August 8, 2019 |
Precision agriculture, infrastructure inspection, construction, real estate, aerial photography—using small unmanned aircraft systems (UAS) is already an everyday reality in many markets and in a regulatory environment that strictly limits how they can be used.
As the FAA releases its first regulations for small UAS, or drones—rules years in the making—it is already under pressure to move quickly in allowing their use to expand beyond the initial limits of daylight, visual-line-of-sight operations to flight beyond line of sight and at night.
Once permitted to fly beyond the operator's line of sight, small UAS of less than 55 lb. gross weight are expected to meet the bulk of the near-term demand for commercial unmanned aircraft. The market looks set to be dominated by a “drones as a service” business model, with customers wanting data.
Next in line could be deliveries by UAS—consumer packages in cities or medical supplies in disaster zones—but this requires a means of enabling safe and efficient access to low-altitude airspace by multiple aircraft, unmanned and manned. NASA is pursuing this under its UAS Traffic Management research project.
Commercial aircraft turbofans are getting bigger. Larger fans and higher bypass ratios mean greater propulsive efficiency and lower fuel consumption. Turbofans entering service in the early 2020s will have bypass ratios of 15-20, compared with 10-12.5 for the latest engines. But their increased size will force changes in wing and landing-gear design and, potentially, aircraft layout and engine location.
Research is biased toward future turbofans being geared, for larger fans; but ultimately nacelle drag and weight will set a limit on their diameter. Open-rotor engines remain an option if demand for reductions in fuel consumption and emissions require even higher bypass ratios. Concerns with the airport noise and aircraft safety implications of open rotors remain to be fully allayed, but work continues.
Over the evolution of aircraft design, aerodynamics have improved continuously but seldom dramatically. The search for future increases in fuel efficiency, however, could lead to significant changes in aerodynamic design including more slender, flexible wings; natural laminar flow and active flow control; and unconventional configurations.
Laminar flow reduces drag, but requires wings with tight tolerances that are difficult to achieve in manufacturing and smooth surfaces that are hard to keep free of contamination in service. But the potential for significant drag reduction has researchers in Europe and the U.S. developing ways to manufacture and maintain laminar-flow wings on airliners that could enter service by 2030.
More slender and flexible wings will reduce drag and weight but require new structural and control technologies to avoid flutter. Techniques under development include passive aeroelastic tailoring of the structure using directionally biased composites or metallic additive manufacturing, and active control of the wing's movable surfaces to alleviate maneuver and gust loads and suppress flutter.
High-speed cruise is a focus for aerodynamic improvement; another is high lift at low speed and potential use of compliant or morphing surfaces to adapt wing shape while reducing the noise and drag generated by conventional slats and flaps. Active flow control could also increase takeoff and landing performance, reduce noise and, NASA/Boeing tests show, increase rudder effectiveness for a smaller tail.
Where humans are headed next in space may still be up for debate, but the technology steps required are becoming clearer. For the U.S., they begin with NASA's development of the heavy-lift Space Launch System (SLS) and Orion crew vehicle to send astronauts and equipment into deep space.
SLS and Orion are scheduled to fly together in 2018 on an unmanned test flight around the Moon and back. A manned flight around the same loop is planned between 2021 and 2023. Both spacecraft are cornerstones of NASA plans to reach Mars with humans in the mid-2030s.
As its launch vehicle and crew capsule mature, NASA plans to shift its human space focus from low Earth orbit to cislunar activities. These could include tests of an in-space habitat in orbit around the Moon, or at the Earth-Moon Lagrangian point, where astronauts can practice for the 200-day transit to Mars.
With NASA's help, Elon Musk's SpaceX plans a private “Red Dragon” mission in 2018 to land a modified Dragon commercial capsule on Mars. Musk wants to fly to Mars on all subsequent launch windows, which come every 26 months, and land humans on the planet as early as 2025.
The U.S. will not have space to itself as it pushes beyond low Earth orbit. China plans to launch its second orbiting laboratory in 2016, in preparation for a permanent space station to be completed in 2022, and wants to put astronauts on the Moon by 2036. India also has ambitions to fly humans there, but its first manned spaceflight is not expected before 2021.
