Within 20 years, the projected growth of air travel will be unsurmountable. According to the International Air Transport Association, the Air Transport Action, and the Boeing Company, commercial passenger trips will increase from 3.3 billion to 7 billion by 2034. In turn, that will create more aviation-industry-related jobs. It is projected that the amount of jobs will rise from 58 million to 105 million, an increase of almost 85%.
Estimates show that approximately 36,000 airplanes will be needed to fulfill flight travel demands—an investment of $5 trillion dollars. The expected increase of planes over the next two decades will further complicate current industry problems.
For instance, in 2015, airplanes worldwide produced 781 million tons of carbon-dioxide emissions. That number will likely triple by 2050 with current technology standards. Noise pollution is also expected to increase without any new developments in airplane technology. To fight this problem, the National Aeronautics and Space Administration (NASA) launched its New Aviation Horizons initiative last year to develop new technologies to improve air transportation.
New Aviation Horizons
For the past year, NASA has been developing its green aviation initiative. In April of 2016, former NASA Administrator Charlie Bolden announced the New Aviation Horizons program. This 10-year initiative will bring back X-planes for research purposes. These are experimental aircraft that hopefully will bring forth the new age of flight, including supersonic travel and more efficient aviation methods. The plan is to take advantage of five large-scale X-planes to test new technologies.
The three main goals for the New Aviation Horizons program are to reduce the amount of fuel used, shrink carbon-dioxide emissions, and eliminate noise pollution. Supersonic is one of the goals for the fifth planned X-plane, which is set to fly in the mid-2020s. It is anticipated that the plane, with its hybrid-electric design, will be able to reach supersonic speeds without necessitating a supersonic boom.
In October of 2016, NASA awarded six-month long contracts to four companies to help define the technical approach, schedule, and cost for one or more large-scale subsonic X-plane concepts. The four companies are Aurora Flight Sciences Corp., Manassas, Va.; Dzyne Technologies Inc., Fairfax, Va.; Lockheed Martin Aeronautics Co., Ft. Worth, Tex.; and The Boeing Company, Hazelwood, Mo. Each company is required to detail the system requirements for the piloted experimental aircraft.
The X-plane must be capable of sustained two- to three-hour powered high subsonic flight and conduct at least two research flight sorties per week for the duration of the year-long program. The X-planes are scheduled to fly no later than 2021, and the build must be completed by said timeframe. NASA’s press release announcing the project lists the four companies and their X-plane approaches: the Aurora Flight Sciences’ D8 Double Bubble, Dzyne Technologies’ Blended Wing Body, Lockheed Martin’s Hybrid Wing Body, and Boeing’s Blended Wing Body and Truss-Braced Wing Concept.
As reported previously by Machine Design, two X-planes have already begun construction. Lockheed Martin’s Quiet Supersonic Technology (QueSST) is a supersonic aircraft that generates a soft thump, rather than the disruptive boom created by modern supersonic aircraft. The other aircraft, NASA’s X-57 aka Maxwell, is the first X-plane to take flight. The Maxwell was previously known as the Sceptor, which stands for Scalable Convergent Electric Propulsion Technology Operations Research. Scheduled for flight in early 2018, the Maxwell uses 14 motors and propellers mounted into a unique wing design.
Industry Experts Provide Their Insights
Upon the announcement of NASA’s green air initiative, several aviation companies were quick to publicize their interest in working on the New Aviation Horizon program. “The goals NASA has outlined are ambitious,” said Dr. Naveed Hussain, Boeing’s vice president of aeromechanical technology. “And that is a good thing…What NASA is doing is very exciting, especially looking at the long-term view. In this business, it’s hard to pivot every 18 or 24 months.”
The Green Aviation Technical Interchange Meeting, which was held in May of 2016 and included over 100 attendees from government, industry, and academia, was the culmination of six years of research and technology demonstrations under NASA’s Environmentally Responsible Aviation Project, which completed in 2015.
The research focused on aircraft drag reduction via flow control concepts; weight reduction by using composite materials; lowering fuel use and noise production via advanced engines; reducing emissions from improved engine concepts like electric and hybrid electric designs; and lastly, airframe innovations and engine integration designs to reduce fuel consumption and noise. “The NASA X-plane program is a great idea,” said Dr. Alan Epstein, Pratt & Whitney’s vice president of Technology & Environment. “It gets people thinking about different approaches. That’s as much a valuable contribution as some of the technology maturation.”
However, the development of green advances does not ensure they will be widely adopted. “We don’t want to be stuck with a product no one is willing to write a check for,” Hussain cautioned. “We try to create a positive business case. And we have to balance all of these competing requirements.”
Dr. Dimitri Marvis, a Georgia Tech Boeing Professor, said that adopting new technology and steering away from legacy equipment is anything but simple: The time gap between widespread adoptions requires an average of four years, and more time can pass before these new advances are found in the majority of the fleet. “The industry today is much more risk-adverse,” he explained. “Refinements have to be less risky.” Epstein stressed that companies need to find immediate value in any new technology innovation. NASA understands these concerns and knows that its research must be relevant with proven results.
