Not much has changed in commercial aircraft design and technology for the last 50 years. That's about to … well … change thanks to efforts to design future commercial aircraft capable of hushing sonic booms to a mere thump as they fly faster than the speed of sound.
Supersonic travel is as cool as it sounds. Imagine flying aboard an aircraft cruising faster than the speed of sound, cutting your coast-to-coast travel time in half. Currently such a thing only exists in the dreams of aircraft designers. And while no passenger will ride aboard NASA’s X-59 Quiet SuperSonic Technology, or QueSST, the experimental aircraft is bringing the agency ever closer to making the quiet commercial supersonic travel over land a reality.
NASA's Ames Research Center in California's Silicon Valley has decades of experience researching supersonic flight, including numerous efforts under the Commercial Supersonic Technology project, or CST – a lot of which has gone into the unique design of the X-59. These efforts cover several areas related to supersonic research, including the use of cutting-edge visualization technology to study shockwaves, and use of unique wind tunnels, supercomputing facilities, and systems engineering expertise. These are but a few of the many areas of research into realizing the goal of CST and of the X-59 QueSST, which includes the eventual demonstration of quiet supersonic flight over land.
Computational Fluid Dynamics
As Lockheed Martin Skunk Works in Palmdale, California, finalized the X-59 airplane’s design, they ran their ideas using an Ames-developed high-resolution, 3D simulation software on multiple supercomputers at Ames – the Pleiades, Electra, and Endeavour. Recent improvements in the software have enabled engineers to get simulation data about the flight characteristics and noise levels even faster – sometimes five times as fast.
With no X-59 flight data – yet – computer simulation is the next best thing to build confidence in the predictions for its supersonic performance. Teams at Ames and NASA's Langley Research Center in Hampton, Virginia, worked together to ensure that multiple software codes would make similar predictions about how loud the X-59 will be in different environments. For example, they know the boom's loudness changes based on the cloud cover and humidity of the areas below a flight path, and can give the pilot information in the cockpit that can help guide the aircraft to areas where the boom may be quieter. Computational fluid dynamics simulations also create visualizations of the X-59 aircraft concept and help researchers determine which features of the aircraft generate shockwaves that contribute to the sonic thump sound below the aircraft.
NASA is working closely with Lockheed Martin to create a large database of computational fluid dynamics simulations to verify the aircraft’s supersonic performance. The database includes simulations for all possible combinations of settings that a pilot uses to control the aircraft and the flight conditions that may be encountered. This database is crucial for supplying data for a flight-planning tool that is being used to assist and teach pilots how to fly the X-59, before it even flies. From there, researchers can determine the best flight conditions to reduce noise when they begin piloted test flights over select U.S. cities. These flights also will provide opportunities to collect, verify, and validate data about community responses. NASA will share the data with U.S. and international regulators which will use it when considering new sound-based rules for supersonic flight over land. New rules could enable new commercial cargo and passenger markets in faster-than-sound air travel.
Wind Tunnel Testing
Some researchers think of computational fluid dynamics as a virtual wind tunnel test. Luckily, Ames has run thousands of hours of supersonic tests using actual wind tunnels since the 1950s. The 9- by 7-foot Supersonic Wind Tunnel facility is part of the Unitary Plan Wind Tunnel complex at Ames where generations of commercial and military aircraft and NASA space vehicles, including the space shuttle, have been designed and tested.
One way to make sure the X-59 will work as intended is to “fly" smaller versions of the real thing in a wind tunnel. While supersonic air flows over precisely crafted small models, engineers can take measurements of the pressure waves and be sure the plane behaves as expected. Some models measured as little as five inches long, while others stretched to more than six feet in length.
But even in the 21st century, with all our technical know-how, measuring supersonic airflow over an airplane model in a wind tunnel is an uncertain process. Even running the same test with the same model can produce slightly different results on different days because the airflows in the tunnels are not perfect. Put the model in another wind tunnel and you’ll get a slightly different version of the data.
This is why Ames continues to contribute its expertise to wind tunnel operations in support of the X-59. Ames contracted a model-building company, Tri Models, Inc. of Huntington Beach, California, to design and fabricate a small 19"-long model of the X-59 for sonic boom wind tunnel testing. The first test of this model took place in 2021, in NASA's Glenn Research Center's 8- by 6-Foot Supersonic Wind Tunnel in Cleveland. The second test will take place in 2022 in the supersonic wind tunnels at the Japan Aerospace Exploration Agency, or JAXA, under a recently-announced collaboration, which will allow researchers to compare results from tests of the same small-scale model.
Systems engineers are responsible for looking at all of the parts of a complex system and then figuring out how these parts can be interconnected. In short, they are looking at the big picture. Systems engineers are responsible for the design, setting and tracking the requirements, implementation and evaluation, technical management, operations, and end-life of a system. Without them, a project like X-59 won't leave the ground, much less the drawing page.
At Ames, systems engineers are focused on ensuring that the different systems such as the life support subsystem – that provides the pilot with oxygen – and the crew escape system – that would eject the pilot seat in case of an emergency – as well as systems for controlling the distribution of power and recording data are "talking" to each other and working as intended. Additionally, mass, airworthiness, and qualification of flight components are managed and tracked by systems engineers at Ames.
Test Component Manufacturing
Engineers at Ames manufactured specialized mounts to test some of the X-59 Life Support Systems flight components one at a time in specialized test chambers at the Environmental Laboratory at NASA’s Armstrong Flight Research Center in Edwards, California. The mounts enabled engineers to test how well Life Support System components performed under the vibration, pressures, and temperatures that the aircraft could experience. These parts are not on the final aircraft, but enabled engineers to qualify components for flight.
- NASA plans to deliver results of the community overflights to the International Civil Aviation Organization and Federal Aviation Administration in 2027. With that information in hand, regulators will be able to decide if a change should be made in rules that prohibit supersonic flight over land – a decision that would be expected in 2028
- NASA plans to fly the X-59 QueSST over select communities to gather information about how the public perceives the quiet noise the X-59 is designed to produce (early 2024)
- NASA will conduct acoustic validation flights (2023)
- Major ground testing will conclude in early 2022, leading to a target date for first flight (late 2022)
- NASA and JAXA agreed to take independent wind-tunnel measurements of the same small-scale model of the X-59, and compare results (2022)
- NASA and Lockheed Martin completed the X-59 assembly (2021)
- Wind tunnel testing at Glenn (September 2021)
- Construction continued in earnest as the project passed its Critical Design Review in October 2019 and another key program management review (December 2019)
- The initial machined parts were delivered to Lockheed Martin Skunk Works (November 2018)
- Quiet Supersonic Flight series research campaign took place over Galveston, Texas (November 2018)
- NASA completed the preliminary design review of its QueSST aircraft design. QueSST is the initial design stage of NASA’s planned X-59 experimental airplane (June 2017)
- NASA selected a team led by Lockheed Martin Aeronautics Company of Palmdale, California, to complete a preliminary design for QueSST. The work was conducted under a task order against the Basic and Applied Aerospace Research and Technology (BAART) contract at Langley. The Lockheed Martin team includes subcontractors GE Aviation of Cincinnati and Tri Models Inc. of Huntington Beach, California. (February 2016)
- NASA began a series of supersonic wind tunnel tests of Lockheed Martin’s and Boeing’s Phase I supersonic aircraft concepts using Ames' 9- by 7-Foot Supersonic Wind Tunnel as part of the project’s Experimental Systems Validations for N+2 Supersonic Commercial Transport Aircraft effort (2010 through 2013)