Proposed Supersonic Aircrat and

Related Noise Issues

A recent resurgence of interest in supersonic air travel has drawn atenion to ongoing research and development, spurred a number of new entrants racing to develop supersonic aircrat and inevitably has sparked discussions of the drawbacks, speciically noise concerns. Since was reired in 2003, there have been no civilian supersonic aircrat in service, and current regulaions in many countries prohibit light in excess of Mach 1 (approximately 767 mph) over land. However, the possibility of shortening long-haul business and commercial lights has fueled compeiion among aircrat manufacturers to produce viable opions. Meanwhile, regulatory agencies and airport operators are considering the implicaions on environmental noise. Proposed Technologies & Interested Manufacturers

Both established irms and new entrants in the aircrat and engine manufacturing arena have taken a strong interest in pioneering the next generaion of air travel. These are described below.

Aerion Corporaion1 is currently developing a supersonic business tri-jet that they expect to put into service in 2025. The AS2® will have the capability to operate at speeds up to Mach 1.5 and has been designed to cruise overland at Mach 0.95 to 1.2, the later thanks to Boomless Cruise (SM), a capability the company says will be achievable under ideal weather and temperature condiions (for an aircrat lying at M1.2 or less at 35,000t or above, the shockwaves do not reach the ground; instead, as they enter warmer air closer to the ground and the speed of sound increases, they are refracted, or bent, upwards away from the 1 Image courtesy of Corporaion ground). Aerion intends to pursue approval of this capability post-type ceriicaion, but is chiely focusing on overwater lights.

Boeing2 is acively invesigaing structural coniguraions intended to reduce noise and increase overall aircrat eiciency at supersonic speeds. Numerous studies have been conducted into the feasibility of concepts such as and engine mount reconiguraion, variable-geometry chevrons and integraion of nonconvenional verical stabilizers. has also indicated that they are exploring a hypersonic aircrat; which would ly at speeds roughly above Mach 5 or above. Image courtesy of Boeing2

Boom Supersonic3 has secured pre-orders for muliple 55-seat supersonic business-class aircrat from Virgin Group and Japan Airlines. Boom states that these delta-wing aircrat will carry passengers at speeds up to Mach 2.2 while producing a “30 imes quieter” than that of Concorde. The company is currently construcing an experimental supersonic , the XB-1, which will serve as a test-bed for much of the technology planned for integraion into the airliner. The company has stated that it intends for its airliner produce noise in the terminal Image courtesy of Boom Supersonic3 area similar to today’s long-haul subsonic airliners. GE Aviaion4 recently revealed its CFM56-based Ainity Class of civilian supersonic jet engines, to be uilized in the Aerion AS2®, per a Memorandum of Understanding the company signed with Aerion and Lockheed Marin. Given substanial R&D and integraion costs on top of the small market segment the engine will serve in its infancy, GE plans to uilize and adapt the Ainity in future subsonic applicaions as well.

Image courtesy of GE Aviaion4

Gulfstream5 has been issued muliple patents protecing eiciency and noise-reducion measures for supersonic aircrat. The company, in tandem with NASA, developed the “” nose extension, which generates its own shockwaves smaller than those of a non-equipped aircrat at subsonic speeds. This results in comparaively less-intrusive noise events on the ground. Image courtesy of Gulfstream5

Lockheed Marin6 has partnered with NASA to build a supersonic test aircrat dubbed the “X-59 QueSST” to be delivered in late 2021. The X-plane is being designed with heavy emphasis on supersonic light over the US mainland, which is currently prohibited. Lockheed is opimisic that the aircrat will not exceed 75 PLdB (perceived noise level) in supersonic light, and plans to use the X-59 to “collect community response data on the acceptability of the quiet sonic boom generated by [the X-59’s] design...” (see next page for more about NASA’s tesing.) Image courtesy of Lockheed Marin6

Rolls-Royce7 has the unique disincion of being the only manufacturer to have experience with civilian supersonic propulsion. Its Olympus engine line powered the Concorde. The company responded to Aerion’s Request for Proposals to develop the AS2’s® engines (the contract that was awarded to GE), and is in discussions with other manufacturers.