Teams and Swarms
Many current military unmanned aircraft are costly and complex to operate, requiring significant manpower and mission preplanning. But advances in autonomy could unlock the power of lower-cost vehicles operating collaboratively in swarms or in teams with other aircraft, both unmanned and manned.
The Pentagon's Strategic Capabilities Office is planning near-term fielding of 3-D-printed micro-UAS that are launched from flare dispensers on fighters to form swarms and conduct surveillance in contested airspace or overwhelm an adversary's defenses. Using more than 30 tube-launched Raytheon Coyotes, the Office of Naval Research is testing swarms of cooperating autonomous small UAS to measure their effectiveness in gathering intelligence, drawing enemy fire or jamming their defenses.
As it looks for ways to penetrate and survive in heavily defended airspace, the Air Force Research Laboratory is pursuing demonstrations of both affordable, limited-life unmanned strike aircraft and autonomous air vehicles that act as “loyal wingmen” to manned fighters, carrying additional sensors and weapons. DARPA is developing methods of airborne launch and recovery of swarming UAS, and software to enable unmanned aircraft to collaborate with minimal human supervision.
As a result of research programs such as these, the next generation of combat aircraft, planned to enter service in the U.S. and Europe in 2030-40, is expected to be a system of systems—a manned fighter controlling a fleet of cooperating UAS with different mission capabilities.
The potential of additive manufacturing, better known as 3-D printing, has almost every industry in its grip, from food to chemicals. Aerospace is embracing additive cautiously because of the safety and reliability implications, but even so, applications are expanding at a rate unheard of for aviation.
As a manufacturing technology, 3-D printing established its foothold with polymers, which the aircraft industry has been able to use for rapid prototyping and some flyable low-strength parts. But the real growth in adoption is coming with the maturing of metal additive-manufacturing processes.
Aerospace manufacturing involves removing a lot of metal from formed pieces, and additive promises dramatic reductions in the “buy-to-fly” ratios—the weight of the raw material versus that of the finished part—for expensive materials such as lightweight, high-strength titanium and nickel alloys.
First, industry must convince itself and airworthiness authorities that 3-D-printed parts are as good as those manufactured by conventional means, preferably better. This is happening, with GE Aviation additively manufacturing fuel nozzles, and Avio Aero making titanium-aluminide turbine blades for turbofans.
These initial production parts are made using lasers or electron beams to melt metal powder. Aircraft structures involve larger parts and that means breaking “out of the box” created by the working volumes of powder-bed machines. Laser wire deposition enables larger components and is entering production.
Additive manufacturing already allows part designs to be optimized to use less material, for lower cost and weight. With time, it will permit the microstructure of the material to be controlled throughout a part to maximize its performance. Eventually it will allow entirely new materials to be tailored.
Spacecraft with additively manufactured parts are already operational, and Silicon Valley startup Made in Space is pursuing the potential for 3-D printing in space itself—to manufacture spacecraft structures such as reflectors, trusses or optical fibers for terrestrial communications.
Controls and Displays
From “steam” gauges developed by watchmakers to cathode ray tubes used in televisions to liquid crystal displays used in laptops, flight decks have taken advantage of technologies developed for wider commercial markets, adapting and ruggedizing them for use in aircraft.
That is happening again as the consumer world embraces wearable technology. The first step is the development of head-mounted, near-to-eye displays that could ultimately replace head-up displays (HUD)—as the helmet-mounted display already has done onLockheed Martin's F-35 fighter.
Elbit Systems and Thales are developing head-mounted displays for commercial aircraft as a lower-cost alternative to HUDs, particularly in smaller cockpits. Elbit's SkyLens wearable display is targeted for certification in 2017 on ATR regional turboprops. NASA and European researchers are experimenting with augmented reality using head-worn displays and sensors to detect and avoid hazards.
Introduced in business aircraft, touch screens are moving to airliners with the Rockwell Collins displays for the Boeing 777-X, and avionics manufacturers are looking at speech recognition as a next step to reduce cockpit workload. Honeywell is experimenting with brain-activity monitoring to sense when a pilot is overloaded or his/her attention is wandering—with the potential to control flight-deck functions.
Fly-by-wire is making its way into smaller aircraft, bringing flight-envelope protection, and this will accelerate with future electric light aircraft. The FAA believes advanced flight controls will emerge with automated takeoff and landing, “refuse-to-crash” hazard avoidance, 4-D flightpath management and “iPad-intuitive” displays that require fewer pilot-specific skills.
