Aerospace innovators from government, commercial, and university arenas are developing technologies that would make supersonic flight over land possible, dramatically reducing travel time anywhere in the world. With these advances, engineers also are working to make aircraft more environmentally friendly, eliminating toxic emissions and reducing the amount of energy required for flight.
NASA's Quiet Supersonic Plane
NASA, for decades, has led the effort to study sonic booms — the loudness of which is considered the key barrier to enabling a future for overland, commercial supersonic aircraft. That future will be closer to reality when the agency's X-59 Quiet SuperSonic Technology (QueSST) airplane takes to the skies in 2022, taking the first steps to demonstrating the ability to fly at supersonic speeds while reducing the sonic boom to sonic thump.
The Low-boom Flight Demonstration mission has two goals: 1) design and build a piloted, large-scale supersonic X-plane with technology that reduces the loudness of a sonic boom; and 2) fly the X-plane over select U.S. communities to gather data on human responses to the low-boom flights and deliver that data set to U.S. and international regulators.
Using this data, new sound-based rules regarding supersonic flight over adopted, which would open the doors to new commercial cargo and passenger markets to provide faster-than-sound air travel. Supersonic travel will cut the time of a U.S. coast-to-coast flight in half — from 5 hours at a speed of 575 mph to 2/ hours at a speed of Mach 1.4.
NASA anticipates that initial flights to prove performance and safety will take about nine months. A single pilot will fly the 96.8-foot-long, 29.5-foot-wide X-59 aircraft powered by a single jet engine.
The plane's design research speed will be Mach 1.42, or 940 mph, flying at 55,000 feet. At the successful conclusion of these flights, NASA will officially take delivery of the aircraft from Lockheed Martin in early 2023. At that time, NASA will fly the X-59 within a supersonic test range to prove the technology works as designed, aircraft performance is robust in real atmospheric conditions, and the X-59 is safe for operation in the National Airspace System.
NASA will measure the sound of the sonic thumps in the Mojave Desert using cutting-edge technology: a state-of-the-art ground recording system. NASA has contracted Crystal Instruments of Santa Clara, CA to deliver a recording system for the high-fidelity sonic boom — and soon to be, a quiet sonic thump — that is capable of providing the data necessary for the agency to validate the acoustic signature of the X-59.
NASA will utilize the Crystal Instruments Ground Recording System (CI-GRS) to gather time, waveform, and spectral data related to sonic booms and sonic thumps. The CI-GRS will also feature the ability for NASA to install custom software and algorithms to perform various specialized operations for real-time sonic thump analysis.
The agency will use the X-59 to gather data on how effective the low-boom technology is in terms of public acceptance by flying over select U.S. cities beginning in 2024 and asking residents to share their response to the sound the X-59 produces. NASA will then provide a complete analysis of the community response data to U.S. and international regulators for their use in considering new sound-based rules regarding quiet supersonic flight over land. Such rules could enable new commercial cargo and passenger markets in faster-than-sound air travel.
Virgin Galactic's Mach 3 Aircraft
Virgin Galactic Holdings is collaborating with Rolls-Royce to design and develop engine propulsion technology for its high-speed commercial aircraft that will soar at speeds beyond Mach 3 — faster than the average Mach-2 cruising speed of the original Concorde.
The company is working with the FAA to ensure that designs can make a practical impact from the start. Virgin Galactic — with representatives from NASA — confirmed that its design concept can meet the high-level requirements and objectives of the mission. Previously, NASA signed a Space Act Agreement with Virgin Galactic to collaborate on high-speed technologies. The project holds many goals in common with NASA's X-59 QueSST aircraft. Both hope to move the industry to further research and development of high-Mach A-to-B travel.
The basic parameters of the design include a targeted Mach 3 certified delta-wing aircraft that would have capacity for 9 to 19 people at an altitude above 60,000 feet and would also be able to incorporate custom cabin layouts to address customer needs including Business or First Class seating arrangements. The aircraft design also aims to help lead the way toward use of state-of-the-art sustainable aviation fuel. Baselining sustainable technologies and techniques into the aircraft design early on is expected to also act as a catalyst to adoption in the rest of the aviation community.
The design is geared around making high-speed travel practical, sustainable, safe, and reliable, while making customer experience a top priority. Virgin Galactic is designing the aircraft for a range of operational scenarios including service for passengers on long-distance commercial aviation routes. The aircraft would take off and land like any other passenger aircraft and be expected to integrate into existing airport infrastructure and international airspace around the world.
Virgin Galactic is working closely with international regulatory communities — including the U.S. FAA — to ensure compliance with safety and environmental standards.
The Clean Flying-V
The Flying-V — developed by Delft University of Technology and the Royal Netherlands Aerospace Centre — was created to be a highly energy-efficient long-distance airplane. The passenger cabin, cargo hold, and fuel tanks have all been placed in the wings, introducing the V-shape that the plane is named after.
In the Flying-V — originally an idea of TU Berlin student Justus Benad — the design is not as long as an Airbus A350 but it has the same wing span. This allows the Flying-V to use the present infrastructure of gates and runways at airports. The Flying-V carries about the same number of passengers and the same amount of cargo.
