How Crossover Jets are creating less noise

Being as environmentally friendly as possible is a goal for every aircraft manufacturer. Cutting down on specific fuel consumption and thus creating fewer emissions is one part of the equation—the other is to create less noise. This is particularly valuable when airlines aim to operate into airports in built-up areas.

Engines are of course the main source of aircraft noise. Across the range of crossover narrowbody aircraft, however, a significant amount of noise has been removed by the use of Pratt & Whitney’s PW1000G family, featuring the geared turbofan (GTF). The Bombardier C Series, Mitsubishi MRJ and Embraer E-Jets E2 families have all chosen models from the engine family.

Martin Gauss, CEO of Bombardier CS300 customer AirBaltic, tells about being at the first flight of the PW1500G-powered CS100. Engrossed in conversation, he heard aircraft noise above him and turned to see that it was the Global Express chase plane. Then he saw that the CS100 was almost level with his position at the side of the runway and on the verge of rotation. He had not heard its takeoff run until that point.

At Pratt & Whitney, Graham Webb, vice president of PW1000G programs, says the family of engines “is unique among powerplants in that the geared architecture allows the fan blades to spin at their optimal speed—1/3 the speed of the turbine. With the fan rotating slower, fan tip speeds are slower, resulting in significant noise reduction. The GTF engine’s technology and architecture result in a 75% smaller noise footprint [than current equivalents],” he emphasizes.

Much is made in the industry of delivering “integrated powerplants” rather than simply engines. Webb agrees with the concept, noting, “Engineers consider both the engine and the nacelle during the design phase, and are able to optimize trade-offs between the two to achieve the lowest noise while considering other metrics such as fuel burn and weight.”

Fernando Antonio Oliveira, program director of E-Jets E2 at Embraer, says “the concept of engine installation noise may be explained in different ways, but it can be roughly defined as all noise generated by the installed engine against the noise generated by the isolated or ‘bare’ engine.”

He moves on to discuss integrated powerplants: “Efficient engine design integration enables the increased application of new noise-suppressing technologies and maximum gains in noise reduction. One example is the use of acoustic liners in different parts of the engine, such as the nacelle air inlet, thrust reverser and internal areas,” Oliveira says. “A key design parameter in these new engines is the acoustic liner area, which may be drastically increased with an efficient integration design.”

He also identifies other potential noise mitigation from integrated powerplants. “[One example is the] reduction of gaps and steps between engine parts, mainly engine movable parts like the thrust reverser, which may generate noise such as a whine,” he says. “The engine air inlet offtake positioning and design may also create loud tones in the engine or aerodynamic interaction noise with other engine noise sources. Making the nacelle air inlet surface as smooth as possible helps to avoid aerodynamic and acoustic interaction with the fan blades, and also helps maximize the acoustic liner area.”

At Mitsubishi Aircraft Corp., Christian Soomarchun, director, propulsion and mechanical systems, highlights that the company’s aerodynamics technology was used collaboratively for the aircraft and engine design. “The GTF engine has been optimized for the MRJ and the MRJ optimized for the GTF engine,” he declares.

“We understand that designing and delivering an integrated powerplant allowed Pratt & Whitney more flexibility and options to achieve noise-reduction goals,” Soomarchun adds.

There have been some issues with the PW1100G-JM used on the Airbus A320neo family and the PW1500G on the C Series. Despite that, Webb says, Pratt expects the Embraer and MRJ engines “to demonstrate better reliability and durability than the initial GTF engines.”

For the other crossover jet, the Sukhoi Superjet 100, PowerJet’s SaM146 engine features two key technologies in its design architecture that led to significant noise reduction, according to the company’s head of communications, Charles Soret. “The first is the new-generation 3D aero fan blades, while the second one is the long duct mixed flow nozzle of the nacelle,” he notes.

On the subject of integrated powerplants, he confirms, “The entire SaM146 powerplant system has been designed to reduce aerodynamic interference between the aircraft and the engine itself. This minimizes the airflow vortex and thus the total noise.”

Although certified in the late 2000s, the SaM146 has undergone incremental changes to increase its efficiency and reduce noise since entry into service. “PowerJet has continuously enhanced the engine, through critical component improvements, such as acoustic panel, fuel nozzle and combustor,” Soret reports.

With a stretched SSJ100 being planned, the PowerJet executive says there is scope for considering a midlife upgrade of the SaM146. “We have regular discussions with Sukhoi Civil Aircraft Co. about how the engine could potentially evolve in response to market demand and their plans to modify the aircraft,” says Soret.