Not much has changed in commercial aircraft design and technology for the last 50 years. That’s about to 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, Calif., 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.
Taken together, this mission work is spread across three projects within NASA’s Aeronautics Research Mission Directorate. They include the Commercial Supersonic Technology project managed out of NASA Langley in Virginia, the Flight Demonstrations and Capabilities project managed out of Armstrong at Edwards, Calif., and the Low Boom Flight Demonstrator project, responsible for the X-59 aircraft itself, managed out of NASA Headquarters in Washington, D.C.
Elements of NASA’s Low-Boom Flight Demonstration mission are organized within two of the agency’s aeronautics programs — the Advanced Air Vehicles Program and the Integrated Aviation Systems Program — and overseen by a mission integration office whose members span both programs and all four of NASA’s aeronautical research field centers: Langley, Glenn, Ames, and Armstrong.
X-59 also relies on the expertise of international collaborators at JAXA as well as contractors here at home, including Lockheed Martin, which is constructing the aircraft at its Skunk Works Facility in Palmdale, Calif., and a team of subcontractors at GE Aviation of Cincinnati and TriModels Inc. of Huntington Beach, Calif.