NASA’s Supersonic Research: Validating Tools for the X-59’s Quiet Supersonic Flight
In a groundbreaking series of flights over the Mojave Desert, NASA conducted a pivotal test with two of its F-15 research jets. These flights, carried out in May, were designed to validate sophisticated tools intended to measure and record the shock waves expected from NASA’s innovative X-59 supersonic experimental aircraft. This effort is a significant step in NASA’s Quesst mission, which aims to pave the way for quiet commercial supersonic flight over land.
The F-15 fighter jets, equipped with state-of-the-art recording tools, flew faster than the speed of sound to emulate the conditions under which the X-59 will operate. The X-59, the focal point of NASA’s Quesst mission, is designed to collect data that could eventually lead to the development of quieter supersonic travel for commercial use. This technological advance could revolutionize air travel by allowing supersonic flights overland, which is currently restricted due to the loud sonic booms produced by conventional supersonic aircraft.
The successful test flights were part of the Schlieren, Airborne Measurements, and Range Operations for Quesst (SCHAMROQ) project, managed by NASA’s Armstrong Flight Research Center in Edwards, California. Here, a team of experts developed tools to measure and visualize the distinctive shock waves of the X-59 as it cruises at Mach 1.4, at altitudes exceeding 50,000 feet. Unlike typical supersonic jets that create deafening sonic booms, the X-59 is engineered to produce only a soft "thump," thanks to its advanced design and technologies.
Cheng Moua, the engineering project manager for SCHAMROQ, likened the validation flight campaign to a “graduation exercise,” where all components are tested in their final form to ensure they function effectively. NASA’s tool development journey began quite some time ago, marked by the acquisition of one of the two F-15s—specifically, an F-15D from the U.S. Air Force, initially delivered without research instrumentation.
Moua explained, “It arrived as a former combat aircraft, lacking any research-capable instrumentation system—no telemetry, no HD video, no data recording. Now, it is transformed into a fully instrumented research platform.”
The validation process involved three critical tools:
- Near-Field Shock-Sensing Probe: This device is essential for measuring shock waves, capturing data on the subtle pressure changes that occur when an aircraft moves faster than sound.
- Airborne Location Integrating Geospatial Navigation System (ALIGNS): This guidance system helps pilots position their aircraft accurately during test flights, crucial for collecting precise data.
- Airborne Schlieren Photography System: This innovative system captures images that make the density changes in air caused by the X-59 visible. Schlieren photography is a technique that visualizes variations in air density, allowing researchers to see the shock waves and airflow around the aircraft.
Prior to the F-15D’s arrival, Armstrong utilized a second F-15, an F-15B, typically employed for equipment testing, pilot training, and supporting various other flight projects. Together, these two aircraft conducted “dual ship flights,” a series of simultaneous flight tests. Both aircraft flew in formation, carrying near-field shock-sensing probes and gathering data from each other to test these probes and validate the tools under real-world conditions. This data is invaluable for confirming how shock waves form and change during flight.
For the Quesst mission, the F-15D will spearhead data collection efforts using the onboard probe, while the F-15B will act as a backup. When trailing the X-59, the probe will measure minor pressure fluctuations caused by the shock waves, validating predictions made during the aircraft’s initial design phase.
The schlieren photography systems on board the F-15s will provide Quesst researchers with vital data. While computer simulations and wind tunnel tests are beneficial, schlieren imagery offers real-world insights, particularly in challenging areas like the engine and air inlet.
To ensure the effectiveness of the schlieren system, precise positioning of the two aircraft during test flights is crucial. Pilots rely on NASA’s ALIGNS software, which acts as a guiding tool. Troy Robillos, a NASA researcher who led the development of ALIGNS, emphasized its importance: “ALIGNS guides pilots, showing them where to position the aircraft to probe a shock wave at a specific point or to align correctly for schlieren photography.”
The schlieren system employs a handheld high-speed camera with a telescopic lens, capable of capturing hundreds of frames per second. It visualizes changes in air density, using the sun as a backdrop. Edward Haering, a NASA aerospace engineer leading schlieren research, described the process: “The photographer holds the camera to their chest, aiming out the side of the cockpit canopy at the sun, while the pilot maneuvers through a 100-foot-wide target zone. If the sun leaves the frame, we lose that data, so we fly multiple passes to ensure we capture the shot.”
Aligning two fast-moving aircraft against the sun’s backdrop is a formidable challenge. The photographer must capture the aircraft flying across the sun’s center, where even slight shifts can affect the shot, diminishing the data’s quality. Robillos compared it to “trying to take a photo through a straw while flying supersonic.”
However, with ALIGNS, the process becomes significantly more accurate. The software, operating on ruggedized tablets, uses GPS data from both aircraft to calculate when they are in the correct position for probing and capturing schlieren imagery, providing pilots with real-time instructions for precise positioning.
The validation of the X-59 team’s schlieren imaging and other systems demonstrates that NASA’s core tools for measuring shock waves are ready to study the X-59 in flight. This will check the aircraft’s unique acoustics, confirming its quieter sonic "thump."
This technological breakthrough is a major step towards the future of aviation, where supersonic travel over land could become a reality without the disruptive noise of traditional sonic booms. As we look forward to these advancements, it is evident that NASA’s dedication to innovation and precision engineering continues to push the boundaries of what is possible in the realm of aerial exploration and travel. For more detailed information, you can visit NASA’s official website.
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