Key Technologies to Get “Green”
In an effort to help achieve its new initiative, NASA selected green technology concepts that potentially can change the aviation industry. NASA believes that these concepts will reduce aircraft fuel use and emissions. The Transformative Aeronautics Concepts Program selected these technology concepts for a two-year study: alternative fuel cells, 3D printing to increase electric motor output, lithium-air batteries for energy storage, mechanisms for changing wing shape during flight, and the use of aerogel (a new lightweight material) in the design and development of the aircraft antenna.
Regarding the design of alternative fuel cells, NASA turns to different methods of generating power for electrically propelled aircraft of general aviation size. The Fostering Ultra-Efficient Low-Emitting Aviation Power (FUELEAP) program combines hydrogen and oxygen in a fuel cell to generate electricity.
Typically, hydrogen and oxygen are stored onboard the vehicle as super-cold liquids, but large tanks and plumbing are impractical for small single-engine airplanes. The difference in this new approach will be that the hydrogen will be pulled from standard hydrocarbon-based aviation gas and oxygen will be pulled from the air. Exhaust products from this process will be used to increase the energy output via a turbine. This type of fuel cell design would generate energy efficiently, saving fuel and reduce emissions—especially when compared to standard piston engines. This system is easy to implement at current airports, since it would not require expensive new facilities or equipment.
Other all-electric and hybrid electric solutions beyond FUELEAP are out there to investigate. NASA engineers must address the challenges associated with electrical power generation and battery storage—in particular, how to improve on power density. The question is: How does one keep size and mass low while increasing power output? One way is to use 3D printing. Engineers create lighter and perhaps smaller electric motor parts. Hence, this allows for the assembly of small and lighter motors with higher power densities.
Lithium-oxygen batteries are another possible answer to the question of how the aviation industry can adopt electric power aircraft. Li-Air batteries are also known as breathing batteries. As the battery drains, oxygen is pulled into it and reacts with the lithium-ion batteries. As the battery charges, oxygen is expelled.
Currently, these batteries do not have a long lifetime. Standard electrolytes, which are used to make Li-Air batteries function, quickly decompose during operation and only last a few charge/discharge cycles. One of the current projects at NASA is researching how to design ultra-stable electrolytes, resistant to decomposing.
Improving aviation battery design represents just one example of how NASA is using the latest technologies. New adaptive wings have the capability to reduce emissions and noise pollution and increase fuel efficiency. The height of the vertical tail depends on the need to keep the airplane centered on runaway in case the engine fails during takeoff or landing. Once the airplane is in the air, however, the tail creates drag and wastes fuel as a result. The solution would be to create adaptive wings that at each end would have a rudder, folding up or down at the beginning and ending of a flight. This would reduce the size of the vertical tail and ultimately lead to a more efficient airplane.
The last of the innovations put forth by NASA relates to the future for drones and unmanned aerial vehicles (UAVs). It is mandated by the National Airspace System that drones and UAVs be operated within a radio line of sight with the ground-based pilot. Using satellite-based tracking systems to relay commands and control communications is a solution, but it results in heavy and protruding antenna systems—thus increasing drag, fuel use, and emissions.
NASA researchers hope to create lightweight, flexible antennas that conform to the curves of the aircraft. This is where the use of aerogel in constructing these antennas shows promise. With aerogel, it is possible to create thin and lightweight antennas, and in turn reduce drag, fuel, and emissions. The ability to curve the antennas allows NASA engineers to direct signals in specific directions, ensuring there will always be a strong link to satellites and minimal interference with the ground in low flight.
Full Steam Ahead Toward Innovation
The six-month timeline given to the first four companies is almost up. By April of 2017, the four companies given X-plane contracts from NASA will be required to show their concepts and paths toward actual prototype build. Currently, NASA is testing its Spanwise Adaptive Wing (SAW) concept on the Prototype-Technology Evaluation and Research Aircraft (PTERA). The SAW concept aims to control outboard wing tip positions as much as 75 deg. to meet optimal demands in landing and takeoff, as well as flight. The PTERA test aircraft will use the SAW concept in flight in the spring of 2017.
NASA also selected Pratt & Whitney to participate in its Ultra-High Bypass Advanced Nacelle Technologies Flight Demonstration. The three-year agreement, which includes the Boeing Company and UTC Aerospace Systems, will involve the design, build, testing, integration, and flight demonstration of new engine technologies meant to improve performance, reduce weight, and produce less noise. The main purpose is to apply theses advances to commercial transport, high-bypass-ratio, jet-engine advanced nacelle systems. The technologies to be used in the prototype include active and laminar flow for drag reduction, lightweight composite structure, and acoustic liners that extend into the nacelle lip region to help with noise reduction.