Commercial Supersonic Flight Research Articles

Mixed-Flow Turbofan Engine Model for the Conceptual Design of Sustainable Supersonic Airplanes

Current research efforts on commercial supersonic flight aim to overcome past challenges by designing a new generation of sustainable supersonic airplanes. Achieving this goal requires careful consideration of the propulsion system during the design process. This study proposes a mixed-flow turbofan engine model coupled with emission estimation routines to increase the reliability of the conceptual design of future supersonic aircraft. The model enables parametric analyses by analyzing variations in main engine design parameters (πc,πf, BPR) as function of the system and mission requirements, such as the Mach number, and suggesting applicability boundaries. The overall methodology was applied to a low-boom Mach 1.5 case study, allowing for both on-design and off-design analyses and generating a propulsive database to support preliminary mission simulations and chemical emission estimation. Finally, the accuracy and reliability of the engine model was validated against GSP 11 data for a generic mixed-flow turbofan engine. A modified version of the Fuel Flow Method, originally developed by Boeing, allowing for emissions estimation throughout the mission for a supersonic engine using biofuels. The application of the methodology led to the definition of an engine with a πc of 30 and BPR of 0.7 for the selected case study, which was successful in meeting the initial mission requirements.

Evaluation of feasibility of commercial supersonic flight based on aeroacoustics

The drive to attain ever higher speeds, to be able to travel ever faster fuels the research and development for a commercial supersonic aircraft. This has previously led to the Concorde which travelled at more than twice the speed of sound. Now, in addition to business considerations about economic viability, supersonic aircraft must be quieter and emit less emissions. Considering the 20 years that have elapsed since Concordes retirement, this study aims to reevaluate the current challenges and limitations to achieving commercial supersonic flight again, in the context of noise. Identifying sonic booms and jet exhaust noise as two main challenges, it reviews current shape optimization methods, plasma as a sonic boom mitigator, sonic boom circumvention, chevron nozzles, variable cycle engines, engine positioning, and their corresponding limitations. Some of the methods have been refined for use and application in final stage design and manufacture of certain supersonic aircraft which indicates a certain feasibility.

Effects of Atmospheric Profiles on Sonic Boom Perceived Level from Supersonic Vehicles

U.S. national research priorities include reducing the disruption caused by sonic booms, which hindered the economic viability of supersonic aircraft in decades past. However, shock waves are unavoidable during supersonic flight; and exposure of people, animals, and structures to these shock waves on the ground cannot be eliminated entirely. It is herein shown that changing atmospheric conditions, gusts, and heights above ground can result in any supersonic aircraft that is acceptably quiet at specific atmospheric conditions becoming uncomfortably loud in other flight conditions. These performance variations are noticeable for periods ranging from 12 h to one year across the continental United States of America. Therefore, strategies to actively mitigate sonic booms may become necessary as researchers work toward resumption of overland commercial supersonic flight.

Sustainability: key to enable next generation supersonic passenger flight

The 2020 global Covid-19 pandemic has shocked the aviation system to its core, showcasing what the loss of this economic engine can do to the world’s economies and societies. This crisis also presents an opportunity to create new capabilities and outlooks. Commercial supersonic flight is one such capability. The availability of advanced computational designs and propulsion systems, new materials, route optimization and alternative fuels means that supersonic aviation can be part of that future in a sustainable manner.Boom’s ultimate goal is to mainstream supersonic air travel and make it accessible to millions of passengers per year. Long-term projections of business-class airline demand suggest a total market of 1,000 to 2,000 commercial supersonic aircraft operating on more than 500 primarily transoceanic routes that will benefit from speeds twice as fast as today’s aircraft.Given the increased focus on mitigating aviation’s environmental impact, bringing a new aircraft to market in the 2020s requires a careful focus on sustainability. To ensure public acceptance supersonic aircraft manufacturers and operators will have to proactively engage with stakeholders to address their concerns and focus on integrating sustainability solutions across their business strategies.Boom is the first commercial aviation OEM to build sustainability into its aircraft programmes from day one, ensuring that sustainability considerations form an integral part of every aspect of the production process. A sustainability commitment to cover every step in the aircraft development cycle, from design and test through in-service operations and end-of-life recycling is key to successfully reintroduce commercial supersonic flight in the years ahead.

Bayesian statistical dose-response models

In the coming years, NASA will collect nationally representative data to support efforts to develop international standards for permissible noise from commercial supersonic flight over land. The data will elucidate the relationship between sonic boom noise exposure and community response. This presentation introduces several Bayesian statistical models and a method to calculate a summary dose-response curve. Additionally, the statistical models illuminate the trade-off between sample size and precision of estimated quantities such as percent highly annoyed. This trade-off will inform sample size decisions for future community surveys. All models are fit to data from a recent NASA community response test, the Quiet Supersonic Flights 2018 (QSF18) test.