Spike Aerospace8 is developing the S-512 Supersonic Jet, which will have the capability to carry up to 18 passengers over 6,200 nm at speeds up to Mach 1.6. Spike is collaboraing with US and internaional regulatory agencies and states that it intends the S-512 to comply with Stage 5 regulaions at airports. The company also states that the aircrat’s en-route sonic signature will resemble that of a sot clap to observers on the ground. Spike has not had a public proile and litle is known about Image courtesy of Spike Aerospace8 them beyond their website. NASA9 is heavily involved in research and tesing eforts to determine feasible ways to reduce the perceived loudness and gauge community response to the noise made from supersonic light. Since 1947, the sound associated with a supersonic light has been called a ‘sonic boom’. In the past 10-15 years, NASA and other industry stakeholders have been working on aircrat designs to minimize sonic boom to be more like a sonic ‘thump’ or to eliminate it enirely. The aforemenioned X-59 will uilize this technology/design. To gauge community response to this new-sounding noise, NASA’s Quiet Supersonic Flights 2018 program was conducted in November 2018 and uilized a NASA FA-18 Hornet to generate a series of sonic “thumps” over part of Galveston, Texas. Through a specially-designed dive maneuver, the Hornet pilot can simulate the ‘thump’ acousic signature anicipated by the up-and-coming X-59 Quiet Supersonic Technology aircrat. Image courtesy of NASA9 The media, industry experts from other organizaions, and the community were invited to paricipate in the response efort, and were encouraged to share comments, quesions and concerns with NASA and Lockheed Marin, who are developing the X-59 together. Noise Standards, Tesing and Manufacturer Concerns ICAO adopted its newest noise standard for subsonic aircrat in 2013. Annex 16, Volume I, Chapter 14 (simply referred to as Chapter 1410 internaionally and (noise) Stage 5 in the US) outlines the noise limits that aircrat must meet while operaing on or in the vicinity of airports. The presently-adopted standard applies to aircrat having a Maximum Takeof Weight (MTOW) of at least 55,000 kg and requires a cumulaive 7 EPNdB (Efecive Perceived Noise Level, in decibels) reducion from the previous Chapter 4 standard. The standard applies to subsonic aircrat built ater December 31, 2017. Supersonic airlines/business jets will have both near-airport noise issues as well as supersonic issues, as the requirements of supersonic propulsion tend to create aircrat that can be noisier than subsonic aircrat at landing and takeof.

While it should be possible for supersonic aircrat manufacturers to meet ICAO’s exising Chapter 4 regulaions (efecive 2006-2017) with current and near-term technology, it may be diicult for these new aircrat to achieve compliance with Chapter 14 standards due to technological, inancial, and regulatory limitaions. In order to meet ceriicaion standards for Chapter 14, manufacturers would likely need to redesign numerous pieces of technology which would require signiicant addiional funding, research, and ime. These concerns will remain among many prevening large-capacity supersonic airliners from achieving near-term feasibility, unless ICAO and the FAA adopt a supersonic-speciic noise standard based on a diferent correlaing parameter, such as speed, akin to the current MTOW parameter, similar to Chapter 14 for subsonic aircrat. To date, Spike9 and Aerion11 have commited to meeing Chapter 14 Standards, although not been clear as to what this means.

Further, 14 CFR part 36, Noise Standards: Aircrat Type and Airworthiness Ceriicaion12 does not apply to supersonic aircrat other than Concorde. 14 CFR Part 91.81713 prohibits light in excess of Mach 1 over land, but its Appendix B allows supersonic operaion under certain condiions granted on an individual basis. The FAA has been conducing two rulemaking aciviies: Domesic Noise Ceriicaion of Supersonic Aircrat (RIN: 2120-AL29) and Special Flight Authorizaions for Supersonic Aircrat (RIN: 2120-AL30). The FAA and ICAO have made progress14 on:

• Idenifying ceriicaion measurement locaions for assessing sonic boom noise on the ground; • Selecing a ceriicaion metric (EPNL) for LTO (landing and takeof) noise; • Selecing an appropriate noise metric for use in a standard that assesses sonic boom noise and shows favorable correlaion between outdoor measurement and indoor human response; and • Evaluaing the beneits of using sonic boom predicions in supersonic noise ceriicaion in addiion to physical measurements.

