The concept of supersonic transport (SST) has been a part of the commercial flight and aerospace sector since the 1970s. But as the Concorde demonstrated, the technology’s commercial viability has always been hampered by various challenges. For starters, supersonic planes must limit their speed to about 965 km/h (600 mph) over land to prevent damage caused by their sonic booms. Given the potential for flying from New York City to London in about 3.5 hours, which otherwise takes about 8 hours on average, aerospace engineers hope to overcome this problem.
Since 2006, the NASA Commercial Supersonic Technology Project (CSTP) has been researching SST as part of its QueSST mission and the X-59 quiet supersonic aircraft to reduce sonic booms, thus removing a crucial barrier to commercial development. Recently, NASA investigated whether commercial supersonic jets could theoretically travel from one major city to another at speeds between Mach 2 and 4 – 2,470 to 4,940 km/h (1,535 to 3,045 mph) at sea level. These studies concluded that there are potential passenger markets along 50 established routes, which could revolutionize air travel.
Ever felt the need to get somewhere really, really quickly? Would Mach 17 work? That’s the speed a new prototype engine from researchers at the University of Central Florida (UCF) could potentially hurl an aircraft through the skies, making a trip from New York to Los Angeles in under half an hour. At the heart of this new technology is a new propulsion technology that stabilizes detonations and then uses their shockwaves to provide hypersonic propulsion to an aircraft.
On Dec.7th, 2020, World War II flying ace and legendary test pilot General Chuck Yeager passed away while in hospital in Los Angeles. He was 97 years of age and is survived by his second wife, Victoria Yeager (nee Victoria Scott D’Angelo), and his three children, Susan, Don, and Sharon. Yeager is interred at Arlington National Cemetery outside of Washington D.C. with full military honors.
And last week (Monday, August 3rd), the company announced that it had entered into a partnership with engine-maker Rolls-Royce to build a supersonic commercial aircraft that would travel three times the speed of sound (Mach 3). If realized, the proposed aerospace vehicle will carry 19 passengers to altitudes of more than 18,000 meters (60,000 ft) while travelling at speeds 50% faster than the Concorde.
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.
NASA has a lot of experience when it comes to developing supersonic aircraft. In fact, testing supersonic craft was how NASA got its start, back when it still known as the National Advisory Committee for Aeronautics (NACA). Beginning with the Bell X-1, the tradition of using X-planes and other experimental aircraft continues, and has progressed to hypersonic scramjets and spaceplanes (like the X-37).
And now, for the first time in decades, NASA is looking to develop a new supersonic aircraft. But whereas previous aircraft were developed for the sake of breaking speed records, the purpose of this latest X-plane is to create a Quiet Supersonic Transport (QueSST). NASA hopes that this craft will provide crucial data that could enable the development of commercial supersonic air travel over land.
To that end, NASA awarded a $247.5 million contract to Lockheed Martin Aeronautics Company on April 2nd to build the X-plane and deliver it to the agency’s Armstrong Flight Research Center in California by the end of 2021. As Jaiwon Shin, NASA’s associate administrator for aeronautics, indicated in a recent NASA press release, this project is like revisiting the old days of NASA research.
“It is super exciting to be back designing and flying X-planes at this scale,” he said. “Our long tradition of solving the technical barriers of supersonic flight to benefit everyone continues.”
In the past, supersonic commercial flights were available, for people who could afford them at least. These included the British-French Concorde (which operated until 2003) and the Russian Tupolev Tu-144 (retired in 1983). However, these craft were incapable of conducting supersonic flights over land because of how breaking the sound barrier would generate a sonic boom – which are extremely loud and potentially harmful.
As a result, current Federal Aviation Administration (FAA) regulations ban supersonic flight over land. The purpose of this latest aircraft – known as the Low-Boom Flight Demonstrator – is to conduct supersonic flights that create sonic booms that are so quiet, they will be virtually unnoticeable to people on the ground. The key is how the X-plane’s uniquely-shaped hull generates supersonic shockwaves.
With conventional aircraft designs, shockwaves coalesce as they expand away from the airplane’s nose and tail, resulting in two distinct sonic booms. In contrast, the X-plane’s hull design sends shockwaves away from the aircraft in a way that prevents them from coming together. Instead, much weaker shockwaves are sent to the ground that would be heard as a series of soft thumps.
Since the 1960s, NASA has been testing the idea using vehicles like the F-5E Tiger II fighter jet. This aircraft, which flew test flights in 2003-2004 as part of NASA’s Shaped Sonic Boom Demonstration program, had a uniquely-shaped nose and demonstrated that boom-reducing theory was sound. More recent flight testing, wind-tunnel testings, and advanced computer simulations tools have also indicated that the technology will work.
As Peter Coen, NASA’s Commercial Supersonic Technology project manager, stated:
“We’ve reached this important milestone only because of the work NASA has led with its many partners from other government agencies, the aerospace industry and forward-thinking academic institutions everywhere.”
