Airplanes have become quieter over the years. They often feature more aerodynamic bodies, which allows air to flow over them more naturally and with less resistance. They also feature newer engines, such as high-bypass turbofans.
Old airplanes, however, often lack the noise-reducing technologies. As a result, they can produce up to 75% more noise than their modern counterparts. The good news is that hush kits can reduce noise in old airplanes, extending their usable life.
What Is a Hush Kit?
A hush kit is an upgrade modification that’s designed to reduce the noise of a jet engine. They are commonly installed on old airplanes, particularly those with turbojets or turbofans. Once installed, hush kits create a smooth air mixture that suppresses the otherwise loud and high-pitched noise of a jet engine.
There are different types of hush kits, but many of them contain some or all of the following components:
- Exhaust mixers
- Acoustic liners
- Aerodynamic nacelles
How Hush Kits Work
Hush kits work by changing the way in which air exits the exhaust. Whether it’s a turbofan or turbojet, all jet engines generate propulsion by expelling hot exhaust gases. They burn fuel and air inside a combustion chamber. Hot exhaust gases are then produced as a byproduct of this combustion process. As the exhaust gases are expelled out the rear, the jet engine produces forward propulsion.
The faster and more turbulent an engine’s exhaust gases, the louder it will be. Hush kits, though, offer a solution. Most are designed to slow and smooth the exhaust gases.
Some hush kits may also mix the exhaust gases with bypass air. In aviation, bypass air is excess air that goes around a turbofan’s core. It’s essentially what distinguishes turbofans from turbojets. Turbojets suck all of the air into their core, whereas turbofans only suck some of the air into their core. The excess, diverted air is known as bypass air. There are hush kits that leverage this bypass air to further reduce engine noise.
The Tradeoff
While hush kits can reduce engine noise, they come at the cost of increased weight. All hush kits add weight. Increased weight, of course, translates into a shorter range and poorer fuel efficiency. Aircraft operators may also experience higher maintenance costs and more frequent maintenance intervals as well.
Even with these drawbacks, hush kits are a popular upgrade for old airplanes. They allow aircraft operators to continue using old airplanes rather than replacing them.
