Why Planes Are So Loud When They Fly Overhead

When airplane noise invades your peaceful day, it can be a source of frustration and annoyance. But have you ever wondered why planes are so loud when they fly overhead? In this article, we will explore the factors that contribute to the loud noise of planes, particularly focusing on turbofan airliners and the different noise sources they generate.

Understanding the Sources of Plane Noise

When discussing plane noise, many factors come into play, from the engines to airframe turbulence. Here, we will delve into each of these factors to provide you with a comprehensive understanding of why planes are so loud during takeoff, approach, and throughout their flight.

Engine Noise Versus Airframe Noise

The noise from airplanes primarily comes from the engines. However, there are also factors such as airframe boundary layer turbulence that contribute to the overall noise level. When a plane is flying close to an airport, airframe boundary layer turbulence causes significant noise. Even gliders without engines generate this noise, though not as prominently as turbofan airliners. Owls, however, are exceptional in their ability to fly without causing noise.

Takeoff and Initial Climb: The Roaring Sound

When a plane takes off and starts climbing, you often hear a roar. While the term "roaring" is often used, it might not be the most accurate term. The noise during takeoff is primarily due to the engines working at full capacity. This noise has significantly reduced in recent decades due to stricter regulations and advancements in technology. Decibel units follow a logarithmic scale, meaning that even a small reduction can make a significant difference.

Propeller Tips and Super Sonic Speeds

Smaller planes driven by propellers often generate a lot of noise due to the high-speed rotation of the propeller tips. When air near the propeller tips reaches near supersonic speeds, it creates pressure changes that result in noise. Additionally, shock waves can occur at these supersonic speeds, which not only create more noise but also cause a lot of drag, limiting the propulsion efficiency of the propellers.

Reducing Noise

It is possible to reduce the noise from airplanes to some extent. For example, in Radio Controlled (RC) models, sanding the propeller tips and rebalancing them can significantly lower the noise level. Similarly, certain piston aircraft engines are also designed with mufflers, which can help reduce noise. However, the primary contributor to noise is the engines.

The Outer Structure of the Plane

The outer structure of the airplane can also contribute to noise. When the engines are in operation, they generate a significant amount of noise that is amplified by the design of the aircraft. The hot air coming out of jet engines and the air being bypassed around the core result in pressure changes, leading to sound. The interaction between these elements creates the characteristic noise that you hear.

Common Noisy Factors

Many other vehicles and machinery can also be noisy, such as cars, buses, trucks, ships, helicopters, and even factories. Sometimes, even the sound of a rocket can be overwhelming. The common denominator among all these noisy sources is their engines. The engines are the primary source of noise in these machines.

Passengers and Cabin Environment

It's not just the engines and airframe that contribute to the noise; sometimes, human factors come into play. Screaming passengers or children can add to the overall noise in the cabin, especially during takeoff and landing. Additionally, crying during the first few flight experiences can be quite common among both adults and children, adding to the noise level.

In conclusion, the noise from airplanes is a combination of engine noise, airframe noise, and even passenger behavior. While technology and regulation have significantly reduced noise levels in recent decades, it remains a factor that affects our daily lives when planes fly overhead. Understanding the sources of this noise can help us appreciate the engineering and design behind modern aircraft better.