How do airplanes fly?

When I was a kid, I wanted to become a pilot. I was so amazed whenever I saw an airplane cruising up in the sky. A lot of questions keep bugging my mind. If it carries passenger, then it may be as huge as a bus, a train or even larger, then how can it fly? Out of curiosity, a lot of children would always ask their parents “How do airplanes fly?” Most of the time, the parents would give a wrong answer, “Airplanes fly because they have engines which makes them fly.” This has been the misconception of a lot of people, I also thought that way before. Yes, it may be a factor, but it is not the reason why airplanes fly.

Now that I am studying about airplanes, I can somehow answer my queries about them. If a child would ask me how airplanes fly, I’ll let him look at a flying bird and ask him how does a bird flies, the very simple answer would be, “Because they have wings.” Same way with an airplane, it flies because of its wings. The engine, whether a propeller or a jet, doesn’t make the airplane fly, it produces thrust but never produces lift.

Take for example a kite. To start flying a kite, the flyer has two options: 1. Run quickly while pulling the kite as it flies up opposing the wind and 2. Let someone throw the kite up in the air as the flyer pulls the string. The pulling of the string accelerates the movement of the kite which generates thrust. This thrust, then, produces lift as it opposes the direction of the wind which pushes the kite upwards. The flyer may then loosen the string to release tension and to increase its altitude, fairly enough to control the stability of the kite. Without enough wind or air, the kite will sink or stall. Like a kite, an airplane also deals with different forces acting on it in order to fly and relies greatly on the relative wind.

Technically Speaking…

In order to understand what makes an airplane fly, he must know the basic concept of the Theory of Flight, particularly about Aerodynamics, which came from the Greek words aerios which means air and dynamis which means force. Thus, aerodynamics is a study of forces and motions of objects through air. There are four aerodynamic forces acting on an airplane during its flight, they are: (A)lift, (B)thrust, (C)weight and (D)drag. These forces were acting perpendicularly along the Center of Gravity (C.G.) of an aircraft. The pilot deals with these forces during flight. See the figure below.



For a level flight, it is assumed that lift is equal to the weight, while the thrust is equal to the drag. In order to climb, lift must be greater than the weight. Hence, lift is directly proportional with the altitude; as lift increases the altitude increases, thus creating a climb. On the other hand, when thrust is greater than the drag, the airplane speeds up; while a decrease in thrust would make the airplane slow down.

Understanding the effects of these forces on the stability and control of an airplane let us now investigate on their nature and how are they produced. To start with; is the weight; the simplest yet the very important factor in flying an aircraft, all of the other forces depend greatly on the weight. It is the gravitational pull of the aircraft towards the center of the earth. In order to fly, a flyer must overcome or overpower the weight of an aircraft. Next is the thrust or the forward force of an airplane. It is produced by the engine or – most of the time – called the powerplant of an airplane. It may be a jet or a propeller. The engine, literally, sucks air from the environment. This air is very massive, such that, it has the power to move the airplane forward. This determines the propulsion system of an airplane. The more power produced by the engine, the more it produces thrust. Next would be the drag or the force that pulls the airplane backwards. We can correlate it with friction. This force can be determined by the structure of an airplane and its design. Any blockage or disturbance of air flowing along the surface of an airplane will produce drag, reacting inversely on the thrust. And lastly is the most vital and very important force is the lift. Without lift, the airplane will not fly. Lift must be greater than the weight of the airplane so that it will ascend. It can be produced by the wings and depends greatly on the wing’s airfoil characteristics and design. The pilot can increase lift by retracting the wing flaps down and increasing the throttle setting, or the thrust, at the same time. This is very important during take-off to lift the airplane off the ground.

This is the basic concept on how airplanes fly. In a very simple, yet factual way, an airplane fly because of the forces acting on it, most especially the lift, which was entailed by the upward force of the wind acting on the airplane’s wings. This action pushes the airplane upwards, which causes it to fly.