Although DOD and NASA have models to support the acousic analysis and evaluaion of sonic boom/thump, the FAA’s Aviaion Environmental Design Tool (AEDT) will not include such capabiliies unil Version 4, which is in the forecast for release in 2022 or later. Because supersonic speeds will not be achieved during the LTO cycle, airports are more likely to deal with issues related to unique noise characterisics of new aircrat, but not sonic booms. As airports have experienced with the introducion of other technologies, “new noise” generally precipitates strong community reacion. Therefore, it will be important for airports to understand the efects of introducing these new aircrat into its exising noise environment, and criical to develop outreach strategies to address community concerns.

Endnotes

1 “Aerion AS2®.” htps://www.aerionsupersonic.com/. 2 Moore, Mathew, Kelly Boren, Edward Marques, and Jusin Lan. Aircrat Coniguraion. US Patent 20120091270, iled April 19, 2012, and issued January 2014, 14. 3 “Supersonic Flight and the Environment.” Boom Supersonic. htps://boomsupersonic.com/contact#faq-secion. 4 “GE’s Ainity: The First Civil Supersonic Engine in 55 Years.” GE Aviaion. htps://www.geaviaion.com/press-release/ business-general-aviaion/ge’s-ainity-irst-civil-supersonic-engine-55-years-–. 5 Trautveter, Chad. “Gulfstream Coninues Supersonic Research.” Aviaion Internaional News. December 06, 2016. htps://www.ainonline.com/aviaion-news/business-aviaion/2016-12-06/gulfstream-coninues-supersonic- business-jet-research. 6 “X-59 QueSST.” Lockheed Marin. htps://www.lockheedmarin.com/en-us/products/quesst.html. 7 “The Spike S-512 Quiet Supersonic Jet.” Spike . March 12, 2018. htp://www.spikeaerospace.com/s-512- supersonic-jet/. 8 “Supersonic Flight and the Environment.” Spike Aerospace. August 30, 2018. htp://www.spikeaerospace.com/ supersonic-light-and-the-environment/. 9 Gipson, Lillian. “Quiet Supersonic Flights 2018.” NASA. htps://www.nasa.gov/QSF18. 10 Airplane Noise Standards, htps://www.federalregister.gov/documents/2017/10/04/2017-21092/stage-5-airplane- noise-standards § ICAO Annex 16, Volume I, Chapter 14/Stage 5. 11 Lampert, Allison. “Aerion’s to Meet U.S. Noise Standards.” Reuters. October 15, 2018. htps:// www.reuters.com/aricle/aerospace-businessjets-supersonic/aerions-supersonic-business-jet-to-meet-us-noise-standards- idUSL2N1WU05Y. 12 Noise Standards: Aircrat Type and Airworthiness Ceriicaion, htps://www.ecfr.gov/cgi-bin/ retrieveECFR?gp=&SID=848a71308ceac7a9cc4798db08de4dac&n=14y1.0.1.3.19&r=PART&ty=HTML § 14 C.F.R. Part 36. 13 Civil Aircrat Sonic Boom, htps://www.ecfr.gov/cgi-bin/text-idx?node=14:2.0.1.3.10#se14.2.91_1817 § 14 C.F.R. § 91.817 14 “Supersonic Aircrat Noise Standards Development.” ICAO Environment. htps://www.icao.int/environmental- protecion/Pages/Supersonic-Aircrat-Noise-Standards-Development.aspx.

For more informaion, please contact: Mary Ellen Eagan [email protected] 781.229.0707