A Commercial Aviation Consultancy

NOT WITH GAME CHANGING AIRCRAFT AND ENGINE TECHNOLOGY

The introduction of the Bombardier CSeries in 2014 will bring the first application of the next generation of engines for narrow-body aircraft, the Pratt & Whitney PurePower 1000G geared turbofan.  The combination of a new engine and an advanced high technology airframe will generate a very substantial change in the environmental impact of airplanes, the largest we’ve seen since the first generation noisy cigar tube engines were replaced by high bypass engines in the 1980s. 

While saving fuel is the major reason airlines are ordering new narrow-body aircraft in record numbers, and why the Airbus A320neo and Boeing 737Max, powered by PW1000G and CFM LEAP engines are basically sold out until 2020.  Both of these engines, the PW1000G, which is flying, and the CFM LEAP, current under development, will offer substantial improvements over today’s engines.

But environmental concerns are also a key factor in many operations, particularly for airlines operating from older airports within highly populated areas, such as Bromma airport in downtown Stockholm, or Billy Bishop airport in downtown Toronto.  Malmo Airlines, which operates at Bromma, and Porter Airlines, which operates at Bishop, have both ordered the CSeries, in part for is unique environmental characteristics.

Reductions in noise are critical in operating in urban areas, and environmental friendliness goes beyond simple reductions in fuel burn and hydrocarbon emissions.  The good news is that phenomenal progress has been made with respect to noise.

How Significant will Noise Reduction Be?

The noise reduction from new technology engines will be very significant, and quite noticeable at and near an airport.  The Pratt & Whitney PW1524G geared turbofan engine used on the CS100 is 15-20 decibels quieter than the engines on competing 110 seat class aircraft in production today.  While 15 decibels doesn’t sound like much, the decibel scale is logarithmic, meaning every 10 decibel difference represents a doubling in noise.  So a 20 decibel reduction means the sound is cut in half, and then that sound is halved again to 1/4 of the original volume.

If you have a television set with numeric noise levels, try this – put the noise up to 20 on the scale, then reduce it to 10, then reduce it to 5.  That’s the equivalent of how much the sound level at the airports will be reduced at the airport with the CSeries and GTF over today’s models.  On our set, that goes from fairly loud to barely audible.  A sound clip linked here illustrates the difference between today’s engines and the new technology PW GTF engine – the difference is quite apparent as the microphones shift back and forth between old and new.

The noise footprint for an airport will be four times smaller for these new technology aircraft than for existing in-production aircraft, dramatically reducing the number of people impacted by 70db noise levels.  This will positively impact airports that are currently environmentally restricted, either by noise-measured curfews or noise levels measured at various points, and enable additional operations without waking up the neighborhood.   Ambient noise levels vary considerably in the city and the countryside, and the following table illustrates the levels of some common noises, using the dbA scale.

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Airports would love to be able to keep noise levels outside the airport below 70dBA, which is about the noise level for a twin engine plane flying at 1,000 feet overhead, but lower than that of a passing diesel truck and about equivalent to a city bus on your street.  Because the noisiest elements of flights is full thrust at take-off or thrust reverse upon landing, the key to noise abatement is to keep the high noise levels on airport property, and reduce noise for abutting neighbors.  For airports like Dallas-Ft. Worth and Kansas City, which were built far from a city, this is quite easy.  But for urban airports, where infrastructure is all around the airport, like Bromma or Bishop, this is more difficult.

Toronto’s downtown Billy Bishop Airport is an example of how new technology can positively impact an airport.  Porter Airlines has conditionally ordered the CSeries and plans to introduce jet service at the convenient downtown airport located on an island in Lake Ontario at the edge of the downtown business district.  Currently, the airport prohibits jet service, because of noise and runway issues.  But because the new technology CSeries will be as quiet as the existing Q400 turboprops currently in use, it could change the potential route structure for the airport, enabling more convenient business trips to not only Montreal, Ottawa and cities in the Eastern US, but to more distant destinations, including Winnipeg, Calgary, Edmonton, Vancouver and Los Angeles.

