NASA will soon test advancements made on a key tool for measuring the unique “sonic thumps” that its quiet supersonic X-59 research aircraft will make while flying. A shock-sensing probe is a cone-shaped air data probe developed with specific features to capture the unique shock waves the X-59 will produce.
Researchers at NASA’s Armstrong Flight Research Center in Edwards, California, developed two versions of the probe to collect precise pressure data during supersonic flight. One probe is optimized for near-field measurements, capturing shock waves that occur very close to where the X-59 will generate them. The second shock-sensing probe will measure the mid-field, collecting data at altitudes between 5,000 to 20,000 feet below the aircraft.
When an aircraft flies supersonic, it generates shock waves that travel through the surrounding air, producing loud sonic booms. The X-59 is designed to divert those shock waves, reducing the loud sonic booms to quieter sonic thumps. During test flights, an F-15B aircraft with a shock-sensing probe attached to its nose will fly with the X-59. The roughly 6-foot probe will continuously collect thousands of pressure samples per second, capturing air pressure changes as it flies through shock waves. Data from the sensors will be vital for validating computer models that predict the strength of the shock waves produced by the X-59, the centerpiece of NASA’s Quesst mission.
“A shock-sensing probe acts as the truth source, comparing the predicted data with the real-world measurements”, said Mike Frederick, NASA principal investigator for the probe.
For the near-field probe, the F-15B will fly close behind the X-59 research aircraft at its cruising altitude of approximately 55,000 feet, utilizing a “follow-the-leader” setup allowing researchers to analyze shock waves in real time. The mid-field probe, intended for separate missions, will collect more useful data as the shock waves travel closer to the ground.
The probes’ ability to capture small pressure changes is especially important for the X-59 research aircraft, as its shock waves are expected to be much weaker than those of most supersonic aircraft. By comparing the probes’ data to predictions from advanced computer models, researchers can better evaluate their accuracy.
“The probes have five pressure ports, one at the tip and four around the cone”, said Frederick. “These ports measure static pressure changes as the aircraft flies through shock waves, helping us understand the shock characteristics of a particular aircraft”. The ports combine their measurements to calculate the local pressure, speed, and direction of airflow.
Researchers will soon evaluate upgrades to the near-field shock-sensing probe through test flights, where the probe, mounted on one F-15B, will collect data by chasing a second F-15 during supersonic flight. The upgrades include having the probe’s pressure transducers – devices that measure the air pressure on the cone – just 5 inches from its ports. Previous designs placed those transducers nearly 12 feet away, delaying recording time and distorting measurements.
Temperature sensitivity on previous designs also presented a challenge, causing fluctuations in accuracy with changing conditions. To solve this, the team designed a heating system to maintain the pressure transducers at a consistent temperature during flight. “The probe will meet the resolution and accuracy requirements from the Quesst mission”, Frederick said. “This project shows how NASA can take existing technology and adapt it to solve new challenges.”
The X-59 is an experimental aircraft that will fly supersonic without the typical loud sonic boom, aiming to revolutionize commercial supersonic flight. It will be the first of its kind to fly with this feature, with the goal of collecting sound data for NASA’s QueSST mission, which could pave the way for commercial supersonic flights over land, not just over oceans, in the future.
Today, commercial supersonic flight is allowed only over oceans. This restriction, implemented in 1973, has hampered commercial supersonic ventures, limiting faster-than-sound travel to oceanic flights. British Airways and Air France, which operated the Concorde, were two airlines that offered such services from 1976 to 2003.
The X-59 is at the heart of NASA’s QueSST (Quiet SuperSonic Technology) mission, which focuses on providing data to help regulators reconsider rules prohibiting commercial supersonic flight over land. For 50 years, the United States and other nations have banned such flights due to the noise impact of loud sonic booms on communities below. The X-59 is expected to fly at 1.4 times the speed of sound, at an altitude of 55,000 feet (16,764 meters). Its design, shape, and technologies will allow it to reach these speeds while generating a quieter sound.
Images: NASA / Steve Freeman, Lockheed Martin