The X-plane’s configuration will be based on a QueSST design that Lockheed Martin developed in 2016 in partnership with NASA, and which completed testing in a wind tunnel at NASA’s Glenn Research Center in 2017 . The proposed aircraft will measure 28.65 meters (94 feet) long, have a wingspan of about 9 meters (29.5 feet), and have a takeoff weight of 14,650 kg (32,300 lbs).
Based on the company’s design, the X-plane will be powered by a single General Electric F414 engine, the same used by F/A-18E/F fighters. It will be flown by a single pilot and have a top speed of Mach 1.5 (1590 km; 990 mph) and a speed of Mach 1.42 (1513 km; 940 mph) at a cruising altitude of 16764 meters (55,000 feet).
As Shin indicated, the development of the X-plan is a joint effort involving all of NASA’s aeronautics research centers:
“There are so many people at NASA who have put in their very best efforts to get us to this point. Thanks to their work so far and the work to come, we will be able to use this X-plane to generate the scientifically collected community response data critical to changing the current rules to transforming aviation!”
The program is divided into three phases which are tentatively scheduled to run from 2019 to 2025. Phase One, which will run from 2019 to 2021, will consist of a critical design review in preparation for construction. If successful, construction will begin at Lockheed Martin’s Skunk Work‘s facility in Palmdale, followed by a series of test flights and culminating with the delivery of the craft to NASA.
Phase Two, scheduled to begin in 2022, will consist of NASA flying the X-plane in the supersonic test range over Edwards Air Force Base in southern California to see if it is safe for operations in the National Airspace System. Phase Three, running from 2023 to 2025, will consist of the first community response test flights (staged from Armstrong Air Force Base) followed by further test flights over four to six U.S. cities.
The data gathered from these community response tests will then be delivered to the FAA and the International Civil Aviation Organization (ICAO) – currently targeted for delivery in 2025 – so they can adopt new rules based on perceived sound levels. If the Low-Boom Flight Demonstrator should prove to be effective, commercial supersonic flights over land may finally become feasible.
And be sure to enjoy this video of the X-plane’s development, courtesy of NASA:
NASA is using a 150-year-old photographic technique with a few 21st century tweaks to capture unique and stunning images of the shockwaves created by supersonic aircraft.
Called schlieren imagery, the technique can be used to visualize supersonic airflow with full-scale aircraft in flight. Usually, this can only be done in wind tunnels using scale models, but being able to study real-sized aircraft flying through Earth’s atmosphere provides better results, and can help engineers design better and quieter supersonic planes.
And a side benefit is that the images are amazing and dramatic, creating a little “shock” and awe.
Earlier this year, NASA released some schlieren imagery taken with a high-speed camera mounted on the underside of a NASA Beechcraft B200 King Air, which captured images at 109 frames per second while a supersonic aircraft passed several thousand feet underneath over a speckled dessert floor. Special image processing software was used to remove the desert background, then combine and average multiple frames, which produces a clear picture of the shock waves. This is called air-to-air schlieren.
“Air-to-air schlieren is an important flight-test technique for locating and characterizing, with high spatial resolution, shock waves emanating from supersonic vehicles,” said Dan Banks, the principal investigator on the project, being done at NASA’s Armstrong Flight Research Center at Edwards Air Force Base. “It allows us to see the shock wave geometry in the real atmosphere as the target aircraft flies through temperature and humidity gradients that cannot be duplicated in wind tunnels.”
But now they’ve started using a technique that might provide better results: using the Sun and Moon as a lit background. This backlit method is called Background-Oriented Schlieren using Celestial Objects, or BOSCO.
The speckled background or a bright light source is used for visualizing aerodynamic flow phenomena generated by aircraft or other objects passing between the camera and the backdrop.
NASA explains the technique:
“Flow visualization is one of the fundamental tools of aeronautics research, and schlieren photography has been used for many years to visualize air density gradients caused by aerodynamic flow. Traditionally, this method has required complex and precisely aligned optics as well as a bright light source. Refracted light rays revealed the intensity of air density gradients around the test object, usually a model in a wind tunnel. Capturing schlieren images of a full-scale aircraft in flight was even more challenging due to the need for precise alignment of the plane with the camera and the sun.”
Then, there are variations on this technique. One recent demonstration used Calcium-K Eclipse Background Oriented Schlieren (CaKEBOS). According to Armstrong principal investigator Michael Hill, CaKEBOS was a proof of concept test to see how effectively the Sun could be used for background oriented schlieren photography.
“Using a celestial object like the sun for a background has a lot of advantages when photographing a flying aircraft,” Hill said. “With the imaging system on the ground, the target aircraft can be at any altitude as long as it is far enough away to be in focus.”
Researchers found the ground-based method to be significantly more economical than air-to-air methods, since you don’t have to have a second aircraft carrying specially mounted camera equipment. The team said they can use off-the-shelf equipment.
Schlieren imagery was originally invented in 1864 by German physicist August Toepler.
Find out more about the air-to-air technique here and the BOSCO techniques here.