NASA’s X-59 Nears Supersonic Speed With a High-Stakes Noise Test Ahead
“The envelope expansion phase of any experimental aircraft is critical, not just for pushing the aircraft higher and faster, but for understanding how the aircraft operates in flight,” said NASA, noting the X-59 has approached the critical threshold of decades of supersonic flights. But what about crossing the threshold without delivering the same window-rattling shock wave effect that contributed to marginalizing overland supersonic flight in recent years?
As NASA conducted the most recent series of high-speed flights above the Mojave Desert, the slender, needle-shaped X-59 demonstrator aircraft approached Mach 0.98, just shy of the speed of sound. These tests involved the aircraft executing roller coaster-like maneuvers, performing bank-to-bank turns, undergoing flutter tests, and extending the landing gear for the purpose of assessing how the aircraft flies when engineers expand its flight envelope. Given that the X-59 project hinges upon creating a controlled acoustic profile for the aircraft, these exercises are not about aerobatics but rather a methodical way of learning about stability, stress, and aerodynamics required to achieve that objective.
All of this is made possible by the aircraft’s unique aerodynamic design. The X-59 has a length of 99.7 feet and a wing span of 29.5 feet. The lengthened forebody helps avoid stacking shock waves produced during supersonic flights into a sharp pressure spike found in earlier designs. NASA’s Quesst project aims to demonstrate the possibility of shaping an aircraft to produce a much less pronounced acoustic phenomenon, referred to by NASA as a sonic “thump” rather than a boom, and then collect this information to support future certification efforts. Targeted cruise speed remains at Mach 1.42 at 55,000 feet, but it comes after overcoming a series of technical hurdles unrelated to speed.
A large portion of the work leading up to these flights had already been done through thousands of simulations based on computational fluid dynamics that allowed engineers to estimate the performance characteristics of the aircraft and the resulting pressure signatures propagated onto the ground below. The NASA supercomputer provided models of the boom profile, aerodynamic optimization, and pilots training material for flying the aircraft to hit particular noise objectives. In other words, the X-59 is as much a computational project as an experimental aircraft. It’s all relevant due to the upcoming phase in the testing process.
NASA has said the ultimate objective of the X-59 project lies in measuring community reaction to overflights over U.S. communities as residents experience the X-59’s quiet sonic thump and report their perception of this event. This information is expected to inform future regulatory standards for supersonic travel over land. Of course, the X-59 aircraft itself will never become a commercial airliner, but it is supposed to provide data to convince regulatory bodies that a new approach to managing supersonic traffic is feasible and safe.
Thus, the X-59 project involves a number of scientific disciplines including aerodynamics, acoustics, and even regulation. The recent flights above the Mojave desert showing the aircraft approaching the regime it was designed for may be less spectacular, but they are extremely important since they prove that speed is no longer the primary challenge for NASA engineers.