With cargo deliveries moving forward and crew flights to begin by 2018, NASA is well on its way to establishing a commercial transportation infrastructure to low Earth orbit. For now, the only destination on this railroad to space is the International Space Station (ISS), but more will come.
Assembled in orbit over 16 years and operated by a partnership of the U.S., Canada, Japan, Russia and 11 member states of the European Space Agency, the ISS is planned to remain operational to 2024. But entrepreneurs are looking at using the space outpost as a starting point for commercial stations.
Fledgling private-sector activity is already underway on the ISS, notably NanoRacks using it as a launch platform for commercial cubesats delivered to orbit in bulk via cargo vehicle. In a next step, a prototype of Bigelow Aerospace's inflatable habitat has been berthed to the station for two years of testing.
Bigelow is in negotiations with NASA to add a full-scale expandable habitat to the ISS, offering 330 m³ (12,000 ft.³) of internal space for commercial operations, and plans to have the first of two modules ready for launch in 2020. The company sees in-orbit satellite manufacturing as a promising application.
Startup Axiom Space plans a small commercial station that, like Bigelow's B330, would start out as a module attached to the ISS. It would stay berthed to the station until a second module with solar arrays and propulsion arrives to take it to a lower-inclination orbit better suited to commercial launches.
Axiom's aluminum habitat would be based on the ISS's existing modules, but the company has a long-term vision of building, within a generation, a free-flying “space city” reminiscent of the wheeled space station in the movie “2001: A Space Odyssey,” slowly rotating to generate artificial gravity at the rim.
Progress with driverless-car technology has rekindled long-held hopes that flying can be made simpler, opening access to personal air travel as a viable alternative to road transport, particularly in gridlocked urban areas.
Unmanned aviation is expected to lead the way in developing the required automated flight control and airspace management technologies, along with the sensors and algorithms needed to autonomously avoid hazards and collisions with other aircraft.
Several startups in Silicon Valley and elsewhere have begun developing vehicles targeting the “on-demand mobility” market that NASA and others see emerging from the convergence of electric propulsion, autonomy, communication and perception technologies.
Air taxis with simplified controls that nonpilots can use, or fully autonomous passenger-carrying aircraft, have significant acceptance and certification hurdles to overcome, along with issues such as energy efficiency or community noise, and remain years away.
Carbon-fiber composites have reduced the weight and increased the performance of aircraft but have made them harder to produce, as the material is made simultaneously with the part. As manufacturers look ahead to future aircraft that can be built at higher rates with lower cost, a focus is on taking labor and time out of composites production.
Automation is a major drive, and automated fiber placement is already displacing manual layup and automated tape laying where economically feasible. A next step, taken on the carbon-fiber wing of Bombardier's C Series, is to lay up easier-to-handle dry fiber, then inject it with resin during curing.
Unlike resin-impregnated, or prepreg, carbon fiber, dry fiber does not require temperature-controlled storage and can be used to make complex preforms that are then resin transfer-molded. Skins can be integrated and cocured with ribs, stringers and other features to simplify assembly.
Manufacturers want to get rid of expensive “monument” tooling that can act as bottlenecks in production, and that includes the autoclaves now used for curing. Out-of-autoclave composites that can be cured on the production line in vacuum bags and mobile ovens are gaining ground.
But design and process advances are required to minimize the dimensional variability inherent in composite laminates, which is essential if the labor-intensive assembly of complex structures is to be automated and intermediate steps such as machining and shimming of joints eliminated.
New design tools, manufacturing simulation software, process controls, tooling concepts and robotic manufacturing technologies are coming together—in research programs such as Europe's Locomachs—that promise significant reductions in cost and time for producing composite structures.
Aviation propulsion has been through two transformations: from propellers to jets and from turbojets to turbofans. A third is underway, in the form of adaptive or variable-cycle engines. Where a turbofan has two streams of air—one flowing through and one bypassing the core—an adaptive-cycle engine has three. The fan can adapt to pump more air through the core for higher thrust or through the bypass ducts for higher efficiency and lower fuel burn, while providing more air to cool aircraft systems.