According to Dr. Roelof Vos, project leader of the Flying-V at TU Delft, the airplane was designed with “an oval pressurized cabin that allows for an efficient structural design, with sufficient design freedom to allow for proper aerodynamic shaping. Our preliminary calculations have shown that the aircraft has significantly less drag than a modern widebody aircraft such as the Airbus A350 or the Boeing 787,” he said. “Structural calculations also have shown that the structural weight is significantly lower. Based on those studies, we've estimated that the Flying-V consumes 20% less fuel than an Airbus A350 for the same flight.”
Vos explained that the Flying-V does not have a separate horizontal tail plane. “It is therefore stabilized by the location of the wing's aerodynamic center, which is behind the most aft center of gravity.” Pitch and roll control, he explained, “is provided by the segmented elevons at the trailing edge of the outboard wing. Yaw control is provided by the rudders, which are integrated in the winglets. The large sweep angle and low aspect ratio of the aircraft imply that a relatively large inclination angle is required to attain enough lift during low-speed conditions. In other words, the aircraft comes in for landing with its nose raised fairly high, just like the Concorde did.”
The Flying-V engines are positioned above and behind the wing; the engine intake is still above the trailing edge of the wing. The engine is located behind the passenger cabin, reducing noise in the cabin. Community noise is reduced due to two factors: the fan noise is partially shielded by the wing and the exhaust noise no longer reflects from the lower surface of the wing.
The interior volume of the aircraft is used primarily by the passenger cabin, the cargo hold, and the fuel tanks. The cabin was configured to hold 314 passenger seats in a two-class configuration. Passengers are seated in both legs of the V as well as in the connecting center body. Structural analysis indicated the need for structural reinforcements in the fuselage in the form of three distinct walls: one at the beginning of each leg of the V and one on the symmetry plane of the aircraft. Large cutouts in these walls at the location of the (cross) aisles allow for a seamless integration of these structural components within the furnishing of the cabin.
The exterior of the Flying-V ensures less fuel consumption by design. The lightweight construction of the interior will contribute to this as well; for example, the “normal” seats used in the design are 4 kg lighter than the typical seats currently used on long-haul flights.
A Quieter “Boom”
Overture — made by Boom Supersonic — is the first airliner in a new era of enduring supersonic flight, building on Concorde's legacy through faster, more efficient, and sustainable technology.
Overture, which is 100% carbon-neutral, can take up to 88 passengers from New York to London in 3½ hours instead of 6½ hours, from Paris to Montreal in less than 4 hours instead of 7 hours, and from Los Angeles to Sydney in 8½ hours instead of 14½ hours. The plane has a cruising altitude of up to 60,000 feet, enabling passengers to see the darkness of space above and the curvature of the Earth below. Overture will be able to perform all phases of flight, from takeoff through supersonic speeds, without afterburners.
Overture's engines can accommodate sustainable aviation fuel and the plane is designed with aircraft end-of-life recycling in mind. The company is targeting per-seat fuel efficiency similar to subsonic business class, taking advantage of technological progress in engine and airframe design.
The company's goal is to build Overture by 2022, roll it out in 2025, and start flying passengers in 2029.
Moving AHEAD with Clean Aircraft
Aircraft today consist largely of a cylindrical fuselage with wings attached; the design has been in use for decades. A European Union-funded consortium is developing an alternative aircraft design called AHEAD (Advanced Hybrid Engines for Aircraft Development).
The AHEAD aircraft has an integrated wing and body, called a blended wing body (BWB) design. Minimizing resistance (or drag) is one of the main challenges in aircraft design. Overcoming drag requires power and this results in greater fuel consumption.
AHEAD involves a totally new engine design — a hybrid engine using two different combustion systems. The first combustor burns either cryogenic hydrogen or liquefied Natural Gas (LNG) and the second combustor burns either kerosene or biofuel. By using two different combustor and fuel systems, the engine's total efficiency increases and emissions are reduced. With the BWB, a larger amount of space is available within the aircraft, thus making it possible to carry cylindrical fuel tanks to store the cryogenic fuel.
A feature of the engine is the use of a counter-rotating fan. The large fan that produces most of the engine thrust is made up of two rows of blades that rotate in opposite directions. The advantage of this design is to improve engine efficiency even further.
AHEAD is designed to carry about 300 passengers. The shorter and wider body of the aircraft makes it aerodynamically more efficient than a conventional cylindrical body aircraft. Combined with the advanced hybrid engine, the multi-fuel BWB is able to reduce CO2 emission by around 65% compared to a conventional Boeing 777-200ER aircraft. The timeframe for introduction of the aircraft is 2050.
London to Australia: A Day Trip?
The UK Space Agency thinks it is possible. The government agency has been teaming up with private companies to explore new territory in hypersonic travel. One of those partner companies, Reaction Engines, is developing an engine that the UK Space Agency thinks might make a day trip to London from Australia a reality.
Founded by three propulsion engineers from Rolls-Royce, the company is working on a Synergetic Air Breathing Rocket Engine (SABRE) propulsion system that can propel an aircraft from zero to five times the speed of sound in the atmosphere. Reaction Engines believes it has the potential to redefine both air and space travel.
SABRE features a precooler — the part of the engine that rapidly cools the incoming air (1,000 °C to ambient), enabling the engine to operate at higher speeds than existing engines. The pre-cooler has been validated for speeds of up to Mach 5 in the Earth's atmosphere. SABRE's heat exchanger and hydrogen preburner subsystems supply heat energy and air to the core of the engine.
SABRE subsystems are undergoing testing and validation in ground-based demonstrations.