Helicopter Noise

As an owner of a landing site, it’s important to understand the risk of creating unwanted helicopter noise for your guests, your animals and your neighbours.

We provide several resources for helipad owners and would ask that they look at the Site Owner section of the Helipaddy Blog.

Helipaddy takes noise abatement very seriously. Any unwanted noise is bad for the industry and a small number of incidents can affect their reputation disproportionately .

We believe that by creating a system for pilots to know how to approach landings is a good way to reduce the risk of unwanted noise.

Similarly, we have made it easy for site owners to understand the importance of approach and departure routes through our 360 Survey system, still free to use at the time of writing in 2023.

Helicopter Noise Signature

Helicopters generate noise differently from fixed-wing aircraft such as small planes and large jets. The primary sources of helicopter noise are the main rotor and tail rotor, the engine, and the interaction of the rotor’s blades with the air. The blade-vortex interaction, which occurs when the rotating blades of the helicopter cut through the air, producing a distinct “chop-chop” sound, is particularly characteristic of helicopters.

How bad is the noise?

The founders of Helipaddy operate a helicopter and a landing site at their home. They have horses and neighbours! As such they have some anecdotal evidence of noise and noise abatement strategies.

Firstly, helicopter noise is relatively brief as compared to a slow-moving paraglider or a commercial jet. Even though the noise intensity of a jet is lower (as the distance from the source of the sound doubles, the intensity of the sound is reduced to a quarter of its original level), it lasts a long time due to the large bubble.

On the other hand, a slow-moving paraglider has a small bubble but their noise cab be irritating due to how long it lasts.

Helicopters have the manoeuvrability to minimise both these conditions, being fast moving and low level.

The primary source of sound emissions from helicopters whilst nearby is the rotors, bit the engine. The causes vary and can include air displacement, forces acting on the air that flows around the blade, and aerodynamic shocks and turbulent boundary layers on the blade surface. Engines and the main gearbox can also generate sound, but this is mainly noticeable only near the helipad and is less audible from a distance.

When starting up, shutting down or hovering, it makes a big difference if you are facing the exhaust at the back of the helicopter. If you want to minimise this ground noise, its important that pilots orientate themselves accordingly.

The noise bubble

Noise is transmitted as a moving bubble around the aircraft.

This is a result of the inverse square law, which states that the intensity of a sound wave decreases with the square of the distance from the source. In simple terms, this means that as the distance from the source of the sound doubles, the intensity of the sound is reduced to a quarter of its original level.

So, while an aircraft flying at a higher altitude may indeed create a larger “noise bubble” on the ground (i.e., the noise from the aircraft will be perceptible over a larger area), the sound will also be less intense (quieter) at any given point within that area, compared to the sound intensity that would be experienced if the aircraft were flying at a lower altitude.

The Role of Approach and Departure Paths

Controlled approach and departure paths for helicopters can significantly reduce noise pollution in residential areas. By avoiding overflying these zones, and making use of geographical features such as valleys and bodies of water, helicopters can minimize their noise footprint on populated areas. Additionally, using steeper ascent and descent angles during takeoff and landing can keep helicopters further from the ground, reducing the impact of their noise.

Moreover, noise abatement procedures, like flying at the highest altitude permissible, can also reduce the noise experienced by communities. Helicopters, unlike jets or small planes, have a great deal of flexibility in their flight paths due to their ability to hover, ascend and descend vertically, and change direction rapidly. This flexibility can be leveraged to further limit noise pollution.

If you are interested in how a pilot approaches private sites, please see Landing a helicopter off-airfield.