General Electric and Pratt & Whitney have each been awarded $1 billion contracts to develop 45,000-lb.-thrust-class adaptive engines to power the next generation of U.S. fighters. Ground tests are to begin in 2019, and both engines could fly competitively in Lockheed Martin's F-35 Joint Strike Fighter in the early 2020s. Three-stream turbofans could also power future supersonic commercial transports, providing the combination of thrust, fuel economy and low airport noise required to meet environmental targets.
The conventional tube-and-wing aircraft has served aviation well, but researchers looking 20-40 years into the future see limits to the configuration's ability to continue delivering efficiency improvements. One is where to put the engines as bypass ratios and nacelle diameters increase. Another is how to keep driving down noise so that it can be entirely contained within the boundaries of the airport.
Researchers are studying alternative locations allowing larger engine diameters—above the wing and on the tail—and where the airframe can provide some shielding of fan and/or jet noise. Aft-mounted engines would also permit a clean wing for drag-reducing laminar flow. Another variation on today's layout is the truss-braced wing, allowing a much longer span and higher aspect ratio for lower drag.
Moving farther from the conventional are designs with turbofans, or electric propulsors, embedded in the tail where they ingest the fuselage boundary layer and reenergize the aircraft wake to reduce drag. Examples are the Aurora Flight Sciences/Massachusetts Institute of Technology “double-bubble” D8 being studied for NASA and the Propulsive Fuselage concept developed by Germany's Bauhaus Luftfahrt.
More unconventional yet are the blended or hybrid wing body (BWB/HWB), a flying wing with increased aerodynamic and structural efficiency. Some remain skeptical of the design's suitability for passengers, but the HWB is a promising freighter/airlifter configuration. Turbofans, open rotors or distributed propulsors can be mounted above the fuselage, where the broad airframe provides significant shielding.
After decades of on-again, off-again development, air-breathing hypersonic propulsion is tantalizingly close to being fielded in the form of high-speed cruise missiles. But much research remains before aircraft can accelerate from runways to beyond Mach 5 on air-breathing engines, for surveillance or strike missions or to lift payloads or passengers into low Earth orbit on reusable first stages.
Recent Chinese and Russian hypersonic weapon tests have added urgency to DARPA and U.S. Air Force plans to fly the Hypersonic Air-breathing Weapon Concept demonstrator by 2020. This is a follow-on to the Boeing X-51 WaveRider scramjet engine demonstrator flown in 2010-13 and the precursor to an operational Mach 5-plus long-range cruise missile.
As a next step, DARPA has resurrected plans to ground-test a turbine-based combined-cycle engine coupling a turbojet to a dual-mode ramjet/scramjet, all sharing the same inlet and nozzle, enabling air-breathing operation from standstill to hypersonic cruise. Such a propulsion system is required for the unmanned “SR-72” Lockheed Martin proposes flying in the 2020s.
Space access vehicles could use a powerplant such as Reaction Engines' SABRE, which operates in both air-breathing and rocket modes. Inside the atmosphere, incoming air is precooled by a heat exchanger and burned with liquid hydrogen in the rocket. Outside the atmosphere, SABRE operates as a conventional rocket. Reaction Engines plans a full-scale ground demo in 2020.
As deep space beckons human exploration, the limitations of chemical propulsion are pushing other technologies to the fore. One of these is solar electric propulsion (SEP), long seen as key to taking humans to Mars.
Because of the long flight times, Mars exploration strategies involve prepositioning infrastructure on the planet's surface for use by astronauts when they arrive. SEP-powered vehicles would slowly but efficiently accelerate large payloads into Martian orbit for eventual landing.
With high-power solar arrays driving electric thrusters, SEP systems are much weaker than chemical thrusters but up to 10 times more efficient. This dramatically reduces the propellant required and therefore the launch mass, making it practical to send large payloads to Mars.
NASA plans to demonstrate SEP on a robotic asteroid sampling mission in 2021, but the first flight could propel a large Mars orbiter scheduled for launch in 2022. Once in orbit, the solar arrays used for propulsion would power a ground-penetrating radar to search for water below the surface.
Astronauts need faster transit times, but a return mission will still take more than three years with the best chemical propulsion. With the ability to generate high thrust with double the efficiency of chemical propulsion, a nuclear thermal rocket (NTR) could cut that time significantly.
