jet engines, but the same thing applies: pushing air backward causes the air to push the plane forward.
The opposite of thrust is drag, and it is the air resistance that opposes the forward movement of the airplane. When the airplane moves forward, it pushes air molecules out of the way, creating friction. Drag is the cause of slowing down an airplane and opposes the engines' thrust. Airplanes are designed to minimize drag as much as possible through a smooth and streamlined exterior structure and materials, maximizing the aerodynamicity. For the speed of an airplane to increase, the magnitude of thrust must be greater than the drag. In the case of level flight at a constant speed, forces in all directions must balance. In addition to these four major flight forces, a pilot can also control the plane through control surfaces that help steer and stabilize the aircraft.
The plane has three primary control surfaces - the elevator (on the tail) controls pitch (angle of attack, whether the nose points up or down), the rudder (also on the tail) controls yaw (left and right turning motion), and the ailerons (on the wings) control roll (tilting from side to side). The pilot controls these control surfaces to turn, climb, descend, and stabilize the plane in several directions.
As a plane takes off, the pilot adjusts engine power to maximum power to maximize thrust and, indirectly, lift. This causes the aircraft to accelerate down the runway and the wings to generate increasing amounts of lift. Once the lift exceeds the force of gravity pushing down on the plane, the aircraft can accelerate upward and take off. During cruise flight, the aircraft is at a constant speed and altitude. In this instance, that means that lift equals weight, and thrust equals drag. To descend, a pilot will roll back the throttle to reduce thrust. As thrust is reduced, drag and weight overpower thrust and lift, and the aircraft will slowly descend.
Citations:
Brain, Marshall. “How Airplanes Work.” Explain That Stuff, 18 Apr. 2024,
“Sheffield Aerospace.” “How Do Airplanes Work?” Sheffield School of Aeronautics, 2024,
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