After more than 10 years of hard work, NASA has reached another milestone. We’re accustomed to NASA reaching milestones, but this one’s a little different. This one’s all about a type of photography that captures images of the flow of fluids.
It’s called Schlieren Photography, and schlieren is German for “streaks.” It was first developed in 1864 by a German physicist named August Toepler to study supersonic motion. Now, NASA is using it to see what happens when jet aircraft break the sound barrier, in an effort to eliminate the sonic boom that accompanies it. And the images they’re getting are pretty cool.
“We never dreamt that it would be this clear, this beautiful.”
– Physical Scientist J.T. Heineck of NASA’s Ames Research.
There’s more to this than eye-candy though. It’s all part of an effort to create quieter supersonic aircraft. Right now, there are strict rules about flying supersonic aircraft over land because the noise is so loud. But if the noise problem can be solved, it’ll allow faster air travel.
These schlieren images were captured by another aircraft as it watched the two T-38 jets from the Edwards Air Force Base. The aircraft with the camera is a B-200, and it’s all part of NASA’s AirBOS (Air-to-air Background Oriented Schlieren) program. AirBOS itself is part of NASA’s Commercial Supersonic Technology Project.
These newest images come from an upgraded schlieren imaging system that can capture higher-quality images of shockwaves than ever before. A sonic boom is created when shockwaves from different parts of the aircraft merge together and travel through the atmosphere. Detailed images like these will advance the study of the sonic boom phenomenon.
“We never dreamt that it would be this clear, this beautiful. I am ecstatic about how these images turned out,” said J.T. Heineck, Physical Scientist at NASA’s Ames Research Center. “With this upgraded system, we have, by an order of magnitude, improved both the speed and quality of our imagery from previous research.”
The data from these schlieren images will be used to design a test aircraft. The aircraft, called the X-59 Quiet Supersonic Technology X-Plane, will be a 94 ft long, 29.5 ft wide single-jet aircraft. The X-59 is part of what NASA calls the Low-Boom Flight Demonstration (LBFD.) The target completion date is sometime in 2021. (Better hurry, NASA.)
The pair of T-38s are flying in a tight formation at supersonic speeds. The lead aircraft is about 30 ft ahead of the trailing aircraft, and they’re offset vertically by about 10 feet. That’s no big deal for highly-trained USAF pilots, but there was an added wrinkle. The B-200 was at about 30,000 feet, with the T-38s 2,000 feet below, closer than the previous imaging system allowed. And the T-38s had to reach supersonic speeds at the exact moment that they flew underneath the B-200 and its schlieren imaging system.
One of the greatest challenges of the flight series was timing. In order to acquire this image, originally monochromatic and shown here as a colorized composite image, NASA flew a B-200, outfitted with an updated imaging system, at around 30,000 feet while the pair of T-38s were required to not only remain in formation, but to fly at supersonic speeds at the precise moment they were directly beneath the B-200. The images were captured as a result of all three aircraft being in the exact right place at the exact right time designated by NASA’s operations team.
“The biggest challenge was trying to get the timing correct to make sure we could get these images.” Heather Maliska, AirBOS sub-project manager.– Heather Maliska, AirBOS sub-project manager.
“The biggest challenge was trying to get the timing correct to make sure we could get these images,” said Heather Maliska, AirBOS sub-project manager. The cameras can only record for about three seconds, and that short recording window had to coincide with the exact three seconds that the T-38s were under the B-200. “I’m absolutely happy with how the team was able to pull this off. Our operations team has done this type of maneuver before. They know how to get the maneuver lined up, and our NASA pilots and the Air Force pilots did a great job being where they needed to be.”
“What’s interesting is, if you look at the rear T-38, you see these shocks kind of interact in a curve,” he said. “This is because the trailing T-38 is flying in the wake of the leading aircraft, so the shocks are going to be shaped differently. This data is really going to help us advance our understanding of how these shocks interact.”
A Level of Detail Never Seen Before
“We’re seeing a level of physical detail here that I don’t think anybody has ever seen before,” said Dan Banks, senior research engineer at NASA Armstrong. “Just looking at the data for the first time, I think things worked out better than we’d imagined. This is a very big step.”
The new schlieren imaging system has some upgrades over previous versions. It has a wider angle lens than previous systems, allowing for more accurate positioning of the aircraft. It also has a faster frame rate. At 1400 frames per second, it’s much easier to see the detail of the sound waves. It also has faster data storage systems to go along with its increased frame rate.
The B200 also received some upgrades with the new imaging system. Avionics engineers developed a new installation system for the camera to make mounting easier and quicker.
“With previous iterations of AirBOS, it took up to a week or more to integrate the camera system onto the aircraft and get it working. This time we were able to get it in and functioning within a day,” said Tiffany Titus, flight operations engineer. “That’s time the research team can use to go out and fly, and get that data.”
NASA has been working on quiet supersonic flight for quite a while, and they’ve used a variety of ways to study it. Wind tunnels have been used, as they are in all aircraft design, but NASA came up with another way. About three years ago, they used the Sun as a backdrop to image the soundwaves from supersonic jets. Check out the video below from CNN.
The Commercial Supersonic Technology Project is not just focused on reducing the noise for sonic booms. It also looks at fuel efficiency, emissions, and structural weight and flexibility, all of which are impediments to better air travel. The data gathered will be shared with regulatory bodies in the US and around the world.