An NTR heats liquid hydrogen to high temperature in a nuclear reactor and expands it through a rocket nozzle to create thrust. Funding permitting, NASA hopes to ground-test a small NTR in 2022-24 and flight-test an engine on a lunar flyby demonstration within 10 years.
Synthetic and enhanced vision systems (SVS/EVS) that enable pilots to land in poor visibility are common on larger business jets. Now they are coming together in combined vision systems (CVS) that are being targeted at airlines to improve pilot situational awareness and schedule reliability.
EVS uses a forward-looking infrared (IR) sensor to augment the pilot's view of the outside world, usually projected in a head-up display (HUD). SVS uses a digital database to create a virtual representation of the outside world, usually presented on a head-down display, but it can be combined with EVS on the HUD.
EVS has evolved, with the development of lower-cost uncooled and multispectral sensors that range from long-wave IR to optical wavelength. Elbit Systems' ClearVision system has six sensors including short-wave IR and visible light and is being expanded to detect other hazards, such as volcanic ash.
Longer-term, sensors and systems developed to enable unmanned aircraft to autonomously detect and avoid other traffic are expected to find their way onto the flight decks of manned aircraft, fixed- and rotary-wing, to help pilots operate in the increasingly complex and diverse airspace of the future.
Civil aircraft development continues to focus on increasing fuel efficiency at subsonic speed, but there is a resurgence of interest in flying faster. NASA research into minimizing sonic boom looks set to remove one of the major barriers to economically and environmentally viable supersonic transports, but work on reducing airport noise and improving cruise efficiency is still needed.
NASA plans to fly an X-plane, the Quiet Supersonic Transport (QueSST), in 2019 to demonstrate that a publicly acceptable level of sonic boom can be achieved through careful shaping of the aircraft. Community response data collected during QueSST flights should pave the way for regulators to remove the ban on civil supersonic flights over land.
Some manufacturers are not waiting—Aerion Corp., for example, seeing a near-term market for a supersonic business jet. But Gulfstream, Boeing and others view quietening the sonic boom to a “soft thump” of 75 PLdB versus Concorde's 105 PLdB “double bang”—a 20-fold reduction—as a prerequisite for the economic viability of a business jet or small supersonic airliner.
Studies continue into hypersonic airliners able to fly from London to Sydney in 2 hr. but are paced by the need to develop propulsion systems that can operate with the safety, reliability and efficiency required for commercial viability. The military, and potentially the suborbital and reusable launch industry, will lead in developing the technology, but it will take decades.
Still in its infancy, electric propulsion attracts interest and skepticism in equal amounts. All-electric power is already feasible for light aircraft, with today's lithium-ion batteries, but anything larger will likely have hybrid propulsion—ranging from using diesel engines or small turbines as range extenders to turboelectric generators driving distributed fans via cryogenically cooled superconducting systems.
All-electric two-seater trainers are on the market. Hybrid-electric four seaters are on the horizon. NASA sees the next step, by the early 2020s, as a nine-passenger “thin-haul” commuter aircraft to restore air service to small communities. Researchers in both Europe and the U.S. believe a hybrid-electric airliner smaller than 100 seats is possible by 2030. But significant improvements in energy storage will be required.
While electric power provides a path to zero emissions using renewable energy sources, it also enables novel aircraft configurations in which distributed propulsion synergistically couples with aerodynamics. These range from multirotor, vertical-takeoff-and-landing air taxis to large transports in which embedded electric propulsors ingest the boundary layer and reenergize the aircraft's wake to reduce drag.
Anticipated improvements in platform and payload capabilities will enable small unmanned aircraft to enter many of the emerging low-altitude markets, from infrastructure inspection to package delivery, but commercial requirements for larger, more capable platforms are expected to materialize.
One of these is for high-altitude, long-endurance aircraft able to stay aloft in the stratosphere for days or weeks to provide internet access in remote regions, restore communications and navigation after disasters or perform remote sensing more affordably and responsively than satellites.
Facebook and Google are developing solar-powered stratospheric UAS, and Europe is pursuing two approaches to such high-altitude“pseudo-satellites”: Airbus Defense and Space's Zephyr S UAV is able to stay aloft for more than two weeks, and Thales Alenia Space's StratoBus autonomous airship for a year. Zephyr will enter service in 2017, and the heavier-payload StratoBus could follow by 2020.