Effects of model fidelity on indoor sonic boom exposure estimates

Commercial supersonic flight is prohibited over land, but this may change in the near future with the introduction of supersonic aircraft that produce a substantially quieter sonic boom. A transient modal interaction model is used to simulate the acoustic and vibration environment inside a large ensemble of residential homes to estimate the range in levels to which residents may be exposed during overflight of low-boom supersonic aircraft. However, the choice of fidelity used in the finite element models of the house structure (e.g., walls, floors, roofs, etc.) may have an impact on these exposure estimates. This presentation documents a recent study in which the fidelity of the structural finite element models was varied. Model fidelity was either an orthotropic panel approximation, in which the stiffening effects of studs were smeared over the entire panel, or a model that explicitly modeled the sheathing and studs. For sonic boom noise, it was found that the orthotropic panel approximation performs well for partitions that have through-the-thickness geometric symmetry, for example walls with two sheathing surfaces. However, the orthotropic approximation does not perform as well for panels with only one sheathing surface, which is typical of floors, ceilings, and roofs.

A study of reflected sonic booms using airborne measurements

In support of ongoing efforts to bring commercial supersonic flight to the public, the Sonic Booms in Atmospheric Turbulence (SonicBAT) flight test was conducted at NASA Armstrong Flight Research Center. During this test, airborne sonic boom measurements were made using an instrumented TG-14 motor glider, called the Airborne Acoustic Measurement Platform (AAMP). During the flight program, the AAMP was consistently able to measure the sonic boom wave that was reflected off of the ground, in addition to the incident wave, resulting in the creation of a completely unique data set of airborne sonic boom reflection measurements. This paper focuses on using this unique data set to investigate the ability of sonic boom modelling software to calculate sonic boom reflections. Because the algorithms used to model sonic boom reflections are also used to model the secondary carpet and over the top booms, the use of actual flight data is vital to improving the understanding of the effects of sonic booms outside of the...

Comparison between multilevel and traditional logistic regression analysis of laboratory indoor annoyance caused by shaped sonic booms

In the 1970s commercial supersonic flight was forbidden over communities because conventional N-wave sonic booms caused excessive annoyance. Through recent advances in aircraft design techniques, conventional sonic booms are being modified into quieter, shaped sonic booms. As noise regulators consider allowing shaped booms over communities, NASA is providing data and expertise. Recently, a laboratory study quantified the additional annoyance caused by directly felt structural vibrations (J. Rathsam and J. Klos, “Vibration penalty estimates for indoor annoyance caused by sonic boom,” J. Acoust. Soc. Am. 139 (4), 2007 (2016)). To confirm experimental results and complement the traditional logistic regression analysis, a multilevel logistic regression model was fit to individual-level data. The multilevel analysis allows us to simultaneously model individual- and group-level factors. As a result, it is straightforward to test for relationships between annoyance and individual-level factors such as noise sensitivity.

Vibration penalty estimates for indoor annoyance caused by sonic boom

Commercial supersonic flight is currently forbidden over land because sonic booms have historically caused unacceptable annoyance levels in overflown communities. NASA is providing data and expertise to noise regulators as they consider relaxing the ban for future quiet supersonic aircraft. One key objective is a predictive model for indoor annoyance based on factors such as noise and indoor vibration levels. The current study quantified the increment in indoor sonic boom annoyance when sonic booms can be felt directly through structural vibrations in addition to being heard. A shaker mounted below each chair in the sonic boom simulator emulated vibrations transmitting through the structure to that chair. The vibration amplitudes were determined from numeric models of a large range of residential structures excited by the same sonic boom waveforms used in the experiment. The analysis yielded vibration penalties, which are the increments in sound level needed to increase annoyance as much as the vibration does. For sonic booms at acoustic levels from 75 to 84 dB Perceived Level, vibration signals with lower amplitudes (+1 sigma) yielded penalties from 0 to 5 dB, and vibration signals with higher amplitudes (+3 sigma) yielded penalties from 6 to 10 dB.

Sonic boom noise exposure inside homes

Commercial supersonic overland flight is presently banned both nationally and internationally due to the sonic boom noise that is produced in overflown communities. However, within the next decade, NASA and industry may develop and demonstrate advanced supersonic aircraft that significantly mitigate the noise perceived at ground level. To allow commercial operation of such vehicles, bans on commercial supersonic flight must be replaced with a noise-based certification standard. In the development of this standard, variability in the dose-response model needs to be identified. Some of this variability is due to differing sound transmission characteristics of homes both within the same community and among different communities. A tool to predict the outdoor-to-indoor low-frequency noise transmission into homes has been developed at Virginia Polytechnic Institute and State University, which was used in the present study to assess the indoor exposure in two communities representative of the northern and southern United States climate zones. Sensitivity of the indoor noise level to house geometry and material properties will be discussed. Future plans to model the noise exposure variation among communities within the United States will also be discussed.