Levels of noise measured at 5 measuring points in the city find that airport noise rarely rises above 70dBA at those downtown locations with current turboprop (and piston) aircraft operations at the field.  But there is, of course, concern that opening the airport to jets will significantly increase ambient noise levels nearby.  This is where the new technology engines come in.

The following diagram illustrates the 70dBA noise contour for both current jets and the CSeries at a typical airport.   The illustration demonstrates just how significant the impact will be for neighbors in those expensive condominiums with the lakefront views for Toronto’s Billy Bishop airport, as the 70dBA level would be well contained to areas within the airport itself with the new technology airplane.

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Why is the noise footprint 4 times smaller for the new technology engines?  In the case of the Pratt & Whitney GTF, it is because of the high bypass ratio design and its innovative design.  In the early days of jet engines, which were very noisy, all of the air was directed through the engine core in which combustion takes place.  Quieter, high bypass ratio, engines evolved when it was discovered that a portion of the air could be directed around the engine core, making the engine both quieter and more fuel efficient, which changed the shape from the old “cigar tubes” to today’s fatter-looking engines.  The PW1000G engine on the CSeries takes this evolution one step further, through the use of a gear, allowing the front engine fan to turn at a lower speed than the engine core.  This further reduces noise, and enables this engine to achieve the highest bypass ratio in the industry, and the proportional reduction in noise.

Aircraft noise restrictions adjust with the size and gross weight of an aircraft, with larger aircraft allowed to be noisier than smaller aircraft, as they need more thrust to lift an aircraft from the runway.  The lighter the aircraft, the lower the noise levels allowed. New technology aircraft including the CSeries, Boeing 787, and Airbus A350, which are lighter than their counterparts,  must meet more stringent noise regulations than their predecessors.

Because these new technology aircraft are lighter, they can climb faster in a shorter distance, and further shrink the area impacted on the ground when compared with today’s aircraft.

Porter Airlines has brought back the phrase “WhisperJet” that was once used by Eastern Airlines to tout the low 3interior noise levels of its rear-engined Boeing 727s when compared with the Boeing 720s and Douglas DC-8s that had under wing engines. But Porter is now applying that term to the exterior noise levels of the Bombardier CSeries as it lobbies for rules changes at Toronto Bishop.

The Bottom Line:

Periodically, technology breakthroughs can be disruptive and so important that they change the nature of how things work.  That is about to happen to some urban airports, first with the PW1000G engines and the Bombardier CSeries, and later with models from Boeing, Airbus, and Embraer with GTF and LEAP engines.  These new airplane-engine combination will be quiet enough to enable operations from close in airports and new routes without waking up the neighborhood.  Given the increasing congestion at many airports, route dispersion using some of the closer in, older airports, is now becoming possible.   For both advertising slogans and older airports, recycling is good for the environment.

© 2013, Ernest S. Arvai. All rights reserved.

2 Responses to Noisy Neighbors?

  • 10 dB more is heart by a human as a doubling of noise. From an energetic point of view twice the sound energy is just 3 dB more. So 15 dB less are about 30 times less sound energy. This is a huge difference.

    The exchange of turboprop aircraft with the new jets will be received even better due to the different spectra. The low frequency noise of turboprop aircraft are harder to shield than high frequencies. High frequencies are quite easy to shield even by windows.

  • IS there a graphic comparing the 70 dBA contour for the C-Series with a Dash 8-Q400?
    Such a graphic could make or break the introduction of the C-Series at Billy Bishop.
    What many do not seem to realise is that some of the most effective resistance to jets at Billy Bishop are people who want no more flights out of there. Adding the expense and impact of the lengthening of the runway, Porter has an uphill climb for this.
    More power to them if they manage to pull it off.

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