How High Can Planes Fly?

Since the Wright brothers invented the first airplane, the plane has truly taken off in terms of its usefulness. But how high are planes capable of flying?

Table of Contents

Introduction

Planes are an incredible feat of engineering. Since their invention by the Wright brothers in 1903, planes have changed how humans cross the lands and oceans. In a world where everything is time-constrained, planes are a quick way to cover enormous distances for work, leisure, adventures, and many other reasons.

The Wright glider in 1902
The Wright glider in 1902, Credit: Wikipedia/Wright Brothers

According to estimates by the Federal Aviation Administration, nearly 500,000 people are in the air at any given time. Most commercial planes cruise at an altitude of 35,000 ft above the ground.

A commercial plane flying in the sky
A commercial plane flying in the sky, Credit: Wikimedia/Adrian Pingstone

But why do planes fly at an altitude of 35,000 ft? How do they stay in the sky when the plane itself is so heavy and is additionally carrying hundreds of people on board? We will try to dissect these questions and to understand the physics behind the hows and the whys. Hopefully, by the time you finish reading this, you will gain a deeper appreciation of this incredible piece of human engineering.

How do planes fly?

We have been admiring the way birds fly since the dawn of humankind. The wings of a bird have played a crucial aspect in the design of planes. Even early Greek mythology tells of how, Daedalus, the master architect, and his son Icarus built wings for flying using feathers and wax.

The wings of a bird served as an inspiration for the design of the plane
The wings of a bird served as an inspiration for the design of the plane, Credit: Wikimedia/Gshashidhar125

For many decades, there has been debate among scientists and engineers about the exact physics behind the flight of a plane. Without getting into the specifics, I want to present a simple explanation of lift. Lift is the upward force that acts on a plane and is responsible for how high up a plane flies. When a plane’s engine is turned on, air rapidly flows over the wings, pushing the air toward the ground. This creates an upward force, termed lift, that balances and overcomes the plane’s weight to help the plane stay in the sky.

 

The details of how the lift is generated can be either explained by Newton’s laws or Bernoulli’s principle. According to Bernoulli’s principle, when a fluid moves at a greater speed, it produces less pressure, and vice-versa. When air flows over the curved upper surface of the wing, its speed is greater than when it moves over the lower flatter portion This creates a pressure difference. Since air always moves from a region of high pressure to low pressure, an upward force is created on the lower side of the wing, this is what is known as lift.

Aerodynamic forces acting on a plane
Aerodynamic forces acting on a plane, Credit: Wikimedia/Yann Kemper

The wings of the plane are responsible for keeping the plane in the air. The engines, however, serve a different purpose. The engines are responsible for moving the plane forward. The thrust, which is the forward force exerted by the plane, overcomes the drag force caused by the wind and moves the plane forward. Lift, thrust, drag, and weight are the four aerodynamic forces acting on the flight of a plane.

The troposphere

The earth’s atmosphere has different layers, from the troposphere to the exosphere. The troposphere is the layer of the atmosphere closest to us. This layer extends from 6 km to about 20 km above the surface of the earth. The peaks of the highest mountain ranges, hot air balloons, and birds are all present in the troposphere. The troposphere is also the region in which most commercial planes fly.

 

The troposphere is the region in which almost all weather phenomena occur. Additionally, it contains 75% of the mass of the entire atmosphere of the earth. Above it, we have the ozone layer, which protects us from the sun’s harmful ultraviolet light.

Atmospheric layers
Layers of atmosphere. Credit:smorescience.com

 Atmospheric layers. You can download the poster here

Why do planes fly that high?

We have established that planes fly in the troposphere. But why do they fly in the troposphere and not the stratosphere? The thickness of the air reduces with height, meaning the air high in the troposphere is very thin, contributing to less turbulence. Lowered turbulence means that the plane has to use less fuel to fight the elements, and therefore saves money. But then, one might ask, why don’t commercial planes fly in the stratosphere, and avoid weather altogether? The issue is the lift. Since the air in the stratosphere is too thin, it can’t generate enough lift to keep a plane in the sky.

 

Another advantage of flying in the troposphere is jet streams. Commercial planes often encounter high-altitude jet streams. Pilots can avoid them, or use them to get a speed boost and make the journey quicker. This only happens for planes traveling from west to east.

Jet stream above the Earth traveling from west to east
Jet stream above the Earth traveling from west to east, Credit: Wikimedia/Fred the Oyster

It is a fine-tuned ecosystem that keeps a plane in the air!

Military aircraft and supersonic travel

The F-22 Raptor
The F-22 Raptor, Credit: Wikimedia/Master Sgt. Andy Dunaway

Supersonic flights are vehicles that can travel faster than the speed of sound, which is greater than Mach 1. The first commercial supersonic aircraft was the Concorde, which was started in the mid-1970s. It is the only civilian aircraft that was regularly serviced to date. By 2003, all supersonic travel had ceased due to various issues with the engineering of the planes. However, over the last few years, many companies have been trying to bring back supersonic aircraft.

British Airways Concorde in 1986
British Airways Concorde in 1986, Credit: Wikimedia/Eduard Marmet

As technology and engineering progress, the prospect of flying at greater heights and at speeds greater than Mach 1.5 seems closer to reality than ever before.

Glossary

Lift: The mechanical force generated when a solid object (like a plane) interacts with a fluid around it (air), generating an upward force.

 

Thrust: A reaction force generated by a system when mass is expelled or accelerated in one direction, causing a reaction (or thrust) in the opposite direction.

 

Drag: An opposing force when an object is moving through a fluid. This force doesn’t exist if there is no movement.

 

Exosphere: The outermost layer of the earth’s atmosphere.

 

Turbulence: The motion in a fluid when the change in pressure and flow velocity is chaotic or irregular.

 

Jet streams: Narrow bands of very strong winds in the higher levels of the earth’s atmosphere.

 

Supersonic: Supersonic speed is one that exceeds the speed of sound. The speed of sound in dry air is 343 m/s.

Flesch Kincaid Grade Level: 7.4

 

Flesch Kinkaid Reading Ease: 69.3

Copyright @smorescience. All rights reserved. Do not copy, cite, publish, or distribute this content without permission.


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