Predicting transmission of shaped sonic booms into a residential house structure

Human perception of sonic booms is a major impediment to commercial supersonic flight. Shaping, which reduces the audible shock waves of a boom, can make outdoor perception of booms acceptable. Perception of sonic booms experienced indoors is of concern, and it is not yet established whether shaped booms offer benefit to indoor listeners. A better understanding of the transmission of shaped booms into building structures is needed. In the authors' earlier work the vibration response of house elements subjected to different sonic boom wave shapes was evaluated using a single degree of freedom model. This paper expands that approach with a modal analysis model. The acceleration of building elements and the resulting sound pressure inside a room are computed in the time and frequency domains. Analytical results are compared with experimental data measured by NASA during sonic boom tests conducted at Edwards Air Force Base in 2007. The effects of wave signature parameters on transmission are studied to evaluate the advantages of various kinds of minimized boom shapes.

Sonic boom: From bang to puff.

For almost 40 years commercial supersonic flight over land has been prohibited because of the negative impact of sonic booms. During that time, technology advances have raised the possibility of a muted sonic boom—a sonic “puff”—that could be acceptable over populated areas. This paper reviews the physics of sonic boom generation and propagation, and why booms from conventional aircraft are usually N‐waves with unacceptably large shock waves. The low‐boom shaping technology that can minimize shocks, thus reducing sonic boom loudness to acceptable levels, is presented. The success of the DARPA/NASA Shaped Sonic Boom Demonstrator in validating shaping theory is discussed. Concepts for attaining practical aircraft configurations, versus ideal optimal shapes, are described.

Sonic boom research in NASA’s supersonic fundamental aeronautics project.

The Supersonics Project of NASA’s Fundamental Aeronautics Program is a broad based effort designed to address the technical challenges associated with flight in the supersonic speed regime. One of the key environmental challenges that must be overcome for successful commercial supersonic flight is sonic boom. The NASA Supersonics Project has chosen this challenge as a focus for its research activity over the next several years. In cooperation with the FAA and the ICAO Committee on Aviation Environmental Protection (CAEP) NASA has initiated the development of a roadmap for research into the community response to sonic booms with noise levels significantly less than those of the Concorde and current supersonic aircraft. The purpose of the roadmap is to define the key research that should be accomplished in order to provide a firm technical basis for future noise-based standards for sonic boom acceptability. This presentation will discuss the elements of this roadmap and outline some of the recent research contributions made by the NASA Supersonics Project.

Realism assessment of sonic boom simulators

Developments in small supersonic aircraft design are predicted to result in low-intensity sonic booms. Booms generated by current aircraft are similar to those that led to the ban on commercial supersonic fli ght over the US, so are unsuitable for parametric studies of psychoac oustic response to low-intensity booms. Therefore, simulators have be en used to study the impact of predicted low-intensity sonic booms. H owever, simulators have been criticized because, when simulating conv entional-level booms, the sounds were observed to be unrealistic by p eople experienced in listening to sonic booms. Thus, two studies were conducted to measure the perceived realism of three sonic boom simul ators. Experienced listeners rated the realism of conventional sonic boom signatures when played in these simulators. The effects on percei ved realism of factors such as duration of post-boom noise, exclusion of very low frequency components, inclusion of ground reflections, a nd type of simulator were examined. Duration of post-boom noise was f ound to have a strong effect on perceived realism, while type of simu lator had a weak effect. It was determined that post-boom noise had t o be at least 1.5 seconds long for the sound to be rated very realist ic. Loudness level did not affect realism for the range of sounds pla yed in the tests (80-93 dB ASEL).

PARTNER Project 8: Sonic boom mitigation

Current U.S. and international laws prohibit commercial supersonic flight over land due to the impact of conventional sonic boom noise. Aircraft manufacturers, however, now have modern computational fluid dynamics and optimization tools, unavailable when those laws were enacted, that will allow them to design and build aircraft with boom signatures that are substantially smoothed compared with traditional N‐waves. One purpose of the FAA/NASA/Transport Canada PARTNER Center of Excellence Project 8 is to determine exactly which waveforms would be heard by the public if low‐boom supersonic aircraft are put into service. Another purpose is to ascertain the acceptability of those waveforms. The project involves the following universities, government, and industry partners: Penn State, Purdue, Stanford, the National Aeronautics and Space Administration, the Federal Aviation Administration, Boeing, Cessna, Gulfstream, Lockheed‐Martin, and Wyle Laboratories. Some of the initial project work includes studies on the propagation of sonic booms through atmospheric turbulence, on the mutual reproducibility of three sonic boom simulators, and on the realism of those simulators as determined by expert listeners. The results of all the studies are intended to provide the FAA with new data to reassess current regulations. [Work supported by NASA, the FAA, and the PARTNER industrial partners.]