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‘SKY’S THE LIMIT’ The Principle of Flight: How the Forces of Lift, Drag, Thrust and Gravity Work Together to Keep an Aircraft Aloft

 ‘SKY’S THE LIMIT’

The Principle of Flight: How the Forces of Lift, Drag, Thrust and Gravity Work Together to Keep an Aircraft Aloft

By Arnav Nagpal

 

INTRODUCTION

Among the greatest achievements of modern science and engineering, aeroplanes have made traveling much easier, carrying millions of passengers to various destinations. But have you ever stopped to wonder, what keeps this giant metal tube airborne? The answer lies in invisible teamwork—a combination of forces acting together to support endless loads of luggage on the aircraft. This short article will take a deep dive—or ‘take off’—into how these natural powers help us fly. To understand this dynamic better, let us first look at some basic parts of an aeroplane.

Basic Parts of an Aeroplane

 

The first force to explore is one that can make apples fall from trees—gravity. It pulls each and every object towards itself and thus, not exactly a hoot and a half for massive aircrafts trying to take to the skies. No, for an aeroplane to fly, it needs the help of another force, one that can compete with gravity, namely, lift.
 They say an enemy’s enemy is a friend, which is exactly what lift is. It is the upward force that helps an aircraft rise in the air and remain there. Lift is generated mainly by the wings, also called airfoil. They are shaped with a gentle curve on top and a flatter surface underneath. The wings push air downward, and by Newton’s Third Law, the air pushes the wings upward, contributing to lift. As the aircraft moves forward, air flows faster over the curved upper surface and slower beneath. This difference in airspeed creates lower pressure above the wing and higher pressure below it, producing an upward force strong enough to counter gravity. The faster the air moves over the wings, the greater the lift, and when it becomes higher than the weight, you climb!

 

                                                    How Lift Works

Coming to a more commonly known force, weight, as you might have guessed, is a force that is always directed toward the centre of the earth, due to its gravity. Its amount depends on the mass of all the airplane parts, plus the amount of fuel, plus any payload on board. This immense weight is actually distributed throughout, but we can think of it as acting through a single point on the aeroplane called the centre of gravity.   In flight, the aeroplane rotates about the centre of gravity, but the direction of the weight force always remains toward the centre of the earth. The aeroplane's weight constantly changes as it consumes fuel. Thus, although weight does not directly support an aircraft’s flight, it ultimately defines the amount of lift the wings must generate to overcome gravity.

It appears we’ve reached our cruising altitude, because another force has come into play—drag! Drag is the aerodynamic force that resists forward motion. In layman’s terms, it is the force exerted by fluids on any object immersed in it. Drag comes in two main forms:
 1) Parasitic drag: Includes form drag, skin friction, and interference drag.
 2) Induced drag: A byproduct of generating lift.
 Taking inspiration from nature, scientists and engineers saw that birds’ streamlined body shape was perfect for overcoming drag. So, they used the same shape for designing aircrafts! Pilots and engineers constantly work to reduce drag using smooth surfaces and features like winglets. During landing, it’s a helpful force that slows the aircraft down. Spoilers and air brakes are designed to increase drag when needed, making descent and landing safer and more controlled.

 

 

                                                      Forms of Drag

For the final destination, let’s explore the principles of thrust. Thrust, also called as perpendicular force, is the force needed to overcome the drag to the passage of an aircraft. To maintain level flight at constant speed, constant thrust is required; to climb or descend the aircraft whilst maintaining constant speed, the thrust must be increased or decreased; to increase or reduce the speed of the aircraft whilst maintaining level flight, the thrust must be increased or decreased.
 The power required to generate thrust depends on a number of factors. In simple terms, the power is proportional to the thrust required times the speed of the aircraft.

 

 

 

 

 

                                             How Thrust Works

CONCLUSION

The next time you see an aeroplane fly by, remember that it is the dream team of 4 invisible forces that have made the fantasy of flying a reality. Inspiration from nature and many brilliant minds made this vision possible. And as the plane descends, a special thanks to the Wright Brothers!

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