Airlander will be significantly quieter than other aeroplanes with a similar payload and range, both in the cabin and on the ground during take-off and landing. But what actually makes Airlander quieter?

Noise inside the cabin

We often talk about the improved passenger experience that Airlander will offer, from the floor-to-ceiling windows to the extra legroom at economy prices. The low noise level also contributes to a much more enjoyable experience. There are a number of reasons why the Airlander cabin is significantly quieter than the cabin of a traditional passenger jet or turboprop.

The constant hum of the mechanical and aerodynamic noises of the turbine engines on aeroplanes are significant contributors to cabin noise. Airlander uses either piston engines or electric motors, which will produce almost no engine noise. For Airlander, the engines are mounted on the hull far away from the cabin so that very little engine noise reaches the cabin. Another benefit is that the two rear engines may be turned off during cruise flight, once the aircraft has climbed, reducing noise further.

The engines on Airlander are virtually inaudible for those travelling in the passenger cabin. The helium lifting gas compartment overhead is a very poor transmitter of sound and so, with the engines located up on the equator of the envelope and a long way away, the is no route for the sound to pass to the cabin. And with two engines shut down for most of the flight, passengers can relax in a cabin without the roar or buzz or vibration that may be encountered on other flights.

David Burns Airlander’s Chief Test Pilot

Cabin pressurisation systems produce a continual whir of noise, which we have become accustomed to on an aeroplane. Airlander flies below 10,000 feet and the cabin is therefore not pressurised – that ever-present noise is simply non-existent for Airlander passengers.

For a point of comparison, we can look at the Zeppelin NT. A recent review of a Zeppelin NT said “it does all this with exceptionally little vibration and noise. With an engine speed of around 2000rpm, it’s around 60dB, which is quieter than most cars at 30mph”. The Zeppelin is a useful comparator as it has similarly sized piston engines to Airlander, which are also placed away from the cabin and are attached to the vibration-absorbing hull material like on Airlander. The cabin distance from the engines reduces the noise in the cabin greatly and the soft hull absorbs the vibration.

When I flew on the prototype with the Chief Test Pilot I was surprised at how low the noise levels were in the cabin. I had my noise cancelling headphones with me, which I need in little aeroplanes, but I switched off the noise cancelling as it was totally unnecessary to have it.

Andrew Barber Head of the Office of Airworthiness who joined the Chief Test Pilot as the Flight Test Engineer

Environmental noise

Our mission is to ensure Airlander will be efficient and environmentally friendly in every way. Noise pollution is one of the factors we take into consideration. While a maximum noise level is not typically a legal requirement for aircraft like Airlander, we are considering noise from the outset of Airlander’s design. Countries like Germany and Switzerland already include take-off and landing noise in their fee structure for the use of airports and we expect that other countries and regulators will follow.

Less power equals less noise

A large proportion of Airlander’s lift is generated by the helium-filled hull, so Airlander requires much less power to fly than an equivalent aeroplane and even less compared with an equivalent helicopter. This means Airlander requires much less powerful engines for the same useful load, burning less fuel and generating less noise energy as a result.

Engine and motor technology

Electric motors are of course very quiet, but what about the engines that are used in the hybrid-electric configuration, and in the all-combustion configuration that we expect to be used for some time in surveillance roles?

Alongside the lower power requirement, we use highly efficient, state-of-the-art turbocharged piston engines. A turbocharger extracts waste energy from the exhaust gases, recycling it to make the engine more efficient. This also reduces the exhaust noise by slowing down the exhaust gases.

Airlander’s engines are similar to medium size truck engines, compared with the massive turbine engines of an aeroplane. Turbine engines rotate at 10,000 rpm or more, while Airlander engines rotate at 4,000 rpm or less. The lower rotation speed also reduces noise levels.

When Airlander is in a hybrid-electric or all-electric configuration we can expect the noise output to be even quieter, just like the reduced noise from an electric car.

Flying slower

Aerodynamic noise is created by airflow around the surfaces of the aircraft. This is especially loud when flying at low altitude and high speeds. Airlander flies more slowly than a conventional aircraft and therefore generates significantly less aerodynamic noise.

Approach to land

On approach Airlander is very quiet, firstly due to a landing speed that is about one quarter that of a large aeroplane. Secondly, on a conventional aeroplane there are features on the wing that are used to create more lift and more drag to help the aircraft fly at a slower speed. That extra drag creates noise, just like when you open your car window while driving. Airlander does not rely on this technique to slow down and land, eliminating those noises.

Keeping a light footprint

Airlander will be quieter than the conventional aeroplanes we are used to in many ways; the low noise and low vibration will make the journey more enjoyable for those onboard. The design of Airlander also means the noise is quieter for those on the ground - aircraft noise is usually a key environmental concern for communities impacted by aviation operations. In the UK, over one million people are exposed to aircraft noise above levels recommended for the protection of health. Airlander will not introduce significant new noise pollution, which will be especially pertinent around built-up areas and transport hubs.

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