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Technologies That Will Shape The Future
24 November 2016
With more than 100 years of dramatic technology advances behind it, what lies ahead for the aerospace industry- at least in the next 20–40 years? As its second century opens, Aviation Week & Space Technology identifies some of the more promising aerospace technologies already taking shape.
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 maintainlaminar-flowwings 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.
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 light weight, 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 on Lockheed 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 Boeing777-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 take off and landing, «refuse-to-crash» hazard avoidance, 4-D flight path management and «iPad-intuitive» displays that require fewer pilot-specific skills.
Progress with driver less-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-anadaptive-cyclee ngine 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-classadaptive 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-breathingengines, 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 andU. S. AirForce plans to fly the Hypersonic Air-breathing Weapon Concept demonstrator by 2020. This is a follow-onto the BoeingX-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-testa turbine-based combined-cycle engine coupling a turbojet to a dual-moderamjet/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.
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-lookinginfrared (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-downdisplay, but it can be combined with EVS on the HUD.
EVS has evolved, with the development of lower-costuncooled and multispectral sensors that range from long-wave IR to optical wavelength. Elbit Systems’ ClearVision system has six sensors includingshort-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 notwaiting-AerionCorp., for example, seeing a near-termmarket 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-take off-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.